[PuxaVida]

[quote name='Brightcolours' timestamp='1288618759' post='3877']

This is not true. If you select a SIMILAR DOF for both FF and APS-C, the diffraction softness effects on the image will be the same for BOTH formats. For FF you need to select a SMALLER f-value to get a similar DOF. And with that smaller f-value, diffraction effects on the image will be the same.



[/quote]



I don't agree with you BC... With the same lens to get the same FoV, you need to get closer to the subject. And to get the similar DoF you have to stop down more in FF. But in what extend? As far as I know, the delta between diffraction limited aperture of a FF and cropped sensor (with the same resolution) is more than the aperture increase to get the similar DoF. Maybe I'm wrong but this is how I know it...



Kind regards,



Serkan

[Brightcolours]

[quote name='PuxaVida' timestamp='1288619936' post='3881']

I don't agree with you BC... With the same lens to get the same FoV, you need to get closer to the subject. And to get the similar DoF you have to stop down more in FF. But in what extend? As far as I know, the delta between diffraction limited aperture of a FF and cropped sensor (with the same resolution) is more than the aperture increase to get the similar DoF. Maybe I'm wrong but this is how I know it...



Kind regards,



Serkan

[/quote]

Comparing the same lens does not make sense either!



You do not choose an f-value to use as standard between sensor formats. You choose an f-value to get the DOF you want.



Likewise: Focal length.



You choose the focal length to get the field of view you want. You do NOT choose a focal length as standard between sensor formats!



Diffraction is solely aperture based.



F-values are NOT aperture, they are focal length divided by aperture. You will find that when you use EQUIVALENT focal lengths and EQUIVALENT f-values, the aperture will be the same for APS-C and FF.



So what will be the same:

* the field of view

* the aperture

* the DOF

* the diffraction (same aperture)



However, there is one factor in play that can make a small difference: the distance from the aperture to the sensor. Usually, when you use a 50mm lens on APS-C the aperture will be closer to the sensor than with a 85mm lens on full frame camera. The bigger distance actually puts the FF sensor camera in a disadvantage diffraction wise.



But generally speaking, the diffraction effects on the IMAGE for FF and APS-C are similar when you use equivalent f-values and equivalent fields of view.



Note that I am referring to the diffraction effects on the IMAGE, the only sensible way to look at diffraction softening. I am not talking about diffraction softening on pixel level, the nonsensical way of looking at diffraction softening effects. What matters is the image, never the pixel.

[PuxaVida]

Diffraction is solely aperture based.

Yes, but the effects of diffraction on the image depends on the sensor characteristics; like the size of the pixels, CoC and the diameter of the airy disk. The diffraction limited f-value is different in cropped sensor and FF sensor (given that they have the same MPs).

But generally speaking, the diffraction effects on the IMAGE for FF and APS-C are similar when you use equivalent f-values and equivalent fields of view.

By "equivalent" if you mean F=10@1,5x crop vs. F=15@FF, you're right. I have to correct myself here. Because,



1,5x crop, 50mm, 10 meters distance, F=10 have the same DoF in meters as in FF, 75mm, 10 meters distance, F=15. And at the same time F10 and F15 are diffraction limited f-values for 1,5x crop and FF sensor (given that they're both 12mp).

[wim]

[quote name='PuxaVida' timestamp='1288616310' post='3868']

After reading most of the threads, I'm still not 100% sure how come a cropped sensor (e.g. APS-C) can have advantages over an FF sensor in the bottomline, except for macro and other tele usage like bird shooting. [/quote]

Not for macro, actually, 1:1 is 1:1 whether you use FF or APS-C. The difference is that you have a 22 mm wide image on APS-C and a 36 mm wide image on FF, the difference being that at 1:1 you capture more on FF than on APS-C of the same subject. And DoF wise there is no diffeence, as DoF with macro is limited effectively by magnification alone.



For tele use, yes.



However, I was thinking abou that today, during the 3 hour drive I had to undergo, and my 21 MP 5D II actually provides me with a 8 MP crop at APS-C size, and I have a few 60 cm X 90 cm prints made from my old trusty 8 MP 350D on my wall. Hmmm. I've started wonderign now how much of an advantage this actually is <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='' />.

And still, the abilities in macro usage can be discussed, because sensors may have pros/contras based on various criterias. For example if we compare 16.2 MP APS-C with 12MP FF, the fine detail in post-cropped image vs. the tonal & dynamic range produced by FF sensor...

There is no advantage IMO, see above <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='' />.

OTOH, I think FF sensors are better in landscape photography even in terms of DoF because I can use smaller apertures before they become diffraction limited.

That's actually a moot point. In order to get the same DoF you need to use an equivalent aperture, 1.6X smaller, so diffraction hits you at the same DoF equivalent whatever format you use.

There are many wide angle lens choices (ok I admit it, a bit more expensive than the APS-C compatible ones but we left the budget out of the IQ discussion). One thing which can be mentioned on the negative side is the vignetting. Bu rather than "wide aperture vignetting", I'd say darker corners because of multiple filter usage on wider FLs.

This is something I doubt. Optical vignetting is exponentially related to AoV. Any other vignetting is due to design, optically and mechanically, hence the current trend to build UWA lenses with very large, bulging front elements to maximize corner IQ for the large AoV required and to cater for the retrofucus design as much as possible.

It's clear that using a FF compatible wide angle on a cropped sensor has it's advantages in terms of vignetting and IQ on the edges/corners. But if you pay the price, you'll get a better quality on FF...

Yep. You need larger glass, generally speaking, hence more expensive. Up the quality as well, and it gets even more expensive.

Regarding portrait shots; no doubt, better subject isolation combined with sharper image (FF lens can be stopped down to get sharper image), go for the FF sensors.



So, all in all, except for the discussions regarding tele usage and (some) macro advantages, I personally cannot count any pros for the cropped format by means of IQ. But of course I'm still open for hearing the advantages of a cropped sensor. (I still did not sell my DX body yet...<img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/cool.gif' class='bbc_emoticon' alt='B)' />)



Kind regards,



Serkan

DX sensor bodies can be build smaller. The mirror housing can be smaller, which allows for extra space underneath the mirror housing to fit some of the circuitry, f.e., and it can be narrower too, making the body in principle less wide, everything else staying the same.



To me, that is the biggest advantage.



However, once you get to 40d, 50D or 7D size, IMO you could just as well go for a 5D or 5D II. Same size, better sensor. Unless of course you need the speed (fps) of these bodies (more room means that faster mechanisms could be housed in the body, f.e.), or the extra reach. And it probably is no different for Nikon.



Kind regards, Wim

[wim]

[quote name='PuxaVida' timestamp='1288623630' post='3884']

Yes, but the effects of diffraction on the image depends on the sensor characteristics; like the size of the pixels, CoC and the diameter of the airy disk. The diffraction limited f-value is different in cropped sensor and FF sensor (given that they have the same MPs).[/quote]

This is actually an opinion, not truth. The guys who wrote this article have been proven wrong by others who weren't as publicized as these guys. If this stuff really was true, we would have seen exactly the same effects with film. Why did we never hear about this? Furthermore CoC and Airy disk are directly related, if not the same. it actually goes a little too far for me to have a discussion about this here, so I want to leave it at that, if you don't mind too much.



Diffraction only depends on aperture, nothing else.

By "equivalent" if you mean F=10@1,5x crop vs. F=15@FF, you're right. I have to correct myself here. Because,



1,5x crop, 50mm, 10 meters distance, F=10 have the same DoF in meters as in FF, 75mm, 10 meters distance, F=15. And at the same time F10 and F15 are diffraction limited f-values for 1,5x crop and FF sensor (given that they're both 12mp).

Nope. Diffraction limits for APS-C are around F/13 and around F/18 for FF. I'd work it out for you if I had the tools handy right now, but I don't. The only thing that differs is apparent resolution. That is what CoCs and Airy disks are about.



Furthermore, the DoF equivalent of F/10 on APS-C is a little over F/16 on FF.



Kind regards, Wim

[Brightcolours]

[quote name='wim' timestamp='1288629132' post='3889']

This is actually an opinion, not truth. The guys who wrote this article have been proven wrong by others who weren't as publicized as these guys. If this stuff really was true, we would have seen exactly the same effects with film. Why did we never hear about this?

[/quote]

Maybe diffraction was different for ISO 1600 film compared to ISO 200 film <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/blink.gif' class='bbc_emoticon' alt='B)' /> <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/laugh.gif' class='bbc_emoticon' alt='' />

[popo]

[quote name='wim' timestamp='1288628483' post='3888']

Not for macro, actually, 1:1 is 1:1 whether you use FF or APS-C. The difference is that you have a 22 mm wide image on APS-C and a 36 mm wide image on FF, the difference being that at 1:1 you capture more on FF than on APS-C of the same subject. And DoF wise there is no diffeence, as DoF with macro is limited effectively by magnification alone.

[/quote]

I'm suffering from thinking fail at the moment introducing magnification into the equation. Is this a variation on the "equivalent FoV and equivalent effective aperture" at low magnifications?



In practical terms, at my level of macro photography I'm finding myself often balancing (badly) between adequate DoF and diffraction softening.



Let's take a simple case: say you have a 12MP APS-C sensor and 12MP FF sensor so we can disregard pixel count effects. For the equivalent *output* magnification, stopping down both systems to their respective diffraction limits, do you get the same or different DoF between them? Side question: does focal length factor in at all here or is it entirely due to magnification? (ignoring FoV effects)

[Brightcolours]

[quote name='popo' timestamp='1288635643' post='3891']

I'm suffering from thinking fail at the moment introducing magnification into the equation. Is this a variation on the "equivalent FoV and equivalent effective aperture" at low magnifications?



In practical terms, at my level of macro photography I'm finding myself often balancing (badly) between adequate DoF and diffraction softening.



Let's take a simple case: say you have a 12MP APS-C sensor and 12MP FF sensor so we can disregard pixel count effects. For the equivalent *output* magnification, stopping down both systems to their respective diffraction limits, do you get the same or different DoF between them? Side question: does focal length factor in at all here or is it entirely due to magnification? (ignoring FoV effects)

[/quote]

You can ALWAYS disregard "pixel count effects" as they do not exist.



For every APS-C size sensor, diffraction is always the same. For every FF sensor, diffraction is always the same. Regardless of resolution/pixel count. Diffraction is ("sits") in the projected image. It does not matter at what rate you sample that projected image, the diffraction will not get worse or less.



Of course, the higher the sample "rate" (resolution), the more detailed the projected image gets registered.



With a higher res. sensor you can magnify (zoom in) the image more. So, you can see the diffraction effects more clearly, when you zoom in more. A lesser resolution would show the blocky pixels before you would be able to see the diffraction effects...



To answer your question:

Yes, diffraction "limits" show up at the same DOF. And that can be "calculated" simply by the crop factor. If you notice that you see diffraction softening of the image at a certain print size with FF at an f-stop of f11 for instance, you will notice the same diffraction softening of an image at a similar print size with APS-C at an f-stop of f11 / 1.6 (canon APS-C crop factor) = f6.9, so about f7.1.

[popo]

[quote name='Brightcolours' timestamp='1288636686' post='3892']

You can ALWAYS disregard "pixel count effects" as they do not exist.[/quote]

I really don't want to go there again. While that is the case for same output size, I just wanted to make that clear I am not looking at pixel level.

To answer your question:

Yes, diffraction "limits" show up at the same DOF. And that can be "calculated" simply by the crop factor. If you notice that you see diffraction softening of the image at a certain print size with FF at an f-stop of f11 for instance, you will notice the same diffraction softening of an image at a similar print size with APS-C at an f-stop of f11 / 1.6 (canon APS-C crop factor) = f6.9, so about f7.1.

That isn't answering the question I posed. Wim made a statement regarding magnification being more important for macro photography. I'm asking if, for the same output magnification, for the same diffraction limiting case, is there a difference between the two formats regarding DoF? Both with and without considering focal length too.



I think I'll have to play with some calculators later... haven't done so so far as I'm not sure if they adequately consider high magnification cases correctly.

[Brightcolours]

[quote name='popo' timestamp='1288640616' post='3894']

I really don't want to go there again. While that is the case for same output size, I just wanted to make that clear I am not looking at pixel level.





That isn't answering the question I posed. Wim made a statement regarding magnification being more important for macro photography. I'm asking if, for the same output magnification, for the same diffraction limiting case, is there a difference between the two formats regarding DoF? Both with and without considering focal length too.



I think I'll have to play with some calculators later... haven't done so so far as I'm not sure if they adequately consider high magnification cases correctly.

[/quote]

If you use the same framing, and consider the magnification on image level, not on sensor size level, then the DOF will be the same for about the same diffraction level. To make the 2 images "equal" you will have to use an equivalent focal length though, else comparing will not make all that much sense.