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Forums > Back > Sigma SD1 ... wow
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[quote name='Brightcolours' timestamp='1285847839' post='3390']

I really fail to see how diffraction softening could happen on pixel level, they are using a wrong term to describe something different.

[/quote]

Think of it as a single slit diffraction experiment... the slit ofcourse is the Foveon pixel opening at the front. Fitting 4800 pixels on a sensor 24mm wide means a pixel is theoretically 5000nm wide. However, Foveon sensors have a fill factor of around 40%. If we round it up to 50%, the width of the slit (pixel opening) is 2500nm wide. This is a bit wider than the longest visible red wavelengths (which are around [url="http://en.wikipedia.org/wiki/Visible_spectrum#Spectral_colors"]700nm[/url] but it's quite close. But I'm giving the benefit of the doubt to Sigma here though... they wouldn't announce the sensor if such a fundamental problem was there.







[quote name='Brightcolours' timestamp='1285847839' post='3390']

Point remains: The foveon sensors will not be affected worse by diffraction. Diffraction is ONLY in the projected image, and the AA-filter-less sampling willnot get a more soft picture than an AA-filtered one.

[/quote]

What is the meaning of soft? Is it when comparing a 14MP Bayer CFA image vs. a 14MP Foveon? You need to establish the pixel sizes first before talking about the effects of diffraction.





[quote name='Brightcolours' timestamp='1285847839' post='3390']

Which brings us back to the reason Sigma images are "sharper"... due to the refusal to use AA-filters. If you remove the AA-filter from a Bayer CFA sensor, you will get the same kind of sharpness. Liked by some, disliked by those in the know (that is why most camera manufacturers put AA-filters in front).

[/quote]

As a person who has a 50D without an AA-filter and lenses that can out-resolve a 50D without an AA-filter, I can say that this is not true. Plain removal of the AA-filter doesn't give the same resolution of a Foveon (again, what sizes are the compared sensors here?). In fact, from my experience, when the AA-filter of a Bayer CFA is properly matched to the pixel sizes of the sensor, that is when the produced images are more "Foveon-like". Removing the AA-filter only helps if it's overly strong, such as in the case of the D3/D700 (i.e. when compared to the original 5D).



Also removing the AA-filter (and when the lenses are not the limiting factor) will lead to funny demosaic'ing artifacts. This is not at all Foveon-like. It might fool the eye in to thinking that it's real detail, but it looks really ugly at 100%. Just look at a full size sharp Leica M9 image for example. With or without the AA-filter, a Bayer CFA still needs to combine roughly 3 adjacent photosite values in to 1 to produce 1 RGB pixel and this is the actual size of a Bayer "pixel" (i.e. 1/3 of the total photosite count). Foveon does this with 1. So Foveon can have a fewer larger number of pixels and get the same resolution.



Don't take my word for it... take a look here at the link below. This guy modified a 4.7MPixel Sigma SD14 to take EOS lenses and compared it against a 50D (15MPhotosites). The lens he used on both was the Canon 200 f/1.8L @ f/4 (i.e. very very sharp). The images are at their native resolutions, but if you upscale the SD14 image (e.g. bridge image) to match the dimensions of the corresponding 50D image, using a good upscaling algorithm, you'll see that it's difficult to tell them apart just by looking at the detail:



http://www.pbase.com/bigflat/sd14_50d



So that's the relationship between the Bayer CFA and Foveon designs... removing the AA filter doesn't equalise them.
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Messages In This Thread
Sigma SD1 ... wow - by Klaus - 09-21-2010, 06:51 AM
Sigma SD1 ... wow - by Guest - 09-21-2010, 07:05 AM
Sigma SD1 ... wow - by mst - 09-21-2010, 07:13 AM
Sigma SD1 ... wow - by Guest - 09-21-2010, 08:01 AM
Sigma SD1 ... wow - by mst - 09-21-2010, 08:12 AM
Sigma SD1 ... wow - by Guest - 09-21-2010, 09:24 AM
Sigma SD1 ... wow - by popo - 09-21-2010, 11:57 AM
Sigma SD1 ... wow - by wim - 09-21-2010, 01:43 PM
Sigma SD1 ... wow - by Guest - 09-22-2010, 03:28 AM
Sigma SD1 ... wow - by Guest - 09-22-2010, 07:19 AM
Sigma SD1 ... wow - by Klaus - 09-22-2010, 10:02 AM
Sigma SD1 ... wow - by popo - 09-22-2010, 11:34 AM
Sigma SD1 ... wow - by boren - 09-22-2010, 11:38 AM
Sigma SD1 ... wow - by popo - 09-22-2010, 11:42 AM
Sigma SD1 ... wow - by wim - 09-22-2010, 01:06 PM
Sigma SD1 ... wow - by Brightcolours - 09-22-2010, 01:32 PM
Sigma SD1 ... wow - by popo - 09-22-2010, 04:40 PM
Sigma SD1 ... wow - by Guest - 09-22-2010, 06:42 PM
Sigma SD1 ... wow - by mst - 09-22-2010, 07:14 PM
Sigma SD1 ... wow - by wim - 09-22-2010, 10:39 PM
Sigma SD1 ... wow - by popo - 09-22-2010, 11:36 PM
Sigma SD1 ... wow - by wim - 09-23-2010, 12:30 AM
Sigma SD1 ... wow - by Guest - 09-23-2010, 06:03 AM
Sigma SD1 ... wow - by Guest - 09-23-2010, 06:06 AM
Sigma SD1 ... wow - by popo - 09-23-2010, 06:56 AM
Sigma SD1 ... wow - by Brightcolours - 09-23-2010, 08:17 AM
Sigma SD1 ... wow - by popo - 09-23-2010, 11:30 AM
Sigma SD1 ... wow - by Brightcolours - 09-23-2010, 11:42 AM
Sigma SD1 ... wow - by popo - 09-23-2010, 11:58 AM
Sigma SD1 ... wow - by Brightcolours - 09-23-2010, 12:08 PM
Sigma SD1 ... wow - by genotypewriter - 09-30-2010, 06:11 AM
Sigma SD1 ... wow - by Brightcolours - 09-30-2010, 11:57 AM
Sigma SD1 ... wow - by genotypewriter - 10-01-2010, 05:51 AM
Sigma SD1 ... wow - by Guest - 10-01-2010, 08:24 AM
Sigma SD1 ... wow - by Brightcolours - 10-01-2010, 10:54 AM
Sigma SD1 ... wow - by Guest - 10-01-2010, 11:23 AM
Sigma SD1 ... wow - by Brightcolours - 10-01-2010, 01:45 PM
Sigma SD1 ... wow - by boren - 10-01-2010, 04:20 PM
Sigma SD1 ... wow - by Brightcolours - 10-01-2010, 04:38 PM
Sigma SD1 ... wow - by boren - 10-01-2010, 04:53 PM
Sigma SD1 ... wow - by Brightcolours - 10-01-2010, 05:03 PM
Sigma SD1 ... wow - by genotypewriter - 10-02-2010, 01:44 PM
Sigma SD1 ... wow - by Brightcolours - 10-02-2010, 03:07 PM
Sigma SD1 ... wow - by Guest - 10-03-2010, 03:09 PM
Sigma SD1 ... wow - by Brightcolours - 10-03-2010, 05:39 PM
Sigma SD1 ... wow - by Guest - 10-04-2010, 08:04 AM
Sigma SD1 ... wow - by Brightcolours - 10-04-2010, 12:02 PM
Sigma SD1 ... wow - by Guest - 10-04-2010, 01:25 PM
Sigma SD1 ... wow - by Brightcolours - 10-04-2010, 04:39 PM
Sigma SD1 ... wow - by genotypewriter - 10-05-2010, 02:22 AM
Sigma SD1 ... wow - by Guest - 10-05-2010, 09:23 AM
Sigma SD1 ... wow - by Brightcolours - 10-05-2010, 09:50 AM
Sigma SD1 ... wow - by Brightcolours - 10-05-2010, 10:09 AM
Sigma SD1 ... wow - by Guest - 10-05-2010, 11:01 AM
Sigma SD1 ... wow - by Guest - 10-05-2010, 11:26 AM
Sigma SD1 ... wow - by Brightcolours - 10-05-2010, 11:30 AM
Sigma SD1 ... wow - by Steinar1 - 10-05-2010, 04:10 PM
Sigma SD1 ... wow - by Brightcolours - 10-05-2010, 07:09 PM
Sigma SD1 ... wow - by borisbg - 10-05-2010, 08:32 PM
Sigma SD1 ... wow - by genotypewriter - 10-06-2010, 12:31 AM
Sigma SD1 ... wow - by Guest - 10-06-2010, 08:32 AM
Sigma SD1 ... wow - by Brightcolours - 10-06-2010, 09:16 AM
Sigma SD1 ... wow - by Brightcolours - 10-06-2010, 11:43 AM
Sigma SD1 ... wow - by Steinar1 - 10-06-2010, 02:46 PM
Sigma SD1 ... wow - by Yakim - 10-16-2010, 10:15 PM

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