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Canon 135mm L lens


jnc71106
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hello all i'm looking at the canon 135mm L series lens with the intention of attaching it to my Atik CCD, i've been dabbling in widefield imaging with an 85mm lens and i like the increase in FOV but in all honesty its a bit to wide for my taste and would prefer something with a bit more FL

what are peoples thoughts on the canon 135mm ? and what would the concensus be on me using it at f/2.8 with the small chip on my atik 314 ? would i get away with it or would i suffer with poor star shapes in the corners ?

i did try my 85mm Samyang at f/2.8 but the corners suffered a bit

of course if there are other lenses that would perform just as well for less money then please say as i'm open to suggestions

many thanks

Edited by jnc71106
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As the 135mm L is an f2 lens then you'd already be stopping down if you run at f2.8. It may work better than an f2.8 lens wide open mind you. Once again it's try it and see. Not what you want to hear for the price though !

Although I wouldn't see it as a particular problem, at f2 you won't have any room for miss alignment. Focus will have to be exact and may be best found near the corner of the lens / chip. There are people who adjust and play with their RC and Newts for weeks before they get them right so a few nights with such a lens shouldn't be too much pain.

I strongly suggest you don't go down the 3nm route and stick to 5nm or 7nm. The sky will be darker the narrower you go but you'll loose signal at 3nm.

I tried a 200mm f2 lens some time ago. I didn't buy it in the end but as a photon hoover it has to be seen to be believed. There are people who have got the Canon 200mm f1.8 to work wide open !

So long as the stars are just stretched out in the corners you'd be able to rescue them to some degree in PS lens adjustments.

Second hand may be the way to go such as - http://www.ffordes.com/product/13080717472381

Dave.

Edited by davew
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Thank you for the reply. I know focus has to be very good at these speeds I did spend a night imaging at F/2 and using some microfocus rings from telescope express it only took about 10 mins to get the FWHM as low as it would go on a 5 second loop from memory it went down to 0.77 in Artemis capture

Oh and s/h is definitely the way to go as I at least know I'd get me money back if it went pear shaped :)

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