At 8:03 AM -0400 2005.07.19, Chuck Norcutt wrote:
>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.
That's what I had in mind (and giving them some incentive to be there).
> 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.
Yes, these figures are more discouraging than I expected. It is possible
to envisage scenarios that would work, but obviously needing a fair degree
of luck. I'm used to limited DoF in close up work, where although frustrating it
is more manageable. Obviously working distance and image size are important
here also.
Of course wrens are a particularly difficult example (although that's what I
most want to do.) I've had some luck with larger and slower birds using a
birdbath, constructing a water spout etc, which can create good localization,
but would still be pushing the boundaries of the above DoF figures. For example
the parrots that frequent our front yard are good for these techniques.
>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.
>
Better to hear than get the wrong tool for the job.
It's not surprising that the best approach in the natural world is
patience, familiarization and blending in.
thanks
Andrew
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