I expected one of the astrophotogs on the list (and there are several)
to pick up Bill's question but since no one has I will give it a stab.
First, I'm not 100 percent sure of the question but I think it's; "Can I
use my Tamron 500 and 2X on Mars or stars?"
My recollection is that the apparent diameter of Mars now is in the
vicinity of 25 arc seconds. Unfortunately, the Tamron 500 (even with 2X
attached) will only create a red dot on the film about 0.12 mm in
diameter. Assuming about 50 lppm on the film that's not a whole lot to
work with image wise.
See <http://www.tmsc.org/astronomy/astrophoto.html>, and many others,
for an image size at prime focus calculator. Even my 2000 mm f/10
Celestron 8 can only get to 0.24 mm at prime focus. That's why I gave
up trying to shoot planets about 30 years ago. One can better this, of
course, using eye piece projection on the telescope but that is not an
option for the Tamron.
You could use the 500 by itself to shoot nebulae, galaxies and extended
star fields but you would need some sort of guidance device for extended
exposures. If you don't have a motor driven telescope on which the
camera can be piggybacked you can use what is called a "barn door" drive
or tracker. You can easily build one at home. Search the web on "barn
door drive" or "barn door tracker". Here's the first one that popped up
on my Google search.
<http://angwin.ece.uiuc.edu/~haunma/proj/barndoor/>
Chuck Norcutt
Woburn, Massachusetts, USA
-----------------------------------
Bill asked:
May I elicit some constructive commentary re where one shifts mentally
from a lens like a telescope (weight - size - cost- etc.) to the option
of high quality mirror telephoto? ........ibid re photography of Mars
to the stars?? <snip>
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