a7S high ISO claim - - -over hyped or not ?

Started 4 months ago | Discussions
LSHorwitz1
Senior MemberPosts: 2,236Gear list
Like?
a7S high ISO claim - - -over hyped or not ?
4 months ago

As a long time satisfied NEX-7 owner contemplating the possible purchase of an a7S, I am trying to clarify just how much of an improvement in low light performance I might expect.

Using DxOMark measurements as a starting point, I see that my NEX-7 is rated at 1016 and that the a7S is measured at 3702.

One might conclude that this measured less than a 4-fold increase in ISO should result in less than a 2 stop benefit, since each stop is a doubling / halving.

The comparison of the published specifications of two camera bodies as described by Sony however suggests a much larger gain, since one camera, the NEX-7, was specified as having a max sensitivity of 16,000 ISO, while the new a7S is described as having a max sensitivity of 102,400, over a six-fold improvement.

Is this claim by Sony over-stated, and thus the promised 6+ fold ISO gain increase claimed only really measureses to less than a 4 fold increase?

I would be disappointed to go from my current NEX-7 and all my associated glass to the a7S at considerable expsnse, only to find that the DxO measured improvement of less than 2 stops was all that I gained.

To avoid the confusion which may arise from Sony's offering extended ISO beyond 102,400 to 409,000, I want to ask anyone who replies to please leave this extended claim out of the discussion. I do realize that further claims by Sony to extend the a7S to yet higher extended ISO of 409,000 makes the a7S appear to have yet additional sensitivity, but I would judge this to be no more than manually "push processing" the sensor further, no different from manually setting my NEX-7 to expose a couple more stops underexposed. I am trying to compare both bodies based entirely on their measured sensitivities for their normal claimed range of ISO.

Thanks for any insights here,

Larry

Sony Alpha 7S Sony Alpha NEX-7
If you believe there are incorrect tags, please send us this post using our feedback form.
JonTafferOfPhotography
Regular MemberPosts: 230Gear list
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to LSHorwitz1, 4 months ago

LSHorwitz1 wrote:

As a long time satisfied NEX-7 owner contemplating the possible purchase of an a7S, I am trying to clarify just how much of an improvement in low light performance I might expect.

Using DxOMark measurements as a starting point, I see that my NEX-7 is rated at 1016 and that the a7S is measured at 3702.

One might conclude that this measured less than a 4-fold increase in ISO should result in less than a 2 stop benefit, since each stop is a doubling / halving.

The comparison of the published specifications of two camera bodies as described by Sony however suggests a much larger gain, since one camera, the NEX-7, was specified as having a max sensitivity of 16,000 ISO, while the new a7S is described as having a max sensitivity of 102,400, over a six-fold improvement.

Is this claim by Sony over-stated, and thus the promised 6+ fold ISO gain increase claimed only really measureses to less than a 4 fold increase?

I would be disappointed to go from my current NEX-7 and all my associated glass to the a7S at considerable expsnse, only to find that the DxO measured improvement of less than 2 stops was all that I gained.

To avoid the confusion which may arise from Sony's offering extended ISO beyond 102,400 to 409,000, I want to ask anyone who replies to please leave this extended claim out of the discussion. I do realize that further claims by Sony to extend the a7S to yet higher extended ISO of 409,000 makes the a7S appear to have yet additional sensitivity, but I would judge this to be no more than manually "push processing" the sensor further, no different from manually setting my NEX-7 to expose a couple more stops underexposed. I am trying to compare both bodies based entirely on their measured sensitivities for their normal claimed range of ISO.

Thanks for any insights here,

Larry

based on the simple dimensions of a full frame sensor, you will gain more than a stop in SNR performance holding everything constant.

then if you factor in just pixel pitch, there is roughly another stop there, if you are comparing at 100%.

finally, if you consider 2 years of sensor and more importantly image processing advancements, I'd estimate another stop if not 1.5 stops based on image samples I've seen compared to my d4

id say you can expect something like a 3 stop improvement over what you have in the nex-7 in terms of SNR and probably more gradual DR and CD fall off as well.

this method above is better for thinking about practical ISO performance gains, rather than comparing max ISO which is, by in large, misleading and manipulated.

also remember dxo ISO ratings are normalized, so a high MP body will benefit due to downsampling. so in reality the ISO performance of the nex-7 is actually far worse at 100% than you would think based just on dxo's ISO rating. the d800 folks can't seem to wrap their heads around that, but it is true. it becomes really obvious once you start cropping.

 JonTafferOfPhotography's gear list:JonTafferOfPhotography's gear list
Nikon D4 Sony a6000 Nikon AF-S Nikkor 24mm f/1.4G ED Nikon AF-S Nikkor 35mm f/1.4G Nikon AF-S Nikkor 85mm f/1.4G +7 more
Reply   Reply with quote   Complain
Pixel Pooper
Regular MemberPosts: 178Gear list
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to LSHorwitz1, 4 months ago

LSHorwitz1 wrote:

As a long time satisfied NEX-7 owner contemplating the possible purchase of an a7S, I am trying to clarify just how much of an improvement in low light performance I might expect.

Using DxOMark measurements as a starting point, I see that my NEX-7 is rated at 1016 and that the a7S is measured at 3702.

One might conclude that this measured less than a 4-fold increase in ISO should result in less than a 2 stop benefit, since each stop is a doubling / halving.

The 2 stop benefit is only at those ISO settings. At higher ISO the A7S will be more than 2 stops better.

The comparison of the published specifications of two camera bodies as described by Sony however suggests a much larger gain, since one camera, the NEX-7, was specified as having a max sensitivity of 16,000 ISO, while the new a7S is described as having a max sensitivity of 102,400, over a six-fold improvement.

The max ISO setting is 6 stops higher, but that doesn't mean the performance is 6 stops better. I don't think Sony ever claimed that both cameras would perform the same at their max ISO settings.

Is this claim by Sony over-stated, and thus the promised 6+ fold ISO gain increase claimed only really measureses to less than a 4 fold increase?

I would be disappointed to go from my current NEX-7 and all my associated glass to the a7S at considerable expsnse, only to find that the DxO measured improvement of less than 2 stops was all that I gained.

To avoid the confusion which may arise from Sony's offering extended ISO beyond 102,400 to 409,000, I want to ask anyone who replies to please leave this extended claim out of the discussion. I do realize that further claims by Sony to extend the a7S to yet higher extended ISO of 409,000 makes the a7S appear to have yet additional sensitivity, but I would judge this to be no more than manually "push processing" the sensor further, no different from manually setting my NEX-7 to expose a couple more stops underexposed. I am trying to compare both bodies based entirely on their measured sensitivities for their normal claimed range of ISO.

With Sony sensors there is no difference between raising ISO and push processing apart from the lower DR at higher ISO. There is only one sensitivity, and every setting above base ISO is push processed.

Thanks for any insights here,

Larry

 Pixel Pooper's gear list:Pixel Pooper's gear list
Sony RX100 Sony Alpha NEX-6 Sony SLT-A58 Tamron SP AF 60mm F/2 Di II LD IF Macro Sony E 35mm F1.8 OSS +2 more
Reply   Reply with quote   Complain
neil holmes
Veteran MemberPosts: 5,405
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to LSHorwitz1, 4 months ago

LSHorwitz1 wrote:

As a long time satisfied NEX-7 owner contemplating the possible purchase of an a7S, I am trying to clarify just how much of an improvement in low light performance I might expect.

Using DxOMark measurements as a starting point, I see that my NEX-7 is rated at 1016 and that the a7S is measured at 3702.

One might conclude that this measured less than a 4-fold increase in ISO should result in less than a 2 stop benefit, since each stop is a doubling / halving.

DXO is measuring low light performance, not high ISO.....some cameras get a score under 100 ISO.

The difference between the NEX-7 and A7S at higher ISOs will actually be greater.

They calculate the low light ISO score...

"The SNR indicates how much noise is present in an image compared to the actual information (signal). The higher the SNR value, the better the image looks, because details aren't drowned by noise. SNR strength is given in dB, which is a logarithmic scale: an increase of 6 dB corresponds to doubling the SNR, which equates to half the noise for the same signal.

An SNR value of 30dB means excellent image quality. Thus low-light ISO is the highest ISO setting for a camera that allows it to achieve an SNR of 30dB while keeping a good dynamic range of 9 EVs and a color depth of 18bits.

A difference in low-light ISO of 25% represents 1/3 EV and is only slightly noticeable.

As cameras improve, low-light ISO will continuously increase, making this scale open."

http://www.dxomark.com/Cameras/Compare/Side-by-side/Sony-A7S-versus-Sony-NEX-7___949_736

Dynamic range drops away on the NEX-7 more steeply.     Signal to noise seems to drop away similarly and colour depth drops away similarly after short slighter drop for the A7S.

Every review I have seen for the A7S says it is the low light king and most think it is pretty special.

Surprising to me since it seems to be more aimed as a video camera and it might get panned for that for rolling shutter and NOT having 15 stops of DR (even though its DR is better than anything like it).

I know I want one and may well get one at years end.

I would be disappointed to go from my current NEX-7 and all my associated glass to the a7S at considerable expsnse, only to find that the DxO measured improvement of less than 2 stops was all that I gained.

I am not sure how much better it will be for you but I don't think there is anything better currently....maybe Canon will have something in a few months.

Larry

Reply   Reply with quote   Complain
tqlla
Senior MemberPosts: 1,766Gear list
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to LSHorwitz1, 4 months ago

LSHorwitz1 wrote:

As a long time satisfied NEX-7 owner contemplating the possible purchase of an a7S, I am trying to clarify just how much of an improvement in low light performance I might expect.

Using DxOMark measurements as a starting point, I see that my NEX-7 is rated at 1016 and that the a7S is measured at 3702.

One might conclude that this measured less than a 4-fold increase in ISO should result in less than a 2 stop benefit, since each stop is a doubling / halving.

The comparison of the published specifications of two camera bodies as described by Sony however suggests a much larger gain, since one camera, the NEX-7, was specified as having a max sensitivity of 16,000 ISO, while the new a7S is described as having a max sensitivity of 102,400, over a six-fold improvement.

Is this claim by Sony over-stated, and thus the promised 6+ fold ISO gain increase claimed only really measureses to less than a 4 fold increase?

I would be disappointed to go from my current NEX-7 and all my associated glass to the a7S at considerable expsnse, only to find that the DxO measured improvement of less than 2 stops was all that I gained.

To avoid the confusion which may arise from Sony's offering extended ISO beyond 102,400 to 409,000, I want to ask anyone who replies to please leave this extended claim out of the discussion. I do realize that further claims by Sony to extend the a7S to yet higher extended ISO of 409,000 makes the a7S appear to have yet additional sensitivity, but I would judge this to be no more than manually "push processing" the sensor further, no different from manually setting my NEX-7 to expose a couple more stops underexposed. I am trying to compare both bodies based entirely on their measured sensitivities for their normal claimed range of ISO.

Thanks for any insights here,

Larry

I dont think the DXO numbers correlate in that manner.

 tqlla's gear list:tqlla's gear list
Sony SLT-A99 Sony Alpha DSLR-A850 NEX5R Sony SLT-A77 Sony 16mm F2.8 Fisheye +11 more
Reply   Reply with quote   Complain
Pixel Pooper
Regular MemberPosts: 178Gear list
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to tqlla, 4 months ago

tqlla wrote:

LSHorwitz1 wrote:

As a long time satisfied NEX-7 owner contemplating the possible purchase of an a7S, I am trying to clarify just how much of an improvement in low light performance I might expect.

Using DxOMark measurements as a starting point, I see that my NEX-7 is rated at 1016 and that the a7S is measured at 3702.

One might conclude that this measured less than a 4-fold increase in ISO should result in less than a 2 stop benefit, since each stop is a doubling / halving.

The comparison of the published specifications of two camera bodies as described by Sony however suggests a much larger gain, since one camera, the NEX-7, was specified as having a max sensitivity of 16,000 ISO, while the new a7S is described as having a max sensitivity of 102,400, over a six-fold improvement.

Is this claim by Sony over-stated, and thus the promised 6+ fold ISO gain increase claimed only really measureses to less than a 4 fold increase?

I would be disappointed to go from my current NEX-7 and all my associated glass to the a7S at considerable expsnse, only to find that the DxO measured improvement of less than 2 stops was all that I gained.

To avoid the confusion which may arise from Sony's offering extended ISO beyond 102,400 to 409,000, I want to ask anyone who replies to please leave this extended claim out of the discussion. I do realize that further claims by Sony to extend the a7S to yet higher extended ISO of 409,000 makes the a7S appear to have yet additional sensitivity, but I would judge this to be no more than manually "push processing" the sensor further, no different from manually setting my NEX-7 to expose a couple more stops underexposed. I am trying to compare both bodies based entirely on their measured sensitivities for their normal claimed range of ISO.

Thanks for any insights here,

Larry

I dont think the DXO numbers correlate in that manner.

The DXO numbers are ISO settings and can be compared as such.

 Pixel Pooper's gear list:Pixel Pooper's gear list
Sony RX100 Sony Alpha NEX-6 Sony SLT-A58 Tamron SP AF 60mm F/2 Di II LD IF Macro Sony E 35mm F1.8 OSS +2 more
Reply   Reply with quote   Complain
Rishi Sanyal
dpreview AdminPosts: 42Gear list
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to Pixel Pooper, 4 months ago

Pixel Pooper wrote:

With Sony sensors there is no difference between raising ISO and push processing apart from the lower DR at higher ISO. There is only one sensitivity, and every setting above base ISO is push processed.

While generally true for Sony, this is actually not the case with the A7S. There appears to be some downstream read noise that limits shadow performance at lower ISOs, and this is what caps the low ISO pixel-level dynamic range below that of the A7R.

Also, to the OP: this article we recently published may give you some idea of real-world ISO performance. If you make it through to the 2nd page, you'll note that ISO performance can't simply be talked of in terms of 'this many stops better', because different tones in the image are affected differently by the various sources of noise. For example, brighter tones (higher signals) will really only improve if the sensor gained efficiency (sometimes referred to as 'effective quantum efficiency'), while shadow performance will increase both by this and by lower read noise. We've only seen a tiny increase in actual efficiency, so we believe most of the benefit comes from optimizations in representing very low signals (lower aggregate read noise due to less pixels, lower upstream read noise, lower quantization error, or any combination of these & other factors). That means most of the benefits of the A7S will only be seen in deep shadows of high ISO shots, or in overall performance above extremely high ISOs (circa ISO 51,200 & above). But have a look yourself - different folks have different cutoffs for what they consider 'significant improvement'

That said - and someone already mentioned this earlier - the increase in sensor size alone will give you at least a stop better ISO performance than the NEX-7. Simply b/c a full-frame sensor literally can capture ~2.25x as much light as a similar APS-C sensor. Factor in other optimizations, and you do really have a 'low light king'. But, again, as we say in our conclusions of that article, the benefit of the A7S over, say, the A7R can only really be appreciated at very high ISOs. And more appreciated in the shadows of these high ISOs.

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.

Hope this helps,

Rishi

-- hide signature --

“It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” -- Sherlock Holmes

 Rishi Sanyal's gear list:Rishi Sanyal's gear list
Sony Alpha 7R Canon EOS 5D Mark III Sony FE 55mm F1.8 Sony E 10-18mm F4 OSS Canon EF 24mm f/1.4L II USM +13 more
Reply   Reply with quote   Complain
TThorne
Senior MemberPosts: 2,608Gear list
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to Rishi Sanyal, 4 months ago

Rishi Sanyal wrote:

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.

This is devastating news to me. I am truly saddened to see this confirmed and thankful at the same time for the work you have put into it. I love everything about the A7S, but for practical issues on the job (for me at least) the A7 and A7R seem like the reigning champions, as I value low ISO DR above much else.

-- hide signature --

A lie gets halfway around the world before the truth has a chance to get its pants on. - Sir Winston Churchill

 TThorne's gear list:TThorne's gear list
Sony Cyber-shot DSC-RX100 III Leica M Typ 240 Sony Alpha 7S Leica M-Monochrom Leica Summilux-M 21mm f/1.4 Asph +7 more
Reply   Reply with quote   Complain
philip pj
Contributing MemberPosts: 693
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to TThorne, 4 months ago

thanks for these comments, Rishi, esp:

'as we say in our conclusions of that article, the benefit of the A7S over, say, the A7R can only really be appreciated at very high ISOs. And more appreciated in the shadows of these high ISOs.

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.'

I had been wondering whether it was possible to quantify 'gains due to technology' as opposed to the 'big pixel effect' plus whatever else Sony is doing in the background; you will understand the topic is best expressed to photographers using different terminology.

And, in view of your comments quoted above, are we seeing a hiatus in sensor improvement - what we have is good enough? Printers report up to 40 inch a7r prints being very close to the smaller MFD units. Sony will soon be providing cost-effective medium format sensors, perhaps they wish more market separation between 'full frame' and the 44x33mm units?

The a7r unit handles almost everything with aplomb, regarding DR certainly - I doubt many need more at base ISO, in RAW anyway. At this level it is a joy to use. Sure a silent shutter would be nice but not at the cost of all that resolution.

Put another way, the a7r appears to be better at high ISO for a given output final file size - than the a7s is likely to be at base ISO compared with an a7r. This is the reverse of MR's point, it will be interesting to get past the brick walls in darkened rooms stage..

Reply   Reply with quote   Complain
Rishi Sanyal
dpreview AdminPosts: 42Gear list
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to philip pj, 4 months ago

Well, I think the bigger issue here is that physics is physics, and once you've already gotten read noise down as low as many of these cameras have (through sophisticated techniques like correlated double sampling), the only way to drastically increase ISO performance is to capture more light. Capturing more light increases SNR by decreasing shot/photon noise contributions.

And the only way to do that is to (1) increase sensor size, or (2) increase sensor efficiency. Or, of course, use faster glass.

So Sony's investment in MF probably reflects these realities, to a certain extent. Increasing sensor efficiency is difficult, as far as I understand. Partly b/c sensors are already so good, and also b/c it's difficult to mitigate perhaps the largest source of light loss - the color filters. Short of making a 3-CCD/CMOS with 3 different light paths, that is.

By the way, the higher SNR due to lower shot noise I referred to above is also what gives medium format 'that medium format look' (aside from conversations about DOF and bokeh, of course). It's the same reason a shot taken at ISO 100 looks better than the same shot taken at ISO 400 on even the best performing camera. The ISO 100 shot received 4x as much light as the ISO 400 shot (assuming you matched exposures accordingly); since bright shot-noise limited tones have SNR = sqrt(signal), the ISO 100 image would have twice the SNR of the ISO 400 shot in well-exposed regions (so we're ignoring read noise and tones of the image affected by read noise).

Sony's new MF CMOS sensor has 1.68x the surface area of full-frame, so theoretically can potentially give you almost 2/3 EV ISO performance advantage. But that's assuming similar aggregate read noise performance (and remember, with 50 million pixels - that's twice as many pixels to be read as a 25 MP sensor), similar QE, and of course similar access to fast lenses (which is definitely *not* the case). And, by the way, before this MF CMOS sensor from Sony, previous MF digital sensors had really, really low performance (either low QE, high read noise, or both) that limited their ISO performance despite their theoretical advantage due to their size. But for well-exposed images (landscapes, studio lighting, etc.), you couldn't beat those MF shots (well, unless you used multi-imaging techniques). Not just because of their resolution, but b/c of the very high SNR due to lower photon/shot noise contributions.

And while we're on this subject - you can increase the SNR any camera is capable of by averaging multiple shots. For example, take two APS-C shots, align them, then average them together and you'll basically get pretty close to what a FF camera might have gotten given the same focal plane exposure. This is simply b/c averaging two shots is like collecting twice the amount of light as far as photon statistics is concerned - and a FF has ~2.25x the surface area of APS-C and so, generally, collects twice as much light given the same shutter speed/aperture. Neat, huh? It doesn't perfectly work out b/c the two APS-C shots together had twice as many pixels read as the FF would have (assuming equivalent resolutions). But, generally speaking, SNR increases as the square root of the # of images averaged.

Anyway, to answer your question: I think it is somewhat fair to say that sensors have gotten so good that we're running up against practical limitations that'll require quite some innovation to overcome. But look at how far we've come since the advent of digital cameras. Who knows what's on the horizon?

-- hide signature --

“It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” -- Sherlock Holmes

 Rishi Sanyal's gear list:Rishi Sanyal's gear list
Sony Alpha 7R Canon EOS 5D Mark III Sony FE 55mm F1.8 Sony E 10-18mm F4 OSS Canon EF 24mm f/1.4L II USM +13 more
Reply   Reply with quote   Complain
D Cox
Senior MemberPosts: 8,403
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to TThorne, 4 months ago

TThorne wrote:

Rishi Sanyal wrote:

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.

This is devastating news to me. I am truly saddened to see this confirmed and thankful at the same time for the work you have put into it. I love everything about the A7S, but for practical issues on the job (for me at least) the A7 and A7R seem like the reigning champions, as I value low ISO DR above much else.

The A7 is a general purpose camera which can be supplemented by the two other models when you need either maximum resolution or very high ISO.

I think these should be seen as optional second cameras for those who already own an A7.

Reply   Reply with quote   Complain
JonTafferOfPhotography
Regular MemberPosts: 230Gear list
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to TThorne, 4 months ago

TThorne wrote:

Rishi Sanyal wrote:

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.

This is devastating news to me. I am truly saddened to see this confirmed and thankful at the same time for the work you have put into it. I love everything about the A7S, but for practical issues on the job (for me at least) the A7 and A7R seem like the reigning champions, as I value low ISO DR above much else.

-- hide signature --

A lie gets halfway around the world before the truth has a chance to get its pants on. - Sir Winston Churchill

if you "value low ISO DR above much else", the a7s is obviously not a camera you should be concerned with.  doesn't the S in a7S indicate that? no reason to be devastated.  that's like claiming to be devastated that the a7r is not medium format, lol.

 JonTafferOfPhotography's gear list:JonTafferOfPhotography's gear list
Nikon D4 Sony a6000 Nikon AF-S Nikkor 24mm f/1.4G ED Nikon AF-S Nikkor 35mm f/1.4G Nikon AF-S Nikkor 85mm f/1.4G +7 more
Reply   Reply with quote   Complain
ProfHankD
Senior MemberPosts: 2,071Gear list
Like?
Dynamic range, ISO-less sensors
In reply to TThorne, 4 months ago

TThorne wrote:

Rishi Sanyal wrote:

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.

This is devastating news to me. I am truly saddened to see this confirmed and thankful at the same time for the work you have put into it. I love everything about the A7S, but for practical issues on the job (for me at least) the A7 and A7R seem like the reigning champions, as I value low ISO DR above much else.

I don't know why people expect cameras with good very high ISO performance to do well at low ISOs -- that's really not how it works. The DR for the A7S at higher ISOs appears to be significantly better than any other camera DxO has tested, and 13+ Evs at low ISOs is pretty amazing for the same sensor. Makes one wonder where they put all that charge....

More specifically, there's been a lot of discussion in the past about sensors being ISO-less: underexposing at a low ISO and digitally adjusting the raw does as well as turning-up the analog gain (ISO setting). In fact, last year I had students do a little project that confirmed even some cheap Canon PowerShots using CHDK are essentially ISO-less. Most Sony sensors seem to be ISO-less, which is what you'd expect if you have good analog signal handling. Anyway, the point is that the A7S clearly is not ISO-less. Perhaps sensor DR really is that 15+ range Sony mentions (without citation) and the analog electronics just are not able to cover it all without a gain adjustment?

Personally, I miss ISO 25 because that's what I was most often shooting at with film (Panatomic-X in 1:100 Rodinal or Kodachrome 25). I know you can (usually) use an ND filter to get the same effect, but adding filters isn't ideal....  And yes: I would use ISO 25 more often than ISO 100K.

 ProfHankD's gear list:ProfHankD's gear list
Nikon Coolpix 950 Olympus C-2020 Zoom Olympus Stylus 1030 SW Sony Cyber-shot DSC-F828 Canon PowerShot G1 +21 more
Reply   Reply with quote   Complain
LSHorwitz1
Senior MemberPosts: 2,236Gear list
Like?
Re: Dynamic range, ISO-less sensors
In reply to ProfHankD, 4 months ago

ProfHankD wrote:

TThorne wrote:

Rishi Sanyal wrote:

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.

This is devastating news to me. I am truly saddened to see this confirmed and thankful at the same time for the work you have put into it. I love everything about the A7S, but for practical issues on the job (for me at least) the A7 and A7R seem like the reigning champions, as I value low ISO DR above much else.

I don't know why people expect cameras with good very high ISO performance to do well at low ISOs -- that's really not how it works. The DR for the A7S at higher ISOs appears to be significantly better than any other camera DxO has tested, and 13+ Evs at low ISOs is pretty amazing for the same sensor. Makes one wonder where they put all that charge....

More specifically, there's been a lot of discussion in the past about sensors being ISO-less: underexposing at a low ISO and digitally adjusting the raw does as well as turning-up the analog gain (ISO setting). In fact, last year I had students do a little project that confirmed even some cheap Canon PowerShots using CHDK are essentially ISO-less. Most Sony sensors seem to be ISO-less, which is what you'd expect if you have good analog signal handling. Anyway, the point is that the A7S clearly is not ISO-less. Perhaps sensor DR really is that 15+ range Sony mentions (without citation) and the analog electronics just are not able to cover it all without a gain adjustment?

Personally, I miss ISO 25 because that's what I was most often shooting at with film (Panatomic-X in 1:100 Rodinal or Kodachrome 25). I know you can (usually) use an ND filter to get the same effect, but adding filters isn't ideal.... And yes: I would use ISO 25 more often than ISO 100K.

Hi everyone! I am the original poster, back from a busy day where I had no opportunity to reply earlier today as the wonderful replies to my original inquiry came in.

First, let me thank you all most sincerely for a rich, insightful, and very informative set of comments and remarks. I have learned a lot and, as is nearly always true, am just amazed at how much great knowledge and helpful people attend this and other DPReview forums.

My consclusions from all of this are that DxOMark ISO sensitivity only tells a very partial story about how the sensor behaves, and DxOMark.s choice of a specific reference SNR and their measurement approach for sensitivity does not characterize the low light behavior in absolute terms but rather only relative to others which they have measured. The amount of noise, the spectral characteristics of the noise, and the changing characteristics of the noise spectrum over the dynamic range of the sensor make a complex, non linear, degredation which can affect shadow detail differently from highlights, etc. I am also concluding that a camera maker can and will, somewhat strategically, specify the top ISO for a specific body, understanding that a continuum of Image Quality versus ISO setting choices will be thus provided, leaving the photogapher to choose how much degredation they will tolerate.

Given the predictable gains in going from APS-C sensor size to full frame, and the additional gain coming from greater sensor efficiency arising from fewer, larger (12Mpixel) photosites (versus my NEX-7's 24Mpixel count), the remaining gain here is attributable to whatever sensor efficiency gains and noise reductions then can be squeezed out of very mature CMOS and DSP technologies. In this regard, the a7S now seems less of a breakthrough and more like a very nice low light optimazation, with 400,000+ ISO a bit fanciful, all things considered.

I am very much looking forward to learning about how the -4 EV autofocus world behaves, and whether the a7S makes focusing decisions which greatly improve upon the a7 and a7R, both of which frightened me off as a buyer given their lackluster performances. I am still very much a prospective owner of an a7S given the discussion of this and other recent threads, but frankly the evidence has yet to fully clinch the deal. The jury is still out, but the initial results seem to make a compelling case.

I especially appreciated the wonderful first offerings from DPReview along with the superb comments from Rishi Sanyal and others here.

Thanks once again,

Larry

Reply   Reply with quote   Complain
andrewD2
Veteran MemberPosts: 7,835
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to Rishi Sanyal, 4 months ago

Rishi Sanyal wrote:

Pixel Pooper wrote:

With Sony sensors there is no difference between raising ISO and push processing apart from the lower DR at higher ISO. There is only one sensitivity, and every setting above base ISO is push processed.

While generally true for Sony, this is actually not the case with the A7S. There appears to be some downstream read noise that limits shadow performance at lower ISOs, and this is what caps the low ISO pixel-level dynamic range below that of the A7R.

Also, to the OP: this articlewe recently published may give you some idea of real-world ISO performance. If you make it through to the 2nd page, you'll note that ISO performance can't simply be talked of in terms of 'this many stops better', because different tones in the image are affected differently by the various sources of noise. For example, brighter tones (higher signals) will really only improve if the sensor gained efficiency (sometimes referred to as 'effective quantum efficiency'), while shadow performance will increase both by this and by lower read noise. We've only seen a tiny increase in actual efficiency, so we believe most of the benefit comes from optimizations in representing very low signals (lower aggregate read noise due to less pixels, lower upstream read noise, lower quantization error, or any combination of these & other factors). That means most of the benefits of the A7S will only be seen in deep shadows of high ISO shots, or in overall performance above extremely high ISOs (circa ISO 51,200 & above). But have a look yourself - different folks have different cutoffs for what they consider 'significant improvement'

That said - and someone already mentioned this earlier - the increase in sensor size alone will give you at least a stop better ISO performance than the NEX-7. Simply b/c a full-frame sensor literally can capture ~2.25x as much light as a similar APS-C sensor. Factor in other optimizations, and you do really have a 'low light king'. But, again, as we say in our conclusions of that article, the benefit of the A7S over, say, the A7R can only really be appreciated at very high ISOs. And more appreciated in the shadows of these high ISOs.

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.

Hope this helps,

Rishi

-- hide signature --

“It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” -- Sherlock Holmes

The A7R is reading better in THEIR DR tests because of the resolution.
What limits DR? It's the detail you can see in the shadows given that the highlights can not be exposed any higher.
So what is better 36Million super clean pixels or 12Million super super clean pixels. In THEIR test the former.
I have a great way of directly comparing DR between cameras, doesn't give you a DR value but it does give you a winner. DXOmark is WAY off on the difference between 5DIII and 6D. So I don't trust their values.
My guess is that for 13 stop scenes the A7R will win out but for 20 stop scenes I'd have to find out.

Andrew

Reply   Reply with quote   Complain
spacemn
Senior MemberPosts: 1,080
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to Rishi Sanyal, 4 months ago

Rishi Sanyal wrote:

Well, I think the bigger issue here is that physics is physics, and once you've already gotten read noise down as low as many of these cameras have (through sophisticated techniques like correlated double sampling), the only way to drastically increase ISO performance is to capture more light. Capturing more light increases SNR by decreasing shot/photon noise contributions.

And the only way to do that is to (1) increase sensor size, or (2) increase sensor efficiency. Or, of course, use faster glass.

So Sony's investment in MF probably reflects these realities, to a certain extent. Increasing sensor efficiency is difficult, as far as I understand. Partly b/c sensors are already so good, and also b/c it's difficult to mitigate perhaps the largest source of light loss - the color filters. Short of making a 3-CCD/CMOS with 3 different light paths, that is.

By the way, the higher SNR due to lower shot noise I referred to above is also what gives medium format 'that medium format look' (aside from conversations about DOF and bokeh, of course). It's the same reason a shot taken at ISO 100 looks better than the same shot taken at ISO 400 on even the best performing camera. The ISO 100 shot received 4x as much light as the ISO 400 shot (assuming you matched exposures accordingly); since bright shot-noise limited tones have SNR = sqrt(signal), the ISO 100 image would have twice the SNR of the ISO 400 shot in well-exposed regions (so we're ignoring read noise and tones of the image affected by read noise).

Sony's new MF CMOS sensor has 1.68x the surface area of full-frame, so theoretically can potentially give you almost 2/3 EV ISO performance advantage. But that's assuming similar aggregate read noise performance (and remember, with 50 million pixels - that's twice as many pixels to be read as a 25 MP sensor), similar QE, and of course similar access to fast lenses (which is definitely *not* the case). And, by the way, before this MF CMOS sensor from Sony, previous MF digital sensors had really, really low performance (either low QE, high read noise, or both) that limited their ISO performance despite their theoretical advantage due to their size. But for well-exposed images (landscapes, studio lighting, etc.), you couldn't beat those MF shots (well, unless you used multi-imaging techniques). Not just because of their resolution, but b/c of the very high SNR due to lower photon/shot noise contributions.

And while we're on this subject - you can increase the SNR any camera is capable of by averaging multiple shots. For example, take two APS-C shots, align them, then average them together and you'll basically get pretty close to what a FF camera might have gotten given the same focal plane exposure. This is simply b/c averaging two shots is like collecting twice the amount of light as far as photon statistics is concerned - and a FF has ~2.25x the surface area of APS-C and so, generally, collects twice as much light given the same shutter speed/aperture. Neat, huh? It doesn't perfectly work out b/c the two APS-C shots together had twice as many pixels read as the FF would have (assuming equivalent resolutions). But, generally speaking, SNR increases as the square root of the # of images averaged.

Anyway, to answer your question: I think it is somewhat fair to say that sensors have gotten so good that we're running up against practical limitations that'll require quite some innovation to overcome. But look at how far we've come since the advent of digital cameras. Who knows what's on the horizon?

-- hide signature --

“It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” -- Sherlock Holmes

I am not sure why you are bringing in MF sensors into this discussion. The first MF sensor which seems to be outperforming the FF sensor when it comes to SNR or high ISO performance is the new Sony CMOS MF sensor. Before this there were only CCD MF sensors and their low light performance was appalling in comparison to modern CMOS FF sensors.

The only place where MF CCD sensors have excelled over FF CMOS sensors have been colour bit depth and tonal range, and then of course bucket loads of resolution especially the 60-80 mpix sensors.

So, can you show us this "MF look" when it comes to SNR where it beats the best FF CMOS sensors? to my knowledge only the new Sony MF CMOS sensor seems to have handsomely beaten the FF counterparts  and hence introduced a new "MF look" when it comes to SNRl, but this sensor is new, and the MF scene is still dominated by way inferior lowlight CCD sensors.

The performance of the sensor is comprised of many factors. Such as chip technology and the signal processing, and not at all only the size of the pixels. It is only matter of time until we will see a new chip tech generation coming along. Perhaps next disruption will be based on organic light sensitive diodes.

No offence, but if you are in any case involved in the A7S review on behalf of DPreview, then I really hope you have your facts under control and won't make fluffy assumptions such as "MF look" etc.

To thread starter, no the A7S low light performance is not overhyped in my opinion. Especially at super high ISOs (>6400) it is significantly better than anything else on the market (we are talking <2 stops better than most popular FF sensors on the market), a little revolution I'd say. Photographers and film makers can now use candle lights and moon light as creative lighting now, which was not really realistic earlier. DXOMark scores indicates this as well. Maybe only the new Sony CMOS MF (medium format) sensor can beat it. It seems it both focusses and performs like a champ in almost total darkness

Reply   Reply with quote   Complain
ProfHankD
Senior MemberPosts: 2,071Gear list
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to andrewD2, 4 months ago

andrewD2 wrote:

The A7R is reading better in THEIR DR tests because of the resolution.

Read the full set of tests at DxO.  Rather than viewing "scores," click on "measurements" and then "dynamic range."  Two plots are available there. The "print" one shows the dynamic range at each ISO when all images are first scaled to 8MP (the default graph). The "screen" one shows the dynamic range at the native pixel resolution -- not giving the A7R (or A7) an advantage, but essentially penalizing them for their higher resolution.

At marked ISO 100 (which is really a bit lower), the A7S has less dynamic range than the A7 or A7R even in the "screen" graph -- there, the A7 beats the A7R and both beat the A7S. However, the A7S dynamic range drops much slower as the ISO is increased, and at higher ISOs the A7S has a couple of Ev more DR.

I have no affiliation with DxO, but they have earned my respect and I have yet to find a case where they were simply wrong based on my own precision measurements. There are some things I like to measure that DxO doesn't (yet?), but unsupported claims that DxO is wrong really annoy me. I think DxO is providing a huge service to the community and should be applauded for making so much high-quality data freely available.

 ProfHankD's gear list:ProfHankD's gear list
Nikon Coolpix 950 Olympus C-2020 Zoom Olympus Stylus 1030 SW Sony Cyber-shot DSC-F828 Canon PowerShot G1 +21 more
Reply   Reply with quote   Complain
TThorne
Senior MemberPosts: 2,608Gear list
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to D Cox, 4 months ago

D Cox wrote:

TThorne wrote:

Rishi Sanyal wrote:

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.

This is devastating news to me. I am truly saddened to see this confirmed and thankful at the same time for the work you have put into it. I love everything about the A7S, but for practical issues on the job (for me at least) the A7 and A7R seem like the reigning champions, as I value low ISO DR above much else.

The A7 is a general purpose camera which can be supplemented by the two other models when you need either maximum resolution or very high ISO.

I think these should be seen as optional second cameras for those who already own an A7.

I already own an A7 that I like a lot for my architecture work. Other than that, I use my M240's. I did do some more research though and found that once we hit ISO400, the DR advantage between the R and the S evens out, with the S taking the lead thereafter.

I gave it some thought and realized that when I am lighting architecture, I do tend to shoot at ISO 320/400 for various reasons, so that really helped, and I picked up my A7S today, and used it for work immediately. I am happy I did. Under certain conditions, I really appreciate the small file sizes, and when I pull the TSE off it and mount some of my Leica glass, it will be a fun time low light camera. Overall, I like the camera, and the only thing negative I would say is not even about the gear, but just that Sony should not have claimed 15+ stops of DR. Otherwise, the camera works splendidly, and the fact that Sony now provides a charger and 2 batteries with the camera gets a thumbs up from me.

I will likely keep the A7S and an A7R for various work loads with my Leica's for travel work and personal.

-- hide signature --

A lie gets halfway around the world before the truth has a chance to get its pants on. - Sir Winston Churchill

 TThorne's gear list:TThorne's gear list
Sony Cyber-shot DSC-RX100 III Leica M Typ 240 Sony Alpha 7S Leica M-Monochrom Leica Summilux-M 21mm f/1.4 Asph +7 more
Reply   Reply with quote   Complain
TThorne
Senior MemberPosts: 2,608Gear list
Like?
Re: a7S high ISO claim - - -over hyped or not ?
In reply to JonTafferOfPhotography, 4 months ago

JonTafferOfPhotography wrote:

TThorne wrote:

Rishi Sanyal wrote:

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.

This is devastating news to me. I am truly saddened to see this confirmed and thankful at the same time for the work you have put into it. I love everything about the A7S, but for practical issues on the job (for me at least) the A7 and A7R seem like the reigning champions, as I value low ISO DR above much else.

-- hide signature --

A lie gets halfway around the world before the truth has a chance to get its pants on. - Sir Winston Churchill

if you "value low ISO DR above much else", the a7s is obviously not a camera you should be concerned with. doesn't the S in a7S indicate that? no reason to be devastated. that's like claiming to be devastated that the a7r is not medium format, lol.

The "S" never needed to indicate that. Sony flat out said it in their marketing of the A7S. Your analogy is not very well thought out.

Still, I like the camera and it works great. DR at low ISO is on par with the others if we start at ISO400 which I consider low still. Base ISO still belongs to the A7 and A7R.

-- hide signature --

A lie gets halfway around the world before the truth has a chance to get its pants on. - Sir Winston Churchill

 TThorne's gear list:TThorne's gear list
Sony Cyber-shot DSC-RX100 III Leica M Typ 240 Sony Alpha 7S Leica M-Monochrom Leica Summilux-M 21mm f/1.4 Asph +7 more
Reply   Reply with quote   Complain
TThorne
Senior MemberPosts: 2,608Gear list
Like?
Re: Dynamic range, ISO-less sensors
In reply to ProfHankD, 4 months ago

ProfHankD wrote:

TThorne wrote:

Rishi Sanyal wrote:

There's also a dynamic range benefit at higher ISOs. At base ISO, however, there's a dynamic range cost compared to the A7R.

This is devastating news to me. I am truly saddened to see this confirmed and thankful at the same time for the work you have put into it. I love everything about the A7S, but for practical issues on the job (for me at least) the A7 and A7R seem like the reigning champions, as I value low ISO DR above much else.

I don't know why people expect cameras with good very high ISO performance to do well at low ISOs -- that's really not how it works.

Simple answer, these were hopes/expectations based on the claims made by Sony. No need be confused as to "why people..."

I agree with you that the DR is still impressive, especially given the other features of the camera and sensor. I still bought it and am happy with it, so that outweighs the let down. But don't discount the let down that some people might experience in the face of a direct claim being shot down. The same would happen in other industries and lead to lawsuits for those who care to do that sort of thing. It doesn't matter that I am happy with the camera nonetheless. A company still is not supposed to make marketing claims they can't substantiate.

Whatever though, I am a happy Sony customer.

-- hide signature --

A lie gets halfway around the world before the truth has a chance to get its pants on. - Sir Winston Churchill

 TThorne's gear list:TThorne's gear list
Sony Cyber-shot DSC-RX100 III Leica M Typ 240 Sony Alpha 7S Leica M-Monochrom Leica Summilux-M 21mm f/1.4 Asph +7 more
Reply   Reply with quote   Complain
Keyboard shortcuts:
FForum MMy threads