Del Johnson wrote:
If stopping your 16 inch mirror down to 6 inches improves the image then you
need to figure out what is wrong with your mirror. It should work best at
or near full aperture. At least investigate the possibility of a
turned-down edge by masking off the outer half inch.

If you do stop down to a 6" f/12 then your maximum useful power will be with
a 6mm eyepiece.

Del Johnson


Thanks for your usual encouraging, positive, cheerful remarks Del.

I'll try to follow your advice.

Jim




"Jim Cate" wrote in message
...

Hi,

I'm hoping to be able to view Mars with reasonable high magnification
and would appreciate advice and suggestions. It happens that Mars will
be closer to earth on my birthday next month than it has been in a long,
long time, so I want to at least give it a try. Here's the plan:


1) Using my 16-inch, 4.5/f Dob light bucket, I intend to use an off-axis
aperture mask, with an opening of about 6 inches, to enhance the viewing
at high magnifications.

2) I have a Tak LE 5 mm, and a Nagler 9-mm. I plan on trying both of
these, and, if seeing is unusually good, adding a 2X Barlow.

3) I plan on using an equatorial platform to assist in keeping the
planet in view for at least a few minutes, permitting family and friends
to see it before it's out of the fov.

4) I will try some filters, but really don't know what would be the best
choice.

From the above, I would appreciate advice and suggestions regarding the
planned approach and regarding changes, combinations, or modifications
that would improve the expected results. What magnifications might be
expected with this scope, and is the use of an aperture mask equivalent
to increasing the effective focal length, and magnification? If so, by
how much? Are good seeing and low levels of light pollution of
significant importance when viewing bright objects such as the planets?
(Should I plan to travel to a remote location?) What color filters, if
any, would be recommended, etc. (incidentally, I also have an f8 -inch
(Chinese) refractor that we might try also)

Thanks for any suggestions or comments.

Jim