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humbleservant888
sage
Reged: 01/14/03
Posts: 295
Loc: Daly City, CA
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Hi Chaps:
I am looking for a good zoom lens (>200mm) for my Nikon FM10. Any suggestions? Please help!
Kelvin
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Celestron NextStar8 GPS
Orion ED80
William Optics - ZenithStar 66mm ED Semi-APO
Orion XT8
Orion AstroView 100mm
Meade ETX90
Bino:Orion Scenix 12x50
LXD75 Mount & Tripod
SAC7 CCD
Philips Toucam
Nikon FM10
Astro-Tech Dielectric mirror diagonal
Lumicon UHC Filter, Baadar Contrast Filter, Orion filter set...
Software:TheSky V5 Professional
Kelvin
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Anonymous
Unregistered
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Howdy,
I'm looking for a lens for my Minolta Maxxum 7000 - I saw a 500mm lens with a Samyang 2x Teleconverter. The lens has only 1 f-stop: f/8. Would this be good for lunar photography? Would it do anything for planets?
I'm new to the astrophotography thing so I am asking if anyone can give their input on this.
Thanx in advance.
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Suk Lee
Post Laureate
Reged: 10/07/03
Posts: 4315
Loc: Pleasanton, CA
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OK, I'll chime in.
If you want a zoom for astrophotography, I wouldn't recommend it. With all those elements inside, you often get reflections on bright objects (my 180mm f2.8 prime is a very well regarded optic, and IT has internal reflections on really bright objects).
Suk
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http://www.siliconvalleyskies.com
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Suk Lee
Post Laureate
Reged: 10/07/03
Posts: 4315
Loc: Pleasanton, CA
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Quote:
I'm looking for a lens for my Minolta Maxxum 7000 - I saw a 500mm lens with a Samyang 2x Teleconverter. The lens has only 1 f-stop: f/8. Would this be good for lunar photography? Would it do anything for planets?
With the 2x converter giving you 1000mm, you'd get decent scale to get the whole disk (see attached simulation). Speed would be slow but the moon's bright.
Way too short for any useful scale on planets. You might be able to just make out the rings on Saturn, which is fun, but that's about it.
Cheers,
Suk
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http://www.siliconvalleyskies.com
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wilash
Fairy Godmother
Reged: 09/30/03
Posts: 5746
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If you want to approximate the image size of the moon (or sun) on a piece of film, simply divide the focal length of the lens by 110. A 500mm lens will make a 4.5mm diameter image of the moon. The teleconverter will double the diameter - 9mm.
The reason the 500mm lens has only one f-stop is because it is catadioptric - uses mirrors and lenses to make an image like a Maksutov Cassegrain telescope. Because of the design, a variable aperture used in normal lenses cannot be used - it would just vignette the image rather than control the amount of light.
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Anonymous
Unregistered
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So i guess it would be better to buy that "camera attaching to the scope thing" - it's a helluva lot cheeper!
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