timz
Topic Author
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Joined: Fri Sep 17, 1999 7:43 am

Long Lenses: Lots Of Glass Or Less?

Thu Feb 28, 2013 12:19 am

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?
 
scopedude
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Joined: Sat Oct 09, 2010 8:05 am

RE: Long Lenses: Lots Of Glass Or Less?

Thu Feb 28, 2013 3:50 am

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.
5DSR, 6D, X-T1, 70-200 IS II, 70-300 L, 18-55, 55-200
 
Geezer
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RE: Long Lenses: Lots Of Glass Or Less?

Sat Mar 02, 2013 8:37 am

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 again and expecting a different result; Albert Einstein
 
N243NW
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RE: Long Lenses: Lots Of Glass Or Less?

Mon Mar 04, 2013 12:15 am

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.
 
megatop412
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Joined: Mon Sep 19, 2005 8:40 am

RE: Long Lenses: Lots Of Glass Or Less?

Mon Mar 04, 2013 2:46 pm

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  
 
Geezer
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Joined: Wed Aug 18, 2010 4:37 am

RE: Long Lenses: Lots Of Glass Or Less?

Wed Mar 06, 2013 4:50 am

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 again and expecting a different result; Albert Einstein

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