comparing lens + sensor size combos for low light

[Abe R Ration]

If I paint two walls, one larger than the other, I have to use more paint on the larger wall. Because its bigger. But the total amount of paint doesn't determine the quality of the paint job.

But you'd have to enlarge the smaller wall to the same output size so your analogy fails.

Yes I used more paint on the bigger wall, but it is spread out across a bigger area, too.

But you observed them at different enlargements.

If you take a picture with a large format camera and a iPhone, and you decide to compare the output, do you print the iPhone image to 4,8 mm by 3,6 mm and the large format image to 254mm by 203mm and then compare from the same distance?

Would that make any sense to you?

How about comparing the same output size?

Light and sensors/film work the same way. A bigger sensor absorbs more light for the same exposure, because the light has to be spread out across a larger area.

So with the same exposure an iPhone and Pentax 645D have identical image quality, same DoF on the same ouput sized image and so on?

Really?

The science of photography is about information. Here are simple facts:

The carriers of information are photons. Photons play by the rules of quantum mechanics and the flow of photons follows Poisson distribution. For poisson distribution standard deviation (or noise) is the square root of the number of photons. Thus the more photons are collected, the larger the signal to noise ratio will be. With the same exposure parameters (scene luminance, aperture number, exposure time) the larger the image, the more photons are collected, thus the higher SNR.

Correct exposure means that the sensor reproduces the real-life image faithfully

Sensor doesn't reproduce anything. The lens draws an image and the sensor samples it.

(let's define it that way) without losing shadow or highlight details. A smaller sensor collects less total light, but that light is spread across a smaller area, so that exposure is the same and our subject is reproduced correctly.

I understand perfectly what exposure is. Scene luminance, aperture number, exposure time. Exposure does not care about image circle size or sensor format or focal length or aperture diameter. However how the image appears does care about those things.

What is "correct exposure" however one wants to define it is not at all relevant to this context.

Anyone who has used a standalone light meter can tell you that there isn't a format adjustment.

And no one has claimed there is. So why you keep on briging this up?

How about reading what I write before answering?

It measures the light and tells you what ISO setting, aperture, and shutter speed combination will provide correct exposure.

ISO is not a part of exposure. Maybe you should check out how it's defined as it would tell you that it can not be.

And "correct exposure" is largely subjective and absolutely irrevant to this topic and context.

Now, there are certainly a host of other effects from changing format.

Indeed. And I've tried to teach you what those are but you keep on sidestepping to exposure being the same for all formats which is true, but irrelevant to this topic.

When you change the format, but keep exposure the same (along with framing and focus point) you change noise, depth of field and depth of focus. (We can ignore the last of those in this context.) I am happy to provide you with relevant formulas to calculate relevant numbers for different formats if you're interested.

And digital noise is influenced by sneers size

Not really. Maybe you should try to understand noise before talking about it. Try the Emil Martinec article. Or if you don't trust a physics professor, I can point you out to blog of a dude who teaches image sensor designers.

, just like grain was influenced by film size. But trying to say that "total light" means a thing is just simply bullhonky.

Ok, please explain photon shot noise to me and how it influences the image and output image?

Or is it just nonsense, scientific mumbojumbo?

 

[Pieterbaan]

Thus naturally also to create the same image on different formata you have to use different exposure settings.

--
Abe R. Ration - amateur photographer, amateur armchair scientist, amaterur camera buff
http://aberration43mm.wordpress.com/

BZZZZZT.

No, that's not how it works.

It sure is.

Sorry it is not how it works. When you ave a cell phone with a tiny sensor, but with an f/2 lens and under a given condition you can take a picture with ISO 100, apperture f/2 and sutterspeed of 1/100 of a second, then under the same conditions, you can take a picture with your FF camerawith exact the same settings.

The pictures will look very different for sure, but the exposure will be the same.

When your FF lens has the same FOV as the cell phone lens then the DOF of teh FF picture will be very different, when the FL of both lenses are the same the FOV will be very different.

When you want exact the same results (so same FOV and same DOF then the apperture of the FF camera lens must be set to a very small apperture, and you have to adjust shutterspeed and/or ISO too.

Problem with these Equivalent talking is that people are messing things up a lot.

Where do you people come up with this stuff?

That is quite insulting. Anyhow, evidence tells physics this and it tells me.

On the other hand your answer is just simple "you're wrong, I know better". No evidence or logic offered.

If different amount of light is collected, then the images are different:

• Different photon shot noise
• Either different DoF, scene illuminance or motion blur

True (as explained above). But when you take a picture with your FF camera and crop it after that, you don't change exposure (as that is impossible) and only get the crop of the original picture. The total amount of light gathered for the crop is different, but the total amount of light gathered per square inch is the same, no matter how much you crop.

If you think that is wrong, then please show some evidence.

You are both right, and you are both wrong!
To get exactly the same picture with aff camera and a crop camera you have to change exposure settings, FL etc. But when you only look at the exposure of the picture the exposure stays the same between the cameras...

It is the same when you crop by changing the FL of your zoom lens. The picture in the end will need the same exposure settings for the cropped version by zooming as that it was for the zoomed out version (when you want the subject to be exposed the same)

I'll present some of mine here (yet again):

Of noise, including photon shot noise by Emil Martinec , a physics professor and the autohor of Amaze-demosaicing algorithm.

DxOMark about normalization (which is related to "total light").

--
Abe R. Ration - amateur photographer, amateur armchair scientist, amaterur camera buff
http://aberration43mm.wordpress.com/

All these links show that when you want exact the same pictures you need to chage things, but when you only look at exposure you don't have to change anything.

Infact even with the equivalence set right the total ammount of exposure stay the same (so you change the apperture by say 2 stops, you have to change the ISO or the shutterspeed 2 stops too in the other direction. When you don't do that your picture will be over or under exposed...

 

[Abe R Ration]

I'm gonna take a wild guess and say that I was shooting large format film before most of you ever took up photography. I'm well-versed in how all this stuff works.

No, you're not. If you were, you would not write what you just wrote, but would explain with evidence, taking advantage of knowledge of physics.

Try this analogy: one may have been driving a car long before most folks on this forum were born, yet that doesn't mean one has a clue on how cars and their engines work.

When you shoot film with large format and miniature format and you plan to have an output the size of let's say 50cm by 50cm, what do you do to the image you've captured with film?

Do you enlarge it?

Do you enlarge the image of large format the same amount you enlarge the image of the miniature format?

Here is an exsample - identical exposure, identical pixels, different formats, thus different total light - would you say that there two crops are identical or not? Equally noisy? If not, what not?

[IMG width="400px" alt="If "total light" is rubbish the above crops have identical signal to noise ratio, or "noise". "]https://aberration43mm.files.wordpress.com/2015/02/compared.png[/IMG]
If "total light" is rubbish the above crops have identical signal to noise ratio, or "noise".

Oh and I'll laugh to myself whenever I see another idiotic total light post. And go back to working on improving my photography.

A pity you're not interested in the science of photogaphy in spite of participating to a thread about it. Maybe you should avoid doing so?



--
Abe R. Ration - amateur photographer, amateur armchair scientist, amaterur camera buff

Abe R. Ration's lens and camera blog

This blog is about camera and lens technology and related sciences

aberration43mm.wordpress.com

 

[Abe R Ration]

Thus naturally also to create the same image on different formata you have to use different exposure settings.

 

[Abe R Ration]

You can call exposure "image brightness" if you want.

Sure as long as you mean the image the lens renders to the focal plane. Otherwise it wouldn't make any sense. Especially if you think of the output image it would make no sense.

Regardless this kind of using of terms it is bound to cause confusion.

As far as I'm concerned there is no distinction.

Brightness is a property of the output image, the one we print out or look at a display. That is a functon of processing the data the image sensor has captured from the information (or image) the lens has drawn.

Exposure has nothing to do with the image sensor, processing or output image.

Using the same vocabulary with the same meanings as the rest of the world would make discussions more easy to comprehend and far less confusing. I am sure we agree on this.

And it's true you can adjust apparent exposure in post processing, but that doesn't change anything either.

Your use or terminology is problematic and confusing. Why not use the standard terminology so everyone in the thread has much easier time to understand what one means?

Brightness: how bright the output image is, a function of processing.

Exposure: how much light per unit are the image is drawn

"Apparent exposure" is a confusing piece of terminology - maybe it means brightness, maybe exposure, who knows, but it's bound to cause problems for the discussion.

Let me quote Wikipedia :

In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance.

The amount of light does not change no matter what you do to the image after it's captured.

f/2.8 is f/2.8 whether you use a 1 inch square of film, or a 10 foot square. As far as exposure is concerned.

Has anyone argued against that?

It's just that the same exposure parameters create a different effect on different formats:

• If exposure time is fixed, but depth of field is not, then a larger sensor can have SNR advantage, but to achieve that the depth of field will have to be narrower.
• If depth of field is fixed, but exposure time is not, then the larger sensor can have SNR advantage, but to achieve that it needs to use a slower shutter speed.
• If both exposure time and depth of field are fixed, then the SNR is the same, regardless of format.
• If both exposure time and depth of field can float freely, the larger sensor will have SNR advantage.

 

[Pieterbaan]

Abe, the thing I tried to explain is that you and lumigraphics have a different way of looking at exposure. Not one is true or false just different.

You want to create exactly the same picture with two cameras with two different sensors, so you have to take in account the equivalent settings for focal length, apperture etc. this is the only way to create to exactly the same pictures with the two systems. So here you are right you need to change settings to get exactly the same picture. (for noise DOF, VOF etc)

On the otherhand lumigraphics is sees the exposure as the settings needed to recreate the scenery in the best way. To make his point of view maybe a little more clear you could say that you take a picture of a gray wall. The only thing you want in your picture is that the grey in the wall is exactly the same as the gray in your picture. If this is the only thing you want (so no other things like noise, VOF and DOF) then the settings with every camera can be the same. This is true too (just as you said in your answer).

So the difference between you two is that you take a very technical approache to exposure, and lumigraphics takes a more practical approache.

People with only an APS camera don't realy care about the equivalent to FF (or MF or LF) they care about their picture exposed the best as possible So with no blown out highlights and no lost of details in the shadows.

Both approaches are good, a photographer with just one camera don't care how his picture will look on a different system he cares how it looks on his system. People with more then one camera may want to know everything about equivalence so they can take exactly the same picture with both cameras, or can use the strong points of their systems for the pictures they want to make.

The only thing I tried to do was show you this. Not telling you are wrong, only showing that you can look at this topic in different ways...

And pleas it is much nicer when you stay polite instead of telling people what to do....

 

[semifast]

To get the equivalent aperture you multiply by the crop factor of 1.31, so the f/2.8 lens on M43 is equivalent to f/3.67 on APS-C, which means the M43 should be 1/4 stop better in low light and will have 1/4 stop less DOF.

So equivalence is not only applicable on DOF (which I knew), but also in terms of exposure? That is, if I have both cameras set at say F4 and at the same ISO, the picture will be darker in m43?

I suppose thats an easy question to answer if only I had a m43 + APS-C camera, or APS-C camera + FF one, I could take two pics and compare.

F2.8 is F2.8. The aperture equivalence pertains to DoF, and has nothing to do with exposure. Aperture is one third of the exposure triangle, Aperture, shutter speed and ISO.

For example, high end smart phones have itty bitty sensors but have "wide open" apertures such as F2.0. However, if you do a macro shot or portrait with them it will be impossible to get subject isolation as one would with a larger sensor. Heck.... tiny cell phone sensors make for some really good landscape shots if the light is good enough to avoid high ISO. That's because the DoF is massive by comparison, so it is easy to get everything in focus.

No, Pixel Pooper is correct. Read the DPReview article on equivalence. It's basic physics.

I believe this is the section you are referring to. Quote (http://www.dpreview.com/articles/2666934640/what-is-equivalence-and-why-should-i-care/2):

The thing that complicates matters is ISO. ISO ensures that, if you expose a sensor to a given light intensity for a given amount of time, then you will get a certain brightness in your final (JPEG) image. Because it's based on intensity of light, it means that ISO depends on F-number, not equivalent aperture. This means that, a Four Thirds camera with a 50mm f/2 lens at ISO100 should produce a JPEG of the same brightness as a Full frame camera with a 100mm f/2 lens at ISO100 and, set to the same F-number and shutter speed, even though its smaller sensor means it is receiving 1/4 as much total light.

ISO is useful, in that it means that the same set of exposures work across all cameras (and frankly, it'd get confusing, otherwise). However, it ends up disguising how much total light each system gets. Since the light intensity is the same (per square mm), the Full Frame camera will receive four times as much light as the Four Thirds camera, during those exposures, because it has four times the sensor area, all experiencing that same intensity.

And this means that, for the same shutter speed, F-number and ISO, the camera with the largest sensor will have more total light to measure. And, unless the large sensor is significantly worse than the smaller one, it will produce a cleaner, less noisy image. It's likely that the large sensor camera will be bigger, heavier and more expensive, but it should provide cleaner images.

The flip-side of this is that, if you can fit a faster lens to a smaller format sensor or use a slower shutter speed then you can match the total light available to the larger system and gain similar image quality. However, this only really works in low light, where you're limited by the availability of light. In bright lighting conditions, where you're more worried about highlights clipping than you are about noise swamping the shadows, you can't simply open the aperture up to match a larger sensor's total light - you'll just end up over-exposing.

Yes, exactly. And this statement:

The equivalent aperture tells you what aperture on a full frame lens would give the same depth-of-field and the same total light as the one you're assessing.

That doesn't change anything about exposure. F/2.8 is f/2.8 as far as exposure, no matter what the sensor size is.

The dof is different. The amount of noise is possibly different. The exposure is the same.

Having more "total light" doesn't change the exposure.

Jesus H Christ, why is this so difficult to understand.

RIGHT, the light intensity at the sensor does not change.

HOWEVER, the total light collected by the sensor does change, which affects image quality. ISO 100 on a MFT sensor is equivalent in quality to ISO 400 on a full frame, because one is 4x the size of the other.

Take two solar panels. One is 6ft x 6ft. Another is 3ft x 3ft. The sunlight intensity hitting both is the same. Both are equally sensitive to light. But one is collecting 4x as much sunlight and producing 4x as much power as the other. Doesn't that make sense to you?

In the real world, solar panel size matters. In the real world, sensor size matters. Do you accept these facts or not?

I know it's hard to follow posts after a while.

I am only talking about one thing, exposure. To refute a couple of comments made about exposure.

I am not talking about image quality, dof, equivalence, or anything else. Just exposure.

The reason why I'm doing so is I don't think it's possible to have a fruitful discussion if there isn't a baseline agreement about what the basic facts are.

 

[Abe R Ration]

Abe, the thing I tried to explain is that you and lumigraphics have a different way of looking at exposure. Not one is true or false just different.

There is only one way of looking at exposure. The other ways are wrong.

Exposure is a function of scene luminance, aperture number and exposure time. Nothing more.

If you use the term exposure to mean something else, then you're creating confusion. Why not use proper termnology, it's not that hard.

You want to create exactly the same picture with two cameras with two different sensors, so you have to take in account the equivalent settings for focal length, apperture etc. this is the only way to create to exactly the same pictures with the two systems.

I'm not sure what you repeat to me what I've already written about a lot.

So here you are right you need to change settings to get exactly the same picture. (for noise DOF, VOF etc)

Ok, so where am I wrong? And please quote me and link to where I said something which is incorrect - you did claim I am wrong in your previous message while not providing any evidence on that.

On the otherhand lumigraphics is sees the exposure as the settings needed to recreate the scenery in the best way.

Which is totally out of context and also incorrect. Exposure settings and camera settings are not the same thing.

When he uses improper terminology he causes confusion as is evident if one reads this thread. He should use words like "camera settings" or whatever.

To make his point of view maybe a little more clear you could say that you take a picture of a gray wall. The only thing you want in your picture is that the grey in the wall is exactly the same as the gray in your picture. If this is the only thing you want (so no other things like noise, VOF and DOF)

Noise in an inherit property of the image. No image is without noise - even if you take a picture of gray wall.

then the settings with every camera can be the same.

Or they can be different.

Anyhow, what you wrote above doesn't have much point. It doesn't serve much purpose and it certainly does not address the context any eway.

This is true too (just as you said in your answer).

So the difference between you two is that you take a very technical approache to exposure, and lumigraphics takes a more practical approache.

Exposure has one very clear definition. He abuses the term.

It's not like my approach is "a very technical one", but it is the correct one.

Abusing well defined terminology to mean something which is totally different is not helpful to anyone. It just makes it harder for anyone to understand the discussion.

People with only an APS camera don't realy care about the equivalent to FF (or MF or LF) they care about their picture exposed the best as possible So with no blown out highlights and no lost of details in the shadows.

Maybe, but if the context is comparing different formats, it's irrelevant to talk about exposure or metering practises. If you want to talk about those, fine, but it has nothing to do with format comparison which kind of seemed to be the topic in this thread.

Both approaches are good,

Except that they are totally different topics. They're not approaches to some common goal. I'm not talking about "correct exposure" or anything like that. I'm comparing formats as that's pretty much what the thread was about, not about how to perform a decent exposure.

a photographer with just one camera don't care how his picture will look on a different system he cares how it looks on his system.

Sure, but how about sticking to the context of the thread. The title was "comparing lens + sensor size combos for low light", and not "how should I exposure for this or that purpose".

People with more then one camera may want to know everything about equivalence so they can take exactly the same picture with both cameras, or can use the strong points of their systems for the pictures they want to make.

How about people who want to compare formats, like the OP? Why discuss something which is not the context of the thread? It just causes confusion and tends to ruin the discussion.

The only thing I tried to do was show you this.

I have no idea what you mean by this?

Not telling you are wrong, only showing that you can look at this topic in different ways...

In the previous post you certainly did tell me how I am wrong. Please make up your mind and then show some evidence if I indeed was wrong. I am happy to learn to to be corrected if that indeed is the case, but simply stating that wihout providing any evidence is rude.

And it was clear from that post that you had either not bothered to read what I wrote or simply did not understand it.

And pleas it is much nicer when you stay polite instead of telling people what to do....

Pot calling kettle black. I am polite up to the point folks take a confrontational or even insulting position. Usually even a bit beyond that point.

If you claim that I am wrong and then don't bother to show where exactly and start talking about somethign which has nothing to do with what I say or what is the context of the thread to obfuscate the discussion, I am not sure why I should consider that to be polite behaviour, so maybe you should do as you prech?

 

[FingerPainter]

To get the equivalent aperture you multiply by the crop factor of 1.31, so the f/2.8 lens on M43 is equivalent to f/3.67 on APS-C, which means the M43 should be 1/4 stop better in low light and will have 1/4 stop less DOF.

So equivalence is not only applicable on DOF (which I knew), but also in terms of exposure? That is, if I have both cameras set at say F4 and at the same ISO, the picture will be darker in m43?

I suppose thats an easy question to answer if only I had a m43 + APS-C camera, or APS-C camera + FF one, I could take two pics and compare.

F2.8 is F2.8. The aperture equivalence pertains to DoF, and has nothing to do with exposure. Aperture is one third of the exposure triangle, Aperture, shutter speed and ISO.

For example, high end smart phones have itty bitty sensors but have "wide open" apertures such as F2.0. However, if you do a macro shot or portrait with them it will be impossible to get subject isolation as one would with a larger sensor. Heck.... tiny cell phone sensors make for some really good landscape shots if the light is good enough to avoid high ISO. That's because the DoF is massive by comparison, so it is easy to get everything in focus.

No, Pixel Pooper is correct. Read the DPReview article on equivalence. It's basic physics.

I believe this is the section you are referring to. Quote (http://www.dpreview.com/articles/2666934640/what-is-equivalence-and-why-should-i-care/2):

The thing that complicates matters is ISO. ISO ensures that, if you expose a sensor to a given light intensity for a given amount of time, then you will get a certain brightness in your final (JPEG) image. Because it's based on intensity of light, it means that ISO depends on F-number, not equivalent aperture. This means that, a Four Thirds camera with a 50mm f/2 lens at ISO100 should produce a JPEG of the same brightness as a Full frame camera with a 100mm f/2 lens at ISO100 and, set to the same F-number and shutter speed, even though its smaller sensor means it is receiving 1/4 as much total light.

ISO is useful, in that it means that the same set of exposures work across all cameras (and frankly, it'd get confusing, otherwise). However, it ends up disguising how much total light each system gets. Since the light intensity is the same (per square mm), the Full Frame camera will receive four times as much light as the Four Thirds camera, during those exposures, because it has four times the sensor area, all experiencing that same intensity.

And this means that, for the same shutter speed, F-number and ISO, the camera with the largest sensor will have more total light to measure. And, unless the large sensor is significantly worse than the smaller one, it will produce a cleaner, less noisy image. It's likely that the large sensor camera will be bigger, heavier and more expensive, but it should provide cleaner images.

The flip-side of this is that, if you can fit a faster lens to a smaller format sensor or use a slower shutter speed then you can match the total light available to the larger system and gain similar image quality. However, this only really works in low light, where you're limited by the availability of light. In bright lighting conditions, where you're more worried about highlights clipping than you are about noise swamping the shadows, you can't simply open the aperture up to match a larger sensor's total light - you'll just end up over-exposing.

Yes, exactly. And this statement:

The equivalent aperture tells you what aperture on a full frame lens would give the same depth-of-field and the same total light as the one you're assessing.

That doesn't change anything about exposure. F/2.8 is f/2.8 as far as exposure, no matter what the sensor size is.

The dof is different. The amount of noise is possibly different. The exposure is the same.

Having more "total light" doesn't change the exposure.

Jesus H Christ, why is this so difficult to understand.

RIGHT, the light intensity at the sensor does not change.

HOWEVER, the total light collected by the sensor does change, which affects image quality. ISO 100 on a MFT sensor is equivalent in quality to ISO 400 on a full frame, because one is 4x the size of the other.

Take two solar panels. One is 6ft x 6ft. Another is 3ft x 3ft. The sunlight intensity hitting both is the same. Both are equally sensitive to light. But one is collecting 4x as much sunlight and producing 4x as much power as the other. Doesn't that make sense to you?

In the real world, solar panel size matters. In the real world, sensor size matters. Do you accept these facts or not?

I know it's hard to follow posts after a while.

I am only talking about one thing, exposure. To refute a couple of comments made about exposure.

I am not talking about image quality, dof, equivalence, or anything else. Just exposure.

The reason why I'm doing so is I don't think it's possible to have a fruitful discussion if there isn't a baseline agreement about what the basic facts are.

I think you are correct that productive discussions are more likely to come from a shared understanding of the facts. I think that is what motivates posters like Abe, AHM, sybersitizen and me.

Furthermore, I think you are correct that f/2.8 is f/2.8 as far as exposure goes. And undoubtedly you are correct that you were only talking about one thing, exposure.

I'd appreciate it if you could quote the specific comments made about exposure that you are trying to refute, because, frankly, I haven''t seen any comments about exposure that disagree with you.

Finally, the subthread you have quoted begins with a post by pixelpooper about "equivalent aperture". Thus this subthread isn't just about exposure, but is also about "image qualify, dof, equivalence", and related matters. Pixelpooper's and AHM's comments in this subthread weren't comments about exposure. so perhaps you could explain the relevance to this subthread of your comments about exposure only.

 

[FingerPainter]

Thus naturally also to create the same image on different formats you have to use different exposure settings.

BZZZZZT.

No, that's not how it works.

Where do you people come up with this stuff?

PING!

Yes, it is.

If you want the same image on different formats, you need to use different apertures to get the same DOF, so you can either change the shutter speed to compensate for the aperture change, or keep the same shutter speed and change your ISO setting. Either way, the exposure settings are different.

Who was talking about DOF? You people are going on about exposure. :roll eyes:

No David, we people are talking about "the same image" I've bolded it in the root of the subthread quoted above so you can't miss it. The same image is more than an image with the same exposure. It is also an image with the same DOF, the same shot noise, the same FOV, the same perspective and the same motion blur.