A question of back focus

[Jose Auger]

I have just acquired a TS APO65Q quadruplet refractor that I reported under a separate topic. I asked TS for the telescope's back focus as I plan to use this telescope with a CCD camera besides the Canon 60D modified that I have. I already have a SBIG STF-8300M and I had to buy adapters for the other refractors I have. Those refractors use field flatteners and I had to acquire adapters relative to the back focus of each refractor. TS says that I do not need to worry since the APO65Q is a quadruplet that incorporates a field flattener in its design and that the back focus is not important. I think they are mistaken and that I need that information as I will have to buy an adapter for the CCD in order to achieve focus.

Can anybody help with this? Is what TS says true?

 Thanks for your help.

[Davey-T]

If you put a reducer / flattener in the light path then generally there is a recommended distance between the f/r and the camera chip, if you fit a camera directly on the scope then it just focuses normally AFIK .

Dave

[Jose Auger]

Just to be clear. Since the TS refracts has a flattener already inside the tube, does this means that I do not need to worry about back focus if I place the CCD directly into the focuser?

[steppenwolf]

If I recall correctly, the TS Quad is essentially a Petzval design so when used 'out of the box' exact spacing of the sensor is not critical.

Unfortunately, I am away from my PC and review notes but TS's assertion does not surprise me.

Sent from my iPhone from somewhere dark .....

[Baffa]

As far as I know with that design any distance is correct!