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