[ATM] More Dall Kirkham Secondary questions

["Rod Brackenridge" <rjbr@lycos.com>]

Hi,

I think my secondary is finished.  I now have 4-8 lines arc lines across the secondary when I place it on the reference.  There is no sign of any zones other than a turned edge.  I am not worrying about the edge because it will either be removed or covered.  The arc shaped lines bend by about a half a fringe.

Does this seem finished or should I persevere until I get perfectly straight lines?

I have another question:

My secondary is 100mm diameter for a 355mm primary.  Using Mike Peck's spreadsheet I designed a system that shields the field of a 50mm diameter eyepiece and fully illuminates the central 12mm.  The secondary baffle is 104mm diameter (about a 30% obstruction).  The useful diameter of the secondary is 84mm.

I am trying to decide whether to leave the secondary its present diameter or reduce it to about 86mm.  If I reduce it I then have the option of removing the secondary baffle and using a smaller (24%) obstruction for planetary observation.  Do you think this is worth doing?  If so, what would be the best method to reduce the secondary's diameter? 

The secondary is made of schott pyrex and is quite thick (20mm).

Thanks,

Rod Brackenridge
Mount Martha
AUSTRALIA
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