Collimating Screws have caused a problem..

[NeilW]

Hi folks,
I have an 8" SW dob and as many here have done, replaced the existing primary collimating screws etc. with stronger springs and some Bobs Knobs type thumbscrews. This of course has resulted in the primary mirror being pushed forward about 1.5cm. Now I find that especially with low power eyepieces such as a 20mm I can't rack the focusser out far enough to get focus. I have to pull the actual eyepiece out a little way and lock it in place.

I have a Moonlight Crayford focusser, with as many spacer plates as the longest screws will allow, but I still can't focus with the eyepiece in the correct position. Has anyone else had this problem and have a solution? I've considered going back to the old SW hex screws for collimating.

Thanks,

[jenchris (Jennifer)]

have you tried popping in a barlow with the lens section removed?

[NeilW]

No, hadn't thought of that, thanks Jennifer. I think I've got an old plastic one around somewhere.

[tlgerdes (Trevor)]

You can just buy and extension tube. I have 1.25" and 2" versions for my OTA if I want to put an eyepiece in since mine is setup for photos

Like this

https://www.bintelshop.com.au/Product.aspx?ID=7083

and

https://www.bintelshop.com.au/Product.aspx?ID=8055

[NeilW]

Ah, cool, that should do the trick nicely, particularly if I can't find that old barlow. Thanks Trevor.

[erick (Eric)]

Originally Posted by NeilW

... I have to pull the actual eyepiece out a little way and lock it in place....

You've already found the free solution, what more do you want?

Mind you it gets a bit tricky when you need a bit more out focus, trying to hold the eyepiece just out of the draw tube and maintain orientation and focus!! Been there, done that

Yes, I agree, a selection of 1.25" and 2" extensions - and, as was said, unscrewing the lens off the end of a barlow makes a free extension!