[rustigsmed (Russell)]

Originally Posted by PRejto

Here are 2 solutions. One is very expensive ($793!)but looks very interesting:

Follow links from here: http://www.astro-physics.com/index.h...ducts/products

Baader Fluorite Flatfield Converter Barlow (BPFFC)

or

2" Advanced Convertible Barlow (BARADV) ($250)

I've used the 2" AP barlow with my KAF8300 CCD and it works very well. You can adjust the power somewhat by moving in/out. I took this photo of M83 using it with my TEC140:

http://www.pbase.com/prejto/image/152287993
and M16

http://www.pbase.com/prejto/image/149151685

TAK also has a good photographic barlow at 1.6X.

I would think you need 2" to avoid vignetting. Personally I'd go with one of these over your standard barlows.

Peter

thanks for that Peter, I did kind of ignore whether coma correction was required i was thinking perhaps f8 might be fairly insignificant but I wasn't aware of these barlow-field correctors which would obviously do a better job as the coma would be still there just less obvious.

I think with the baader it would need be setback around 57mm (TSOAG9 44+11+2mm and magnifications and the back spacing required: 2x = 42 mm, 3x = 96.2 mm, 4x = 150 mm,) which would give a magnification of about 2.3 which would make the scope f9.2 ish - a little slower than I was after but not diabolical.

if I interpret the AP barlow info correctly a setback from the chip needs to be 90mm (for 2x) so I've got more room to play with (plus its in my price range) so i'd need about a 33mm spacer which is doable... well a 10mm spacer think my existing variable spacer is 17-23mm (for my TSOAG9 + RCCi combo) so that's easy enough.

thanks for the tips (again) that's exactly the type of info I was after.

Rusty