FreeLists / az-observing / [AZ-Observing] Re: Mars Is Not "Too Bright"

[Jeff Hopkins <phxjeff@xxxxxxxxxxx>]

Jack Jones wrote:

>I wonder if that's what it mostly is then. When an aperture mask is used on
>a large telescope the view is usually improved because on par large mirrors
>are just not that great. Cutting off the edge and bad parts of the mirror
>would give a surprising improvement, esp. on planets. At star parties you
>continually hear from light bucket owners 'well the seeing isn't that great
>right now'. It's amazing how quickly the seeing improves in the time it
>takes to walk to another telescope.
>
There are aperture masks and there are aperture masks. The big 
advantage I have heard about is using an off axis aperture mask on a 
large scope so that you have a clear view with no obstruction due to 
the secondary and secondary supports.

I have tried a 5" round opening off axis mask on my 13.1" DOB, but 
really did not see any improvement. Using a full aperture mask would 
seem to just reduce the resolution and light grasp.

Jeff


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