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The multi-element, spherical lens-based lens MUST DIE!!
On Fri, 04 Mar 2011 01:04:51 +0000, Bruce wrote:
RichA wrote: On Mar 3, 8:38*am, Bruce wrote: RichA wrote: On Mar 2, 7:44 pm, Bruce wrote: RichA wrote: They must eliminate the multi-element lens. It is too heavy. It is too complex inside therefore TOO expensive. 14-17 elements? Why, in this day of hybrid aspherics and ED glass? Pentax makes a 400mm f4 telescope with 4 elements that produces a highly-corrected (colour, astigmatism, spherical aberration) FLAT image across an entire medium format film plane. With FOUR elements! WHERE is the Nikon or Canon lens that can do that with so few elements? For about $3k. Takahashi (Japanese) has a similar lens. And those lenses do it diffraction- limited without stopping down! Multi-element lens systems based on spherical lenses are DINOSAURS. You need to compare the MTF of those telescopes with the MTF of top quality fixed focus DSLR lenses of comparable focal lengths. I suspect that will give you the answer you need. A top quality 400mm DSLR lens is about $10,000 and still won't be diffraction-limited wide open. Then let's all shoot through telescopes and see how good they are. Modern Photography in 1977 tested a TeleVue (Pearl River, New York, maker of high-performance apochromatic telescopes) Renaissance telescope. This was a 4" aperture, 500mm f5.0 refractor retailing for about $2000.00. It beat every lens they had EVER tested when it came to contrast and resolution. TeleVue has had 6 interations (improvements) of that scope since then, each of them providing better performance. The scope is now called the NP101 and is similar to what is called the Petzval design, 2 main elements up front, a smaller doublet midway down the tube. And there are even better telescopes than the TeleVue available from places like AstroPhysics, TEC, etc. The average camera lens is corrected to about 1-2 waves (yellow-green light). The average telescope is 1/4 wave, a high-end scope like those mentioned is 1/10th wave. The mirror that went into the Hubble was 1/100th wave. The reason telescopes have to be so accurate is that unlike a camera lens that is used at what is called, Prime focus (no extra magnificational elements) a telescope may be used in conjunction with projection optics. Imaging trying to put a 10-20x teleconverter on a camera lens and trying to get an image out of it. They do it with telescopes all the time, to shoot planets. If all this is true, why aren't we all using telecopes instead of telephoto lenses? Perhaps because a telescope costing $2000 in 1977 would be way out of reach in today's money. Plus, it would produce an inverted image. Plus, there is a lot more to optical performance than resolution and contrast. I suggest you read any "Optics 101" literature that is readily available before you ever talk about anything even remotely related to the subject again. Then you wouldn't so swiftly remove all doubts about your blatantly obvious fool-troll status. (Hint: all camera lenses also produce an inverted image.) You obviously have an obsession about telescopes. Don't worry, in a few days it will go away, and you will start ranting about something else that is completely unrelated, but equally implausible. Do try to smile. ;-) |
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The multi-element, spherical lens-based lens MUST DIE!!
On Thu, 03 Mar 2011 20:25:16 -0600, Outing Trolls is FUN!
wrote: : On Fri, 04 Mar 2011 01:04:51 +0000, Bruce wrote: : : RichA wrote: : On Mar 3, 8:38*am, Bruce wrote: : RichA wrote: : On Mar 2, 7:44 pm, Bruce wrote: : RichA wrote: : They must eliminate the multi-element lens. It is too heavy. It is : too complex inside therefore TOO expensive. 14-17 elements? Why, in : this day of hybrid aspherics and ED glass? Pentax makes a 400mm f4 : telescope with 4 elements that produces a highly-corrected (colour, : astigmatism, spherical aberration) FLAT image across an entire medium : format film plane. With FOUR elements! WHERE is the Nikon or Canon : lens that can do that with so few elements? For about $3k. Takahashi : (Japanese) has a similar lens. And those lenses do it diffraction- : limited without stopping down! Multi-element lens systems based on : spherical lenses are DINOSAURS. : : You need to compare the MTF of those telescopes with the MTF of top : quality fixed focus DSLR lenses of comparable focal lengths. I : suspect that will give you the answer you need. : : A top quality 400mm DSLR lens is about $10,000 and still won't be : diffraction-limited wide open. : : Then let's all shoot through telescopes and see how good they are. : : Modern Photography in 1977 tested a TeleVue (Pearl River, New York, : maker of high-performance apochromatic telescopes) Renaissance : telescope. This was a 4" aperture, 500mm f5.0 refractor retailing for : about $2000.00. It beat every lens they had EVER tested when it came : to contrast and resolution. TeleVue has had 6 interations : (improvements) of that scope since then, each of them providing better : performance. The scope is now called the NP101 and is similar to what : is called the Petzval design, 2 main elements up front, a smaller : doublet midway down the tube. And there are even better telescopes : than the TeleVue available from places like AstroPhysics, TEC, etc. : The average camera lens is corrected to about 1-2 waves (yellow-green : light). The average telescope is 1/4 wave, a high-end scope like : those mentioned is 1/10th wave. The mirror that went into the Hubble : was 1/100th wave. The reason telescopes have to be so accurate is : that unlike a camera lens that is used at what is called, Prime focus : (no extra magnificational elements) a telescope may be used in : conjunction with projection optics. Imaging trying to put a 10-20x : teleconverter on a camera lens and trying to get an image out of it. : They do it with telescopes all the time, to shoot planets. : : : If all this is true, why aren't we all using telecopes instead of : telephoto lenses? : : Perhaps because a telescope costing $2000 in 1977 would be way out of : reach in today's money. Plus, it would produce an inverted image. : Plus, there is a lot more to optical performance than resolution and : contrast. : : : : I suggest you read any "Optics 101" literature that is readily available : before you ever talk about anything even remotely related to the subject : again. Then you wouldn't so swiftly remove all doubts about your blatantly : obvious fool-troll status. Twice in the preceding five minutes you said exactly the same thing about Rich. I guess you really are nothing but a mindless trolling machine. Bob |
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