Where does the back focus begin on FSQ

[Paul Haese]

Hi guys,

where exactly does the back focus begin on an FSQ106? Is it from the focusor without any adapter?

I know the Back focus for my FSQ is 178mm but I cannot seem to find much on where the back focus begins.

BTW does it matter if the focusor is racked in or out?

regards
Paul

[Octane]

Backfocus begins at the end of the camera angle adjuster. At least in the case of my FSQ-106N, it does.

H

[Paul Haese]

I have an FSQ 106 ED but the one with the captains wheel. So the CAA is not on my scope.

[Octane]

I'd guess from the back of the tube, then. :)

H

[LewisM]

All I ever could find out was "Metal back to metal back" - real helpful I know.

You could do a search of OptCorp's online catalogue - that I how I found out how much backfocus spacing I needed with the reducer to SBIG ST series - Optcorp conveniently tell you the part dimensions most of the time :)

Don't bother asking Takahashi directly - it's like waiting for light from supernova in a galaxy 42 trillion light years to arrive... and when you finally get it, they will tell you to contact TNR/Tak America anyways. (though Vixen is even worse)

[Hans Tucker]

With all the adapters removed I thought it began at the end of the racked in focuser. Thats how I have been taking it with my FSQ-106ED. If you add the CAA then the BF starts at the end of the CAA. This adapter eats up 25mm of back focus so the native 178mm now becomes 153mm. I probably have this totally wrong.

[Paul Haese]

So if it starts from the back of the focusor racked in then I assume you need to rack the focusor half way out measure that, subtract that and then the balance is the back focus that is left. Otherwise using the focus racked all the way in would mean you cannot do V curves correctly. Am I right in thinking this?

[Hans Tucker]

This is where I stumbled across the BF when searching information a few months ago.

http://telescopes.net/store/fsq-106nuh-fsq-106ed-inchnew-qinch-f-5-astrograph-telescope.html

[Paul Haese]

Ah that makes a lot of sense Hans. Ok that has now sorted my adapter lengths.

Thanks so much.