OO OMC140 Focus Problem

[PaulG]

Hi

I'm having problems achieving prime focus with my Nikon D70.

The Orion has a 50mm pipe sticking out the back of the OTA with a 2" to 1.25" adapter.

The pipe is 43mm long.

The T ring screws straight onto the adapter.

When focusing I have to turn the focuser counter clockwise, it almost reaches focus but stops just short .

What do I need to do, lengthen or shorten the optical path ?.

Cheers

Paul

[GazOC]

Lengthen, I think. Clockwise pushed the mirror forward (shortens the system), anti clockwise brings it back (lengthens the system)

[PaulG]

Thanks Gaz for the reply

I tried a little test tonight after reading your reply.

I wrapped some card around the 2" optical back and sellotaped it into position.

I then pushed my Nikon D70 against the paper tube and it is certainly closer to the focus point .

The make shift tube was around 50mm long.

As it was chucking it down outside with rain, this test was performed inside on the dining room table with the OTA propped up by numerous books .

I need to get the OTA on the mount to try and figure out how long to make the extension tube.

It's a bit hit and miss but at least I know now I'm heading in the right direction.

Thanks

Paul