[beholder3]

I do not really understand what you mean, but if I take a picture with same distance to the object, FF 50mm F2,8 and APS-C 33mm F2,8 (both have the same angle of view) the DOF is for sure shorter with the FF - or have I understood complete wrong

That is right. If you can switch lenses (e.g. that also means in the tele range you can replace the 300/2.8 with a 450/2.8 ...).

I just meant that when keeping the same lens and only changing the body APS-C to FF and then adjusting the distance to the subject accordingly (so you get the same width/height on the picture) the blur of the background is not different.

[falconeye]

Sorry for all the confusion. But it seems to be a healthy one as this theme is recurring all the time.

This is why I kindly asked to follow the link before replying, an advice not taken. I considered writing an own blog article about the topic but if nobody is ever reading ...

This is faulty logic because formats aren't equivalent

Pål, you are the last I would have expected this comment from. I thank drougge for explaining it.

Maybe, a general comment about the words equivalence and equality. Two things can be equivalent w/o being equal. You then have to define by what properties you go to define equivalence.

And here we go:

Two camera systems (lens, sensor, resolution, exposure/aperture/ISO setting etc.) are equivalent if they deliver equal images; equal in the sense that you cannot tell them apart w/o inspecting exif.

In any format discussion, it is important to first understand what are equivalent cameras. As otherwise, you focus your discussion on trivial differences.

They are not equivalent lenses. A 40/2.8 and a 27/2.8 are equivalent lenses.

This is why I kindly asked to follow the link before replying, an advice not taken.

Falk has it right, for the definition of equal that he uses. You seem to disagree on what is equal. I'll side with Falk. He describes what is required to get an identical image. That seems like a reasonable definition of equal to me. You describe what is needed to get the same exposure parameters but different images. That seems less equal.

Your definition gives the same amount of light per sensor area, Falk gives the same amount per whole sensor. So you give a noise advantage to the bigger format, Falk doesn't. Again, he seems to get it more equivalent.

Note that he's not anywhere suggesting that you need the equivalents, he's just describing what they are.

Thanks for your explaination which I fully endorse.

The following have to scale for equivalent cameras but different crop factors:

focal/crop, f-stop/crop, ISO/crop^2

Only scaling focal w/o scaling the other two parameters leads to confusion which is what is constantly hapenning.

One more thing:

Two equivalent camera systems but with different crop factors have interesting properties:
- same FoV, DoF, #pixels and pixel noise
- same blur due to diffraction
- same physical aperture in mm; i.e. same lens size/cost

But: the higher crop factor has
- a higher lines/mm requirement on optical quality,
- to be delivered at a lower f-stop figure
which work against each other and making equivalent lenses physically impossible for too high a crop factor. Moreover, the registration distance better scale with registration/crop too; which it normally doesn't except for some mirrorless designs. And last but not least, the crop-factor sensor
- needs ISO/crop^2
which (if FF is ISO100) needs ISO50 on the crop camera typically not available putting the crop camera onto a dynamic range disadvantage.

So, the real concerns with a crop camera are:
- registration distance.
- optical flaws running out of control.
- AF accuracy if tolerances not scaled by /crop.
- unavailable lens options like no APSC 32/0.9 or µFT 25/0.7 which used to be the standard prime on FF.
- (one stop) less dynamic range.
- VF magnification.

These real concerns remain completely un-understood if one isn't getting the concept of lens equivalence, and getting it right.

A typical sign are discussions centered around low light performance in the context of FF, or claims that FF is the more expensive system. The opposite is true considering that sensor costs are going down and lens costs are going up over time. FT used to be the sweet spot wrt price, now it is APSC and soon it will be FF.

[dave216]

With the same lens (same A setting e.g. 2.8) and same FOV you will have less blur and larger DOF whith crop sensor. with FF i can come closer to the subject stop down to F4 and will get razor sharp image with same blur and same DOF as i have at 2.8 with crop.
And i really want K mount FF camera so still waiting for Pentax and still using film pz-1p along with K5

[beholder3]

With the same lens (same A setting e.g. 2.8) and same FOV you will have less blur and larger DOF whith crop sensor. with FF i can come closer to the subject stop down to F4 and will get razor sharp image with same blur and same DOF as i have at 2.8 with crop

If you mean "blur" in the same way I meant it (blur of the far background), none of your statements about blur is true under the same physics as I know. DOF statement is roughly right.

[gazonk]

Except that the 27mm already needs a retrofocus design with a FF mount like the K mount. Which was my point actually, the choice of available glass.

Maybe, we actually want to say the same: i.e., that a FF camera needs more moderate F-stop figures for equal performance. But I wouldn't call it slower glass as this would imply lower cost while in fact cost is equal (except for wide angle and apertures below f/2).

Yes, "a FF camera needs more moderate F-stop figures for equal performance" is a different way to put what I wanted to say.

I said "you can get better high ISO and narrower DoF without the fastest glass" - my point was really a very practical one, that if you're interested in achieving e.g. narrow DoF, you can do fine with rather inexpensive lenses, especially in the normal FoV range.

But I have to agree with Pål that often the problem is quite opposite, that you need MORE DoF than you get. He takes the rather extreme position that you almost never want shallow DoF, which I have to disagree very strongly with. But for a lot of photography, getting enough DoF is the real problem. Of course this applies to landscape, but I just started to use the DA55-300 and was amazed (I really haven't used longish teles before) how shallow the DoF is even at its rather slow 5.8 max aperture @300 mm. I imagine bird photographers really have more use for good high ISO than f/2.8. So if they get equivalent-per-magnification high ISO, I guess a birder is much better off with APS-C than with FF.

[dave216]

Dont forget that you can always crop image from FF (of course if its 20-25mpix sensor)

[Jodokast96]

Pardon this interruption while we bring you this late breaking announcement.

Pentax has not, I repeat not, announced any plans for a full frame digital camera.

We now return you to your regularly scheduled bickering.

[gazonk]

Pardon this interruption while we bring you this late breaking announcement.

Pentax has not, I repeat not, announced any plans for a full frame digital camera.

We now return you to your regularly scheduled bickering.

Pentax has not announced any plans for anything, not even updated their lens road map for a couple of years. Which makes speculation so fun, except for the occasional "Pentax is doomed" posts!

[stanleyk]

Wow, as a person who uses both a Full Frame camera and K5, I have to say you guys are really making a mountain out of a mole hill on this DOF issue. The only real advantage I see with the FF is it's easier to manual focus than the K5.

[kswier]

I have to protest again
There are no more control over DOF with FF. APS and FF have exactly the same control over DOF as long as lenses with comparable aperture range is used, but DOF will be different at the same aperture value and the same magnification. You need to stop down more on the larger format to get the same DOF - genereally not seen as a plus (thats why large format have tilt/shift). APS have in fact a more useful DOF range as hardly anyone will use shallower DOF than what is possible at F:1.4 and F 1.2 on APS, (a DOF so shallow that is hardly usable), but plenty of situations where F:22 on FF is not adequate (eg in landscape photography). But in real life, the DOF differences between APS and FF is negligible.

Correct. Depth of field is a function of focal length. A 40mm lens is a 40mm lens whether it is on a aps-c sensor of full frame sensor. However on a very small cropped sensor (like a small point and shoot), the a 40mm lens may have the field of view of a 200 or 300mm lens on full frame. This can make obtaining that depth of field impractical in most circumstances. Thus, when I want the field of view of a 28mm lens (on a full frame camera) I need to use a 18mm lens on aps-c. The 18mm lens will have a greater depth of field (with matching distances from the subject and apertures) than the 28mm lens.

I also agree for the most part that in real life conditions the aps-c sensor is adequate, and that many times the small increase in depth of field can be an advantage.

[falconeye]

But I have to agree with Pål that often the problem is quite opposite, that you need MORE DoF than you get.

You can always stop down, esp. on FF where equivalent F-stops (i.e. where diffraction is the same) are numerically higher. The advantage with FF then is that chances are the lens then really is diffraction limited (more likely to happen at e.g., f/8 than f/5.6). Moreover, AF will appear to be more accurate when stopping down to f/8 rather than to only f/5.6. Still, the images will be the same (with an ideal lens and focus).

As for birders ... I really would prefer to shoot with a 300mm lens on a 36MP full frame camera (and crop) than a 300mm lens on a 16MP APSC camera. Everybody who tried to frame a bird at flight with a ~500mm (35mm equiv.) lens will understand why. Agreed, 36MP FF cameras are only going to appear this year, but still, they are the desirable thing for birders.

[Pål Jensen]

You can always stop down, esp. on FF where equivalent F-stops (i.e. where diffraction is the same) are numerically higher. .

No you can't. I've seen images shot on APS that can only be shot with APS or large format with tilt/shift. You can make images with flowers close to the lens element and the mountain in the distance all in focus. APS has opened up typical large format look without the hassle or cost...

[Pål Jensen]

But I have to agree with Pål that often the problem is quite opposite, that you need MORE DoF than you get. He takes the rather extreme position that you almost never want shallow DoF, which I have to disagree very strongly with..

I've never said that you never need shallow DOF, but shallow DOF is available on APS. There are several examples posted on this forum where no one can say it isn't shot on FF. A 50/1.2 on APS will give you shallower DOF than what is useful....

[Pål Jensen]

I imagine bird photographers really have more use for good high ISO than f/2.8. So if they get equivalent-per-magnification high ISO, I guess a birder is much better off with APS-C than with FF.

Bird photography is almost hopeless at F:2.8 because of lack of DOF. This speed isn't neccesary anylonger; eg. 300/2.8 is from the time when serious photography was done at a max ISO of 100!
It was also a speed useful with converters. Converters aren't that useful anylonger as you arguably get just as good result by cropping (and increasingly so with better sensors)

[falconeye]

No you can't. I've seen images shot on APS that can only be shot with APS

Another comment which catches me in surprise

And I don't agree. You can stop down equally on either format. Not only wouldn't you go to closest apertures with APSC due to diffraction at f/22 and beyond. But even if you would, then an equivalent lens on FF tends to have an even higher max. F-stop (like f/32 rather than f/22) because the absolute apertures remain the same. As I tried to explain so many times now.

The max. aperture stop is limited by the remaining aperture hole diameter which scales with crop like everything else. E.g., an FA 100mm f/32 and DA 70mm f/22 min. apertures are both 3mm holes. And both apertures limit resolution to about HD video (2 MP) where they are fine.