Seconary Mirror

[von]

Hi all,
      I have a 125mm 5 inch primary mirror with a focal lenght of 1025mm,I plan to use a R&P focuser.What type and size of secondary mirror do you guys sugest i use?
Thanks in advance,

[Rick]

That'll depend a bit on how far from the axis you're going to mount the focuser, so you need to work that out first. There's some advice on that in the ATM FAQ here:

http://home.comcast.net/~cassarole/atmfaq/atmsect2.htm#24

[Rick]

Oh, and there's a mind-boggling bit of JavaScript here:

http://www.atmsite.org/contrib/Fly/scopecalc/

[von]

Hi Rick,
       thanks for your quick reply,so have i got this right, the closer your eye to the secondary mirror the smaller it can be?being under the thumb of her indoors i can only get one 1 quality eye piece{well to start with anyway lol}which size do you sugest?
Thanks in advance.

[Rick]

You need the focuser to be close enough to allow the telescope to be focused with a range of eyepieces, and you need a flat wide enough to capture the light-cone for the entire focal plane. Eyepiece choice depends on what you want to look at. If you're really limited to just the one then don't make it too short a focal length. For my refractor, which has a similar focal length, I find the 12.5mm is a reasonable general purpose eyepiece, giving me about 85x. For the more extended deep-sky objects I prefer the 30mm one though. Maybe an 18mm one would work as a compromise?