Backfocus with planetary

[tooth_dr]

My new scope (VC200L) has a built in corrector that requires 149mm of backfocus. It isn’t a problem achieving this, but I’m just curious if this is important for planetary imaging, and secondly, if I use a barlow 2x how does this affect that spacing?

 

Thanks

[tooth_dr]

Anyone know?

[globular]

I don't know - and to an extent it will depend on the barlow as they all move the focal point by different amounts.

You can find out though, with a once only test that will give you the answer.

1. set up without the barlow and with back focus of 149.
2. focus on something - ideally at night, but if in the day make sure it's a long way away.
3. without moving the focuser again, add the barlow and add/remove spacers so that it is focused. Trial and error.
4. you now know the back focus with the barlow and can just use that in future.

Edited November 3, 2023 by globular
typo

[Louis D]

Also, if using a traditional long Barlow, be careful when inserting it into the rear port to avoid hitting the corrector lens if indeed it is at the back of the scope and not on the secondary.

[tooth_dr]

On 03/11/2023 at 12:28, Louis D said:

Also, if using a traditional long Barlow, be careful when inserting it into the rear port to avoid hitting the corrector lens if indeed it is at the back of the scope and not on the secondary.

I was out last night and definitely need to be careful inserting anything into the focuser too far as the corrector is just in behind it.