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05/15/2004 07:17:41 PM · #1 |
Twice today I saw a 500mm lens that comes with a 2x extender for 150-160 USD. WHAT? LOL Are these lenses for real? One was a Quantaray and I don't know what the other was - but seriously! That's 1600 mm on the D300 and 10D. That's insane! It's f8 - is this even a remotely working lens?!
M |
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05/15/2004 07:23:41 PM · #2 |
Remember the old saying: You get what you pay for...
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05/15/2004 07:41:49 PM · #3 |
At f8 you'd probably have a hard time with AF. I think only two of the more expensive Canon film bodies can even try to focus at f/8, while the rest of the EOS lineup will only give usable AF results down to f/5.6.
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05/15/2004 07:42:54 PM · #4 |
Try putting one of those cheap Sigma 500m mirrors on a 10D and you will only get an error 99 reported, it won't even release the shutter. These may not be the same but try before you buy is my recommendation.
Falc |
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05/15/2004 08:04:37 PM · #5 |
| Sounds like it's a mirror lens. |
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05/16/2004 12:54:12 AM · #6 |
Originally posted by Falc:
Try putting one of those cheap Sigma 500m mirrors on a 10D and you will only get an error 99 reported, it won't even release the shutter. These may not be the same but try before you buy is my recommendation.
Falc |
I think there is a way around that by taping some of the mount contacts... but that might be some other problem I'm vaguely remembering, lol.
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05/16/2004 01:20:27 AM · #7 |
What is a mirror lens? Is it like a reflector telescope?
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05/16/2004 09:13:40 AM · #8 |
Originally posted by TooCool:
What is a mirror lens? Is it like a reflector telescope? |
As far as I know (which isn't that far) a mirror lens IS a reflector telescope, just on a minature scale.
To bad there are some serious quality issues and AF (or lack thereof) issues because mirror lenses can get some incredible magnification in very small packages... |
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05/16/2004 10:33:51 AM · #9 |
Originally posted by Count:
Originally posted by TooCool:
What is a mirror lens? Is it like a reflector telescope? |
As far as I know (which isn't that far) a mirror lens IS a reflector telescope, just on a minature scale.
To bad there are some serious quality issues and AF (or lack thereof) issues because mirror lenses can get some incredible magnification in very small packages... |
Yes, the mirror lenses are a special class of reflecting telescope. They are typically "Maksutov Cassegrains" or similar designs, incorporating a "corrector plate" which is actually a lens element, a concave primary mirror, and a convex secondary mirror. Here is a short tutorial on the evolution of this type of optical system.
With reference to the original question, the mirror telephotos can provide alot of magnification in a very small package. The downsides are:
- Constant aperture (no aperture adjustment)
- Slow, usually f/8
- Low constrast
- Donut-shaped OOF highlights, which can be quite distracting
- Purely manual focus, and difficult at that.
Bottom line is, the catadioptric systems make much better astronomical instruments than telephotos. If you are interested in using a catadioptric 'scope for terrestrial photographic work, buy a good 125mm f/10 design, like the Celestron C5, and make your own lens hood; you'll obtain decent results, and you'll have an instrument that is much more flexible in it's possible uses and available accessories.
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05/16/2004 10:54:31 AM · #10 |
That particular lense is a fixed 500mm or 1000mm. In this case the 2x Extender takes the fixed focal length of 500mm and makes it a 1000mm, again fixed focal length.
As I understand it, like all of the Ritz Camera Quantaray Lenses it is made by Sigma.
I was under the impression that fixed focal length lenses were inherently less expensive due to the lack of moving parts and possibly fewer pieces of glass(?).
Anyway, I am far from an expert when it comes to lenses, I am mostly guessing based on some of the prices that I have seen for variable and fixed focal length lenses from various manufacturers. |
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