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Old 03-01-2009, 12:06 PM
Ian Robinson
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Ian Robinson is offline
Join Date: Jan 2007
Location: Gateshead
Posts: 2,205

Filter Diameter:

Horizontal Angle of View:
29 - 10

Filter Size:


Angle of View:
34 degrees to 12 degrees

Extra 10mm aperture (not much but enough to help get that little bit deeper for the same exposure).
Extra stop means if you had the same size objective (front) lens you need 1/2 the exposure to record fuzzy or diffuse stuff like comets, galaxies, nebulae with the f2.8 cf f4 lens for a given ISO setting.

If you are worried about an additional 810g then your mount is way too small anyway, so go for the f4 and use the $ saved to upgrade to go towards a more capable GEM.

In non-astro photography , I think the extra stop is certainly worth having , so is the IS , means you can shoot in lower light without needing to resort to using a flash (esp handy if you are interested in sports, dance, and photography of wild life and scenary when on holidays), and it also means you can get away without a tripod for longer exposures (is like an extra 3 or 4 stops it is said).

Some think the IS results in less crisp images , I've not seen anything published that indicates this for astroimaging , where the IS option would be disabled anyway.

I plan on getting an EF 70-200mm f2.8 L IS USM + a 2x TII EF Teleconvertor when the exchange rate is more acceptable.

Last edited by Ian Robinson; 03-01-2009 at 12:37 PM.
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