Back Focus

[keybaud]

Having read about Gina's issues with back focus in this thread, http://stargazerslounge.com/topic/198330-ginas-esprit-80ed-pro-unboxing-and-first-impressions/?hl=%20gina, are there any rules, guidance or pit falls I need to be aware of before choosing a telescope to use with a DSLR? I've tried searching but back focus has the word focus in, which appears to be in every thread on here.

I assumed it would be better putting this sort of query in this section instead of the Getting Started with Imaging sub-forum, but apologies if it should have gone there.

[wxsatuser]

All I know is back focus with a SW 80ED Pro+reducer is no problem, just attach the camera to the reducer with a 48mm T ring.

[cantab]

Regarding the forum, just put the phrase in quotes, "back focus", and it should search just for that.

[baggywrinkle]

I used my Canon 650D on a my SW80ED, no reducer and it worked fine, could achieve focus very easily.

[Alien 13]

Refractors generally have lots of backfocus to allow for the use of a diagonal, once the diagonal is removed it is often necesary to use a 2" piece to get focus with a DSLR with a reasonable amount of eyepiece tube extension.

When using a field flattener/reducer things get more difficult the back focus from the flattener is normally only enough for a T adapter and DSLR and maybe 1 or 2 1mm spacers, the real problem is when using a ccd filter assembly.

[keybaud]

Regarding the forum, just put the phrase in quotes, "back focus", and it should search just for that.

Ah, haa. Thank you.

[keybaud]

The best description of back focus and how to mange it that I've found on Google was this post:

http://www.televue.com/engine/TV3b_page.asp?id=85#.UrxFocaYZaQ

[keybaud]

The best description of back focus and how to mange it that I've found on Google was this post:

http://www.televue.com/engine/TV3b_page.asp?id=85#.UrxFocaYZaQ

Key points in this post via wikipedia, on these forums, for DSLR users:

http://stargazerslounge.com/topic/38049-back-focus-distance-for-dslr-lenses/#entry387208

Systems with short flange-to-film distances include Canon's FD (42.00 mm) and EF mounts (44.00 mm), Konica's AR (40.70 mm), and Olympus's Four Thirds System (38.67 mm). These can readily take many other brands of lens.

Systems with larger flange-to-film distances include Nikon's F-mount (46.50 mm), Olympus's OM mount (46.00 mm), and the Pentax K mount/M42 (45.46 mm) universal thread mount. These lenses can be adapted to many camera bodies.