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Author Topic: Full Frame Sharper Than Crop?  (Read 13770 times)

GuyF

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Re: Full Frame Sharper Than Crop?
« Reply #15 on: October 20, 2012, 07:24:50 AM »
I suspect it may simply come down to the size of the photosites on a crop sensor. They tend to be smaller than those on full-frame sensor and thus the laws of physics and diffraction come in to play sooner on a crop sensor.

For a fuller and more in-depth answer just hang on, I see our friend Neuro on the horizon with his usual top-notch explanations for the witchcraft that is optical physics.

Pah! Just as I type this, there he comes!

I have a question also. Diffraction. I have read about it, and there are several places that warns against closing the lens too much (some say you should not go to F22, but stay at F16 due to diffraction. Does anyone have a practical example on how this would alter a picture, besides a theoretical argument? Otherwise, when shooting landscape for instance, why would one not go minimum aperture all the time, given that you control the other factors?


Whilst it was only speculation on my part, check out the examples here:

http://www.luminous-landscape.com/tutorials/understanding-series/u-diffraction.shtml

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

Also the table near the top of the page here http://www.the-digital-picture.com/Reviews/Canon-EOS-7D-Digital-SLR-Camera-Review.aspx gives values for apertures where diffraction might start to creep in. Note that they say it may not be visible depending on what size and how you view the image.

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Re: Full Frame Sharper Than Crop?
« Reply #15 on: October 20, 2012, 07:24:50 AM »

Quasimodo

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Re: Full Frame Sharper Than Crop?
« Reply #16 on: October 20, 2012, 09:32:02 AM »
I suspect it may simply come down to the size of the photosites on a crop sensor. They tend to be smaller than those on full-frame sensor and thus the laws of physics and diffraction come in to play sooner on a crop sensor.

For a fuller and more in-depth answer just hang on, I see our friend Neuro on the horizon with his usual top-notch explanations for the witchcraft that is optical physics.

Pah! Just as I type this, there he comes!

I have a question also. Diffraction. I have read about it, and there are several places that warns against closing the lens too much (some say you should not go to F22, but stay at F16 due to diffraction. Does anyone have a practical example on how this would alter a picture, besides a theoretical argument? Otherwise, when shooting landscape for instance, why would one not go minimum aperture all the time, given that you control the other factors?


Whilst it was only speculation on my part, check out the examples here:

http://www.luminous-landscape.com/tutorials/understanding-series/u-diffraction.shtml

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

Also the table near the top of the page here http://www.the-digital-picture.com/Reviews/Canon-EOS-7D-Digital-SLR-Camera-Review.aspx gives values for apertures where diffraction might start to creep in. Note that they say it may not be visible depending on what size and how you view the image.

Ok, thanks. I will look at them :)
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ahsanford

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Re: Full Frame Sharper Than Crop?
« Reply #17 on: October 22, 2012, 05:08:35 PM »

@Quasimodo, regarding diffraction:

Depending on the lens, you see a resolution/sharpness 'sweet spot' (usually between F/4 and F/8 or so) where the sharpness is optimal.  As I understand it, when you stop down beyond that, you are effectively trading a little bit of sharpness to extend your depth of field.

http://www.photozone.de/canon_eos_ff has this well documented if you are a data guy.  Grab any lens and see it's 'analysis / resolution' section to see the drop off in sharpness with narrow apertures -- it happens to all glass, apparently.


There is also a body/sensor related issue on how well stopped down images are handled.  From Bryan Carnathan's http://www.the-digital-picture.com, he states:

"* DLA (Diffraction Limited Aperture) is the result of a mathematical formula that approximates the aperture where diffraction begins to visibly affect image sharpness at the pixel level. Diffraction at the DLA is only barely visible when viewed at full-size (100%, 1 pixel = 1 pixel) on a display or output to a very large print. As sensor pixel density increases, the narrowest aperture we can use to get perfectly pixel sharp images gets wider.

DLA does not mean that narrower apertures should not be used - it is simply the point where image sharpness begins to be compromised for increased DOF and longer exposures. And, higher resolution sensors generally continue to deliver more detail well beyond the DLA than lower resolution sensors - until the "Diffraction Cutoff Frequency" is reached (a much narrower aperture). The progression from sharp the soft is not an abrupt one - and the change from immediately prior models to new models is usually not dramatic."



Getting back to real world shooting with all this...  I had a bad habit with my landscapes of maximally stopping my lens down (F/22, F/25, etc.) simply because I could -- I  was on a tripod, I had more light than I needed, etc.  When I was shooting, say, a far off mountain range with nothing in the foreground, I was simply throwing some sharpness away by stopping down so far.

Perhaps this is what gets people into using hyperfocal tables (e.g. http://www.dofmaster.com/dofjs.html) to choose the right aperture for large DOF work, but as a novice, I can't speak to that.  I defer to the pros in this forum to speak to that.

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JBeckwith

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Re: Full Frame Sharper Than Crop?
« Reply #18 on: October 22, 2012, 09:06:32 PM »
I don't have any technical knowledge about this, but I can certainly express my opinion.  When I upgraded from crop to FF I noticed a "change" in my pictures.  Yes they became sharper, but that could have been due to a lens upgrade as well.  FF images seem to have a different feel to them.  I don't really know how to explain it, but I believe anyone who has gone from crop to FF will probably be able to relate.
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crasher8

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Re: Full Frame Sharper Than Crop?
« Reply #19 on: October 22, 2012, 10:05:57 PM »
You can throw all the science at this and yadda yadda yadda all you want but for someone who has just made the leap, the answer is YES.

LetTheRightLensIn

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Re: Full Frame Sharper Than Crop?
« Reply #20 on: October 22, 2012, 10:07:56 PM »
So I've been doing some research and comparing different lenses on The Digital Picture's ISO comparison tool.  What I am seeing is that the the same lens on both full frame and crop cameras shows a sharper image on the full frame camera.  According to Ken Rockwell, he states that full frame will always be sharper.  I know people don't like quoting him much, but from what I see, he appears to be right. 

FF is sharper than APS-C using the same lens at the same aperture at the 100% view if it has lower photosite density than the APS-C camera (very often this is the case) and the AA filters are not radically different between the two.


Dylan777

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Re: Full Frame Sharper Than Crop?
« Reply #21 on: October 22, 2012, 11:22:17 PM »

I don't know sharper or not with FF, the #1 reason I went with FF is because I want to take pictures under low light - without flash.

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Re: Full Frame Sharper Than Crop?
« Reply #21 on: October 22, 2012, 11:22:17 PM »

AlanF

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Re: Full Frame Sharper Than Crop?
« Reply #22 on: October 23, 2012, 07:25:38 AM »
Here are some simple calculations and experiments that show the 7D does give extra reach of about 45% over a 5D III. Theory tells us that in order to resolve two parallel lines, their images should be at least 2 pixels apart. On a 7D, which has a 4.3 µ pixel, that would be 8.6 µ apart and on a 5D III, with a 6.25 µ pixel, that would be 12.5 µ apart. For an object at a distance v, which is much further away than the focal length of the lens f, the size of the image is given by the size of the object times f/v. For the same lens on a 7D and the 5D III with a lens aperture wide enough so it is not diffraction limited (wider than f/6.9 for the 7D, 10.1 for the 5D III), the sizes of images on both sensors will be the same for the same distances but the image will span more pixels on the 7D. In order to cover two pixels, the object will be 1.45 times further away for the 7D. I did some experiments to test the resolution of the 7D fitted with an f/2.8 300mm II and 2xteleconverter to give f = 600mm and f/5.6. I photographed a feather whose barbs (middle right, below halfway) in the photo were approximately parallel lines separated by 0.27 mm or 0.31 mm (middle right, above halfway). At 5 m distance, nearly all the barbs, including others that were not parallel to the rows or columns of the sensors were very clearly resolved the calculated distances in the image were 16.1 and 18.7 µ, respectively, for the lower and upper sets. At 9 m separation, the barbs were still clearly resolvable, with calculated image sizes of 8.9 and 10.4 µ, just above the supposed limit for resolution of 8.6 µ. The barbs were just resolved at 12 m, with image sizes of 6.7 and 7.8 µ respectively. The images became unresolvable between 14 and 16 m. My calculations of height of image are reliable within 3 percent since the same calculations gave a pixel size of 4.4 µ for the 4.3 µ pixel. So, despite all its supposed limitations, the 7D resolves images at the closest theoretical limits. In order to have the clean separation seen at 9 m on a 7D, the feather would have to be at 6.2 m from the 5D.  The transition of just being resolvable at 12 m from the 7D would be 8.3 m from the 5D, and the complete loss at 14-15 m from the 7D would be 9.6-10.7 m on the 5D. It doesn’t matter how superior the 5D III is than the 7D, the laws of optics and information theory dictate that at 9 m you can resolve the barbs of feathers on a 7 D but you see a blur with the 5D using a 600mm lens.


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neuroanatomist

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Re: Full Frame Sharper Than Crop?
« Reply #23 on: October 23, 2012, 08:10:15 AM »
Thanks, Alan.

I wonder, though - were you shooting at ISO 100?  Many times, even with a stop more light than you've got at 600mm (bare 600 II at f/4), I find myself needing to use ISO 6400 on the 1D X to get the necessary motion-stopping shutter speed.  How do you think the resolving power of the 7D's higher pixel density would hold up compared to the 1D X at ISO 6400?
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AlanF

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Re: Full Frame Sharper Than Crop?
« Reply #24 on: October 23, 2012, 08:58:58 AM »
I was shooting at iso 200. I post photos on a very picky bird website - if it's not tack sharp or free of noise, it will be rejected by the moderators. The noise level at 6400 on a 1D X would be unacceptable for that site. My data are useful for when you have to resolve fine detail at the limits of theoretical resolution. When you are not at those limits and you have more than enough pixels to play with, the FF will outperform the 7D any day because the lower noise and better dynamic range will be more important. But, when those little birds are so far away that they are just a small part of the image, the 7D is better. If you can sneak up on them so they fill the frame, give me a 1D X (please).
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neuroanatomist

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Re: Full Frame Sharper Than Crop?
« Reply #25 on: October 23, 2012, 09:22:57 AM »
I post photos on a very picky bird website - if it's not tack sharp or free of noise, it will be rejected by the moderators. The noise level at 6400 on a 1D X would be unacceptable for that site.

Picky, indeed!
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crasher8

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Re: Full Frame Sharper Than Crop?
« Reply #26 on: October 23, 2012, 09:35:44 AM »
I'd reject that 2nd bird if I was a moderator.

neuroanatomist

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Re: Full Frame Sharper Than Crop?
« Reply #27 on: October 23, 2012, 09:40:16 AM »
I'd reject that 2nd bird if I was a moderator.

It was in a tree and eating seeds.  I get confused easily...   :o
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Re: Full Frame Sharper Than Crop?
« Reply #27 on: October 23, 2012, 09:40:16 AM »

AlanF

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Re: Full Frame Sharper Than Crop?
« Reply #28 on: October 23, 2012, 10:31:39 AM »
This was rejected for being too noisy.
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neuroanatomist

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Re: Full Frame Sharper Than Crop?
« Reply #29 on: October 23, 2012, 10:35:15 AM »
This was rejected for being too noisy.

Is that a 100% crop, or is that the full or slightly cropped image?
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Re: Full Frame Sharper Than Crop?
« Reply #29 on: October 23, 2012, 10:35:15 AM »