Why only 4.6MP?
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From: Alfred Molon on 1 Mar 2010 02:03 In article <hmfn20$7ch$1(a)news.eternal-september.org>, david- taylor(a)blueyonder.co.uk.invalid says... > If, as you say, it only needs a 7MP Bayer camera to equal a 4.6MP Foveon > camera, then Sigma has already lost the battle. Not exactly equal, but the resolution would be roughtly equal (depending on the scene). > My original question remains, although I choose to rephrase it: how big a > print and how close to it do you need to be (more accurately, what angle > does a pixel subtend) to see the extra colour resolution in today's Foveon > cameras versus today's Bayer cameras? I think you can answer that question by yourself. > As the pixel size in a 10MP Foveon camera would be smaller than the 4 > Bayer pixels in a 12-15MP DSLR, not larger, it could place higher demands > on the lenses, not less, and diffraction could be more of a problem. Same photosite size, but higher effective resolution. The pixels in a bayer camera would have to be roughly sqrt(1.5) times smaller to equal the resolution of a full colour sensor. Example (pixel size): Full-colour: 8 micrometers Bayer with equivalent resolution: 8/1.224= 6.5 micrometer The Bayer pixels are smaller because you need more of them. That means, with a full colour sensor you get an effective resolution increase without making the pixels smaller. Fewer demands on the lens, fewer diffraction problems. -- Alfred Molon ------------------------------ Olympus E-series DSLRs and micro 4/3 forum at http://tech.groups.yahoo.com/group/MyOlympus/ http://myolympus.org/ photo sharing site
From: David J Taylor on 1 Mar 2010 02:49 "Alfred Molon" <alfred_molon(a)yahoo.com> wrote in message news:MPG.25f584d0bca48c7b98c240(a)news.supernews.com... > In article <hmfn20$7ch$1(a)news.eternal-september.org>, david- > taylor(a)blueyonder.co.uk.invalid says... > >> If, as you say, it only needs a 7MP Bayer camera to equal a 4.6MP >> Foveon >> camera, then Sigma has already lost the battle. > > Not exactly equal, but the resolution would be roughtly equal (depending > on the scene). > >> My original question remains, although I choose to rephrase it: how big >> a >> print and how close to it do you need to be (more accurately, what >> angle >> does a pixel subtend) to see the extra colour resolution in today's >> Foveon >> cameras versus today's Bayer cameras? > > I think you can answer that question by yourself. No, I can't. It needs tests with real subjects. You say that the full-colour has an advantage, but appear unwilling to back up your claim. >> As the pixel size in a 10MP Foveon camera would be smaller than the 4 >> Bayer pixels in a 12-15MP DSLR, not larger, it could place higher >> demands >> on the lenses, not less, and diffraction could be more of a problem. > > Same photosite size, but higher effective resolution. The pixels in a > bayer camera would have to be roughly sqrt(1.5) times smaller to equal > the resolution of a full colour sensor. > > Example (pixel size): > Full-colour: 8 micrometers > Bayer with equivalent resolution: 8/1.224= 6.5 micrometer > > The Bayer pixels are smaller because you need more of them. > > That means, with a full colour sensor you get an effective resolution > increase without making the pixels smaller. Fewer demands on the lens, > fewer diffraction problems. > > -- > > Alfred Molon False, if the low-pass filter does the correct job for Bayer pixels. Cheers, David
From: nospam on 1 Mar 2010 03:10 In article <hmfn20$7ch$1(a)news.eternal-september.org>, David J Taylor <david-taylor(a)blueyonder.co.uk.invalid> wrote: > If, as you say, it only needs a 7MP Bayer camera to equal a 4.6MP Foveon > camera, then Sigma has already lost the battle. exactly. when the sd14 came out, most reviews said it was comparable to 6-8 mp. unfortunately for sigma, competing cameras at the time were 10 mp and half the price of the sd14. plus, those cameras actually worked and didn't lock up.
From: nospam on 1 Mar 2010 03:10 In article <MPG.25f582cc4fd3a9f698c23f(a)news.supernews.com>, Alfred Molon <alfred_molon(a)yahoo.com> wrote: > > it makes a lot of sense, since competing cameras are 12 mp (and up). > > Do you also compare APS-C cameras with medium format ones? nobody is comparing aps with medium format. the 4.6 mp foveon sensor has a 1.7x crop, so it's reasonable to compare it with a 15 megapixel 1.6x crop canon sensor or a 12 megapixel 1.5x nikon sensor (and new nikon slrs are expected soon). it's also reasonable to compare the sd14 with the 21 mp canon 5d ii, since they are both pretty much the same size (a few millimeters difference in each dimension, nothing major). > > the lens isn't the limiting factor, yet. > > Yes it is when you have 18MP in an APS-C sensor. nope, but even if it was, foveon is stuck at 4.6, so the lens is not the limit.
From: nospam on 1 Mar 2010 03:10
In article <MPG.25f58223fc5db46c98c23e(a)news.supernews.com>, Alfred Molon <alfred_molon(a)yahoo.com> wrote: > > a sensor with three layers is going to be much more complex to > > manufacture than one with only one layer, not to mention that there > > isn't the manufacturing volume to keep costs low. > > Most modern chips have multiple layers. bayer sensors have one layer. that's the whole *point* of foveon. > > also, the thickness of each layer must be held to extremely tight > > tolerances or there will be a colour shift, > > Generally speaking every semiconductor manufacturing process must be > kept in tight tolerances to maximise the yield. yes, but the foveon has an *additional* need to keep the three layers consistent. a little variation on a bayer sensor might give a particular pixel a little more noise, but it's not something that's likely to be noticed. people *do* notice the colour banding on foveon, even after it's been corrected. > > and to help address that, > > foveon has said that *each* camera has to be individually calibrated, > > adding yet another expense. > > But the camera calibration step does not depend on whether the number of > pixels is 4.6 or 10 million. true, but it's one *more* step versus bayer. cipa numbers state 106 million cameras were sold in 2009. imagine if every single one of those had to have its sensor profiled and loaded into the camera's rom. |