8 replies to this topic

[Blackmyst]

Hi all

 

I've been putting off adjustment of my scope for a while (over 10%), however after reading some of the guidelines on CN I've decided to move forward.

 

I see there are threads on the rear edge of the dec mounting plates for grub screws which will push against the DEC mounting plate screws (adjustment), but I have not been able to identify what size grub screws (or socket head screws) these are.

 

 

Based on the other screws on the scope these would be imperial and unc, but I'm not sure of the exact size - near as I can tell they're around 2.4mm (3/32).

 

Does anyone know what the size they should be?

 

regards

Jon

[Blackmyst]

for those curious to the method, see here - https://www.cloudyni...ity-adjustment/

[Piet Le Roux]

for those curious to the method, see here - https://www.cloudyni...ity-adjustment/

I am still curious and I have looked at the link and found that very confusing! I would appreciate some clarification of what is being adjusted? 

[MikeBY]

I am still curious and I have looked at the link and found that very confusing! I would appreciate some clarification of what is being adjusted? 

What is being adjusted is the optical axis of the OTA to be orthogonal with the ALT and AZ axis of the mount to reduce/eliminate cone error.

 

The screws are definitely SAE English thread although I couldn't tell you definitively what size.

I agree that if clearances allow,  use a longer cap head screw rather than a grub screw and leave them in place to keep tension on the threads.

 

I wouldn't think that focusing on a spot on the RA axis would be precise enough.

 

Perhaps an artificial star or laser collimation tool. with the scope on an optical bench, or very precisely leveled bench. 

 

Then you can adjust by rotating AZ and ALT through precisely 180°

Adjust out 1/2 the error, realign exactly to center and repeat the rotations and adjustment.

[Blackmyst]

You're correct - probably not accurate enough.

 

A false star is a good idea, need to see if I have enough adjustment on my wedge and clearance over the observatory wall - failing that a terrestrial target thats far away...

 

first step though, is size - I know its not a 1/8 (was able to source), but smaller is proving elusive this side.

[michael8554]

On a LX200GPS the long screws that hold the bottom plate onto the mount are the correct Imperial size for that mounts Ortho adjustment.

 

If you have measured 3/32" that's probably the correct size.

[Blackmyst]

tx Michael, let me try source.

[bdoyle]

The small screws are 4-40. I have used them to set optical tube in other that original mounts.

[Blackmyst]

tx, I was able to source 4-40 locally