Hmm. Apart from a couple of quick shots on an OM the only thing I've
ever used this thing for is the sky. I hadn't stopped to think about
the DOF problem. I see that at 50 feet it's only about 1.1 feet. But
going to f/8 doesn't help much as it's still less than 1.6 feet. Maybe
it will be necessary to make an aperture mask for it.
My only other mirror lens is my 2000mm f/10 Celestron which will focus
down to 25 feet. Now *there's* a DOF problem. At 25 feet it's about 1/4".
Hmmm. Don't know if I ever noticed this before but, using the DOF
calculator just now, I suddenly realized that DOF increases by the
square root of 2 when closing down one stop and by a factor of 2 for two
stops.
Chuck Norcutt
Moose wrote:
> Chuck Norcutt wrote:
>> This reminds me that I have an Orion 500mm f/5.6 mirror lens/spotting
>> scope that I've almost never used......
>> so maybe I'll give this lens a whirl again. At f/5.6 I may actually be
>> able to focus it.
>>
> I sure hope so, because DOF is going to be 'interesting'.
>
> I think all those 500-600/8 lenses are f8 not just because of size and
> cost, but for DOF reasons.
>
> Have fun and let us know, maybe even, gasp, post some samples. :-)
>
> Moose
>
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