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The multi-element, spherical lens-based lens MUST DIE!!

 
 
Bruce
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      03-06-2011
Rich <(E-Mail Removed)> wrote:
>On Mar 3, 8:04*pm, Bruce <(E-Mail Removed)> wrote:
>> RichA <(E-Mail Removed)> wrote:
>> >On Mar 3, 8:38 am, Bruce <(E-Mail Removed)> wrote:
>> >> RichA <(E-Mail Removed)> wrote:
>> >> >On Mar 2, 7:44 pm, Bruce <(E-Mail Removed)> wrote:
>> >> >> RichA <(E-Mail Removed)> 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.
>>
>> 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. *

>
>Obsession with instruments that have superior optical quality. Some
>microscopes meet that spec. Some telescopes do. Virtually no camera
>lenses do. But the use of a lens at an equivalent f.l. of
>25,000-50,000mm and getting quality results is so alien to camera
>users that there is little point in trying to educate them as to how
>such a thing is possible.



<yawn>

Someone wake me up when Rich finally says something sensible.

 
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