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Old 04-03-2010, 06:07 PM
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mick pinner
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Lens Choice

from an astrophotographic point l am looking for opinions on both the Canon 135 f/2 and 70-200 f/2.8 and any preferences on one over the other.
l realise they are completely different lenses and they each have their good points which makes it a decision l am looking for opinions on.
thanks.
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Old 04-03-2010, 06:19 PM
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Octane (Humayun)
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Mick,

The 135mm f/2L is a superb lens.

I'm not sure why you'd consider the telephoto zoom lens. You're better off sticking with primes as they are far better suited to astrophotography.

The 200mm f/2.8L II USM is around $1,000 and is excellent. I've used it with great success.

H
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Old 04-03-2010, 07:28 PM
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RB (Andrew)
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Mick, if you can only choose one out of those two, I'd go with the 70-200mm simply because it's more versatile and would allow you to frame things just right for astro.
The 135mm is excellent indeed and I love using it for astro, but if I had to choose, I'd pick up the 70-200mm first.
It's a top performer and the quality is very close to a good prime.
I own both and I usually consider the 70-200mm first unless what I am imaging will fit perfectly in the 135mm.

The 135mm is superb for terrestrial shots though, it's one of my favourite lenses.

But like I said if I could only pick one, I'd pick the 70-200mm.

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Old 04-03-2010, 08:33 PM
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I described my experience with Canon 200mm F2.8 FD lens previously in another thread..

http://www.iceinspace.com.au/forum/s...ad.php?t=51866

It is sort of quite good at full aperture, excellent at F5.6 - BUT with external diaphragm (with internal iris it shows significant lateral CA, while with external one - just before front element - it is almost non-existent).
I paid for it $250 on ebay.

Now, I also did the same experiment with Tamron 200mm F2.8.
It behaves just slightly worse than Canon in terms of lateral CA (almost nothing, and I am talking about pixel-peeping at the corners of the frame).. but this was at a price of $60 at ebay (and my fiddling with mechanical modification).

I will do something similar with yet another 200mm lens soon (Sun.. is it Pentax?) that I obtain on trash market for $25. I expect the same results as with Tamron.

The crops are sized 200%, directly from DPP, from lower left corner of the frame, they are attached below (this is where the resolution of Canon FD lens is worse, it mildly suffers from astigmatism here while it is visibly better at the opposite corner). First two images were taken with external diaphragm set to f5.6 (the third image was taken with Tamron, internal iris at f5.6. Canon behaves better with its internal iris, but lateral CA was still very visible.)

BTW, I strongly believe this is the only right way to evaluate the lens suitability for astro photography and to compare them.

And if I knew all this above earlier, I would not buy this Canon.. yes it is better (less CA), but not THAT MUCH better.

So here you go...

However, for what I intend to do (photometry and later spectrometry) all this is not that important.

One more thing to note: All those lenses discussed above are designed for full frame sensor (24x36 film)- so smaller sensor of my Canon 400D is not showing what is happening that far away from optical axis (and I do not really want to know this )
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Last edited by bojan; 05-03-2010 at 03:21 PM.
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Old 05-03-2010, 10:30 AM
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This webpage http://www.astrosurf.com/~buil/
is a good start for lots of very useful information about lenses and their
suitability for astro work.

Have a look here:
http://www.astrosurf.com/~buil/testopt/50mm.htm

This is another one with lots of relevant information:
http://www.samirkharusi.net/

The number that describes the quality of the lens system is MTF (Modulation Transfer Function). Unfortunately, this parameter is not available for every lens (Canon is the only company that published it for their lenses, but should we trust them? )

http://software.canon-europe.com/fil...Book_10_EN.pdf


BTW, MTF is in principle equivalent to star test, results of which I have presented in my previous post (However, my comparison test was very crude because it is not standardised.. but it does reveal everything what is really important).

Last edited by bojan; 05-03-2010 at 01:39 PM.
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