Top five longest back focus refractors ??

[coldlegs]

Need some help here folks.

Always wanted to by a refractor but have been reluctant due to the back focus problems that can occur when trying to add bits and pieces. I would particularly like to use an ONAG to guide through the scope with as I already have one so I'm looking at about 100-110mm of back focus needed.
What I would like to do is use my QHY9M (22.5mm diagonal) to LRGB image 1-3 degrees of view if possible but I'm not sure what the focal length would be needed. The cost needs to be less than $2k if possible. I know there's some really nice Taks out there that would do the job but they are way over my budget. Size? Well I guess 102mm would be the minimum but 80mm can do some very nice images as well.

so the question is...

What are the top five longest back focus short F/L refractors that could fit my requirements?

Cheers
Stephen

[troypiggo]

I have a TMB92SS. It has a section at the back that you can remove for more back focus. Maybe 100mm long. More than enough on top of what the lovely 3" FeatherTouch can give.

[coldlegs]

Now that's an interesting beast. It's cleverly organised to have lots of back focus which is what I need. That's now on my list of potentials.
Thanks Troy

Cheers
Stephen

[brian nordstrom]

Sellarvue 80mm 'Aplanet' , sadly no longer made :sadeyes: , an awesome scope in every way .
Over 140mm.
Brian.

[troypiggo]

I'm very happy with it. One word of warning, though. It's a triplet but does need a flattener for stars in corners. I tried about 4 different ones and by far the best was, surprisingly, the Orion Flattener. (Not reducer)

[The Mekon]

Astro-tech 106 has too much for me. To use it visually straight through I have to add over 120mm of extensions. Cannot use a 1 1/4 diagonal, only 2" and then focuser is extended 65mm out of 80mm travel. Tube should have been made at least 50mm longer to make me happy.

[coldlegs]

Astro-tech 106 is now on my list. I checked out the specs and it's quite an interesting beast and will easily fit my ONAG.
Thanks John
Cheers
Stephen