Can't focus through barlow after scope rebuild

[badgers]

Hi All,

I disassembled my scope to flock it and sort out a few issues on the focuser.

Everything reassembled fine and I recollimated everything.

During a quick test tonight, I find I can't focus my webcam through the 5x barlow any more. It's very close to reaching focus but can't quite make it before I run out of focuser.

It's possible I didn't put the focuser back correctly, but it appears to be working perfectly and operating as before.

Is it possible that after recollimation that the primary (or secondary) is just a little closer or further away than it had been previously ? i.e. just enough to stop me reaching focus.

[Tinker1947]

Just try a wide FOV EP, test it like this, you can even do it in day like on a distant object.

[MBJ]

maybe the primary isnt in the position it was before you stripped the scope as i had a problem focusing my dslr and i moved the primary up the tube about 5 mm and it gave me focus.

[Tribal-Wolf]

did you separate the secondary from the spider anf you did then did you realign the mirror when you refitted it? When I got my scope the secondary mirror was too far down the tube, when I aligned it properly my focus points changed. It must be because the focus point on the mirror is closer or further away depending on how far the mirror is into the tube. Not sure if this is why but my focus point changed a fair bit.

[badgers]

I adjusted the secondary, but only by a tiny fraction to get a better alignment, stripping down the scope seemed like a good time to get really dead on collimation.

I'll shift the primary back a mm or two if I can and see if that works, if not I'll have a tweak with the secondary.

[steelfixer]

Did you strip the focuser down (ie remove the rack.)

[badgers]

Yes, but I'm almost certain its working as before. They skywatcher one rolls along a flat part of the tube and I can feel it hit both ends as it did before.

I can remove it and double check if the mirror tweaking doesn't get me barlowed webcam focus back again though.

[coulthamst]

In some Skywatcher R&Ps it is possible to replace the rack the wrong way round and affect the focuser travel. I don't know if this is the case with yours, but it is something to check.

Jim.

[haitch]

Is it in travel or out travel that you don't have enough of?

If your focuser is square with the secondary then I doubt focuser or secondary position is out enough to cause the problem.

Most likely at one end or other (or both) of the focal train. I.e. Primary position or height of focuser. If you haven't got enough in travel try using the collimation bolts to pull the mirror further down the tube or shove it up if out travel is the problem. oh, and of course check the focuser itself has gone back together right but if it's the one I'm thinking of (the single speed crayford style with the rubber that drops off the wheels) there isn't a rack. Actually just took a couple of photos ('scuse the rubbish quality, low light & one handed with an iphone) to show height fully in & out (add 1/2 cm for the end of the ruler & they're measure from the top of the base) so hopefully you can rule that out.

[badgers]

Thanks for all the info and help!

I'll hopefully get to the bottom of this tonight.

[badgers]

All sorted again.

Primary and Secondary mirror adjustment and a proper collimation seem to have fixed it.

Thanks for the help