If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
Math question - sort of
John McWilliams wrote:
It's not just about the maths. Way too many other factors affecting IQ, and I suspect most photographers will soon forget about how equivalent one framing on one camera is to another body he's used. He'll go for the highest IQ he can in the moment. IQ is IQ. But the question the OP posted is about the _math_, as he stated in the subject. Also, the way it is formulated in the message body, it is about the math and math alone. I think the OP knows perfectly well that the IQ is not just about the math, which is why he made a specific effort to extract and isolate just the math part of the problem in his question. |
#12
|
|||
|
|||
Math question - sort of
In article , John Navas
wrote: I don't think that my 10D was pushing up against the resolution limit of my 400 f/5.6L and while I may not realize the all the resolving potential with that lens on the 7D, I was more interested in the difference in potential resolution, the conversion puzzle and not so much the practicality, i.e., don't spoil my fun! If we assume a top (not cheap) non-zoom telephoto lens will resolve 80 LPM (check the MTF charts for your lens), then the maximum resolution of the lens on a Canon APS-C sensor of 22.3 mm x 14.9 mm (like the 7D) is 22.3 x 80 x 2 x 14.9 x 80 x 2 = 8.5 MP, far less than the 18 MP spec of the 7D, and anything more is wasted. nonsense. there is a very clear and visible difference between an 8 mp camera such as a canon 20d and an 18 mp camera such as a canon 7d. dpreview measured the resolution of the 8mp 20d at 1850/1650 lines and the 15 mp 500d at 2400/2350 lines (the 7d has not yet been reviewed). moving up to the 24 megapixel nikon d3x, it's 2700/2600 lines. if the excess megapixels beyond 8 were wasted there would be no difference, yet there is. http://www.dpreview.com/reviews/canoneos20d/page27.asp http://www.dpreview.com/reviews/canoneos500d/page28.asp http://www.dpreview.com/reviews/nikond3x/page32.asp |
#13
|
|||
|
|||
Math question - sort of
"Andrey Tarasevich" wrote in message ... I think the OP knows perfectly well that the IQ is not just about the math, which is why he made a specific effort to extract and isolate just the math part of the problem in his question. You read me well. Eric Miller www.dyesscreek.com "When the only tool you have is a hammer, every problem begins to resemble a nail." - Abraham Maslow |
#14
|
|||
|
|||
Math question - sort of
John Navas wrote in
: If we assume a top (not cheap) non-zoom telephoto lens will resolve 80 LPM (check the MTF charts for your lens), then the maximum resolution of the lens on a Canon APS-C sensor of 22.3 mm x 14.9 mm (like the 7D) is 22.3 x 80 x 2 x 14.9 x 80 x 2 = 8.5 MP, far less than the 18 MP spec of the 7D, and anything more is wasted. Aliased imaging ... shift everything 1/2 pixel horizontally and vertically, and what do you get? Gray nothing. It takes *SIX* pixels, exclusive, to properly sample a line pair. And there is usable contrast at much higher than 80 LP/mm with a lens like the 400mm f/5.6, especially if the noise is low and you can sharpen aggressively. |
#15
|
|||
|
|||
Math question - sort of
Eric Miller wrote in
: I went from the 10D to the 5D. When I had my 10D, I learned to like the 1.6x way of fooling myself into thinking my 400mm lens was a 560mm lens. I don't find that a very useful way of looking at things. A lens is the focal length that it really is. The *sensor* captures a certain area of the focal plane, with certain potential MTF curves, depending on sensel spacing, effective fill factor (photosite or microlens, whichever is wider), and AA filter strength. The size of the sensor, combined with the focal length, determine the *breadth* of the capture, IMO, and the term "reach" (which, also IMO, is poorly selected), if used at all, should be related to the pixel spacing and pixel qualities rather than the "crop factor". A 5D2 with the same lens has more "reach" than a 10D, in the sense that it puts the subject over more pixels. Going by crop factors, one might erroneously assume that the 10D will get you more subject detail. Now I am thinking of getting myself another birding camera and am trying to figure out if there is a way to think of resolution as effective focal length versus the 10D. So, for example, if I were to get a 7D at 18 megapixels how would that compare to 10D resolution wise in terms of what focal length lens would I have had to put on the 10D to get a 5 inch tall bird at 20 meters (or any distance) to be rendered by the same number of pixels (one dimension only or my head will hurt too much) on the 10D that it would be rendered on the 7D using the 400mm lens. I would just think of it as 400mm, same FOV, but with higher subject resolution and less subject noise. |
#16
|
|||
|
|||
Math question - sort of
In article , John Navas
wrote: If we assume a top (not cheap) non-zoom telephoto lens will resolve 80 LPM (check the MTF charts for your lens), then the maximum resolution of the lens on a Canon APS-C sensor of 22.3 mm x 14.9 mm (like the 7D) is 22.3 x 80 x 2 x 14.9 x 80 x 2 = 8.5 MP, far less than the 18 MP spec of the 7D, and anything more is wasted. nonsense. there is a very clear and visible difference between an 8 mp camera such as a canon 20d and an 18 mp camera such as a canon 7d. That depends on the lens. "assume a top (not cheap) non-zoom telephoto lens" Read what I wrote more carefully. likewise. |
#17
|
|||
|
|||
Math question - sort of
|
#18
|
|||
|
|||
Math question - sort of
In article , Andrey Tarasevich
writes John McWilliams wrote: It's not just about the maths. Way too many other factors affecting IQ, and I suspect most photographers will soon forget about how equivalent one framing on one camera is to another body he's used. He'll go for the highest IQ he can in the moment. IQ is IQ. But the question the OP posted is about the _math_, as he stated in the subject. Also, the way it is formulated in the message body, it is about the math and math alone. If it is just about the math then you need to quantify the lens quality contribution as well - your math is less than half the story, dealing only with pixel geometry. To include the lens contribution you need to use significantly more complex math, convolving pixel geometry with lens aberration geometry, or a completely different type of math using pixel MTF and lens MTF to scale resolved spatial resolutions at equal contrast. That is what the discussion on the LL site is trying to explain. -- Kennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's ****ed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) |
#19
|
|||
|
|||
Math question - sort of
Kennedy McEwen wrote:
In article , Andrey Tarasevich writes John McWilliams wrote: It's not just about the maths. Way too many other factors affecting IQ, and I suspect most photographers will soon forget about how equivalent one framing on one camera is to another body he's used. He'll go for the highest IQ he can in the moment. IQ is IQ. But the question the OP posted is about the _math_, as he stated in the subject. Also, the way it is formulated in the message body, it is about the math and math alone. If it is just about the math then you need to quantify the lens quality contribution as well No, the question posed in the original post had nothing to do with that. - your math is less than half the story, dealing only with pixel geometry. That would actually be the whole story, since the original question strictly concerned the pixels. To include the lens contribution you need to use significantly more complex math, convolving pixel geometry with lens aberration geometry, or a completely different type of math using pixel MTF and lens MTF to scale resolved spatial resolutions at equal contrast. That is what the discussion on the LL site is trying to explain. Pertinence to this thread? Eric Miller www.dyesscreek.com |
#20
|
|||
|
|||
Math question - sort of
In article , Eric Miller
writes Kennedy McEwen wrote: If it is just about the math then you need to quantify the lens quality contribution as well No, the question posed in the original post had nothing to do with that. I suggest you read what you wrote in your question again and, in future ask what you mean or mean what you ask! You specifically refer to resolution and that is a lot more than just pixel density! - your math is less than half the story, dealing only with pixel geometry. That would actually be the whole story, since the original question strictly concerned the pixels. No, you stated: "if there is a way to think of resolution as effective focal length versus the 10D". Pixels are only one component of resolution: optics contribute significantly and, in this particular case, dominate. Others have tried to explain this to you in the thread, but it is clearly making your "head hurt too much"! To include the lens contribution you need to use significantly more complex math, convolving pixel geometry with lens aberration geometry, or a completely different type of math using pixel MTF and lens MTF to scale resolved spatial resolutions at equal contrast. That is what the discussion on the LL site is trying to explain. Pertinence to this thread? If you have to ask that question then the answer is clearly beyond you, but it is pertinent on at least three counts: 1. It is the full answer to your question, which you clearly seem unable to understand. Even perfect optics have a finite resolution, and when the sensor resolution approaches that, which is certainly the case in the 7D, that needs to be included in any scaling comparison, as explained in the LL article. The optical resolution is limited in terms of the minimum blur spot, while the sensor is limited in resolution by the pixel area. The cameras limits are determined by convolution of optical blur spot and pixel area. Convolution is a fairly complicated mathematical procedure and it is simpler to represent these parameters in terms of MTF curves simplifying the calculation of the camera resolution as it is just the product of the MTFs. The effective focal length scaling, in terms of reach, is simply then the ratio of the spatial resolutions at which the limiting contrast is achieved. That is the COMPLETE answer to your question. Whether you understand it or not, pixel scaling is only part of the issue and, in the case of comparing anything to the high pixel density of the 7D, will yield highly optimistic scaling on its own. 2. It has already been linked to in this thread, but obviously ignored by you. I suggest you read it again and make some effort to understand it before claiming it is irrelevant, since optics dominate the question you have asked, NOT pixels. 3. Others who read this thread in future, which will be archived forever, may be less mentally challenged than you and be looking for a more complete answer, not a simple pixel scaling answer which is trivial to calculate but optimistic at best and wrong in general. -- Kennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's ****ed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
a techie sort of question about p&s cameras and optical viewfinders | albert | Digital Photography | 9 | December 15th 08 07:03 PM |
A meter math question | Steven Woody | 35mm Photo Equipment | 7 | April 11th 07 04:51 PM |
help with aperture math | Beach Bum | Digital SLR Cameras | 18 | February 15th 06 02:18 AM |