The myth of the large sensor "high ISO advantage"

[sportyaccordy]

I have been waffling back and forth between moving to a Sony A7 or A6000, and looking at DxOMark's low light sensor rating I think I realized something kind of interesting.

First of all, correct me if I'm wrong, but sensitivity across formats is not really equivalent, and smaller sensors are inherently more sensitive than larger sensors for a given DoF & shutter speed length. I.e. if you have the same ISO, aperture diameter & shutter speed in front of two different size sensors, the larger sensor will have a dimmer exposure due to the given volume of light being spread over a larger area.

With that in mind, FF has 1.2 stops/2.36 times more sensor area than APS-C. So correct me if I'm wrong, but if an APS-C sensor is rated at ISO1000 for some low light S/N metric, a FF sensor with equivalent performance per unit of area will be rated at ISO2360 for the same metric, correct?

Well when you apply that math to the A6000 and A7 something interesting happens. The A6000 is rated at ISO1350 for DxO's 30db low light S/N test, and the A7 is rated at ISO2248. You do some quick math and realize that if the sensors are supposed to be equivalent, either the A7 should be rated at ISO3186 or the A6000 should be rated at ISO950. That's half a stop!

What's the practical impact of that? If you have a low light scene and two equivalent lenses wide open on the two cameras (i.e. the 24 1.8 & the 35 2.8), the A7 will have half a stop more noise. Yes, you will be able to bump up to a "higher ISO", but that's meaningless- you will have to up your ISO to have an equivalent picture (same shutter speed and depth of field) on the bigger sensor as it has inherently dimmer exposures than the smaller sensor.

Does this mean I won't get the A7? Probably not though I might go for the A7R as it somehow claws back most of that missing half a stop. Plus my legacy lenses will work a lot better on the full frame sensor naked than on a crop sensor through a focal length reducer. So there are other considerations to make. But my point is it might be time to change how we look at "high ISO" performance, and create a new metric to normalize it to sensor area. To really compare apples to apples ISO performance between formats you have to use a correction factor. If my math is correct it is pretty much the crop factor between the two formats squared. I.e. Sony APS-C has a crop factor of 1.536 vs Sony FF, so to compare the two you have to either divide the FF ISO or multiply the APS-C ISO by 1.536^2 (the 2.36 I referenced before which is the ratio of the two sensor areas).

This has other implications as well. A little 1/2.3 sensor at ISO100 is operating at a sensitivity equivalent to ISO3500 on a full frame. No wonder dynamic range and color sensitivities are so much worse.

Anyways I just thought that was interesting.

 

[Dennis]

First of all, correct me if I'm wrong, but sensitivity across formats is not really equivalent, and smaller sensors are inherently more sensitive than larger sensors for a given DoF & shutter speed length.

Well, that's the practical implication, but technically, the sensor is no less sensitive; the lens is transmitting light at a lower intensity for a given DOF. That's a technicality, but I think it's useful to keep the distinction clear.

I.e. if you have the same ISO, aperture diameter & shutter speed in front of two different size sensors, the larger sensor will have a dimmer exposure due to the given volume of light being spread over a larger area.

Correct.

With that in mind, FF has 1.2 stops/2.36 times more sensor area than APS-C. So correct me if I'm wrong, but if an APS-C sensor is rated at ISO1000 for some low light S/N metric, a FF sensor with equivalent performance per unit of area will be rated at ISO2360 for the same metric, correct?

I've forgotten how to do logarithms, but something like that.

So without being able to verify your numbers, I can say that while sensor size affects how much light the sensor sees at a give t-stop, there's definitely more that impacts performance. Interestingly, someone posted a link to a review of one of the A7 models at photographylife.com and the reviewer also expressed a little disappointment in the A7s high ISO abilities relative to other current cameras.

But you're right; if you set exposure on two cameras to get the same SS and DOF, and set ISO accordingly, the smaller sensor may very well end up being a little cleaner.

Does this mean I won't get the A7? Probably not though I might go for the A7R as it somehow claws back most of that missing half a stop.

You also have greater potential image quality, at base ISO, not to mention that a lot of low light shooters don't necessarily stop down to match the DOF that an APS-C shooter would get with a fast lens; depends on what you're shooting, but in some cases, you might be able to exploit the larger sensor.

- Dennis
--
Gallery at http://kingofthebeasts.smugmug.com

 

[SKersting66]

First of all, correct me if I'm wrong, but sensitivity across formats is not really equivalent, and smaller sensors are inherently more sensitive than larger sensors for a given DoF & shutter speed length. I.e. if you have the same ISO, aperture diameter & shutter speed in front of two different size sensors, the larger sensor will have a dimmer exposure due to the given volume of light being spread over a larger area.

Nope. With a given scene/exposure settings the exposures will be the same between different sensors/formats. It doesn't matter if it's a cell phone or 8x10.

In fact, for a given FL (lens FOV) a smaller sensor will collect less light due to crop factor (recording a smaller area), but that's irrelevant...

The advantage of larger formats is larger pixels. It's like trying to catch rain with teacups vs catching rain with large buckets. The large buckets will have more rain (light) per pixel and that's what gives it an advantage.

 

[SKersting66]

If the DOF is kept the same the smaller aperture on the larger format *may* negate the large pixel advantage.

--
https://www.flickr.com/photos/skersting/

 

[John Sheehy]

I have been waffling back and forth between moving to a Sony A7 or A6000, and looking at DxOMark's low light sensor rating I think I realized something kind of interesting.

First of all, correct me if I'm wrong, but sensitivity across formats is not really equivalent, and smaller sensors are inherently more sensitive than larger sensors for a given DoF & shutter speed length.

Well, they're pretty close across the board by that metric. For the last several years, compact sensors have had generally higher quantum efficiency than FF sensors, but greater read noise "per unit of sensor area" at higher ISOs.

I.e. if you have the same ISO, aperture diameter & shutter speed in front of two different size sensors, the larger sensor will have a dimmer exposure due to the given volume of light being spread over a larger area.

You can't quantify "exposure" based on physical aperture diameter without focal length. The f-number, rather than the aperture, determines exposure without knowledge of focal length. Aperture alone does, however, determine the amount of light collected from the subject in total (assuming equal lens t-factors and sensor quantum efficiency).

With that in mind, FF has 1.2 stops/2.36 times more sensor area than APS-C. So correct me if I'm wrong, but if an APS-C sensor is rated at ISO1000 for some low light S/N metric, a FF sensor with equivalent performance per unit of area will be rated at ISO2360 for the same metric, correct?

No; you can only count one dimension. AOTBE, a FF sensor should give the same noise as a 1.5x crop sensor at 1.5x the ISO, or 1.6x as high as a 1.6x crop. Personally, I find these singular, monolithic "acceptable ISO" metrics based on simple noise measurements to be nonsense.

Well when you apply that math to the A6000 and A7 something interesting happens. The A6000 is rated at ISO1350 for DxO's 30db low light S/N test, and the A7 is rated at ISO2248. You do some quick math and realize that if the sensors are supposed to be equivalent, either the A7 should be rated at ISO3186 or the A6000 should be rated at ISO950. That's half a stop!

You're making the same mistake as above; you're setting your FF expectations too high because of your misunderstanding.

 

[PerL]

I have been waffling back and forth between moving to a Sony A7 or A6000, and looking at DxOMark's low light sensor rating I think I realized something kind of interesting.

First of all, correct me if I'm wrong, but sensitivity across formats is not really equivalent, and smaller sensors are inherently more sensitive than larger sensors for a given DoF & shutter speed length. I.e. if you have the same ISO, aperture diameter & shutter speed in front of two different size sensors, the larger sensor will have a dimmer exposure due to the given volume of light being spread over a larger area.

With that in mind, FF has 1.2 stops/2.36 times more sensor area than APS-C. So correct me if I'm wrong, but if an APS-C sensor is rated at ISO1000 for some low light S/N metric, a FF sensor with equivalent performance per unit of area will be rated at ISO2360 for the same metric, correct?

Well when you apply that math to the A6000 and A7 something interesting happens. The A6000 is rated at ISO1350 for DxO's 30db low light S/N test, and the A7 is rated at ISO2248. You do some quick math and realize that if the sensors are supposed to be equivalent, either the A7 should be rated at ISO3186 or the A6000 should be rated at ISO950. That's half a stop!

What's the practical impact of that? If you have a low light scene and two equivalent lenses wide open on the two cameras (i.e. the 24 1.8 & the 35 2.8), the A7 will have half a stop more noise. Yes, you will be able to bump up to a "higher ISO", but that's meaningless- you will have to up your ISO to have an equivalent picture (same shutter speed and depth of field) on the bigger sensor as it has inherently dimmer exposures than the smaller sensor.

Does this mean I won't get the A7? Probably not though I might go for the A7R as it somehow claws back most of that missing half a stop. Plus my legacy lenses will work a lot better on the full frame sensor naked than on a crop sensor through a focal length reducer. So there are other considerations to make. But my point is it might be time to change how we look at "high ISO" performance, and create a new metric to normalize it to sensor area. To really compare apples to apples ISO performance between formats you have to use a correction factor. If my math is correct it is pretty much the crop factor between the two formats squared. I.e. Sony APS-C has a crop factor of 1.536 vs Sony FF, so to compare the two you have to either divide the FF ISO or multiply the APS-C ISO by 1.536^2 (the 2.36 I referenced before which is the ratio of the two sensor areas).

This has other implications as well. A little 1/2.3 sensor at ISO100 is operating at a sensitivity equivalent to ISO3500 on a full frame. No wonder dynamic range and color sensitivities are so much worse.

Anyways I just thought that was interesting.

You hear this over and over from small format supporters, but less DOF = better subject isolation and more creative options.

Greater DOF control is one of the main reason of getting a larger sensor. The"everything in focus" is the curse of phone cameras and one reason 35 mm film shots looks often more attractive and interesting than modern, sharp but flat looking, digital shots with small sensors.

But if you dont care much for this creative option, sure - the smaller the sensor - the better. "At the same DOF".

 

[John Sheehy]

First of all, correct me if I'm wrong, but sensitivity across formats is not really equivalent, and smaller sensors are inherently more sensitive than larger sensors for a given DoF & shutter speed length. I.e. if you have the same ISO, aperture diameter & shutter speed in front of two different size sensors, the larger sensor will have a dimmer exposure due to the given volume of light being spread over a larger area.

Nope. With a given scene/exposure settings the exposures will be the same between different sensors/formats. It doesn't matter if it's a cell phone or 8x10.

In fact, for a given FL (lens FOV) a smaller sensor will collect less light due to crop factor (recording a smaller area), but that's irrelevant...

The advantage of larger formats is larger pixels. It's like trying to catch rain with teacups vs catching rain with large buckets. The large buckets will have more rain (light) per pixel and that's what gives it an advantage.

That is only an advantage when you can keep the read noise, as measured in electrons, constant or relatively low as you increase photosite size/capacity, and in that case you are trading off resolution for lower read noise "per unit of sensor area".

Otherwise, if you have 25 teacups in place of each bucket, that does not increase photon "noise" except in pixel-level metrics, which have no direct relationship to image-level metrics - if you are looking at an image and you don't know how many original capture pixels it is made from, pixel-level noise metrics are completely worthless information. You have teacups set up in a large array, and you decide that you don't want to deal with the so-called noise of having so many samples, so you hire someone to go out and pour every unique 5x5 square of teacups into a bucket. How has your data improved? All you have done is thrown away fine location information; a net loss of information (resolution), with nothing to gain, as far as your data is concerned, other than having less of it.

 

[J A C S]

I have been waffling back and forth between moving to a Sony A7 or A6000, and looking at DxOMark's low light sensor rating I think I realized something kind of interesting.

First of all, correct me if I'm wrong, but sensitivity across formats is not really equivalent, and smaller sensors are inherently more sensitive than larger sensors for a given DoF & shutter speed length.

You are wrong. See sensorgen.info for estimated QE numbers. There is no huge difference (on a log scale). Some of the really small sensors are a bit better, maybe.

Also, QE determines the noise at low ISO only. The high ISO performance depends on the way the signal is handled, on the read noise, etc. The A7S is a good example of that.

I.e. if you have the same ISO, aperture diameter & shutter speed in front of two different size sensors, the larger sensor will have a dimmer exposure due to the given volume of light being spread over a larger area.

So? ISO is irrelevant, BTW.

With that in mind, FF has 1.2 stops/2.36 times more sensor area than APS-C. So correct me if I'm wrong, but if an APS-C sensor is rated at ISO1000 for some low light S/N metric, a FF sensor with equivalent performance per unit of area will be rated at ISO2360 for the same metric, correct?

ISO rating by DXO is a measure of the Full Well Capacity, not efficiency.

Well when you apply that math to the A6000 and A7 something interesting happens. The A6000 is rated at ISO1350 for DxO's 30db low light S/N test, and the A7 is rated at ISO2248. You do some quick math and realize that if the sensors are supposed to be equivalent, either the A7 should be rated at ISO3186 or the A6000 should be rated at ISO950. That's half a stop!

Wrong, see above. The A7 is not really a low light champion, and DXO show that be a bit less than 1 stop ahead, and it should be a bit more than one stop ahead. The A7R however behaves exactly as one would expect.

What's the practical impact of that? If you have a low light scene and two equivalent lenses wide open on the two cameras (i.e. the 24 1.8 & the 35 2.8), the A7 will have half a stop more noise. Yes, you will be able to bump up to a "higher ISO", but that's meaningless- you will have to up your ISO to have an equivalent picture (same shutter speed and depth of field) on the bigger sensor as it has inherently dimmer exposures than the smaller sensor.

Exposure is irrelevant, total light is.

To really compare apples to apples ISO performance between formats you have to use a correction factor. If my math is correct it is pretty much the crop factor between the two formats squared. I.e. Sony APS-C has a crop factor of 1.536 vs Sony FF, so to compare the two you have to either divide the FF ISO or multiply the APS-C ISO by 1.536^2 (the 2.36 I referenced before which is the ratio of the two sensor areas).

See the equivalence article in this site. This is discussed there. For equivalent shots, you need equivalent ISOs, as well.

 

[sportyaccordy]

I have been waffling back and forth between moving to a Sony A7 or A6000, and looking at DxOMark's low light sensor rating I think I realized something kind of interesting.

First of all, correct me if I'm wrong, but sensitivity across formats is not really equivalent, and smaller sensors are inherently more sensitive than larger sensors for a given DoF & shutter speed length.

Well, they're pretty close across the board by that metric. For the last several years, compact sensors have had generally higher quantum efficiency than FF sensors, but greater read noise "per unit of sensor area" at higher ISOs.

I.e. if you have the same ISO, aperture diameter & shutter speed in front of two different size sensors, the larger sensor will have a dimmer exposure due to the given volume of light being spread over a larger area.

You can't quantify "exposure" based on physical aperture diameter without focal length. The f-number, rather than the aperture, determines exposure without knowledge of focal length. Aperture alone does, however, determine the amount of light collected from the subject in total (assuming equal lens t-factors and sensor quantum efficiency).

Yes, the f-number determines exposure; however aperture diameter/depth of field and shutter speed determine the total quantity of light. I thought it was pretty clear I was talking about a given field of view.

With that in mind, FF has 1.2 stops/2.36 times more sensor area than APS-C. So correct me if I'm wrong, but if an APS-C sensor is rated at ISO1000 for some low light S/N metric, a FF sensor with equivalent performance per unit of area will be rated at ISO2360 for the same metric, correct?

No; you can only count one dimension. AOTBE, a FF sensor should give the same noise as a 1.5x crop sensor at 1.5x the ISO, or 1.6x as high as a 1.6x crop. Personally, I find these singular, monolithic "acceptable ISO" metrics based on simple noise measurements to be nonsense.

This doesn't bear out in reality. For example the last gen of 16 MP APS-C Sony sensors were good for about ISO1000. Current 24MP APS-C Sony sensors are good for about ISO1200-1400. By your logic full frame sensors of the same generations should have equivalent ISO thresholds of 1500-2100. But the D700 hit ISO2300 in 2008. The A7R/D800 with the same pixel density as a 16MP APS-C sensor are in the ISO2800 range, well above what your math indicates. So I'm not seeing what your contention is?

Well when you apply that math to the A6000 and A7 something interesting happens. The A6000 is rated at ISO1350 for DxO's 30db low light S/N test, and the A7 is rated at ISO2248. You do some quick math and realize that if the sensors are supposed to be equivalent, either the A7 should be rated at ISO3186 or the A6000 should be rated at ISO950. That's half a stop!

You're making the same mistake as above; you're setting your FF expectations too high because of your misunderstanding.

 

[tko]

It's really dangerous to start doing your own engineering analysis unless you know the pitfalls!

First of all, correct me if I'm wrong, but sensitivity across formats is not really equivalent, and smaller sensors are inherently more sensitive than larger sensors for a given DoF & shutter speed length. I.e. if you have the same ISO, aperture diameter & shutter speed in front of two different size sensors, the larger sensor will have a dimmer exposure due to the given volume of light being spread over a larger area.

Yes, but for the final print size, the larger sensor will require less magnification, making noise less visible. Its not light per unit area at the sensor size, it's light per unit area at the viewing size, which is for equal physical aperture size and shutter speed is the same for all formats.

People always forget about the magnification to make a print. A 8X10 sensor (!) wouldn't require any, a cell phone, quite a lot for the same print.

Engineers always use sniff tests. First sniff test: "Smaller sensors are inherently more sensitive than larger sensors" makes no sense.

Second sniff test: "With a two minutes of calculation I have proved 10 years of debate wrong." Nothing personal, but unless you have two Phd's, it's pretty unlikely that you've just discovered a myth everyone else has missed.

Next time don't title your post "the myth of . . . " How about "help me find my mistake!"

~~~~~~~~~~~~~~~~~~~~~~
professional cynic and contrarian: don't take it personally
http://500px.com/omearak

 

[sportyaccordy]

Engineers always use sniff tests. First sniff test: "Smaller sensors are inherently more sensitive than larger sensors" makes no sense.

They are. An APS-C camera with AOTBE to an FF with regards to DoF and ISO settings will have a faster shutter speed for a given scene.

Second sniff test: "With a two minutes of calculation I have proved 10 years of debate wrong." Nothing personal, but unless you have two Phd's, it's pretty unlikely that you've just discovered a myth everyone else has missed.

Don't mistake your misunderstanding as me being wrong. Again, show me the proof. I have various reputable sources that say/demonstrate what I'm saying. Do you?

And since when are PhD's required to post here? How many do you have?

 

[SKersting66]

That is only an advantage when you can keep the read noise, as measured in electrons, constant or relatively low as you increase photosite size/capacity, and in that case you are trading off resolution for lower read noise "per unit of sensor area".
Otherwise, if you have 25 teacups in place of each bucket, that does not increase photon "noise" except in pixel-level metrics, which have no direct relationship to image-level metrics - if you are looking at an image and you don't know how many original capture pixels it is made from, pixel-level noise metrics are completely worthless information. You have teacups set up in a large array, and you decide that you don't want to deal with the so-called noise of having so many samples, so you hire someone to go out and pour every unique 5x5 square of teacups into a bucket. How has your data improved? All you have done is thrown away fine location information; a net loss of information (resolution), with nothing to gain, as far as your data is concerned, other than having less of it.

Sure, but it's not quite as simple as that. There is space between the pixels that is "lost," and the more pixels there are, the more space that is lost.

Plus we are talking about low light/high ISO performance... so shot/amplification/read noise is higher for the smaller pixels. Plus a smaller FWC for smaller pixels which can cause noise issues. And we are talking about the system's ability/technique required to resolve to a smaller pixel size. And the need (human capability) to resolve to those levels in the final image (we can't).

IME it all matters. My low light/high ISO limit is 400 for the 14mp Nikon V2 (2.9um pixel size), 1000 for the 36mp D810 (4.9um), and 6400 for the D4 (7.5um)... cropped or not. Above those limits I will not be very happy with the image.
If I can keep the ISO within those limits, my choice of camera is the D810...

At one point I did a field test between the V2/D800/D4 using the same lens and a small/finely detailed subject, a Snowy Owl at ~90m.

 

[sportyaccordy]

Sure, but it's not quite as simple as that. There is space between the pixels that is "lost," and the more pixels there are, the more space that is lost.

The % of space lost between pixels is the same regardless of their size.

It does appear that larger pixels = better low light sensitivity though, based on the data.

 

[Aur]

I think ISO in itself is far less important than it used to be and the full frame advantage has diminished in the last couple of years.

A lens with good VR (VC / IS) is far more important to me than ISO performance of the camera. Some of the tamron lenses have ridiculous VC, the shots are so incredibly steady and it allows a slower lens to perform several stops better.

The in-camera algorithms to reduce noise are so much better now. A light amount of noise can easily be reduced without too much problems.

If you look at ISO in isolation, full frame perform slightly better still, but there are many other factors now, that make ISO performance less important.

 

[JP Scherrer]

Sure, but it's not quite as simple as that. There is space between the pixels that is "lost," and the more pixels there are, the more space that is lost.

The % of space lost between pixels is the same regardless of their size.

It does appear that larger pixels = better low light sensitivity though, based on the data.

Wrong !

 

[Lab D]

I have been waffling back and forth between moving to a Sony A7 or A6000, and looking at DxOMark's low light sensor rating I think I realized something kind of interesting.

First of all, correct me if I'm wrong, but sensitivity across formats is not really equivalent, and smaller sensors are inherently more sensitive than larger sensors for a given DoF & shutter speed length. I.e. if you have the same ISO, aperture diameter & shutter speed in front of two different size sensors, the larger sensor will have a dimmer exposure due to the given volume of light being spread over a larger area.

With that in mind, FF has 1.2 stops/2.36 times more sensor area than APS-C. So correct me if I'm wrong, but if an APS-C sensor is rated at ISO1000 for some low light S/N metric, a FF sensor with equivalent performance per unit of area will be rated at ISO2360 for the same metric, correct?

Well when you apply that math to the A6000 and A7 something interesting happens. The A6000 is rated at ISO1350 for DxO's 30db low light S/N test, and the A7 is rated at ISO2248. You do some quick math and realize that if the sensors are supposed to be equivalent, either the A7 should be rated at ISO3186 or the A6000 should be rated at ISO950. That's half a stop!

What's the practical impact of that? If you have a low light scene and two equivalent lenses wide open on the two cameras (i.e. the 24 1.8 & the 35 2.8), the A7 will have half a stop more noise. Yes, you will be able to bump up to a "higher ISO", but that's meaningless- you will have to up your ISO to have an equivalent picture (same shutter speed and depth of field) on the bigger sensor as it has inherently dimmer exposures than the smaller sensor.

Does this mean I won't get the A7? Probably not though I might go for the A7R as it somehow claws back most of that missing half a stop. Plus my legacy lenses will work a lot better on the full frame sensor naked than on a crop sensor through a focal length reducer. So there are other considerations to make. But my point is it might be time to change how we look at "high ISO" performance, and create a new metric to normalize it to sensor area. To really compare apples to apples ISO performance between formats you have to use a correction factor. If my math is correct it is pretty much the crop factor between the two formats squared. I.e. Sony APS-C has a crop factor of 1.536 vs Sony FF, so to compare the two you have to either divide the FF ISO or multiply the APS-C ISO by 1.536^2 (the 2.36 I referenced before which is the ratio of the two sensor areas).

This has other implications as well. A little 1/2.3 sensor at ISO100 is operating at a sensitivity equivalent to ISO3500 on a full frame. No wonder dynamic range and color sensitivities are so much worse.

Anyways I just thought that was interesting.

You hear this over and over from small format supporters, but less DOF = better subject isolation and more creative options.

True, but there is more to this. (see below)

Greater DOF control is one of the main reason of getting a larger sensor.

OK, the keyword there is "control". But there is a problem with this thinking.

The"everything in focus" is the curse of phone cameras and one reason 35 mm film shots looks often more attractive and interesting than modern, sharp but flat looking, digital shots with small sensors.

I am sure we agree smartphones are very different from 1 inch sensors, M43, and APS-C and lumping them in the same group is disingenuous.

But if you dont care much for this creative option, sure - the smaller the sensor - the better. "At the same DOF".

Here are some points you are missing. Larger formats do offer greater control but at a price. For example, as the OP mentioned if you try to get the same DoF with a FF camera as an APS-C camera, image quality can suffer slightly. Next, the shallower the DoF the more lightly one is to have focus errors or more noticeable focus errors (front/back focus). Finally, while it is possible to reduce the DoF with software, it is near impossible to increase it (except via multi-exposures). I can take any image and make it look like it was shot with a 1 stop wider aperture pretty easily and it would be near impossible to tell (above that it gets more difficult and things such as fine hair become problematic). I can't go the other way though.

So we are left with, which is better for the individual? If a FF owner shoots 70+% of the time wide open, then I would never suggest switching to a smaller format. If an M43 users is happy with the DoF the is getting and doesn't want anything shallower most of the time, then switching may only serve to reduce IQ (if same DoF is use).

I like to error on the side of caution. I'll use a slightly larger DoF and make sure focus is nailed. If later I want something a little shallower, I can easily make some simple changes (just as anyone would with softening skin). If focus is off or DoF is too shallow, there is little one can do.

Of course by using caution and a slightly wider DoF, it allows me to use a smaller/lighter lens.

 

[Aur]

The advantage of larger formats is larger pixels. It's like trying to catch rain with teacups vs catching rain with large buckets. The large buckets will have more rain (light) per pixel and that's what gives it an advantage.

--
https://www.flickr.com/photos/skersting/

here's a good article about the water bucket argument

http://www.clarkvision.com/articles/does.pixel.size.matter/

it holds up, on the condition that the larger sensor also has larger pixel size, which is usually the case, but not always

it is really because of the lens it's apeture though, the larger pixels just allow you to capture more of the incoming light, but it is the lens on a full frame that brings in more light

a full frame camera physically lets in more light, the larger pixels are just taking advantage of that, but it's both the lens and the pixels creating the cleaner ISO on full frame, not just the pixel size (sensor)

f/1.4 on a full frame is not f/1.4 on a smaller sensor, it's more like f/2.8

 

[SKersting66]

Yes, the f-number determines exposure; however aperture diameter/depth of field and shutter speed determine the total quantity of light. I thought it was pretty clear I was talking about a given field of view.

You can't have both the same aperture and DOF...not even if you change distance/FL for the same recorded FOV (although the DOF may be very close to the same). Are you talking about recorded FOV or lens FOV? (it doesn't actually matter in regards to light recorded)

On the basis of light, different sized sensors record the same amount of light per area.

I think you are mixing too many variables in your understanding (and our discussions). Sensor size does not equate (necessarily/directly) to pixel size/density. The ISO performance capabilities of smaller pixels (same size sensor) comes from oversampling/downsampling.

In the end, it comes down to enlargement for display, and pixel count/size is *fairly irrelevant in that regards... it's enlargement of the sensor's physical size to the final display's physical size.

*(as long as the pixel size is ~ 10um or less)

 

[SKersting66]

here's a good article about the water bucket argument
http://www.clarkvision.com/articles/does.pixel.size.matter/

it holds up, on the condition that the larger sensor also has larger pixel size, which is usually the case, but not always

it is really because of the lens it's apeture though, the larger pixels just allow you to capture more of the incoming light, but it is the lens on a full frame that brings in more light

a full frame camera physically lets in more light, the larger pixels are just taking advantage of that, but it's both the lens and the pixels creating the cleaner ISO on full frame, not just the pixel size (sensor)

I hadn't seen that article... thanks for that.

Again, we're mixing too many variables... The sensor size has no affect on how much light is "let in." If you keep the aperture/SS the same, the amount of light let in is the same per area. And it's the difference in area (physical size) that gives the larger sensor the advantage (mostly irrelevant of pixel size).

 

[zxaar]

I have been waffling back and forth between moving to a Sony A7 or A6000, and looking at DxOMark's low light sensor rating I think I realized something kind of interesting.

First of all, correct me if I'm wrong, but sensitivity across formats is not really equivalent, and smaller sensors are inherently more sensitive than larger sensors for a given DoF & shutter speed length. I.e. if you have the same ISO, aperture diameter & shutter speed in front of two different size sensors, the larger sensor will have a dimmer exposure due to the given volume of light being spread over a larger area.

With that in mind, FF has 1.2 stops/2.36 times more sensor area than APS-C. So correct me if I'm wrong, but if an APS-C sensor is rated at ISO1000 for some low light S/N metric, a FF sensor with equivalent performance per unit of area will be rated at ISO2360 for the same metric, correct?

Well when you apply that math to the A6000 and A7 something interesting happens. The A6000 is rated at ISO1350 for DxO's 30db low light S/N test, and the A7 is rated at ISO2248. You do some quick math and realize that if the sensors are supposed to be equivalent, either the A7 should be rated at ISO3186 or the A6000 should be rated at ISO950. That's half a stop!

What's the practical impact of that? If you have a low light scene and two equivalent lenses wide open on the two cameras (i.e. the 24 1.8 & the 35 2.8), the A7 will have half a stop more noise. Yes, you will be able to bump up to a "higher ISO", but that's meaningless- you will have to up your ISO to have an equivalent picture (same shutter speed and depth of field) on the bigger sensor as it has inherently dimmer exposures than the smaller sensor.

Does this mean I won't get the A7? Probably not though I might go for the A7R as it somehow claws back most of that missing half a stop. Plus my legacy lenses will work a lot better on the full frame sensor naked than on a crop sensor through a focal length reducer. So there are other considerations to make. But my point is it might be time to change how we look at "high ISO" performance, and create a new metric to normalize it to sensor area. To really compare apples to apples ISO performance between formats you have to use a correction factor. If my math is correct it is pretty much the crop factor between the two formats squared. I.e. Sony APS-C has a crop factor of 1.536 vs Sony FF, so to compare the two you have to either divide the FF ISO or multiply the APS-C ISO by 1.536^2 (the 2.36 I referenced before which is the ratio of the two sensor areas).

This has other implications as well. A little 1/2.3 sensor at ISO100 is operating at a sensitivity equivalent to ISO3500 on a full frame. No wonder dynamic range and color sensitivities are so much worse.

Anyways I just thought that was interesting.

You hear this over and over from small format supporters, but less DOF = better subject isolation and more creative options.

True, but there is more to this. (see below)

Greater DOF control is one of the main reason of getting a larger sensor.

OK, the keyword there is "control". But there is a problem with this thinking.

The"everything in focus" is the curse of phone cameras and one reason 35 mm film shots looks often more attractive and interesting than modern, sharp but flat looking, digital shots with small sensors.

I am sure we agree smartphones are very different from 1 inch sensors, M43, and APS-C and lumping them in the same group is disingenuous.

But if you dont care much for this creative option, sure - the smaller the sensor - the better. "At the same DOF".

Here are some points you are missing. Larger formats do offer greater control but at a price. For example, as the OP mentioned if you try to get the same DoF with a FF camera as an APS-C camera, image quality can suffer slightly. Next, the shallower the DoF the more lightly one is to have focus errors or more noticeable focus errors (front/back focus). Finally, while it is possible to reduce the DoF with software, it is near impossible to increase it (except via multi-exposures). I can take any image and make it look like it was shot with a 1 stop wider aperture pretty easily and it would be near impossible to tell (above that it gets more difficult and things such as fine hair become problematic). I can't go the other way though.

So we are left with, which is better for the individual? If a FF owner shoots 70+% of the time wide open, then I would never suggest switching to a smaller format. If an M43 users is happy with the DoF the is getting and doesn't want anything shallower most of the time, then switching may only serve to reduce IQ (if same DoF is use).

For 90% or more of what an average joe shoots Rx10 is more than enough. By your logic there is no reason for m43 format to exist. With FF DoF control is one major reason to get the format.

FF plus pentax Q and one has best of both worlds.

I like to error on the side of caution. I'll use a slightly larger DoF and make sure focus is nailed. If later I want something a little shallower, I can easily make some simple changes (just as anyone would with softening skin). If focus is off or DoF is too shallow, there is little one can do.

Of course by using caution and a slightly wider DoF, it allows me to use a smaller/lighter lens.