A reminder for some memebers as to what the F stop is all about.

Started Jan 26, 2014 | Discussions
Great Bustard Forum Pro • Posts: 43,425
Re: You think so?

Sergey_Green wrote:

Great Bustard wrote:

Of course, 4/3 lenses are sharper than FF lenses, which offsets that advantage for FF somewhat. That is, if a 4/3 lens is twice as sharp as a FF lens, it will resolve as well as a FF lens for sensors with the same pixel count and AA filter.

I don't believe this is necessarily true.

Not necessarily true, and it does depend on the particular lenses being compared as well as where in the frame we are looking.

They are told to be sharper because they resolve more lines per mm, but that is only because those lenses are tested with the sensors that have the highest pixel density. Third party lenses that are ported and adapted to different formats show that twice as sharp Olympus lenses are nothing but the myth.

For a given lens sharpness, the difference in resolution (lw/ph) between two systems will be between the ratio of the sensor heights (enlargement ratio) and the ratio of picture height in pixels (linear pixel density). The sharper the lens, the closer the balance will be to the ratio of linear pixel density, the less sharp the lens, the closer the balance will be to the enlargement ratio.

For example, if a lens were very sharp relative to the pixel size of either system, the resolution advantage would go to the sensor with more pixels.  If the lens were not so sharp relative to both systems, the resolution advantage would go to the larger sensor.

Take Sigmas for example, many on this very same forum will agree that Sigma 17-50/2.8 will indeed deliver more detail than the celebrated Zuiko 14-54 (Bootstrap made several comments on it, even Ray agreed and echoed it), whereas the same Sigma is not necessarily the best or better lens than many Nikon equivalents when used on APS-C cameras. Or Sigma 150 macro, whenever there is a mention of it on this very same forum you will hear nothing but a praise. Yet again, Nikon 105 and Nikon 200 are at least as good if not better alternatives. I tried Tamron sp90 in the past, it was very much the same story - excellent lens on FT, good but not the best on APS-C.

And of course, how many times do we hear how good 50-200 is, some will not even change to the system that does not have such a lens, yet it is not really that great when you spend time and really compare it.

Again, it will depend on the particular pair of lenses you compare.  Also, lenses for 4/3 have to be twice as sharp as lenses for FF to resolve as well for sensors with the same pixel count and AA filter, but FF sensors tend to have more pixels, so they have to be more than twice as sharp to resolve as well.  So, let's say the 4/3 lens was 1.5x as sharp.  That would help narrow the gap, but the gap would be there, nonetheless.

DonSC Senior Member • Posts: 1,032
Re: And the answer is:

Great Bustard wrote:

Instead of "same ISO", how about we say, "same f-ratio and shutter speed", as the ISO setting isn't particularly relevant to the matter at hand, and the cameras may not meter the scene the same at the same ISO setting.

Then the EM1 photo will have less noise since it has a more efficient sensor. The EM1 photo will be more detailed since it has 4x as many pixels on the subject.

Now let's assume we had a FF sensor made with the exact same pixels as the EM1 sensor. Then the photos would be all but identical.

I don't know the answer but I'm thinking that the 1Dx image would have less noise (because the pixels are so much larger and larger pixels are less noisy because the signal increases faster than the noise) and the E-M1 image would be more detailed.

I was thinking of giving it a try but there is this pesky lens issue (among other issues) and I'm not sure how to get around that.

DonSC Senior Member • Posts: 1,032
Re: And the answer is:

No idea really. For me "same ISO" is just a shorthand for same shutter speed and aperture. I've always assumed that for different ISO the electronics are optimized for different amounts of light.

Great Bustard Forum Pro • Posts: 43,425
Re: And the answer is:

DonSC wrote:

Great Bustard wrote:

Instead of "same ISO", how about we say, "same f-ratio and shutter speed", as the ISO setting isn't particularly relevant to the matter at hand, and the cameras may not meter the scene the same at the same ISO setting.

Then the EM1 photo will have less noise since it has a more efficient sensor. The EM1 photo will be more detailed since it has 4x as many pixels on the subject.

Now let's assume we had a FF sensor made with the exact same pixels as the EM1 sensor. Then the photos would be all but identical.

I don't know the answer but I'm thinking that the 1Dx image would have less noise (because the pixels are so much larger and larger pixels are less noisy because the signal increases faster than the noise) and the E-M1 image would be more detailed.

I just now realized you said "1Dx" -- in my initial reply, I thought you said "1Ds", so that will change my answer to what you were thinking.  That is, the noise would be about the same for both, but the EM1 photo would be more detailed.

I was thinking of giving it a try but there is this pesky lens issue (among other issues) and I'm not sure how to get around that.

It would be an interesting demonstration, if you could swing it.

Great Bustard Forum Pro • Posts: 43,425
Re: And the answer is:

DonSC wrote:

No idea really. For me "same ISO" is just a shorthand for same shutter speed and aperture.

I think most people think that way, but it really depends on how the particular camera meters.

I've always assumed that for different ISO the electronics are optimized for different amounts of light.

Changing the ISO setting applies either an analog or digital amplification to the signal.  In the case of analog amplification with non-ISOless sensors, this results in less read noise.  That's why, for example, a photo at f/2.8 1/200 ISO 3200 will look less noisy than a photo of the same scene at f/2.8 1/200 ISO 100 pushed 5 stops in the conversion.  On the other hand, if the amplification is digital, then the two photos would look the same.

Sergey_Green
Sergey_Green Forum Pro • Posts: 12,001
If I am makeing any sense with this ..

Great Bustard wrote:


...

Again, it will depend on the particular pair of lenses you compare. Also, lenses for 4/3 have to be twice as sharp as lenses for FF to resolve as well for sensors with the same pixel count and AA filter,

Yes, but we can not say if the FF lenses will not resolve twice just as well, as they are always tested on cameras that have larger pixel sensors. And as time goes by and technology evolves I see that those same FF lenses (that were supposedly resolving only half of what FT lenses were) are only getting better and better with every wave of the new cameras.

Good indication of their real sharpness, I think, would be a comparison against the 3-rd part lenses that are (can be) used on both systems.. If the FT lenses are to be twice as good in resolution, then they would simply outclass and outshine anything else that is not done by Olympus. So far I have not see this happening.

but FF sensors tend to have more pixels, so they have to be more than twice as sharp to resolve as well. So, let's say the 4/3 lens was 1.5x as sharp. That would help narrow the gap, but the gap would be there, nonetheless.

And the gap is always there. The only time it narrows is when the comparison is done around the same numeric apertures, like wide open against wide open, without and hint or point that wide open on FT is like half closed on FF.

I just don't believe they are (or need to be) twice as sharp as most of the FF lenses are. Not from what I see at least. And we were to test FF lenses on as packed sensors as what FT's are, then the lines per mm numbers would be likely similar as well.

-- hide signature --

- sergey

Great Bustard Forum Pro • Posts: 43,425
Re: If I am making any sense with this ..

Sergey_Green wrote:

Great Bustard wrote:

...

Again, it will depend on the particular pair of lenses you compare. Also, lenses for 4/3 have to be twice as sharp as lenses for FF to resolve as well for sensors with the same pixel count and AA filter,

Yes, but we can not say if the FF lenses will not resolve twice just as well, as they are always tested on cameras that have larger pixel sensors. And as time goes by and technology evolves I see that those same FF lenses (that were supposedly resolving only half of what FT lenses were) are only getting better and better with every wave of the new cameras.

Good indication of their real sharpness, I think, would be a comparison against the 3-rd part lenses that are (can be) used on both systems.. If the FT lenses are to be twice as good in resolution, then they would simply outclass and outshine anything else that is not done by Olympus. So far I have not see this happening.

You raise some good points, here. It would be interesting to see lenses tested on the same sensor, since this also takes care of the issue of the AA filter.

but FF sensors tend to have more pixels, so they have to be more than twice as sharp to resolve as well. So, let's say the 4/3 lens was 1.5x as sharp. That would help narrow the gap, but the gap would be there, nonetheless.

And the gap is always there. The only time it narrows is when the comparison is done around the same numeric apertures, like wide open against wide open, without and hint or point that wide open on FT is like half closed on FF.

For sure. But, as we both know, comparing, for example, f/2 on 4/3 to f/2 on FF would only make any sense if the scene were within the DOF since, by definition, the portions of the scene outside the DOF are going to have less and less resolution as you move from the focal plane.

I just don't believe they are (or need to be) twice as sharp as most of the FF lenses are. Not from what I see at least. And we were to test FF lenses on as packed sensors as what FT's are, then the lines per mm numbers would be likely similar as well.

Like I said, it would be interesting to test. However, the results would vary considerably, depending on the particular lenses being compared and where in the frame you are looking, even presuming the same DOF.

bobn2
bobn2 Forum Pro • Posts: 62,699
Re: And the answer is:

DonSC wrote:

No idea really. For me "same ISO" is just a shorthand for same shutter speed and aperture.

I think most people think that way, but it really depends on how the particular camera meters.

I've always assumed that for different ISO the electronics are optimized for different amounts of light.

Changing the ISO setting applies either an analog or digital amplification to the signal.  In the case of analog amplification with non-ISOless sensors, this results in less read noise.  That's why, for example, a photo at f/2.8 1/200 ISO 3200 will look less noisy than a photo of the same scene at f/2.8 1/200 ISO 100 pushed 5 stops in the conversion.  On the other hand, if the amplification is digital, then the two photos would look the same.

But the ISO exposure index standards don't specify at all how much 'amplification' should be applied. So how can 'ISO' be about amplification?
--
Bob

bobn2
bobn2 Forum Pro • Posts: 62,699
Re: And the answer is:

No idea really. For me "same ISO" is just a shorthand for same shutter speed and aperture. I've always assumed that for different ISO the electronics are optimized for different amounts of light.

Can't be that, because then you'd always set the same EV at the same ISO, but you don't.
--
Bob

Lab D Veteran Member • Posts: 6,938
Think of a fat lady and thin supermodel on the beach
8

A fat lady and a thin supermodel are laying on the beach.   Who will get sun burnt faster?  Answer: both will burn/tan the same despite the fat lady having 4x the skin area.

Maybe they need a good UV filter.

Anyway, Four Thirds is the hot supermodel.

 Lab D's gear list:Lab D's gear list
Panasonic FZ1000 Panasonic Lumix DMC-GH4 Nikon D600
surfingmaltman Regular Member • Posts: 185
+1 and THANKS (NT) Re: A reminder for some memebers as to what the F stop is all about.
1

gsergei wrote:

Hi, all.

I've just had a quick look at the thread started by Dave Gaines about equivalence , again. He has made a very good point overall. Surprisingly, there are still photographers who fundamentally don't know what the aperture is all about. They say things like " convince me, that the amount of light going through Olympus 25/2.8 is the same compared to Canon, e.g., 50/1.4 set to 2.8". I have to disappoint you: YES ,it is the same. Why? -because it is a relative measure, not absolute. F2.8 on a Lumix LX3 allows the same illumination of sensor as PL 25/1.4 set to F2.8, the same as Canon 50/1.4 set to F2.8 !!!

also there is a lot of "expert talk" that bigger lenses allow more light and therefore this results in less noise in the image. This is total BS.

Now let's go through some lesson of optics. Some people visiting this website have no knowledge about the school items like : candela (don't confuse with Nelson Mandela), lumen, brightness, decibel, voltage, Amper, semiconductor electronic noise level, relative to signal vs absolute, etc.

So, F2 on a lens means that this diameter of the opening of the optical instrument can fit TWO times into its focal length. For a 50 mm F2 lens it means that the aperture diameter at F2 is 25 mm. That's it, people. It has never meant FF versus 4/3 versus whatever sensor/film size you had in your camera. Just the optical geometry. Easy ? Accordingly , F11 means that this diaphragm /aperture diameter will fit 11 times into the instrument's focal length. It's been like that since the inception of photography in the 19th century.

Now about the sensor noise on FF cameras vs. 4/3 vs anything else. The ONLY reason why they (FF) have less noise and better dynamic range is because their individual photosites are BIGGER electronic devices. Any semiconductor/ transistor/ diode has its electronic noise, because inside its P-N-P or N-P-N layers there are electrons which move randomly even when there is no "useful" signal. This chaotic movement is called "noise". A bigger semiconductor device can put through higher DC current and have "relatively" less noise.

The DPR once had a very useful parameter in the camera specification table describing the sensor's photosite in micrometers. there one could easily see that larger Canikons had bigger photosites, something like 8 micrometers vs Olympus's (don't remember precisely) 4.6 or something like that, therefore their light sensitive "transistors" were bigger and could provide higher DC current compared to Olympus's or any other smaller sensor. It is This DC micro current that gives you higher DR and less noise, NOT the size of the sensor. Mind you , if Canon were to put 50 megapixel into its FF sensor it will have a much worse performance for noise and DR compared to their own 16 Mp or whatever on their current offerings. Again it has to do with pixel density (diodes per square mm) and size of the electronic device,it has nothing to do with 36x24 mm. If Olympus were to put only 3 Mp into their 4/3 sensor it would be the same of better than any Canikon you know in terms of noise and DR, but then you would complain about the low resolution, yeah, right !

The megapixel race is for stupid consumers and marketing boys/ploys, it has nothing to do with photography. I am totally against it. I don[t need even 16 MP on my EM1 and would love to see a new Olympus sensor with 10 or even 8 MP but with a higher quality sensor properties. That's it.

In the mean time : kudos to Olympus engineers for designing their fine lenses !

thank you for reading and now I will retire to my morning coffee.

Photo amen to all of you.

 surfingmaltman's gear list:surfingmaltman's gear list
Olympus E-M1 II Olympus 12-40mm F2.8 Pro Olympus Zuiko Digital ED 7-14mm 1:4.0 Olympus M.Zuiko Digital 45mm F1.8 Olympus 40-150mm F2.8 Pro +2 more
Roger Engelken
Roger Engelken Veteran Member • Posts: 5,439
Re: Think of a fat lady and thin supermodel on the beach
4

Lab D wrote:

A fat lady and a thin supermodel are laying on the beach. Who will get sun burnt faster? Answer: both will burn/tan the same despite the fat lady having 4x the skin area.

Maybe they need a good UV filter.

Anyway, Four Thirds is the hot supermodel.

This begs the question, when will the Fat Lady sing and put a merciful end to this thread?

 Roger Engelken's gear list:Roger Engelken's gear list
Panasonic Lumix DMC-GX8 Olympus E-M1 Olympus OM-D E-M10 Olympus E-M1 II Olympus PEN E-P5 +10 more
philosomatographer
philosomatographer Contributing Member • Posts: 539
Re: Question:
1

Great Bustard wrote:

If you want to say that you enjoy using your E5 and SHG lenses, and are pleased with the photos they produce, I would never argue against it. If you want to go further and say that you prefer the output of the E5 and your SHG lenses to any other system, I would never argue against it. Indeed, I've heard people make the same types of comments about the original 5D vs its successors.

It's when you imply that the E5 and SHG lenses are "better than" any other system out there as a blanket statement that I take exception.

In my opinion, the SHG lenses *are* better than anything similar to what Canon, Nikon or Leica have been able to produce in those ranges. If this blanket statement bothers you, you are fully within your rights to ignore it. Have you used a wide-enough range of lenses and systems to really tell, though? If so, let's just agree to disagree.

The E-5 is most certainly not even 'competitive' - the sensor is horribly outdated, and these lenses are starved of a worthy sensor. From a detail rendition aspect, it's just about the best 12MP sensor you're going to ever find.But it's a noisy, DR-limited 12MP.

 philosomatographer's gear list:philosomatographer's gear list
Nikon Df Carl Zeiss Makro-Planar T* 2/100 Nikon AF-S Nikkor 14-24mm f/2.8G ED Nikon AF-S Nikkor 200mm f/2G ED-IF VR Olympus Zuiko Digital ED 14-35mm 1:2.0 SWD +3 more
Great Bustard Forum Pro • Posts: 43,425
Re: Question:
1

philosomatographer wrote:

Great Bustard wrote:

If you want to say that you enjoy using your E5 and SHG lenses, and are pleased with the photos they produce, I would never argue against it. If you want to go further and say that you prefer the output of the E5 and your SHG lenses to any other system, I would never argue against it. Indeed, I've heard people make the same types of comments about the original 5D vs its successors.

It's when you imply that the E5 and SHG lenses are "better than" any other system out there as a blanket statement that I take exception.

In my opinion, the SHG lenses *are* better than anything similar to what Canon, Nikon or Leica have been able to produce in those ranges.

You are, of course, welcome to your opinion.

If this blanket statement bothers you, you are fully within your rights to ignore it.

Well, "bothers" isn't really the word.  I simply prefer "aficionado" statements to be backed up with something more substantial.

Have you used a wide-enough range of lenses and systems to really tell, though? If so, let's just agree to disagree.

Truth be told, I don't think the IQ differential really matters to the vast majority.  Post a nice pic with stripped EXIF from the 50-200 / 2.8-3.5 and say it was from the 35-100 / 2, and no one will doubt you.  Post a bad pic from the 35-100 / 2, and people will praise you just because you own something so expensive.  It's the same in all the forums.

The E-5 is most certainly not even 'competitive' - the sensor is horribly outdated, and these lenses are starved of a worthy sensor.

Will they not work on the EM1?

From a detail rendition aspect, it's just about the best 12MP sensor you're going to ever find.But it's a noisy, DR-limited 12MP.

To me, you can't get a photo with just a lens or just a sensor.  You kind of need both.  So what matters is how the lens performs on the available sensors.  I mean, would you brag about owning a Ferrari if it sported wheels and tires from a Camry?  I mean, why not just get a Camry -- it's a pretty decent car.

philosomatographer
philosomatographer Contributing Member • Posts: 539
Re: Question:

Great Bustard wrote:

philosomatographer wrote:

Have you used a wide-enough range of lenses and systems to really tell, though? If so, let's just agree to disagree.

Truth be told, I don't think the IQ differential really matters to the vast majority. Post a nice pic with stripped EXIF from the 50-200 / 2.8-3.5 and say it was from the 35-100 / 2, and no one will doubt you. Post a bad pic from the 35-100 / 2, and people will praise you just because you own something so expensive. It's the same in all the forums.

Well, there we go - agreeing again. Technical quality is almost completely orthogonal to artistic merit, and it usually just doesn't matter. Pity it gets everytbody knickers in a knot when one dares talk about technicalities though!

The E-5 is most certainly not even 'competitive' - the sensor is horribly outdated, and these lenses are starved of a worthy sensor.

Will they not work on the EM1?

Oh yes - they work fine. Problem is, an EM1 sensor is no match for a good full-frame sensor, and the SHG lenses at f/2.0 hopelessly out-resolve the 16MP sensor to the point of creating moíre aliasing across the frame. The EM1 is a small step-up in image quality from the E-5.

From a detail rendition aspect, it's just about the best 12MP sensor you're going to ever find.But it's a noisy, DR-limited 12MP.

To me, you can't get a photo with just a lens or just a sensor. You kind of need both. So what matters is how the lens performs on the available sensors. I mean, would you brag about owning a Ferrari if it sported wheels and tires from a Camry? I mean, why not just get a Camry -- it's a pretty decent car.

The same situation applies to your high-resolution full-frame DSLR cameras and the so-so lenses you have to put on them. Seems we just can't win whichever way we go!

 philosomatographer's gear list:philosomatographer's gear list
Nikon Df Carl Zeiss Makro-Planar T* 2/100 Nikon AF-S Nikkor 14-24mm f/2.8G ED Nikon AF-S Nikkor 200mm f/2G ED-IF VR Olympus Zuiko Digital ED 14-35mm 1:2.0 SWD +3 more
robert1955 Veteran Member • Posts: 4,455
Re: Think of a fat lady and thin supermodel on the beach

Roger Engelken wrote:

Lab D wrote:

A fat lady and a thin supermodel are laying on the beach. Who will get sun burnt faster? Answer: both will burn/tan the same despite the fat lady having 4x the skin area.

Maybe they need a good UV filter.

Anyway, Four Thirds is the hot supermodel.

This begs the question, when will the Fat Lady sing and put a merciful end to this thread?

When she weighs in at 150 [metric]

 robert1955's gear list:robert1955's gear list
Fujifilm X-E3 Fujifilm XF 16mm F1.4 R WR Fujifilm 50mm F2 R WR Samyang 12mm F2.0 NCS CS XF 90mm
Bmoon Regular Member • Posts: 291
Re: Think of a fat lady and thin supermodel on the beach

Lab D wrote:

A fat lady and a thin supermodel are laying on the beach. Who will get sun burnt faster? Answer: both will burn/tan the same despite the fat lady having 4x the skin area.

Maybe they need a good UV filter.

Anyway, Four Thirds is the hot supermodel.

But the million dollar question is which one requires more sunscreen to reduce their exposure to the sun ?

 Bmoon's gear list:Bmoon's gear list
Nikon D3X Nikon D300S Pentax K10D Pentax K-5 Canon EOS 5D Mark II +7 more
DonSC Senior Member • Posts: 1,032
Re: Um...

Great Bustard wrote:The total light is the total amount of light that falls on the portion of the sensor used to for the photo during the exposure: Total Light = Exposure · Effective Sensor Area. The same total amount of light will fall on the sensor for equivalent photos but, for different formats, this will necessarily result in a different exposure on each format, since the same total light distributed over sensors with different areas will result in a lower density of light on the larger sensor.

I've always wondered if this were really true. For sure it's true if you mount the SAME lens on cameras with different sized sensors. But what if the lens creates a smaller image circle? A lens isn't a tube. A 300mm f/2.8 lens doesn't have to create a FF image circle. It can create a larger image circle or a smaller one. A 300mm f/2.8 m43 lens which creates an image circle with half the diameter of a 300mm f/2.8 FF lens will deliver the same amount of total light to the sensor. While the area will be smaller the density of light will be higher.

Isn't this what the speed boosters do?

CollBaxter
CollBaxter Forum Pro • Posts: 12,724
A simple Yes or No.

Great Bustard wrote:

gsergei wrote:

Or why the light meter doesn't care.

Hello, again.

Let me repeat my point:

Given the same light source conditions and ISO setting the illumination, measured in lumens, received by any size of sensor is equal across all formats (no Ifs , no buts) , when cameras are set to the same A , S, ISO values. So, in practical terms this means, that the illumination received by my tiny c7070 at 125/5.6 and ISO 100 is exactly the same as on the so called FF sensor camera set to the same values. This will result in the same picture brightness/darkness , subject to DR and noise differences.

No one that I'm aware of claims that f/2 will not result in the same exposure regardless of format or focal length for a given scene luminance and shutter speed.

Please, do not feed me things like "amount of light", "sensor area", "light power" , "bigger lens opening" etc. and try to operate , using known physical terms and concepts.

If the difference between the amount of light per area that falls on the sensor (exposure), and the total amount of light the sensor records is difficult to understand, well...

Is the amount/intensity  of light on a say a square cm at the center 4/3 , APS-C , APS-H , 1 inch , FF , 36X49 sensors at say f/2.8 not equal ?

A simple Yes or No.

Here is the final word. Please, do me a favor:

get hold of ANY light meter (be it a 40 year old analogue one, or a modern Sekonic) and look at it carefully and then tell me , where do you see "Canon FF" or "Olympus c2020" or Fujifilm X100s ??? And then prove me wrong.

Speaking of "final words", understanding the difference between the amount of light per area on the sensor (exposure), the total amount of light that falls on the sensor, and how these relate to the visual properties of the recorded photo is rather fundamental:

http://www.josephjamesphotography.com/equivalence/#exposure

This section will answer the following four questions:

  • For a given scene, what is the difference in exposure, if any, between f/2.8 1/200 ISO 400 and f/5.6 1/200 ISO 1600?
  • What role does the ISO setting play?
  • What role does the sensor size play?
  • What does any of this have to do with the visual properties of the photo?

As mentioned in the introduction of this essay, the concept of Equivalence is controversial because it replaces the paradigm of exposure, and its agent, f-ratio, with a new paradigm of total light, and its agent, aperture. The first step in explaining this paradigm shift is to define exposure, brightness, and total light.

The exposure is the density of light (total light per area -- photons / mm²) that falls on the sensor during the exposure, which is usually expressed as the product of the illuminance of the sensor and the time the shutter is open (lux · seconds, where 1 lux · second = 4.1 billion photons / mm² for green light -- 555 nm). The only factors in the exposure are the scene luminance, t-stop (where the f-ratio is often a good approximation for the t-stop), and the shutter speed (note that neither sensor size nor ISO are factors in exposure).

For example, two pics of the same scene, one at f/2.8 1/200 ISO 100 and another at f/2.8 1/200 ISO 400 (on any system, regardless of format) will both have the same exposure, since the same number of photons per unit area will fall on the sensor, but the ISO 400 photo will appear 4x (2 stops) brighter than the ISO 100 photo since the signal is amplified by a factor of four due to the higher ISO setting.

The brightness, then, is the brightness of the final image after an amplification is applied to the exposure either by adjusting the ISO and/or a push/pull in the RAW conversion, and is often what people mean when they say "exposure". For example, pics of the same scene at f/2.8 1/200 ISO 100 and f/5.6 1/200 ISO 400 will be processed to have the same brightness, even though the f/2.8 photo has 4x (two stops greater) exposure than the f/5.6 photo.

The role of the ISO setting in exposure is in how the setting indirectly results in the camera choosing a different f-ratio, shutter speed, and/or flash power, any and all of which will change the exposure. For example, changing the ISO from 100 to 400 may result in the camera choosing f/5.6 instead of f/2.8, 1/200 instead of 1/50, f/4 1/100 instead of f/2.8 1/50, etc. Aside from that, the ISO control on the camera will apply an analog gain (which results in less read noise for higher ISOs with cameras that use non-ISOless sensors) and/or a digital push/pull (usually for intermediate ISO settings).

The total light is the total amount of light that falls on the portion of the sensor used to for the photo during the exposure: Total Light = Exposure · Effective Sensor Area. The same total amount of light will fall on the sensor for equivalent photos but, for different formats, this will necessarily result in a different exposure on each format, since the same total light distributed over sensors with different areas will result in a lower density of light on the larger sensor. Using the same example above, pics of the same scene at f/2.8 1/200 on mFT (4/3) and f/5.6 1/200 on FF will result in the same total light falling on each sensor, but the exposure will be 4x (2 stops) greater for the mFT photo, and thus the FF photographer would usually use a 4x (2 stops) higher ISO setting to get the same brightness for the LCD playback and/or OOC (out-of-the-camera) jpg.

Lastly, the Total Light Collected (signal) is the amount of light that is converted to electrons by the sensor, which is the product of the Total Light that falls on the sensor during the exposure and the QE (Quantum Efficiency of the sensor -- the proportion of light falling on the sensor that is recorded). For example, if QE = 1, then all the light falling on the sensor is recorded. For reference, the Olympus EM5, Canon 5D3, and Nikon D800 all have a QE of approximately 0.5 (50%).

In terms of IQ, the total light collected is the relevant measure, because both the noise and DR (dynamic range) of a photo are a function of the total amount of light that falls on the sensor (along with the sensor efficiency, all discussed, in detail, in the next section). That is, noise is determined by the total amount of light falling on the sensor and the sensor efficiency, not the ISO setting on the camera, as is commonly believed (the ISO setting is simply a matter of processing the signal, discussed in more detail here). In other words, the less light that falls on the sensor, the more noisy and darker the photo will be. Increasing the ISO setting simply brightens the captured photo making the noise more visible.

For a given scene, perspective, and framing, the total light depends only on the aperture diameter and shutter speed (as opposed to the f-ratio and shutter speed for exposure). Fully equivalent images on different formats will have the same brightness and be created with the same total amount of light. Thus, the same total amount of light on sensors with different areas will necessarily result in different exposures on different formats, and it is for this reason that exposure is a meaningless measure in cross-format comparisons.

Mathematically, we can express these four quantities rather simply:

  • Exposure (photons / mm²) = Sensor Illuminance (photons / mm² / s) · Time (s)
  • Brightness (photons / mm²) = Exposure (photons / mm²) · Amplification (unitless)
  • Total Light (photons) = Exposure (photons / mm²) · Effective Sensor Area (mm²)
  • Total Light Collected (electrons) = Total Light (photons) · QE (electrons / photon)

So, we can now answer the questions posed at the beginning of the section...

I know, I know -- anything that takes more than a sentence or two to explain isn't worth knowing, right?

-- hide signature --

Collin
(Aficionado Olympus DSLR )
http://collinbaxter.zenfolio.com/
http://www.pbase.com/collinbaxter
http://www.outdoorphoto.co.za/gallery/showgallery.php?ppuser=21652&username=collin
Life is not measured by the number of breaths we take, but by the moments that take our breath away. (George Carlin)
New Seventh Wonder of the World.
http://www.pbase.com/collinbaxter/image/95297052.jpg

 CollBaxter's gear list:CollBaxter's gear list
Canon PowerShot SX230 HS Olympus E-5 Olympus E-30 Olympus E-620 Olympus E-500 +15 more
Bmoon Regular Member • Posts: 291
Re: A simple Yes or No.

CollBaxter wrote:

Great Bustard wrote:

gsergei wrote:

Or why the light meter doesn't care.

Hello, again.

Let me repeat my point:

Given the same light source conditions and ISO setting the illumination, measured in lumens, received by any size of sensor is equal across all formats (no Ifs , no buts) , when cameras are set to the same A , S, ISO values. So, in practical terms this means, that the illumination received by my tiny c7070 at 125/5.6 and ISO 100 is exactly the same as on the so called FF sensor camera set to the same values. This will result in the same picture brightness/darkness , subject to DR and noise differences.

No one that I'm aware of claims that f/2 will not result in the same exposure regardless of format or focal length for a given scene luminance and shutter speed.

Please, do not feed me things like "amount of light", "sensor area", "light power" , "bigger lens opening" etc. and try to operate , using known physical terms and concepts.

If the difference between the amount of light per area that falls on the sensor (exposure), and the total amount of light the sensor records is difficult to understand, well...

Is the amount/intensity of light on a say a square cm at the center 4/3 , APS-C , APS-H , 1 inch , FF , 36X49 sensors at say f/2.8 not equal ?

A simple Yes or No.

Let’s take the camera out of the equation, I will build a box and at the back of the box I place a negative with a iso rating of 200 . I use a quarter as my subject that I want to make prints of.

Now I cut a hole in front of the box and use 2 exposures with 2 different lenses. For the first exposure I use a 25mm F2.8 lens , for the next I use a 50mm F2.8 lens.

Now I make 8x10 wet prints of each exposure such that the quarter will appear the same size in the prints, with the 25mm F2.8 I would have to enlarge the image 2 times more than I would the 50mm F2.8. Would this not affect how noise would appear between the exposures in print?

Would it not make sense that between the 2 photos the one that had more negative exposed to light will have less noise.

Here is the final word. Please, do me a favor:

get hold of ANY light meter (be it a 40 year old analogue one, or a modern Sekonic) and look at it carefully and then tell me , where do you see "Canon FF" or "Olympus c2020" or Fujifilm X100s ??? And then prove me wrong.

Speaking of "final words", understanding the difference between the amount of light per area on the sensor (exposure), the total amount of light that falls on the sensor, and how these relate to the visual properties of the recorded photo is rather fundamental:

http://www.josephjamesphotography.com/equivalence/#exposure

This section will answer the following four questions:

  • For a given scene, what is the difference in exposure, if any, between f/2.8 1/200 ISO 400 and f/5.6 1/200 ISO 1600?
  • What role does the ISO setting play?
  • What role does the sensor size play?
  • What does any of this have to do with the visual properties of the photo?

As mentioned in the introduction of this essay, the concept of Equivalence is controversial because it replaces the paradigm of exposure, and its agent, f-ratio, with a new paradigm of total light, and its agent, aperture. The first step in explaining this paradigm shift is to define exposure, brightness, and total light.

The exposure is the density of light (total light per area -- photons / mm²) that falls on the sensor during the exposure, which is usually expressed as the product of the illuminance of the sensor and the time the shutter is open (lux · seconds, where 1 lux · second = 4.1 billion photons / mm² for green light -- 555 nm). The only factors in the exposure are the scene luminance, t-stop (where the f-ratio is often a good approximation for the t-stop), and the shutter speed (note that neither sensor size nor ISO are factors in exposure).

For example, two pics of the same scene, one at f/2.8 1/200 ISO 100 and another at f/2.8 1/200 ISO 400 (on any system, regardless of format) will both have the same exposure, since the same number of photons per unit area will fall on the sensor, but the ISO 400 photo will appear 4x (2 stops) brighter than the ISO 100 photo since the signal is amplified by a factor of four due to the higher ISO setting.

The brightness, then, is the brightness of the final image after an amplification is applied to the exposure either by adjusting the ISO and/or a push/pull in the RAW conversion, and is often what people mean when they say "exposure". For example, pics of the same scene at f/2.8 1/200 ISO 100 and f/5.6 1/200 ISO 400 will be processed to have the same brightness, even though the f/2.8 photo has 4x (two stops greater) exposure than the f/5.6 photo.

The role of the ISO setting in exposure is in how the setting indirectly results in the camera choosing a different f-ratio, shutter speed, and/or flash power, any and all of which will change the exposure. For example, changing the ISO from 100 to 400 may result in the camera choosing f/5.6 instead of f/2.8, 1/200 instead of 1/50, f/4 1/100 instead of f/2.8 1/50, etc. Aside from that, the ISO control on the camera will apply an analog gain (which results in less read noise for higher ISOs with cameras that use non-ISOless sensors) and/or a digital push/pull (usually for intermediate ISO settings).

The total light is the total amount of light that falls on the portion of the sensor used to for the photo during the exposure: Total Light = Exposure · Effective Sensor Area. The same total amount of light will fall on the sensor for equivalent photos but, for different formats, this will necessarily result in a different exposure on each format, since the same total light distributed over sensors with different areas will result in a lower density of light on the larger sensor. Using the same example above, pics of the same scene at f/2.8 1/200 on mFT (4/3) and f/5.6 1/200 on FF will result in the same total light falling on each sensor, but the exposure will be 4x (2 stops) greater for the mFT photo, and thus the FF photographer would usually use a 4x (2 stops) higher ISO setting to get the same brightness for the LCD playback and/or OOC (out-of-the-camera) jpg.

Lastly, the Total Light Collected (signal) is the amount of light that is converted to electrons by the sensor, which is the product of the Total Light that falls on the sensor during the exposure and the QE (Quantum Efficiency of the sensor -- the proportion of light falling on the sensor that is recorded). For example, if QE = 1, then all the light falling on the sensor is recorded. For reference, the Olympus EM5, Canon 5D3, and Nikon D800 all have a QE of approximately 0.5 (50%).

In terms of IQ, the total light collected is the relevant measure, because both the noise and DR (dynamic range) of a photo are a function of the total amount of light that falls on the sensor (along with the sensor efficiency, all discussed, in detail, in the next section). That is, noise is determined by the total amount of light falling on the sensor and the sensor efficiency, not the ISO setting on the camera, as is commonly believed (the ISO setting is simply a matter of processing the signal, discussed in more detail here). In other words, the less light that falls on the sensor, the more noisy and darker the photo will be. Increasing the ISO setting simply brightens the captured photo making the noise more visible.

For a given scene, perspective, and framing, the total light depends only on the aperture diameter and shutter speed (as opposed to the f-ratio and shutter speed for exposure). Fully equivalent images on different formats will have the same brightness and be created with the same total amount of light. Thus, the same total amount of light on sensors with different areas will necessarily result in different exposures on different formats, and it is for this reason that exposure is a meaningless measure in cross-format comparisons.

Mathematically, we can express these four quantities rather simply:

  • Exposure (photons / mm²) = Sensor Illuminance (photons / mm² / s) · Time (s)
  • Brightness (photons / mm²) = Exposure (photons / mm²) · Amplification (unitless)
  • Total Light (photons) = Exposure (photons / mm²) · Effective Sensor Area (mm²)
  • Total Light Collected (electrons) = Total Light (photons) · QE (electrons / photon)

So, we can now answer the questions posed at the beginning of the section...

I know, I know -- anything that takes more than a sentence or two to explain isn't worth knowing, right?

-- hide signature --

Collin
(Aficionado Olympus DSLR )
http://collinbaxter.zenfolio.com/
http://www.pbase.com/collinbaxter
http://www.outdoorphoto.co.za/gallery/showgallery.php?ppuser=21652&username=collin
Life is not measured by the number of breaths we take, but by the moments that take our breath away. (George Carlin)
New Seventh Wonder of the World.
http://www.pbase.com/collinbaxter/image/95297052.jpg

 Bmoon's gear list:Bmoon's gear list
Nikon D3X Nikon D300S Pentax K10D Pentax K-5 Canon EOS 5D Mark II +7 more
Keyboard shortcuts:
FForum MMy threads