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Long Lenses: Lots Of Glass Or Less?  
User currently offlinetimz From United States of America, joined Sep 1999, 6902 posts, RR: 7
Posted (1 year 9 months 3 weeks 4 days 9 hours ago) and read 4256 times:

I was surprised to see that in the 1970s the Telyt 400 mm and 560 mm had two elements-- a cemented doublet, so not even a telephoto, strictly speaking.

When a 400 mm lens now has 16 elements, several of those are needed for the internal focusing? And maybe a few more for image stabilization? And the modern lens is faster, but still one wonders: how good was a Telyt? You'd think it was supposed to be as good as anything available at the time; how good was the best 400 mm available in 1976?

5 replies: All unread, jump to last
 
User currently offlinescopedude From Indonesia, joined Oct 2010, 53 posts, RR: 0
Reply 1, posted (1 year 9 months 3 weeks 4 days 6 hours ago) and read 4201 times:

Today's high end astronomical telescopes costing thousands of $ feature only 2 to 3 elements only (some can be 4 or 5 elements if it's meant to be flat field). One or two elements are usually Fluorite or ED element. The old Telyt is probably the same - optimized only for long distance. More complex construction is necessary if the lens should be sharp at its MFD. The old lenses can be sharp but the coating can't lie. Modern lenses will have better contrast due to much better multi-coating.

So if you have to ask how good, probably not good by today's standard. If you use Canon, the relatively inexpensive 400/5.6L is your best bet right now. If it goes IS later, it won't be less than $1600 I'm afraid.



5D2, 650D, 70-200/4 IS, 70-300 L, 135 L
User currently offlineGeezer From United States of America, joined Aug 2010, 1479 posts, RR: 2
Reply 2, posted (1 year 9 months 3 weeks 2 days 1 hour ago) and read 4050 times:

I never had any experience with the Telyt, but I guy I ran with from grade school into our married years when we both had families, had some kind of a 400 mm for a Topcon 35 mm camera he had; it was pretty damned good ! There were no zoom lens back then; (probably before 1950 or so.) and you can never compare camera lenses to telescope lenses, especially anything designed for astronomy; with astronomy, is all about "bigger aperture, and more light"; If you want to see some fine small optics, just check out anything from Takahashi ! Veyry simple optics, compared to camera lenses, but anything BUT cheap!

What really bugs/ surprises me, is every time I'm looking at Nikon lenses on eBay, I'm forced to wade through dozens of adverts for "500 mm telephoto, see more stuff with this fantastic f 19 , 500 mm looooong lens ! "only $119.99 !" What "surprises me" is the fact that there are apparently sufficient idiots born every day to keep these shysters in business !



Stupidity: Doing the same thing over and over and over again and expecting a different result; Albert Einstein
User currently offlineN243NW From United States of America, joined Jul 2003, 1640 posts, RR: 20
Reply 3, posted (1 year 9 months 3 weeks 9 hours ago) and read 3972 times:

Quoting scopedude (Reply 1):
it won't be less than $1600 I'm afraid.

My guess is $2000. Given the latest L-glass prices and the narrowing of any price advantage Canon had over Nikon, I'm definitely not optimistic that any future Canon telephotos will be marketed with affordability in mind.  



B-52s don't take off. They scare the ground away.
User currently offlinemegatop412 From United States of America, joined Sep 2005, 316 posts, RR: 0
Reply 4, posted (1 year 9 months 2 weeks 6 days 19 hours ago) and read 3919 times:

Quoting Geezer (Reply 2):
What really bugs/ surprises me, is every time I'm looking at Nikon lenses on eBay, I'm forced to wade through dozens of adverts for "500 mm telephoto, see more stuff with this fantastic f 19 , 500 mm looooong lens ! "only $119.99 !" What "surprises me" is the fact that there are apparently sufficient idiots born every day to keep these shysters in business !

Charlie I think those are 'mirror' lenses, I think I read that they basically need an incredible amount of light to deliver decent images. Not sure about the sharpness but pretty sure not sharp enough for here  


User currently offlineGeezer From United States of America, joined Aug 2010, 1479 posts, RR: 2
Reply 5, posted (1 year 9 months 2 weeks 5 days 5 hours ago) and read 3858 times:

Quoting megatop412 (Reply 4):
Charlie I think those are 'mirror' lenses, I think I read that they basically need an incredible amount of light to deliver decent images. Not sure about the sharpness but pretty sure not sharp enough for here  

Nope; Not mirror lenses at all; I haven't played with telescopes all my life not to know the difference between mirror lens and an ordinary refracting lens; what they are are is elcheapo junquo, made in Madagascar by termites, in the hope that if they advertise them enough, some poor kid that doesn't know any better will waste his money and buy one.

Not that the old mirror lenses were very much better; using mirrors works just fine on astronomical telescopes, but telescopes have a completely different job to do, from camera lenses. They found out over a hundred years ago that when you reached 36 to 40 inches of aperture, that it was as big as you could go with a refracting telescope; since that time, the technology involved in mirror making has allowed reflecting telescopes to just keep on getting bigger and bigger.

Mirror lenses for cameras are completely impractical for a whole bunch of reasons; you have no way of controlling the aperture for one thing; the only way you can control exposure is by varying the shutter speed; it spite of all of their inherent problems, Nikon dabbled around with them for years and never made enough to cover all of their R&D expenses.

Almost all young kids get interested in telescopes at a very early age, so even reputable telescope makers like Meade and Celestron build a "beginners" line of 3" and 4 inch scopes that aren't worth bringing home; in the meantime, thousands of young kids buy this crap, never get enough performance out of it to even satisfy a kid, so they end up getting discouraged, deciding that astronomy is "for the birds", which is really sad. A few years back, eBay was a great place to buy stuff, and also to get rid of stuff; it still is up to a point, but over the last 3 or 4 years, it's become a haven for shysters selling cheapo junk from the third world, and you can't find anything any more for all of their cheapo advertising.



Stupidity: Doing the same thing over and over and over again and expecting a different result; Albert Einstein
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