View Single Post
  #416  
Old 03-07-2016, 01:24 PM
codemonkey's Avatar
codemonkey (Lee)
Registered User

codemonkey is offline
 
Join Date: Jul 2013
Location: Kilcoy, QLD
Posts: 1,945
Thanks for taking the time Ray, really appreciate it! I've got some old measurements here for my focuser which tells me that it's about 2.7u per step and I think it needed to be about 7.5k steps further out, so that should mean I need about 20mm. I'll double check all of that before I order anything.

Edit: You corrected your post just as I was posting mine. So, based on those numbers, I should expect a change in focal plane ~4x the focal length of the doublet lens taken from a plossl. So if I need 20mm, and a plossl contains 2 doublets that are individually about twice their advertised length, I would need to divide the distance needed by about 8 and that should tell me (roughly) what eyepiece focal lengths I should look at... which gives me 2.5mm for 20mm, correct?

And by moving the lens element further away from the OAG prism, I would push the new focal plane out further, is that correct? I can only get it "so close" to the prism, maybe 20mm or so.
Reply With Quote