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#61
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Telephoto Reach and Digital Cameras - lens comparison
On Sat, 18 Dec 2010 08:24:53 -0800, Paul Furman
wrote: Ofnuts wrote: Superzooms Still Win wrote: As for your physics proving everything, it FAILS because it does NOT take into account the figure of the lenses. The lenses on the superzoom camera can and ARE polished to diffraction-limited quality. Yes, they are polished to diffraction-limited quality at the top of a high moutain by virgin girls under the full moon. They are then laid on silk cushions and brought back in the valley using buffalo carts, and the tiny moves of the lenses on the cushions caused by the gentle rocking of the cart finishes the polishing to perfection. Panasonic's Leica lenses are finished off wrapped in silk between Swiss virgin's breasts trotting on horseback down the mountain as they sing the praises of their fine accuracy and innovative engineering; instilling emotional warmth, impact, and subtlety. http://www2.panasonic.com/webapp/wcs...tGroupId=24999 The text makes a virtue out of necessity: "The DC Vario-Summicron is Leica's preeminent lens. Its exceptional optics give photos an exquisite soft-focus effect, ... " Eric Stevens |
#62
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Telephoto Reach and Digital Cameras - lens comparison
Roger N. Clark (change username to rnclark) wrote:
Paul Furman wrote: Now some more abstract comparisons, I suspect the reason you don't see super fast P&S lenses with shallow DOF is the exact same reason they cost a lot in 35mm format. P&S are designed for economy and it would be too expensive to grind lenses that small to such tolerance; unmarketable. Now I'm talking '35mm equivalent aperture' which is a concept with little acceptance but it's valid if you want shallow DOF. If you just scale down a 50mm f/1.4 lens to fit a P&S, it would still be f/1.4 but there would be more DOF which means you'd need to redesign it as something like 10mm f/0.7, Paul, If the crop multiplier is 5x, so the 10mm lens on the P&S is the same as the 50 mm lens on the 35mm sized sensor, the aperture diameter must be maintained for the same depth of field. Thus the 50 mm f/1.4 becomes 1.4/5 = f/0.28 on the 10 mm lens, which is pretty much impossible to build. Thanks, I am not to be trusted with math g. As I wrote my rant/lecture above, one thing that helped me make sense of why DOF changes with smaller formats at the same f-stop is this visualization: Imagine instead of shrinking the lens and camera, that the world grew larger by a factor of five. Or imagine a studio setting scaled up five times if that's too much of a stretch. The enlarged studio scene and subjects would be five times as far away from the camera. DOF gets shallower the closer you focus: macro shooting has very shallow DOF whereas subjects out near infinity will be rendered with more 'thick' DOF. Or, to get a shallow DOF look from a P&S, you could make a scale model at 1/5th the size and be in macro range, if you could get a 10mm f/1.4 lens. There are c-mount video lenses that come close like maybe 12mm f/1.8. Of course, if you want more DOF, none of this matters but I thought it's an interesting way to put things into perspective. |
#63
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Telephoto Reach and Digital Cameras - lens comparison
Val Hallah wrote:
On Dec 6, 5:20 pm, "David J Taylor"david- wrote: A comparison of fixed focal length lenses& consumer zooms on DSLRs when photographing distant objects: http://www.clarkvision.com/articles/telephoto_reach/ including a comparison with a super-zoom P&S. http://www.clarkvision.com/articles/...vs.dslr.compar... A longer zoom may not be better than a shorter fixed focal length lens. better off with a spacecraft though... http://www.dailymail.co.uk/sciencete...ed-detail.html Tell me about it. Spacecraft do a lot more than simply get better resolution. See: http://www.sciencemag.org/content/326/5952/562.abstract or the Moon as never before seen: http://www.lpi.usra.edu/meetings/lpsc2010/pdf/2302.pdf (I'm working on the full resolution, full coverage results now.) Spacecraft are great, if you have a few hundred million dollars! The cost from superzoom to DSLR telephotos is roughly proportional to the resolution increase. The jump to orbital spacecraft at the Moon is a huge jump in cost for the resolution increase. And even so, a spacecraft in orbit around the Moon makes a lousy camera for sports and wildlife photography on Earth! Roger |
#64
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Telephoto Reach and Digital Cameras - lens comparison
On 12/18/2010 08:58 PM, Eric Stevens wrote:
On Sat, 18 Dec 2010 08:24:53 -0800, Paul wrote: Ofnuts wrote: Superzooms Still Win wrote: As for your physics proving everything, it FAILS because it does NOT take into account the figure of the lenses. The lenses on the superzoom camera can and ARE polished to diffraction-limited quality. Yes, they are polished to diffraction-limited quality at the top of a high moutain by virgin girls under the full moon. They are then laid on silk cushions and brought back in the valley using buffalo carts, and the tiny moves of the lenses on the cushions caused by the gentle rocking of the cart finishes the polishing to perfection. Panasonic's Leica lenses are finished off wrapped in silk between Swiss virgin's breasts trotting on horseback down the mountain as they sing the praises of their fine accuracy and innovative engineering; instilling emotional warmth, impact, and subtlety. http://www2.panasonic.com/webapp/wcs...tGroupId=24999 The text makes a virtue out of necessity: "The DC Vario-Summicron is Leica's preeminent lens. Its exceptional optics give photos an exquisite soft-focus effect, ... " Yes, made me smile too. -- Bertrand |
#66
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Telephoto Reach and Digital Cameras - lens comparison
bobwilliams wrote:
Roger posts a lot of Quantitative data that are not available anywhere else. I use them a lot. Some of his photos are awesome. Thanks Bob. I don't enter many contests (little time). I did enter Natures Best this year. This one was selected as Highly Honored in this year's contest: http://www.clarkvision.com/galleries...130.f-900.html It should be in the fall issue of Natures Best that should be out shortly if not already. Roger |
#67
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Telephoto Reach and Digital Cameras - lens comparison
Dudley,
The relevant equation above is Diffraction spot diameter = 2 * 1.22 w * f / D = 2.44 * w * f_ratio, whe w = wavelength f = focal length D = aperture diameter f_ratio = the f/ratio of the optical system So if you specify wavelength of light in microns, the diffraction spot diameter is in microns. The diffraction spot size for green light of 0.53 microns (5300 angstroms) is: f/2: 2.6 microns, f/4: 5.2 microns, f/8: 10.3 microns. The above from: http://www.clarkvision.com/articles/...il/index.html# diffraction So you see that cameras with small pixels (P&S cameras typically have pixels under 2 microns, and superzoom cameras with f/4 and slower lenses thus have pixels much smaller than the diffraction diameter. But more important is resolution on the subject. With more real focal length, the diffraction spot becomes a smaller angular diameter if you keep f/ratio the same. That is because the diameter of the aperture is getting larger. So the longer focal lengths found in DSLR telephotos provides proportionally greater resolution on a subject. Resolution on a subject is given by: resolution = constant / lens diameter, where the constant is determined by the wavelength. The Dawes limit is the limit at which no more detail on a subject can be resolved, or in other words, zero contrast on closely spaced detail, like line pairs in a test target, or hairs on an animal. e.g.: http://en.wikipedia.org/wiki/Dawes'_limit resolution in arc-seconds = 4.56 /D where D is the clear aperture in inches and the 4.56 is for a particular wavelength (green light). With D on the bottom of the equation, the finest detail one can resolve goes down as the lens aperture goes up. That dictates the fundamental difference between P&S superzoom cameras and DSLRs, and the field of view lens multiplier is now a great confusing factor among photographers selecting digital cameras. Roger Thanks, Roger, that gives me a fair bit to think about. After a quick scan, I just have a couple of supplemental questions: 1. When you refer to the Diffraction spot diameter, I'm having a tough time wrapping my head around what's occuring at the pixel site. Does the diameter represent the area where photons (of finite size) get focused, with individual photons diverging somewhat due to diffraction? (ie: the diffraction spot diameter represents some sort of a scatter zone., Or, does the energy charge of the photon somehow get spread out over a larger area, due to the wave-like nature of light? If I knew a bit more about the nature of photons, this probably would not be so mystifying. Anyway, the second question is a bit less theoretical, I hope: 2. When you say that the crop factor of the small sensored DSLR's is causing a lot of confusion, is it because of the diffraction spot diameter? I mean, if one takes a regular lens and puts it on the smaller-sensored body, one would expect the diffraction spot diameter to remain the same size as it would be on a full-frame body. But, of course, the smaller sensor would have more resolving power, due to the larger number of tinier pixels packed tighter, so the level of detail should suffer as long as the lens's focal length is not altered. Correct? But, because of the crop factor, the resulting image would look more like a pic taken with a longer lens, which on a full- frame body would actually result in smaller diffraction spot diameters for the longer focal length, so the degradation of detail would actually be compounded. All in all, the crop sensored body should exhibit considerably less detail in a picture if the lens from a full-frame camera is used. Take Care, Dudley |
#68
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Telephoto Reach and Digital Cameras - lens comparison
Dudley Hanks wrote:
Thanks, Roger, that gives me a fair bit to think about. After a quick scan, I just have a couple of supplemental questions: 1. When you refer to the Diffraction spot diameter, I'm having a tough time wrapping my head around what's occuring at the pixel site. Does the diameter represent the area where photons (of finite size) get focused, with individual photons diverging somewhat due to diffraction? (ie: the diffraction spot diameter represents some sort of a scatter zone., Or, does the energy charge of the photon somehow get spread out over a larger area, due to the wave-like nature of light? If I knew a bit more about the nature of photons, this probably would not be so mystifying. Actually, it is complex. It has to do with the dual nature of light, acting both as a particle and a wave. Consider the diffraction spot in the focal plane before the pixel. A point source, like a star, will form an approximately shaped Gaussian distribution with ringe around it. The diameter I was referring to is where the intensity drops from the high in the center to zero before rising a little in the first ring. But in an extended image, like in a everyday photo, there are numerous overlapping diffraction disks, with the effect of smearing the fine detail and reducing contrast of the fine detail. The lens focuses the light, but diffraction diverges the angles of the light rays bent by the lens, so the lens can't make perfect focus. You could think of the diffraction spot as kind of a "scatter zone." Wikipedia has a pretty good write-up of the dual nature of light: http://en.wikipedia.org/wiki/Wave–particle_duality Anyway, the second question is a bit less theoretical, I hope: 2. When you say that the crop factor of the small sensored DSLR's is causing a lot of confusion, is it because of the diffraction spot diameter? No, not just DSLR, but P&S cameras too. Some people think that the crop sensor gives them more telephoto reach. For example, put the same lens on a Canon 5D mark II 21 megapixel full-frame camera and then on a Canon 30D 8-megapixel 1.6x crop camera and they think the 1.6 crop camera gives them more telephoto reach, meaning detail on a distant subject, like the Moon, or a distant bird would be better. But the Canon 5DII and 30D have the same pixel pitch, so get the same numbers of pixels on a subject. It is pixel size and true focal length that controls pixels on subject, not sensor size. It is the lens quality and diffraction that limits the detail that the pixels sample. Camera manufacturers have added a lot of confusion in this area too. They often specify focal length without saying it is 35-mm equivalent field of view focal length. Significant confusion also occurs in the f/ratios. For example, Ziess makes a spotting scope with a small sensor build in and claims the the scope, with an 85 mm clear apertu "As a digital camera, the PhotoScope provides a truly superior telephoto lens: photographically the equivalent of a 600mm @ f4.0 to 1800mm @ f5.6 zoom lens on a 35mm camera" http://www.zeiss.com/c1256bcf0020be5...25755c006de445 Claiming f/ratio is completely bogus. An 1800 mm f/5.6 lens would have an aperture of 321 mm and collect 14.3 times more light, and have a very different depth-of-field than the 85 mm telescope. And, of course, they ignored the detail limiting effects of diffraction. I mean, if one takes a regular lens and puts it on the smaller-sensored body, one would expect the diffraction spot diameter to remain the same size as it would be on a full-frame body. Yes, but in the digital image might appear different if the pixel spacing is different. The actual diffraction would be the same, but the pixel sampling could be different for different pixel pitches. But, of course, the smaller sensor would have more resolving power,due to the larger number of tinier pixels packed tighter, so the level of detail should suffer as long as the lens's focal length is not altered. Correct? That is not necessarily true. For example, the Canon 5DII and 30D have the same pixel sampling yet are different sized sensors. It has to do entirely with pixel pitch (spacing) and not crop factor. Sensor size affects total field of view, of course. But, because of the crop factor, the resulting image would look more like a pic taken with a longer lens, which on a full- frame body would actually result in smaller diffraction spot diameters for the longer focal length, so the degradation of detail would actually be compounded. All in all, the crop sensored body should exhibit considerably less detail in a picture if the lens from a full-frame camera is used. Not at all. You are saying the commonly believed ideas, but crop factor does not control detail on a subject. A cropped sensor does not magically give more telephoto reach because of the crop. Take any image and crop it. Do you get more detail on a subject? No. This is illustrated in Figure 2 at: http://www.clarkvision.com/articles/telephoto_reach/ The 1D Mark II image on the left is a 1.3x crop sensor, and shows less detail than the 5D Mark II full frame image next to the 1DII image, yet both were taken with the same lens. Pixel pitch is controlling the detail, not sensor size. And that is illustrated by the right-most image in the figu a Canon 7D 1.6x crop sensor shows the most detail because the pixel pitch is smallest, not because of the crop. And for this lens, diffraction is smaller than the all the pixel sizes. See: http://www.clarkvision.com/articles/cropfactor/ Roger |
#69
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Telephoto Reach and Digital Cameras - lens comparison
"Roger N. Clark (change username to rnclark)" username@qwest.
net wrote: Dudley Hanks wrote: Thanks, Roger, that gives me a fair bit to think about. After a quick scan, I just have a couple of supplemental questions: 1. When you refer to the Diffraction spot diameter, I'm having a tough time wrapping my head around what's occuring at the pixel site. Does the diameter represent the area where photons (of finite size) get focused, with individual photons diverging somewhat due to diffraction? (ie: the diffraction spot diameter represents some sort of a scatter zone., Or, does the energy charge of the photon somehow get spread out over a larger area, due to the wave-like nature of light? If I knew a bit more about the nature of photons, this probably would not be so mystifying. Actually, it is complex. It has to do with the dual nature of light, acting both as a particle and a wave. Consider the diffraction spot in the focal plane before the pixel. A point source, like a star, will form an approximately shaped Gaussian distribution with ringe around it. The diameter I was referring to is where the intensity drops from the high in the center to zero before rising a little in the first ring. But in an extended image, like in a everyday photo, there are numerous overlapping diffraction disks, with the effect of smearing the fine detail and reducing contrast of the fine detail. The lens focuses the light, but diffraction diverges the angles of the light rays bent by the lens, so the lens can't make perfect focus. You could think of the diffraction spot as kind of a "scatter zone." Wikipedia has a pretty good write-up of the dual nature of light: http://en.wikipedia.org/wiki/Wave–particle_duality Thanks, I appreciate the info. As I was reading your summary, I got to wondering if there is more to the cause of diffraction than just the lens bending the light. It occured to me that there are a few other opportunities for diffraction: 1) The light passing through the lens would no doubt encounter obstacles, at least on an atomic level, i.e., the constituent particles of the glass. 2) air particles surrounding lens elements could knock a few photons off course, and 3) for all I know, some of the diffraction could occur as photons bump into each other as they cross paths after being focused and head towards their inverted image destination. Any thoughts on whether or not these could contribute to diffraction? Anyway, the second question is a bit less theoretical, I hope: 2. When you say that the crop factor of the small sensored DSLR's is causing a lot of confusion, is it because of the diffraction spot diameter? No, not just DSLR, but P&S cameras too. Some people think that the crop sensor gives them more telephoto reach. For example, put the same lens on a Canon 5D mark II 21 megapixel full-frame camera and then on a Canon 30D 8-megapixel 1.6x crop camera and they think the 1.6 crop camera gives them more telephoto reach, meaning detail on a distant subject, like the Moon, or a distant bird would be better. But the Canon 5DII and 30D have the same pixel pitch, so get the same numbers of pixels on a subject. It is pixel size and true focal length that controls pixels on subject, not sensor size. It is the lens quality and diffraction that limits the detail that the pixels sample. Camera manufacturers have added a lot of confusion in this area too. They often specify focal length without saying it is 35-mm equivalent field of view focal length. Significant confusion also occurs in the f/ratios. For example, Ziess makes a spotting scope with a small sensor build in and claims the the scope, with an 85 mm clear apertu "As a digital camera, the PhotoScope provides a truly superior telephoto lens: photographically the equivalent of a 600mm @ f4.0 to 1800mm @ f5.6 zoom lens on a 35mm camera" http://www.zeiss.com/c1256bcf0020be5...25755c006de445 Claiming f/ratio is completely bogus. An 1800 mm f/5.6 lens would have an aperture of 321 mm and collect 14.3 times more light, and have a very different depth-of-field than the 85 mm telescope. And, of course, they ignored the detail limiting effects of diffraction. I mean, if one takes a regular lens and puts it on the smaller-sensored body, one would expect the diffraction spot diameter to remain the same size as it would be on a full-frame body. Yes, but in the digital image might appear different if the pixel spacing is different. The actual diffraction would be the same, but the pixel sampling could be different for different pixel pitches. But, of course, the smaller sensor would have more resolving power,due to the larger number of tinier pixels packed tighter, so the level of detail should suffer as long as the lens's focal length is not altered. Correct? That is not necessarily true. For example, the Canon 5DII and 30D have the same pixel sampling yet are different sized sensors. It has to do entirely with pixel pitch (spacing) and not crop factor. Sensor size affects total field of view, of course. But, because of the crop factor, the resulting image would look more like a pic taken with a longer lens, which on a full- frame body would actually result in smaller diffraction spot diameters for the longer focal length, so the degradation of detail would actually be compounded. All in all, the crop sensored body should exhibit considerably less detail in a picture if the lens from a full-frame camera is used. Not at all. You are saying the commonly believed ideas, but crop factor does not control detail on a subject. A cropped sensor does not magically give more telephoto reach because of the crop. Take any image and crop it. Do you get more detail on a subject? No. This is illustrated in Figure 2 at: http://www.clarkvision.com/articles/telephoto_reach/ The 1D Mark II image on the left is a 1.3x crop sensor, and shows less detail than the 5D Mark II full frame image next to the 1DII image, yet both were taken with the same lens. Pixel pitch is controlling the detail, not sensor size. And that is illustrated by the right-most image in the figu a Canon 7D 1.6x crop sensor shows the most detail because the pixel pitch is smallest, not because of the crop. And for this lens, diffraction is smaller than the all the pixel sizes. See: http://www.clarkvision.com/articles/cropfactor/ Roger Indeed, I've been listening to too much of the populist hype on these groups, when I should have been reading a few more tech sheets. I guess I just kind of suspected cropped sensor cams would have tighter packed pixels, i.e. an increase in pitch. It didn't occur to me they can be on a par with full- framed bodies. Yesterday, I did a bit of snooping around, and I came up with: http://www.the-digital-picture.com/r...eos-rebel-xsi- 450d-digital-slr-camera-review.aspx I was surprised at how well my XSi stacks up against the 40D in particular. I was also surprised that the pixel size of the XSi is in the same range as some of the full-frame bodies, and not all that far off the Canon heavy hitters like the 5D2. I guess I'll have to brush off my math skills, and start looking into camera internals a bit more, paying a lot more attention to pixel pitch instead of crop factor. Thanks, Roger, for taking the time to point me in the right direction. Take Care, Dudley |
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