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[OM] Re: Sigma 600mm mirror lens

Subject: [OM] Re: Sigma 600mm mirror lens
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Tue, 19 Jul 2005 08:03:54 -0400
Andrew L Wendelborn wrote:
> 
> Now I've been thinking about what I want from "more telephoto". It would
> be mostly to take pictures of small birds. Especially the highly elusive
> wrens et al that flit frustratingly around our favourite campsite. So then
> I would want to stick the 2XA on the mirror lens to get an unfocusable
> 1200/16. :(
> 
> So I'm going to pass on this one and do some more background work.
> There are some interesting things in the spreadsheet Chuck kindly sent
> me offline, like the 1250/10 Celestron. More dollars of course ...
--------------------------------------------------------

As the owner of a 2000/10 Celestron I'm sure you will be pleased with 
the optical performance of the 1250/10... or the 1000/11.  However, 
capturing wrens with any of these would be extraordinarily difficult. 
About the only way to do it would be to park the lens on the spot where 
the birds are expected to be some time in the future.  Even then, DOF 
looms as a problem.  At 25 feet the 1250/10 has DOF of about 3/4 inch. 
At 50 feet it's still only 3.6 inches.  And the 300 + 2XA doesn't do you 
much better.  At 600mm and f/9 and 25 feet it has the same 3.6 inch DOF 
as the larger lens at 50 feet.

Better you should put a shorter, faster lens in a blind prefocused to 
the correct spot and then fire the camera remotely.  Probably not what 
you wanted to hear.

Good luck,
Chuck Norcutt


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