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PostPosted: Mon Sep 27, 2010 5:26 pm 
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I don't know whether any lens is better than another purely for astrophotography (AP). I think in general the better the lens is, say for general photography, the better it will perform at AP.

As with most aspects of astronomy aperture is king therefore if you have a nice f2.8 or 1.8 lens then you can easily stop it down to around f5.6 to be using the sweet spot whereas a slower lens may need to be stopped down to f11 or more before you hit this sweet spot. This obviously means less light is hitting the sensor requiring longer subs, better tracking etc etc.

With AP the argument that the capture device i.e. the camera sensor, is what matters is more apparent. Just take for example Canons 20Da - a purpose built DSLR for AP because Canon know that their sensors / cameras are more sensitive to IR than say Nikon which is less sensitive to IR. In any case, as Im sure you are aware Canon and Nikon cameras (as well as others I would imagine) can be modded for AP.

The length of the lens really depends on what you want to capture, i.e. a nice wide starfield or a particular aspect of a nebula.

HTH

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PostPosted: Mon Sep 27, 2010 5:30 pm 
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But imho it isnt very smart to start with a -lets say- 400mm lens. Youll learn the best with starting with shorter focal lenghts, and growing in lenghts as you get more experience.

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PostPosted: Mon Sep 27, 2010 5:33 pm 
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I completely agree, you want something fairly wide to get a feel for what you can capture and what beauties are up there to capture.

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PostPosted: Mon Sep 27, 2010 5:36 pm 
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If you set the 18-55 @ 18mm with 2 min tracking the stars, you will (not you btw) see what they call the MilkyWay.

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Ruben

Panasonic DMC-FZ18, Panasonic DMC-FZ28, Canon G5, Canon 350D, Canon 50D + BG-E2N
Tamron 17-50 2.8, Canon EF 70-200mm f/4L USM,
Canon 18-55 II plus lots of Minolta MD/M42 lenses and bodies


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PostPosted: Mon Sep 27, 2010 5:39 pm 
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I have a small collection of fast wider primes for starters, technically from 8mm to 150mm, but I was thinking the 85/1.8 might be most interesting. Not sure exactly what for yet!

I really should get the light pollution filter on order...

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PostPosted: Mon Sep 27, 2010 5:42 pm 
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Go for it, by all accounts its a very worthwhile buy.

I reckon 85mm would be a good start, my shot at the start was 70mm and If I had framed a little better (i.e. put Deneb slightly higher in the frame) then I would have picked up more interesting detail in NGC7000.

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PostPosted: Mon Sep 27, 2010 5:43 pm 
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O really, 85 1,8?!
I shot M31 with the 135mm 2,8, and if you shoot more (and of course a bigger aperture like 1,8) you can get really stunning results!
Just try ISO 3200 and 30s exposure, tracked of course. If you cant track, then try 15s.

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Ruben

Panasonic DMC-FZ18, Panasonic DMC-FZ28, Canon G5, Canon 350D, Canon 50D + BG-E2N
Tamron 17-50 2.8, Canon EF 70-200mm f/4L USM,
Canon 18-55 II plus lots of Minolta MD/M42 lenses and bodies


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PostPosted: Mon Sep 27, 2010 7:22 pm 
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I've used the 50/1.8 untracked before. Can't remember how long I could get away without too bad trailing, but bigger issues were a combination of light pollution, and funniness (coma?) going on in the image corners. That and the focus ring was impossible to get exactly spot on.

Why am I looking at reviews of the 85 f/1.2... :D

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.


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PostPosted: Mon Sep 27, 2010 8:27 pm 
@ popo-
In my experience, I've been able to get away with 15 sec. at ISO-100, but only 4-5 sec. at ISO-3200 with no/minimal trailing.
Then again, my kit lenses only go down to about F/4.3 or so :(

Floyd.


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