I still think the Celestron 750/6 would have been about perfect for
those eagles at (assumed) 100 yards. The size of the image at 750mm vs
300mm would have been not much larger than the area that I cropped and,
even at f/6, the depth of field would have given nearly 10 feet both
ahead of and behind the point of focus... certainly sufficient to get
both birds in focus even when they weren't setting on the same branch.
f/6 would also have allowed almost 2 additional stops on shutter speed.
I suspect that an f/6 mirror will have relatively low contrast due to
the large central obstruction but, as you said, you can deal with that
in post. My Orion 500/5.6 also has low contrast but I've not tried to
use that since starting digital post processing. Tells you how long
it's been setting in the closet unused. I even bought a Canon T ring
for it but have never mounted the 5D.
Chuck Norcutt
On 3/8/2012 1:57 AM, Moose wrote:
> On 3/7/2012 3:18 PM, Chuck Norcutt wrote:
>> I didn't know there was (or had been) a 750/6. I just found one on
>> ebay. Nice size and speed. Probably would have been perfect for my 100
>> yard shots. My Celestron 8 is just too big to haul around.
>
> Those are nice efforts. For many years, we had a Red Tailed hawk nest in the
> back yard of a house across the street. One
> year, I set up with sturdy tripod, OM-4 and various lenses and
> tele-converters.
>
> The best lens, overall, was a Meade 1000/11 telescope. The Vivitar 600/8 is
> faster and probably a better lens, but
> simple magnification wins out for this subject. The Meade is a bit low
> contrast, but post can deal with that.
>
> The two biggest problems were tree movement and DOF. The nest was very high
> up.The yard is down slope, so the birds
> weren't as far away as they would otherwise have been, but there was still
> considerable movement of the tree at that
> height in even very moderate breezes. Hmmm. Now I wonder if it's worth
> digging up those old shots and trying Focus Magic
> motion correction...
>
> I wasn't able to entirely separate pure DOF issues from those exacerbated by
> subject movement. But I know I would
> certainly think carefully about DOF before getting a 750/6.
>
> I was not particularly happy with a Tamron 350/5.6, and DOF was part of that.
> When you've got only one aperture, it
> makes sense to make sure it is the one you want. :-)
>
> Another solution to reach is the one I've recently used, a smaller sensor.
> That makes the Tokina mirror an effective
> 960/8, and that is mighty fine.
> <http://galleries.moosemystic.net/MooseFoto/index.php?gallery=California/Yosemite/Yosemite_2011/Yosemite_Valley&image=_MG_0382oof80m.jpg>
>
> I did, of course, have to correct contrast for the effects of shooting
> through about eight miles of late afternoon air. :-)
>
> Long Distance Moose
>
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