lct Posted November 14, 2008 Share #301 Posted November 14, 2008 Advertisement (gone after registration) ...More photons => less noise, because the measurement of the light intensity becomes more reliable if you have a larger no. of counts... Yes i know this thanks but that's the link between noise and CoC i don't understand. I mean, a FF sensor generates the same CoC whatever MPs it has i.e. 0.03mm for the 12.7 MP sensor of the Canon 5D for instance but also 0.03mm for the 24.6 MP sensor of the Sony A900 as well. In other words, the CoC does not depend upon the pixel count but only the size of the sensor, so that there is no link at all between CoC and digital noise AFAIK. Am i missing something here? Quote Link to post Share on other sites More sharing options...
Advertisement Posted November 14, 2008 Posted November 14, 2008 Hi lct, Take a look here A new sensor that can be upgraded is now an obligation. I'm sure you'll find what you were looking for!
SJP Posted November 14, 2008 Share #302 Posted November 14, 2008 For whatever reason people want a "full frame look" which you will achieve with a FF sensor. If you have a full frame sensor then the CoC is given and does not depend on anything, I think/hope you will agree with me on that. So then it boils down to deciding what no.of pixels you need to reach that level of resolution on the sensor. On the M8 the pixels are 6.8 micron so roughly 3 pixels for one CoC of 21 micron. On a FF Mx (x>8.2) you need to resolve a Circle of Confusion of about 31 micron, so using again 3 pixels they could be as big as 10 micron. The surface per pixel would then be (10/6.8)^2 times higher which is about 2.5 so you get that number of photons extra per pixel. So you are right that the sensor dimensions and resulting CoC has nothing to do with noise per-se but it gives you more design freedom to trade sensitivity vs. resolution. Quote Link to post Share on other sites More sharing options...
jaapv Posted November 14, 2008 Share #303 Posted November 14, 2008 Yes i know this thanks but that's the link between noise and CoC i don't understand. I mean, a FF sensor generates the same CoC whatever MPs it has i.e. 0.03mm for the 12.7 MP sensor of the Canon 5D for instance but also 0.03mm for the 24.6 MP sensor of the Sony A900 as well. In other words, the CoC does not depend upon the pixel count but only the size of the sensor, so that there is no link at all between CoC and digital noise AFAIK. Am i missing something here? Yep- the Nyquist frequency;) If the resolution of the lens is less than the resolution of the sensor - a very real possibility and a near-certainty in the case of 20Mp+ sensors in 24x36- the lens will use more than one pixel for every image "point". That will even out the noise. Quote Link to post Share on other sites More sharing options...
SJP Posted November 14, 2008 Share #304 Posted November 14, 2008 the lens will use more than one pixel for every image "point". That will even out the noise.It will primarily waste precious disk space. There is no reason physical, esthetic or otherwise to exceed the CoC value to any major extent in standard photography. Even a prehistoric lens can probably handle the optical resolution to get a focal point smaller than a 20 micron CoC, its primarily about the lack of distortions, abberations, flare resistance, contrast & micro contrast etc. etc. Thats what we are paying for. Quote Link to post Share on other sites More sharing options...
lct Posted November 14, 2008 Share #305 Posted November 14, 2008 ...If you have a full frame sensor then the CoC is given and does not depend on anything, I think/hope you will agree with me on that... I'm afraid i can't sorry. A FF sensor has a 0.03mm CoC because it is full frame and the CoC of 24x36 film is 0.03mm as well. If the film CoC had been 0.02mm, then the FF digital CoC would have been 0.02mm as well. AFAIK the CoC depends upon the size of the film or the sensor, not the pixel count of the sensor or ISO of the film. This way, given a 'classic' CoC of 0.03.mm for FF, the M8 has a CoC of 0.03 : 1.33 = 0.023mm. The result will remain the same if the M9 has a 50 MP sensor of the same size as that of the M8. But i'm no techie at all so i may be wrong of course. Quote Link to post Share on other sites More sharing options...
jaapv Posted November 14, 2008 Share #306 Posted November 14, 2008 The COC is indeed a source of confusion.. It is an arbitrary value, based on the characteristics of an early 20th century film and the small prints that were usual back then. Nowadays with sharply defining sensors, thin, highly resolving films and large standard prints, it is totally obsolete. For normal daily use 0.02 is on the large side for 24x36 capture media and even a COC of 0.015 is defensible. For the M8 I would use 0.01. Quote Link to post Share on other sites More sharing options...
lct Posted November 14, 2008 Share #307 Posted November 14, 2008 Advertisement (gone after registration) ...So you are right that the sensor dimensions and resulting CoC has nothing to do with noise per-se but it gives you more design freedom to trade sensitivity vs. resolution. Sure it gives more freedom but we agree that digital noise does not depend upon CoC right? Quote Link to post Share on other sites More sharing options...
lct Posted November 14, 2008 Share #308 Posted November 14, 2008 The COC is indeed a source of confusion.. It is an arbitrary value, based on the characteristics of an early 20th century film and the small prints that were usual back then.... I beg to disagree Jaap. The DoF markings of our lenses are based on what you call those arbitrary values, i.e. a 0.03mm CoC for 24x36 lenses. As long as those markings will work, they will stay valid IMHO. For me they worked with film and they still work with digital. Quote Link to post Share on other sites More sharing options...
lct Posted November 14, 2008 Share #309 Posted November 14, 2008 ... The circle of confusion... is not governed by the size of the pixels ... but by the CROP FACTOR.... Hence by the size of the sensor. I had not read this part of your post sorry so i agree of course. Quote Link to post Share on other sites More sharing options...
t024484 Posted November 15, 2008 Share #310 Posted November 15, 2008 There is just another important sensor parameter to be regarded, The size of a pixel is not equal to the size of the photodiode. The ratio between the two is called "fill factor". Quite some effort has been put lately in increasing this fill factor a much as possible. An 1D MkII has a pixel size of 8,2*8,2 micron, against 7,2*7,2 for the 1D MkIII, but the photodiode is just as large because of a higher fill factor. This another step forward to reduce noise. Hans Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Quote Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/63256-a-new-sensor-that-can-be-upgraded-is-now-an-obligation/?do=findComment&comment=716236'>More sharing options...
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