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Does sensor anti-aliasing affect diffraction limits?
Posted 19-03-12 at 07:11 PM by Ian
One of my technical articles from last year has been brought back to life by one of our newest forum members, Mike (chicagonature) who has pre-ordered the special version of Nikon's new D800 - the 'E' version which doesn't have an anti-aliasing (AA) filter. Mike is a nature and landscape photographer and the D800E is aimed precisely at him because without an AA filter the camera will record even more detail, in theory, than the standard version of the 36 megapixel full frame DSLR. In nature there is less chance of recording regular pattern details that can cause moiré, which AA filters prevent - at the expense of sensor resolving power.
But in a forum post responding to my old article Mike has been puzzling over some technical notes for D800E users that suggest that the already tightened diffraction limit of the D800 is tightened further by the D800E. In other words, the D800's already relatively wide aperture limit before diffraction limitation sets in (I estimated that the D800 diffraction limit is around f/9 compared to f16 for the much lower resolution D700). Mike is naturally worried that if he is investing in such a high resolution camera as the D800E that some of that resolving power may be wasted because he can't use smaller lens apertures to obtain adequate depth of field.
I offered to try and shed some light on this question by taking some comparison pictures using two cameras that are very similar apart from the AA strength on their respective sensors; the Olympus E-30 (strong AA) and the Olympus E-5 (weak AA). Both cameras have the same 12.3MP LiveMOS Four Thirds sensor made by Panasonic, but Olympus decided to adopt a weaker anti-aliasing filter with the later E-5 model.
It's easy to see how the E-5's weaker AA filter compares to the strong AA filter on the E-30 at wider apertures; it gives much more crisp details with noticeably better resolution; exactly what Mike wants from his D800E. Interestingly, the Four Thirds 12.3MP sensor is about a quarter of the area of the Nikon's full frame sensor and has a third of the Nikon's pixels, so the pixel density of the Olympus cameras is slightly higher, and in theory the diffraction limit is around f/7.1-8 compared to the D800's f/9. So by looking at a sequence of images using a very sharp lens on the Olympus cameras (in this case the highly-revered Zuiko Digital 50mm f/2.0 ED Macro) at decreasing apertures, maybe we could detect a difference in diffraction effect between the two different AA strength cameras.
The area of the frame reproduced in the links below.
I have uploaded 100% (1 displayed pixel to 1 image pixel) crops of from the test images showing the same area of the frame. This was done in Lightroom 3.7 without any post processing apart from slight sharpening for on-screen viewing. Each sample image is still around 500-600K so I haven't embedded them in this page. Instead there are links to the images here:
Before I analyse the results myself, I'd be interested to know what your thoughts are. Does the weaker AA bring on diffraction faster as the aperture gets smaller? Over to you...
But in a forum post responding to my old article Mike has been puzzling over some technical notes for D800E users that suggest that the already tightened diffraction limit of the D800 is tightened further by the D800E. In other words, the D800's already relatively wide aperture limit before diffraction limitation sets in (I estimated that the D800 diffraction limit is around f/9 compared to f16 for the much lower resolution D700). Mike is naturally worried that if he is investing in such a high resolution camera as the D800E that some of that resolving power may be wasted because he can't use smaller lens apertures to obtain adequate depth of field.
I offered to try and shed some light on this question by taking some comparison pictures using two cameras that are very similar apart from the AA strength on their respective sensors; the Olympus E-30 (strong AA) and the Olympus E-5 (weak AA). Both cameras have the same 12.3MP LiveMOS Four Thirds sensor made by Panasonic, but Olympus decided to adopt a weaker anti-aliasing filter with the later E-5 model.
It's easy to see how the E-5's weaker AA filter compares to the strong AA filter on the E-30 at wider apertures; it gives much more crisp details with noticeably better resolution; exactly what Mike wants from his D800E. Interestingly, the Four Thirds 12.3MP sensor is about a quarter of the area of the Nikon's full frame sensor and has a third of the Nikon's pixels, so the pixel density of the Olympus cameras is slightly higher, and in theory the diffraction limit is around f/7.1-8 compared to the D800's f/9. So by looking at a sequence of images using a very sharp lens on the Olympus cameras (in this case the highly-revered Zuiko Digital 50mm f/2.0 ED Macro) at decreasing apertures, maybe we could detect a difference in diffraction effect between the two different AA strength cameras.
The area of the frame reproduced in the links below.
I have uploaded 100% (1 displayed pixel to 1 image pixel) crops of from the test images showing the same area of the frame. This was done in Lightroom 3.7 without any post processing apart from slight sharpening for on-screen viewing. Each sample image is still around 500-600K so I haven't embedded them in this page. Instead there are links to the images here:
- E-30 f/4: http://dpnow.com/files/forum/anti-al...0141_f_4.0.jpg
- E-30 f/5.6: http://dpnow.com/files/forum/anti-al...0142_f_5.6.jpg
- E-30 f/8: http://dpnow.com/files/forum/anti-al...0143_f_8.0.jpg
- E-30 f/11: http://dpnow.com/files/forum/anti-al...144_f_11.0.jpg
- E-30 f/16: http://dpnow.com/files/forum/anti-al...145_f_16.0.jpg
- E-30 f/22: http://dpnow.com/files/forum/anti-al...146_f_22.0.jpg
- E-5 f/4: http://dpnow.com/files/forum/anti-al...0004_f_4.0.jpg
- E-5 f/5.6: http://dpnow.com/files/forum/anti-al...0005_f_5.6.jpg
- E-5 f/8: http://dpnow.com/files/forum/anti-al...0006_f_8.0.jpg
- E-5: f/11: http://dpnow.com/files/forum/anti-al...007_f_11.0.jpg
- E-5 f/16: http://dpnow.com/files/forum/anti-al...008_f_16.0.jpg
- E-5 f/22: http://dpnow.com/files/forum/anti-al...010_f_22.0.jpg
Before I analyse the results myself, I'd be interested to know what your thoughts are. Does the weaker AA bring on diffraction faster as the aperture gets smaller? Over to you...
Total Comments 2
Comments
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Diffraction transition IMHO
E-30 f8-f11
E-5 f8 -f11
but the E-30 is obviously softer
So about where you would expect...so set a 4/3 12.3Mp camera to no more than f8
Interestingly the OM-D with those extra pixels calculates at around f7.1 max
http://www.cambridgeincolour.com/tut...tography-2.htmPosted 19-03-12 at 08:18 PM by crimbo 
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Hi Ian,
Good test and I concure with the f/8-f/11 zone, at least for the magnification used here. I don't recall Mike mentioning his print size for his landscape work, but I remember his scene setup and that he needed max DOF. Back in the film days, that was Large Format Land especially for large wet prints.
I downloaded your OMD shot of this scene, so it was interesting to see theses after playing with that one.
BobPosted 20-03-12 at 03:10 AM by Bob Ross
