Age old question revisited

Does APSC really have deeper DOF for macro?

Been researching this and this link:


have some really good info.

But there are a lot of arguments and confusion.

Base one BobAtkins's page, I am trying to figure out if I consider pixel on target or a fixed output number of pixel (say 4680 × 3166) for my frame, does APSC fair better?

Basically, I am ignoring magnification definition of 1X equal image size on sensor == real object size. But just want to get a 4680 × 3166 framing of the subject.

So if we consider the MP the sensor have:

(using macro DOF calculator from http://www.cambridgeincolour.com/tutorials/macro-lenses.htm)

FF DOF at 1X is 1.02 mm

So to have the same 4680 × 3166 frame as the FF ref above, my 24MP APSC (1.5x) should have the following magnification (ie magnification that can give the same framing above).

FF MP : APSC Magnification : DOF

22 : 0.4074074074 : 2.86 mm

35 : 0.6481481481 : 1.32 mm

42 : 0.7777777778 : 0.99 mm

50 : 0.9259259259 : 0.76 mm

Note: According to BobAtkins's page, Mag of 0.625x on APSC give the same framing as the 1X FF.

So, am I correct to conclude that if I want the same MP on subject, unless my FF is 45MP and above, my 24 MP APSC will be slightly better in terms of DOF?

If I include pixel pitch (pixel size) and its impact on noise into consideration, how will this chance my choice of sensor?

And if I include consideration for diffraction softening, will the 24MP APSC be less sharp (ie have more diffraction softening) compare to 35MP FF?

-kk

kkx said:

Does APSC really have deeper DOF for macro?

Been researching this and this link:

http://www.bobatkins.com/photography/technical/format_vs_macro_dof.html

have some really good info.

But there are a lot of arguments and confusion.

Base one BobAtkins's page, I am trying to figure out if I consider pixel on target or a fixed output number of pixel (say 4680 × 3166) for my frame, does APSC fair better?

Basically, I am ignoring magnification definition of 1X equal image size on sensor == real object size. But just want to get a 4680 × 3166 framing of the subject.

So if we consider the MP the sensor have:

(using macro DOF calculator from http://www.cambridgeincolour.com/tutorials/macro-lenses.htm)

FF DOF at 1X is 1.02 mm

So to have the same 4680 × 3166 frame as the FF ref above, my 24MP APSC (1.5x) should have the following magnification (ie magnification that can give the same framing above).

FF MP : APSC Magnification : DOF

22 : 0.4074074074 : 2.86 mm

35 : 0.6481481481 : 1.32 mm

42 : 0.7777777778 : 0.99 mm

50 : 0.9259259259 : 0.76 mm

Note: According to BobAtkins's page, Mag of 0.625x on APSC give the same framing as the 1X FF.

So, am I correct to conclude that if I want the same MP on subject, unless my FF is 45MP and above, my 24 MP APSC will be slightly better in terms of DOF?

If I include pixel pitch (pixel size) and its impact on noise into consideration, how will this chance my choice of sensor?

And if I include consideration for diffraction softening, will the 24MP APSC be less sharp (ie have more diffraction softening) compare to 35MP FF?

-kk

Click to expand...

Megapixels play no role in this equation. It all has to do with the size of the sensor, not how many MPs that sensor has.

The APS-C sensor will have lesser magnification if you try to get a fly to fit the frame, whereas the FF sensor will have greater magnification if you try to fit the same fly in the frame. That has to do with sensor size, not MPs.

Thanks for the reply.

I think I got that.

What I am trying to say is, if I ignore magnification (what I am giving up by doing this?) and just say I want a picture of a bee of 4680 × 3166.

Yes, using APSC with the smaller sensor, I am using less magnification to fill the bee in the 4680 × 3166 frame. But I accept that.

I am thinking, it doesn't matter what magnification I am using. Just trying to focus on pixel on subject. And the table I gave show that If I allow the magnification to change in the APSC camera to give me the framing I want, what DOF am I getting.

Does that make sense?

Since APS-C sensors were introduced everyone has been trying to make them sound as if they are somehow magical.

An APS-C sensor is just a physical crop of the image circle -and fundamentally no different than cropping in post. Since cropping in post does not increase magnification and APS-C sensor does not increase magnification. Some peeps might jump into this tread with some really twisted logic, but it's all BS...

Thanks John for the reply.

The "noise" in thread like this is really a problem for me. Trying to read them and figure out what is correct is not easy. I am really trying to figure this out.

I agree that APSC does not change magnification. But if my focus is just on pixel on subject and don't care about actual magnification. Does that help to clarify what I am trying to figure out?

As the final result of my macro work, I would like an image of a particular size (in pixel, say 4680 × 3166) and I try to fill my subject in that.

So using both FF and APCS, I try to do that. And I am comparing the pro and cons of the choices. The first is DOF ( and later, once I understand the DOF implication, will think about noise and other image quality items).

-kk

kkx said:

Thanks John for the reply.

The "noise" in thread like this is really a problem for me. Trying to read them and figure out what is correct is not easy. I am really trying to figure this out.

I agree that APSC does not change magnification. But if my focus is just on pixel on subject and don't care about actual magnification. Does that help to clarify what I am trying to figure out?

As the final result of my macro work, I would like an image of a particular size (in pixel, say 4680 × 3166) and I try to fill my subject in that.

So using both FF and APCS, I try to do that. And I am comparing the pro and cons of the choices. The first is DOF ( and later, once I understand the DOF implication, will think about noise and other image quality items).

-kk

Click to expand...

What we're trying to say is that pixels play no part in this. You're traveling the wrong path by focusing on the pixels because pixels can be bigger or smaller, the same number of pixels can fit on a bigger sensor or a smaller sensor. Therefore, even including pixels in this discussion is a non-sequitur.

I think I am starting to get it.

I am focusing on pixel (as a proxy for image quality, punting the other factor that affect image quality for now) to see if I try to get a final result with comparable image quality (hence the 4680 × 3166 frame for both FF and APSC) from both system.

But you are saying that it does not matter. If I am concern with final image quality, I should directly focus on sensor area on subject (I guess after I take into account all the factors that affect image quality, it will be proxy by sensor area). Basically boil down to magnification.

If that is the case, my quest for getting the same image quality (now same sensor area, or magnification) with APSC will always result in shallower DOF.

Is that what you are trying to say? I hope I have got this right.

kkx said:

I think I am starting to get it.

I am focusing on pixel (as a proxy for image quality, punting the other factor that affect image quality for now) to see if I try to get a final result with comparable image quality (hence the 4680 × 3166 frame for both FF and APSC) from both system.

But you are saying that it does not matter. If I am concern with final image quality, I should directly focus on sensor area on subject (I guess after I take into account all the factors that affect image quality, it will be proxy by sensor area). Basically boil down to magnification.

If that is the case, my quest for getting the same image quality (now same sensor area, or magnification) with APSC will always result in shallower DOF.

Is that what you are trying to say? I hope I have got this right.

Click to expand...

Image quality and magnification are two separate subjects and don't necessarily have anything to do with one another.

Magnification and DOF can be discussed as a single subject because they are related - the greater magnification, the shallower the depth of field.

So, let's decide which subject we're going to tackle, and then we can help you figure out what you need to do.

Thanks you for your patient and your effort in trying to help me understand.

I don't get the point about IQ is separated from magnification and DOF. So let me show my thinking process and you can point out what I start to get it wrong.

I think magnification (sensor area on subject) is directly link to IQ. Because we could just take a photo and crop like crazy and get a fly/bee in the photo frame but end up with just using a tiny area of the sensor. So the IQ will be terrible.

So macro shooter aim to get the best magnification i.e trying to use their sensor area as much as they could for a given subject. If you said IQ and magnification is not linked, then I am at a lost.

That is how I start to think about pixel on subject. Thinking that if we maintain a similar pixel on subject, the IQ will be maintained (or it limit how much cropping I can do). Since we have different sensor size and different MP count, I just try to focus on what I get as a final result, a photo with a particular pixel count on my subject.

kkx said:

Thanks you for your patient and your effort in trying to help me understand.

I don't get the point about IQ is separated from magnification and DOF. So let me show my thinking process and you can point out what I start to get it wrong.

I think magnification (sensor area on subject) is directly link to IQ. Because we could just take a photo and crop like crazy and get a fly/bee in the photo frame but end up with just using a tiny area of the sensor. So the IQ will be terrible.

So macro shooter aim to get the best magnification i.e trying to use their sensor area as much as they could for a given subject. If you said IQ and magnification is not linked, then I am at a lost.

That is how I start to think about pixel on subject. Thinking that if we maintain a similar pixel on subject, the IQ will be maintained (or it limit how much cropping I can do). Since we have different sensor size and different MP count, I just try to focus on what I get as a final result, a photo with a particular pixel count on my subject.

Click to expand...

You're correct in terms of cropping. However, let's take two cameras, one full frame and the other APS-C. Each camera is 20mp. You take a picture of a fly. The fly is 36mm in length. When you take a picture of the fly with a full frame camera at 1:1 magnification, the entire fly will fit. So, your picture will be of the ENTIRE fly at 20mp.



Now, let's take the same fly and shoot it with an APS-C camera so that it will fit the entire frame. When you take a picture of the entire fly on an APS-C camera, your magnification will be 1:2 (half lifesize), but you STILL have the entire fly in the frame at 20mp.

So, your image quality is the same with both cameras, BUT your DOF will be GREATER with the APS-C camera because you're shooting at a LESSER magnification in order to get the fly into the frame. Why are you shooting at a lesser magnification to get the fly into the frame? Because the APS-C sensor is SMALLER, therefore, you need LESS magnification to get the SAME SIZE object to fill a SMALLER frame.

I hope that makes sense.

kkx said:

Does APSC really have deeper DOF for macro?

Been researching this and this link:

http://www.bobatkins.com/photography/technical/format_vs_macro_dof.html

have some really good info.

But there are a lot of arguments and confusion.

Base one BobAtkins's page, I am trying to figure out if I consider pixel on target or a fixed output number of pixel (say 4680 × 3166) for my frame, does APSC fair better?

Basically, I am ignoring magnification definition of 1X equal image size on sensor == real object size. But just want to get a 4680 × 3166 framing of the subject.

So if we consider the MP the sensor have:

(using macro DOF calculator from http://www.cambridgeincolour.com/tutorials/macro-lenses.htm)

FF DOF at 1X is 1.02 mm

So to have the same 4680 × 3166 frame as the FF ref above, my 24MP APSC (1.5x) should have the following magnification (ie magnification that can give the same framing above).

FF MP : APSC Magnification : DOF

22 : 0.4074074074 : 2.86 mm

35 : 0.6481481481 : 1.32 mm

42 : 0.7777777778 : 0.99 mm

50 : 0.9259259259 : 0.76 mm

Note: According to BobAtkins's page, Mag of 0.625x on APSC give the same framing as the 1X FF.

So, am I correct to conclude that if I want the same MP on subject, unless my FF is 45MP and above, my 24 MP APSC will be slightly better in terms of DOF?

If I include pixel pitch (pixel size) and its impact on noise into consideration, how will this chance my choice of sensor?

And if I include consideration for diffraction softening, will the 24MP APSC be less sharp (ie have more diffraction softening) compare to 35MP FF?

-kk

Click to expand...

I believe the short, and correct, answer to your question "Does APSC really have deeper DOF for macro?" is what John K has said. "No".

Perhaps I could tackle this from a different angle.

I use cameras with different sensor sizes. I don't have a full frame camera but I do have an APS-C camera, a micro four thirds camera and a bridge camera with a very small sensor.

As I understand it (happy to be corrected of course)...

I can get a very similar maximum DOF with each of them, but I have to use a different aperture on each to do so. If I capture the same scene (same angle of view) I will get pretty much the same DOF using f/28 on my APS-C camera, f/22 on my micro four thirds camera and f/8 on my bridge camera. This accords both with my own experience and with what the Depth of Field Equivalents calculator says on this page from Cambridge in Colour.

The loss of sharpness/detail from diffraction is the same in these three cases. For example see http://www.josephjamesphotography.com/equivalence/#diffraction where it says that "All systems suffer the same diffraction softening at the same DOF". Note though that it goes on to say "but do not necessarily resolve the same detail at the same DOF, as diffraction softening is merely one of many forms of blur (e.g. lens aberrations, motion blur, large pixels, etc.)"

Also note what it says next: "As the DOF deepens, all systems asymptotically lose detail, and by f/32 on FF (f/22 on APS-C, f/16 on mFT -- 4/3), the differences in resolution between systems is trivial, regardless of the lens, sensor size, or pixel count." That is why I can get as good resolution with my bridge camera as with my other cameras because I use minimum aperture to get maximum DOF, and the apertures I use are one stop less than those stated here.

You are quite probably not using minimum aperture; most people don't. However you need to be aware that (unless you are using a Nikon camera and lens) it is the effective aperture (the actual aperture) that you are using that matters rather than the nominal aperture (what the camera says you are using). And the effective aperture depends on the magnification. The usual formula (an approximation I believe) used to calculate the effective aperture is:

Effective aperture = Nominal aperture x (1 + magnification)

Therefore, if you have set the camera lens to f/11 and are working at a magnification of 1:1 the effective aperture will be f / (11 x (1 + 1)) = f/22. So if you are using APS-C you will be in (and if you are using FF you will be near) the range of "trivial" difference in resolution "regardless of lens, sensor size, or pixel count".

Note 1: The qualification about Nikon cameras and lenses is that they may tell you the effective aperture rather than the nominal aperture.

Note 2: The formula applies to macro lenses, extension tubes, teleconverters, reversed lenses and bellows, but not to close-up lenses.

I found this hard to believe and tried hard to prove it wrong, trying to capture the same scene with my Canon 70D and first (and briefly) a Canon 100L IS macro and later with a Sigma 105 Macro DG HSM. At f/22 with the either of these lenses on my 70D I did not obtain significantly better resolution than I could obtain with my bridge camera using a close-up lens at f/8. Similarly using a close-up lens at f/22 on a telephoto zoom with my micro four thirds camera or up to f/32 with a close-up lens on a telephoto zoom on my 70D.

To the extent that you will be using effective apertures which take you into the asymptotically resolution-degraded area it seems that it won't matter too much which camera you use from the point of view of achievable resolution.

It might be a good idea to do some practical experiments rather than getting too concerned about the theoretical aspects. Various equipment and techniques work fine for some people and not so well or not at all for other people. Only by practical testing will you be able to establish what works for you - and by what works I mean the whole sequence from finding subjects through image capture, selection, post processing and display. For example, I use several techniques which many other people know are not effective/practical/useful/possible, but they work fine for me, for my purposes. There are lots of ways of handling close-up and macro work. Try some of them and see how it goes.

Well, that's how it seems to me anyway. FWIW.

--
Nick
http://www.flickr.com/photos/gardenersassistant/collections/
GardenersAssistant Photography Videos - https://www.youtube.com/channel/UCmBgEwRDfiQMYTPORSzDxvw
https://www.talkphotography.co.uk/t...-dslr-primes-a-journey-of-exploration.531050/

Macro guy said:

kkx said:

Thanks you for your patient and your effort in trying to help me understand.

I don't get the point about IQ is separated from magnification and DOF. So let me show my thinking process and you can point out what I start to get it wrong.

I think magnification (sensor area on subject) is directly link to IQ. Because we could just take a photo and crop like crazy and get a fly/bee in the photo frame but end up with just using a tiny area of the sensor. So the IQ will be terrible.

So macro shooter aim to get the best magnification i.e trying to use their sensor area as much as they could for a given subject. If you said IQ and magnification is not linked, then I am at a lost.

That is how I start to think about pixel on subject. Thinking that if we maintain a similar pixel on subject, the IQ will be maintained (or it limit how much cropping I can do). Since we have different sensor size and different MP count, I just try to focus on what I get as a final result, a photo with a particular pixel count on my subject.

Click to expand...

You're correct in terms of cropping. However, let's take two cameras, one full frame and the other APS-C. Each camera is 20mp. You take a picture of a fly. The fly is 36mm in length. When you take a picture of the fly with a full frame camera at 1:1 magnification, the entire fly will fit. So, your picture will be of the ENTIRE fly at 20mp.

Now, let's take the same fly and shoot it with an APS-C camera so that it will fit the entire frame. When you take a picture of the entire fly on an APS-C camera, your magnification will be 1:2 (half lifesize), but you STILL have the entire fly in the frame at 20mp.

So, your image quality is the same with both cameras, BUT your DOF will be GREATER with the APS-C camera because you're shooting at a LESSER magnification in order to get the fly into the frame. Why are you shooting at a lesser magnification to get the fly into the frame? Because the APS-C sensor is SMALLER, therefore, you need LESS magnification to get the SAME SIZE object to fill a SMALLER frame.

Click to expand...

In other words (to paraphrase), to get 'the less' magnification on a crop-sensor, the subject needs to be further away with the same lens/focal length. And with the subject furter away one 'automatically' gets more DOF.

Right, right?

thinker said:

In other words (to paraphrase), to get 'the less' magnification on a crop-sensor, the subject needs to be further away with the same lens/focal length. And with the subject furter away one 'automatically' gets more DOF.

Right, right?

Click to expand...

No, the magnification that matters for DOF is the difference in size between life size and final display size. You use less optical magnification on the APS-C sensor, but the image from the sensor is then magnified more to get to the same display size, so it cancels out and DOF is the same. As for IQ, the larger sensor has the advantage at base ISO because you can capture more light before you saturate the sensor. Macro is just like every other type of photography in that regard, the largest sensor delivers the best results as long as you have enough optical magnification to use the whole sensor. If you have to crop the FF to match the FOV of the smaller sensor, the playing field is leveled and the sensor with the highest pixel density wins.

thinker said:

Macro guy said:

kkx said:

Thanks you for your patient and your effort in trying to help me understand.

I don't get the point about IQ is separated from magnification and DOF. So let me show my thinking process and you can point out what I start to get it wrong.

I think magnification (sensor area on subject) is directly link to IQ. Because we could just take a photo and crop like crazy and get a fly/bee in the photo frame but end up with just using a tiny area of the sensor. So the IQ will be terrible.

So macro shooter aim to get the best magnification i.e trying to use their sensor area as much as they could for a given subject. If you said IQ and magnification is not linked, then I am at a lost.

That is how I start to think about pixel on subject. Thinking that if we maintain a similar pixel on subject, the IQ will be maintained (or it limit how much cropping I can do). Since we have different sensor size and different MP count, I just try to focus on what I get as a final result, a photo with a particular pixel count on my subject.

Click to expand...

You're correct in terms of cropping. However, let's take two cameras, one full frame and the other APS-C. Each camera is 20mp. You take a picture of a fly. The fly is 36mm in length. When you take a picture of the fly with a full frame camera at 1:1 magnification, the entire fly will fit. So, your picture will be of the ENTIRE fly at 20mp.

Now, let's take the same fly and shoot it with an APS-C camera so that it will fit the entire frame. When you take a picture of the entire fly on an APS-C camera, your magnification will be 1:2 (half lifesize), but you STILL have the entire fly in the frame at 20mp.

So, your image quality is the same with both cameras, BUT your DOF will be GREATER with the APS-C camera because you're shooting at a LESSER magnification in order to get the fly into the frame. Why are you shooting at a lesser magnification to get the fly into the frame? Because the APS-C sensor is SMALLER, therefore, you need LESS magnification to get the SAME SIZE object to fill a SMALLER frame.

Click to expand...

In other words (to paraphrase), to get 'the less' magnification on a crop-sensor, the subject needs to be further away with the same lens/focal length. And with the subject furter away one 'automatically' gets more DOF.

Right, right?

Click to expand...

Not quite. In order to fill the frame with an object on a crop sensor, you need less magnification than you do with a full frame sensor. Less magnification = greater depth of field. We're talking about magnification, not distance because you can get the same magnification by using different focal length lenses, which will affect our distance. So a longer lens will allow us to be further away with THE SAME magnification, whereas a shorter focal length lens will require us to move closer to achieve THE SAME MAGNIFICATION.

John K said:

Since APS-C sensors were introduced everyone has been trying to make them sound as if they are somehow magical.

An APS-C sensor is just a physical crop of the image circle -and fundamentally no different than cropping in post. Since cropping in post does not increase magnification and APS-C sensor does not increase magnification. Some peeps might jump into this tread with some really twisted logic, but it's all BS...

Click to expand...

The problem is not magnification. It is resolution. You can take a blurry picture of a bee and blow it up to 2 meters wide, and have enormous but useless magnification.

What you want is to see the finest details on the subject, not the biggest picture. This is where the sizes of pixels come in. You want whichever setup gives the highest number of pixels on the subject.

Depth of field is a different problem again. It is increased by stopping down (with problems from diffraction) and by using lower on-sensor magnification. So again, smaller pixels are good, because they give you some leeway to use a lower on-sensor magnification, without losing too much detail.

The number of pixels on the sensor doesn't matter much. Their size does. And in most cases, FF sensors have larger pixels than APS-C sensors. (And the cameras cost more.)

Macro guy said:

kkx said:

Thanks John for the reply.

The "noise" in thread like this is really a problem for me. Trying to read them and figure out what is correct is not easy. I am really trying to figure this out.

I agree that APSC does not change magnification. But if my focus is just on pixel on subject and don't care about actual magnification. Does that help to clarify what I am trying to figure out?

As the final result of my macro work, I would like an image of a particular size (in pixel, say 4680 × 3166) and I try to fill my subject in that.

So using both FF and APCS, I try to do that. And I am comparing the pro and cons of the choices. The first is DOF ( and later, once I understand the DOF implication, will think about noise and other image quality items).

-kk

Click to expand...

What we're trying to say is that pixels play no part in this. You're traveling the wrong path by focusing on the pixels because pixels can be bigger or smaller, the same number of pixels can fit on a bigger sensor or a smaller sensor. Therefore, even including pixels in this discussion is a non-sequitur.

Click to expand...

No, the size of the pixels is crucial. But the number of them on the sensor doesn't matter much, as you don't have to use them all.

Pixel Pooper said:

thinker said:

In other words (to paraphrase), to get 'the less' magnification on a crop-sensor, the subject needs to be further away with the same lens/focal length. And with the subject furter away one 'automatically' gets more DOF.

Right, right?

Click to expand...

No, the magnification that matters for DOF is the difference in size between life size and final display size. You use less optical magnification on the APS-C sensor, but the image from the sensor is then magnified more to get to the same display size, so it cancels out and DOF is the same.

Click to expand...

Does it exactly cancel out ? I would like to see a demonstration of that.

Pixel Pooper said:

As for IQ, the larger sensor has the advantage at base ISO because you can capture more light before you saturate the sensor.

Click to expand...

That would depend on the full well capacity of the pixels rather than the size of the sensor.

Pixel Pooper said:

Macro is just like every other type of photography in that regard, the largest sensor delivers the best results as long as you have enough optical magnification to use the whole sensor. If you have to crop the FF to match the FOV of the smaller sensor, the playing field is leveled and the sensor with the highest pixel density wins.

Click to expand...

I think you guys are confusing the OP by lumping together sensor size, sensor resolution, magnification and introducing other variables such as pixel size.

It is better, I think, to concentrate on one issue at a time, explaining it and then moving on to the same issue. Otherwise, the explanations cause more confusion than they solve.

D Cox said:

Pixel Pooper said:

No, the magnification that matters for DOF is the difference in size between life size and final display size. You use less optical magnification on the APS-C sensor, but the image from the sensor is then magnified more to get to the same display size, so it cancels out and DOF is the same.

Click to expand...

Does it exactly cancel out ? I would like to see a demonstration of that.

Click to expand...

If the result is the same size subject displayed at the same size then yes, it cancels exactly.

D Cox said:

D Cox said:

As for IQ, the larger sensor has the advantage at base ISO because you can capture more light before you saturate the sensor.

Click to expand...

That would depend on the full well capacity of the pixels rather than the size of the sensor.

Click to expand...

It depends more on sensor size. The larger sensor will either have larger pixels, or more pixels. Either way it can collect more light in total.

Macro guy said:

kkx said:

Thanks you for your patient and your effort in trying to help me understand.

I don't get the point about IQ is separated from magnification and DOF. So let me show my thinking process and you can point out what I start to get it wrong.

I think magnification (sensor area on subject) is directly link to IQ. Because we could just take a photo and crop like crazy and get a fly/bee in the photo frame but end up with just using a tiny area of the sensor. So the IQ will be terrible.

So macro shooter aim to get the best magnification i.e trying to use their sensor area as much as they could for a given subject. If you said IQ and magnification is not linked, then I am at a lost.

That is how I start to think about pixel on subject. Thinking that if we maintain a similar pixel on subject, the IQ will be maintained (or it limit how much cropping I can do). Since we have different sensor size and different MP count, I just try to focus on what I get as a final result, a photo with a particular pixel count on my subject.

Click to expand...

You're correct in terms of cropping. However, let's take two cameras, one full frame and the other APS-C. Each camera is 20mp. You take a picture of a fly. The fly is 36mm in length. When you take a picture of the fly with a full frame camera at 1:1 magnification, the entire fly will fit. So, your picture will be of the ENTIRE fly at 20mp.

Now, let's take the same fly and shoot it with an APS-C camera so that it will fit the entire frame. When you take a picture of the entire fly on an APS-C camera, your magnification will be 1:2 (half lifesize), but you STILL have the entire fly in the frame at 20mp.

So, your image quality is the same with both cameras, BUT your DOF will be GREATER with the APS-C camera because you're shooting at a LESSER magnification in order to get the fly into the frame. Why are you shooting at a lesser magnification to get the fly into the frame? Because the APS-C sensor is SMALLER, therefore, you need LESS magnification to get the SAME SIZE object to fill a SMALLER frame.

I hope that makes sense.

Click to expand...

Sorry for the late reply. Was sick and been trying to think about this and trying some experiments to check out what I read here.

I think that make sense. I have tested it and it seems to be correct.

But what if I stop down my FF lens by one stop to match the APS-C? Would that not make the DOF the same for the two system?

FF one one stop of noise advantage, with the same amount of light, I can stop down 1 stop and raise iso by one stop. Isn't it?