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#1
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Math question - sort of
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. 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. Eric Miller www.dyesscreek.com |
#2
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Math question - sort of
"Eric Miller" wrote in message ... 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. 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. You could play square root games, but the easiest thing to do is to compare the vertical (short) direction pixel counts. The 7D is 3456 pixels in the short direction. The 10D is 2048 pixels in the short direction. So the 7D (cropped to 6MP) is like putting a (3456/2046)x (that is, a 1.6x) TC on your 10D. The only problem, though, is that nothing's for free. Any infelicities in your 400mm lens will be magnified by the extremely fine pixel pitch on the 7D. To get pixel sharp images from the 7D, you need to project images onto the sensor that are "1.6 times better" than the images you are now putting on your 10D's sensor. That may mean a bigger tripod and not shooting wide open. By the way, I think you'll enjoy the 7D. The 5D2 was a noticeable improvement over the 5D, and the 7D has a few niceties beyond the 5D2; it should be a great camera. -- David J. Littleboy Tokyo, Japan |
#3
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Math question - sort of
Eric Miller wrote:
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. 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. It's all relative, the noise level matters too for how much you can enlarge but yes it would be useful to have a common terminology for describing pixel magnification rather than 35mm equivalent FOV. Hmm, I was thinking macro when I wrote "pixel magnification" but at infinity I guess it would be pixels/field of view in degrees? Set the number relative to a 'normal' lens, which coincidentally is very close to 50 degrees for the diagonal FOV of a 50mm lens on a 35mm camera. Then let's use 300dpi as a standard metric for enlargement, on an 8x10 print that's 2400x3000 or 7.2MP. So, a full frame 7.2MP camera making an acceptable 8x10 print with a normal lens of 50 degrees diagonal field of view represents the basepoint. Damn, now I've exceeded my mathematical skills and/or patience and cannot figure out how to set up a formula to calculate/express this. It would look something like if you doubled the focal length, the number would be 2 and the number is 1 with the default setup. A 500mm lens on FX would be a 10 and a 10mm FX fisheye would be -5. I'm not certain what doubling the megapixel count would do to the number, probably not double it. Can anyone finish my logic? A chart would be nice g. -- Paul Furman www.edgehill.net www.baynatives.com all google groups messages filtered due to spam |
#4
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Math question - sort of
Eric Miller wrote:
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. 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. My take is that while you can come up with an approximation of what the comparables are, so what? You'll still want to maximize sharpness and detail on each shot, and won't be telling yourself, well, I can stay back and crop later to get an image I would have had on a previous set up. Besides the math part, there're different curves for each ISO setting, as well as available light and so on. I am thinking of picking up a 7D, and still shoot with my 20 D and 5D..... -- john mcwilliams |
#5
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Math question - sort of
On Tue, 22 Sep 2009 22:47:35 -0500, Eric Miller wrote:
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. 400*1.6 = 640 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. Dunno - what's the resolution of the 10d? But your question will be answered by taking the square root of the ratio. Eric Miller www.dyesscreek.com |
#6
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Math question - sort of
"ray" wrote in message ... On Tue, 22 Sep 2009 22:47:35 -0500, Eric Miller wrote: 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. 400*1.6 = 640 Yep, caught that after posting. I mixed up my 1.4x converter with the 1.6x sensor. Eric Miller www.colibrihotsauce.com |
#7
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Math question - sort of
"David J. Littleboy" wrote in message ... The only problem, though, is that nothing's for free. Any infelicities in your 400mm lens will be magnified by the extremely fine pixel pitch on the 7D. To get pixel sharp images from the 7D, you need to project images onto the sensor that are "1.6 times better" than the images you are now putting on your 10D's sensor. That may mean a bigger tripod and not shooting wide open. 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! Eric Miller www.colibrihotsauce.com |
#8
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Math question - sort of
"Eric Miller" wrote in message ... 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. 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. Eric Miller www.dyesscreek.com Both the 10D and the 7D are APS-C sized sensors, so your 400mm lens will have a 1.6 FOV crop, so both will be similar to a 640mm (not 560mm). I never work in pixel pitch in photography. |
#9
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Math question - sort of
Eric Miller wrote:
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. If we assume that sensors in both cameras have the same physical size (and they basically do), then all we need to know is the size of each sensor in physical pixels. I don't know the numbers for 7D, but we can just assume a square pixel (for both sensors) and use the square root of the total physical pixel count instead 10D has a 6.5Mpix sensor. Sqrt(6.5) = 2.55 7D has a 19Mpix sensor, Sqrt(19) = 4.36 The above immediately means that given the same bird and fixed distance to the bird (as you requested in your message), you'd have to increase the focal length of 10D lens by a factor of 4.36/2.55 = 1.7. If you are using a 400mm lens on 7D, the 10D would require a 680mm lens. |
#10
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Math question - sort of
Andrey Tarasevich wrote:
Eric Miller wrote: 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. If we assume that sensors in both cameras have the same physical size (and they basically do), then all we need to know is the size of each sensor in physical pixels. I don't know the numbers for 7D, but we can just assume a square pixel (for both sensors) and use the square root of the total physical pixel count instead 10D has a 6.5Mpix sensor. Sqrt(6.5) = 2.55 7D has a 19Mpix sensor, Sqrt(19) = 4.36 The above immediately means that given the same bird and fixed distance to the bird (as you requested in your message), you'd have to increase the focal length of 10D lens by a factor of 4.36/2.55 = 1.7. If you are using a 400mm lens on 7D, the 10D would require a 680mm lens. 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. -- john mcwilliams I know that you believe you understood what you think I said, but I'm not sure you realize that what you heard is not what I meant. |
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