[normhead]

But with DOF, we aren't talking about areas of sharp focus. There is only ever one point (or plane of distance) that is ever in sharp focus, and yes that will be in focus at any size. EVERY OTHER POINT is out-of-focus to some degree, but we still consider some of those areas to be in the "depth of field" of *acceptable* focus GIVEN a certain print size, etc etc. So his example of a slightly out-of-focus point becoming less and less acceptable (moving from being in the DOF to out of the DOF) as it is magnified is right on the money.

That would be an argument for the DoF of APS-c being narrower, since it requires more magnification to produce the same size image, enlarging the circles of confusion and making them visible sooner... no?

[vonBaloney]

That would be an argument for the DoF of APS-c being narrower, since it requires more magnification to produce the same size image, enlarging the circles of confusion and making them visible sooner... no?

Not actually making any argument, just explaining DoF. But yes, and that was exactly the query in the very first post of this thread -- why is the calculator telling me that DoF is less on APS-C than FF when all I ever hear is "FF has less DOF"? Explaining the difference between switching formats but not switching lenses and apertures and switching formats AND lenses and apertures to give an "equivalent" image (all while maintaining the same print size for all) is how this thread got started. (And what I said in the 4th post of this thread is what you just said.) And now we've come full circle.

[BrianR]

That would be an argument for the DoF of APS-c being narrower, since it requires more magnification to produce the same size image, enlarging the circles of confusion and making them visible sooner... no?

Yes, exactly. Under these circumstances- focal length remains fixed, aperture remains fixed, distance to subject remains fixed, print size remains fixed, then APS-C will have a shallower DoF than Full Frame. This is exactly the situation that the OP entered into the calculator and what prompted this thread. It's no contradiction to anything, we just need to clearly lay out the parameters that are changing and those that are fixed.

[tuco]

...
On my screen, the nose looks to be pretty much in focus on the Full Frame version. Less so on the 2/3 Full Frame, and definitely distressingly out of focus at 1/3 Full Frame.

Amazing! The dog never moved one pixel in the time it took to mount and shoot 3 different cameras. Perhaps it's a stuffed animal.

[BrianR]

Amazing! The dog never moved one pixel in the time it took to mount and shoot 3 different cameras. Perhaps it's a stuffed animal.

Image stabilization, aka tranquilizer dart. Unfortunately, it still managed to drool on my shoes.

[noser]

Well actually the stops go 1, 1.4, 2, 2.8, 4 etc., so 2.8 to 1.4 is 2 stops... if you can't tell the difference between one stop and two stops the whole conversation is moot. One stop is the difference between APS-c and FF.

Uuhmm..DUH,that's what I said (one stop difference), but you omitted the logic in the rest of the post, in terms of aperture ranges, ie 1.2-1.8 for shallower options on APS-C (that might be soft) to achieve a more FF look at say from 2.0 to maybe 3.5 on longer lenses to maintain a useable DoF (as opposed to a minimal DoF), and also get a sharper image by staying away from max aperture. Yes, I could have been more exact in my example.

Anyone dialing in aperture by rote or by calculator should reconsider maybe what they are seeing, and not try to be in constant competition with a mental FF shot that will never exist by cranking the aperture on a wide lens and hoping for the best. FF's get less distortion and don't have to use max apertures, but us APS-C's have to delve into 1.4-2.0 territory to keep sharp and thin due to this mania, and sometimes the image suffers for it when 2.8 on either would be just fine (though not equivalent)

And the real point was that distortion at wider FL's is just plain gross, regardless of what the math says is equivalent.

Unless you are a plastic surgeon selling rhinoplasty; then 16mm is your new best friend.

Edit: no nose job for the dog though! It's just the right size!

[normhead]

OK, I don't think I have it yet, can we go around one more time?

[traderdrew]

The calculator isn't cropping the FF image, no. You're getting a different image if all you change is the format but leave distance and focal length the same, eg. a tight shot of someones face on the APS-C will become a head and shoulders shot on the Full Frame since focal length and distance to the subject remain the same. The pictures are then both printed at 8x10, and to get to the 8x10 size you need to enlarge the image from the APS-C sensor 1.5 times more than you need to enlarge the FullFrame sensors image and stuff gets less in focus the more you enlarge it.

I should have included pictures from the start, this hopefully will help clarify. It's a bit of a cheat, since the image on the left is from my k100d, but it illustrates what's happening.

Imagine you take a photo of a wet, sloppy, smiling dog at 50mm, f4, using your full frame camera. This is the image on the left. Swap out to an APS-C camera (which has a sensor 2/3 the size of a 'full frame'), but stay in the same spot and leave the lens and aperture at the same settings. Do this again with our hypothetical camera with a sensor size 1/3 that of full frame (the more extreme the sensor size difference, the easier the difference is to see). Now send the files to the lab to print out 8x12's, or just look at them on your screen at the same size.

On my screen, the nose looks to be pretty much in focus on the Full Frame version. Less so on the 2/3 Full Frame, and definitely distressingly out of focus at 1/3 Full Frame. All that's changed here is the smaller sensor needs to enlarge the dogs face more to get the same final print size. This makes the blur that already exists on the nose less and less tolerable since this extra enlargement magnifies it.

Oh.. Okay. So what is happening with the DOF calculations is the hyperfocal range is subjective?

[wombat2go]

OK, I don't think I have it yet, can we go around one more time?

Hold the phone for a while will ya ?..., its Friday evening and cocktail hour.

[BrianR]

Oh.. Okay. So what is happening with the DOF calculations is the hyperfocal range is subjective?

No more subjective than the rest of the DoF equations. Namely pick an acceptable circle of confusion depending on print size, viewing distance, and how drunk the viewer is and go from there.

Same focal length and aperture, then the hyper focal distance is further away on APS-C then on Full Frame, i.e. 'less DoF' on APS-C with the same lens. Different framing of the scene in this case.

If you change lenses on the Full Frame to match the field of view, but keep the aperture the same, the reverse happens, hyper focal distance is further away on Full Frame then on APS-C, i.e. 'less DoF' on Full Frame with 'equivalent lenses. Similar framing of the scene in this case.

[ElJamoquio]

Dunno. I've only ever used F22 and above when I didn't bring along my ND filters.

[wombat2go]

Dunno. I've only ever used F22 and above when I didn't bring along my ND filters.

Didn't you learn anything from this thread?? You should only be at f/19.3333

[normhead]

Dunno. I've only ever used F22 and above when I didn't bring along my ND filters.

Cause you don't take macros, or pictures of shrooms....

SIgma 70 macro @ ƒ22



You can see the back edge of the shroom is a little out of focus, I should have gone to ƒ32.

[traderdrew]

No more subjective than the rest of the DoF equations. Namely pick an acceptable circle of confusion depending on print size, viewing distance, and how drunk the viewer is and go from there.

Same focal length and aperture, then the hyper focal distance is further away on APS-C then on Full Frame, i.e. 'less DoF' on APS-C with the same lens. Different framing of the scene in this case.

If you change lenses on the Full Frame to match the field of view, but keep the aperture the same, the reverse happens, hyper focal distance is further away on Full Frame then on APS-C, i.e. 'less DoF' on Full Frame with 'equivalent lenses. Similar framing of the scene in this case.

It seems you don't want to calculate DOF between FFs and crop sensors without factoring in the field of view. When I think about it, it is kind of a paradox. Very good answers and thanks for participating. You have some cool photos in your flickr stream.

I would still guess FOV is subjective because it depends on your own perception. At what point do pixels stop becoming sharp and start to become blurry? At what point does the hyperfocal length cease to become a factor? I'm not asking you to explain but i'm just making another point.

Edit: Getting a bit off topic, I'm still interested in a FF but i'm not sure I will be buying one. I know someone who uses a Nikon D4 (perhaps Nikons best FF camera) with the 600mm F/4. After seeing his photos on the net, I would say I'm not impressed with its noise performance as I can still see noise in his photos. What I hear and what I see are sometimes two different things. What I'm impressed with is how that camera operates in the field.

I have my hopes up the K-3 will give us better performance in the field because wildlife photography will inevitably push your camera to its limits.

[BrianR]

It seems you don't want to calculate DOF between FFs and crop sensors without factoring in the field of view.

Keeping the field of view or the framing of the subject the same is a sensible way to compare the formats, and is the one people usually have in mind when they make the claim "FF has shallower DoF than crop" so I think it's usually worth mentioning. However, I don't really care what parameters are changed when comparing the DoF as long as they're explicitly stated. I've lost count of the disagreements I've seen between two people who were both right but failed to clearly indicate what exactly they were comparing and thus seemed to have reached different conclusions when all they had done was answer different questions.

Change focal length, distance, aperture, format, print size, or don't, it doesn't matter but being clear about it cuts confusion by at least one stop. Maybe two.

When I think about it, it is kind of a paradox. Very good answers and thanks for participating. You have some cool photos in your flickr stream.

Glad to help! Thanks for checking out my flickr stream and the compliment is appreciated.