Secondary Mirrors

[Figgis]

Dear All.

                 I've only been imaging with my 'Frac up until now, leaaving a perfectly good Newt sitting in the corner.  I'm looking at upgrading it  a little and trying it out for size.  It's a SW 200p.  I've swapped out the Crayford for a Baader, flocked the inside, the Collimation will now be with an Ocal 3, thanks to Backyard Universe I have masked the Primary and upgraded the Spider.  On choosing a Secondary Mirror Mask, I've  discovered that the 200PDS has a 58mm diameter while my P only has a 52mm.  Is this just to accomodate the PDS shorter tube?  Will it be beneficial to swap it for a larger size?  I have planned to move the primary slightly further deeper into the tube to help with increasing Backfocus.

[Cornelius Varley]

11 minutes ago, Figgis said:

Is this just to accomodate the PDS shorter tube? 

Yes. The distance between the primary and secondary is now shorter, so the secondary has to be larger to accommodate the light cone.

18 minutes ago, Figgis said:

Will it be beneficial to swap it for a larger size?

Not on its own, the distance between the secondary and primary will need to be reduced to benefit.

19 minutes ago, Figgis said:

I have planned to move the primary slightly further deeper into the tube to help with increasing Backfocus.

See above.