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Author Topic: Foveon  (Read 3655 times)
david o
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« on: January 04, 2007, 07:32:43 AM »
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Beyond what I could read so far,
it seems something interesting, I did the research on the forum and not to much about it.
What is the opinion of the "ingeener"
Thanks
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John Sheehy
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« Reply #1 on: January 04, 2007, 09:22:37 AM »
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Beyond what I could read so far,
it seems something interesting, I did the research on the forum and not to much about it.
What is the opinion of the "ingeener"
Thanks
[a href=\"index.php?act=findpost&pid=93615\"][{POST_SNAPBACK}][/a]

Foveon is a very religious subject.  You have people who own a Sigma that uses it, and think that its god's gift to photography, people who used to use it but don't anymore, people who would like to use it but don't want to invest in a proprietary lens/accessory system, people who think the images look defective, etc, etc.

The issues are compounded by the fact that the Sigma cameras that use the Foveon sensors have not only a different type of sensor than most digitals, but they also omit the anti-alias filter, which prevents a camera from recording distorted high-resolution detail that isn't accurate to the subject, but the output *looks* sharp.

They do resolve three bands of color at each pixel, unlike most digitals, but the discrimination between those color bands are much poorer than the results with the colored filter arrays used in most digitals.  The blue channel doesn't distinguish well from green in the overlapping ranges, and the blue channel is not very well saturated; IOW, the blue channel is very close to being a panchromatic grey channel, with a slight bias towards blue.  The result is lots of chromatic noise in some cases, and large blotches of off-color in the deep shadows.
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stefan marquardt
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« Reply #2 on: January 04, 2007, 02:41:02 PM »
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the files from a sigma sd9 or sd10 - both with foveon-sensors - can (!) be absolutely outstanding.
i  switched from a sd9 to a canon 1ds and 5d and now medium format. i few nights ago I opend an old sigma file and it nearly knocked me over. the 3 mp resolution isnŽt very good -but there is something that makes some (!) images look much better than bayer images. you can upsize them a lot - and they get softer - but still look good . whereas bayer-files start to look ugly.
i would love to use the sigma cameras for my work - if they would only have a full frame sensor i would cladly drop my other cameras.   noisewise the behave very much like the older dalsa sensor.  the small sensor, the noise, the artifacts the can show and the little resolution make them not very usefull for paid jobs. nearly all the pics on my work-website (www.architekturbild.de) are from the canons - but nearly all the photos from my personal/play-website (www.stefanmarquardt.de and particuarly all of these: http://stefanmarquardt.de/special/special.html) are from the little sigmas.

stefan marquardt

p.s. I forgot: youŽll never get any moire with foveon!
« Last Edit: January 04, 2007, 03:25:25 PM by stefan marquardt » Logged

stefan marquardt
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BJL
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« Reply #3 on: January 04, 2007, 04:20:57 PM »
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p.s. I forgot: youŽll never get any moire with foveon!
[a href=\"index.php?act=findpost&pid=93709\"][{POST_SNAPBACK}][/a]
Not color moiré, but similar monochrome aliasing artifacts are possible. In fact, some resolution test chart charts shots with Foveon sensors show the wrong number of black and white lines at the high resolution end, a classic aliasing error, due to the lack of a low-pass (AA) filter.

P. S. It is ironic that this thread is in a medium format forum, since Foveon has not managed to up-size its sensors even to match the "APS-C" format for which Sigma's DC lenses are designed, leaving Sigma DSLR's with slightly cramped wide angle options. Indeed, Foveon said at the time of the original Sigma DSLR launch that technical difficulties made it unlikely that the sensors would be up-sized to match 35mm film format (so forget about MF.)
« Last Edit: January 04, 2007, 04:26:25 PM by BJL » Logged
John Sheehy
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« Reply #4 on: January 04, 2007, 04:33:46 PM »
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p.s. I forgot: youŽll never get any moire with foveon!
[a href=\"index.php?act=findpost&pid=93709\"][{POST_SNAPBACK}][/a]

Actually, you can get color moire, especially from the SD9, but it takes a very unusal circumstance.

Luminance aliasing, however is very common with sharp lenses.

Aliasing has always been considered bad - it is much more annoying to more people in audio than in visual media, and many people have found that they like it.  I can't like it.  I don't like seeing edges that arent there, and I don't like the "snap-to-grid" effect.  I've printed crops of SD9 images large, and I can't see what you see in them - they look like egg carton textures to me.
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John Sheehy
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« Reply #5 on: January 04, 2007, 04:38:58 PM »
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P. S. It is ironic that this thread is in a medium format forum, since Foveon has not managed to up-size its sensors even to match the "APS-C" format for which Sigma's DC lenses are designed, leaving Sigma DSLR's with slightly cramped wide angle options. Indeed, Foveon said at the time of the original Sigma DSLR launch that technical difficulties made it unlikely that the sensors would be up-sized to match 35mm film format (so forget about MF.)
[a href=\"index.php?act=findpost&pid=93739\"][{POST_SNAPBACK}][/a]

That's rather unfortunate, as a 22MP foveon might be a bit more forgiving on the aliasing.  Dropping the AA filter is something you might do when you have lots of pixels, and they are well below the threshold of resolution.  To leave out an AA filter on a 3.43MP camera seems a bit strange to me, but perhaps Sigma was banking on a certain demographic liking the aliasing.  Many think it is detail, but it is sharpness of the medium and sampling process, not of the subject.  A lot like looking at a mediocre scene through shattered glass - nice and sharp looking!
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Graeme Nattress
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« Reply #6 on: January 10, 2007, 02:10:47 PM »
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To ignore the need for an anti-alias filter either shows a lack of engineering understanding, or a wish to pull the wool over people's eyes by saying "wow - look how SHARP" it is, when it's all aliassed and really quite horrible.
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