Ed L wrote:
I'm looking for anyone with experience using a longer FL like a Pentax XL
40mm in a Celestron C5+ (125mm, F/10).

I am thinking of expanding my EP collection for wider FOV. I have a 32mm TV
Plossl, which is currently my favourite EP, followed by a 20mm Orion
Expanse.

My concern is that with such a large FOV that a 40mm will offer, will I hit
the FOV limit of my scope?

Should I re-consider and look at a longer FL in a plossl?

The C5+ has a 1-1/4-inch visual back. The Pentax XL 40 is, I think, a
2-inch eyepiece. To use the 40 on the C5+ would require the addition of
a 2-inch back (and probably diagonal, to save neck strain). Not only
would this get to be expensive, but I think the vignetting will probably
be fairly severe.

I would, instead, get a focal reducer/corrector. Both Meade and Celestron
sell one, and they're OEM, so get the less expensive one--usually, it's
been the Celestron. This will allow your telescope to work as though it
were a 5-inch f/6.3, giving you around a 1.8-degree TFOV with your 32 mm
Plossl. There's also vignetting with this configuration, but it's not
severe enough to ruin visual work.

Typically around $125 U.S., but shop around.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt