Achieving focus on an SCT

[Daniel]

Ok, this will sound like a very dumb question but, I took the 12" meade out for the first time last night, no mount, just plonked it on my lap to see what I could see, for the life of me, i couldn't get focus, is there anything i should know?

I made sure to take out the mirror lock screw and tried the in built focuser aswell as a crayford, both times i used a William Optics Diaganol but just couldn't get focus, is the primary mirror supposed to be in a particular position to work with the crayford?

Thanks

Daniel
:O)

Oh by the way, the CGE i took out for the first time last night is amazing, managed 3 mins unguided with almost no drift, and no polar scope!!!

[Daniel]

Oh, actually, I've just cracked it, turns out I have to have the primary mirror slightly let out before I can focus with the crayford.

One question I still have though, is thaat I've just put a longer screw into the mirror lock to keep the focus where it is, is it safe to do this?

[Mac]

If i remember correctly, the 12 & 14" meades have a long screw which is installed during shipping and this has to be removed before you use the scope, keep it safe in case you need to ship it anywhere, if you dont then you will probably break the mirror!!

As for focus, the minimum focus should be about 75ft, use the primary mirror focus to get the object roughly in focus and then use your crayford to fine tune the focus.

The mirror lock is used when you have the object roughly in focus and stops the mirror from shifting. whilst you are slewing across the sky.

[Daniel]

Hi Mac, thanks for that, I took it out last night and got the primary mirror to rough focus with the inbuilt focuser and the crayford about half way through its focus, then locked the mirror with the screw so that I can now use the crayford for all my other focusing after that, just hoping that the focus isn't wildly out when I hook up the DSLR now!

Daniel
:O)

[Mac]

your probably find the focus is way out,
Mine normally is.

you will probably need a hartman mask to assist you in your final focusing.

Unless you have live view or similar and can zoom in to your image.

what wedge have you got?

[Daniel]

I've got a CGE mount which im going to be mounting to but right now im awaiting a losmandy dovetail so all i've been able to do is hold it in my lap to test it out (easyer said than done)

The hartman mask is this weekends project, I made one for my 8" and coupled with live view that im also using the focus was amazing!