Replace collimation screws

[roger94]

Hi, fellow astronomers:)

I need to replace the collimation screws for my C8N to some longer ones.

1) What kind of threads are there on these screws?

2) How can i replace them? Will my primary fall out when I unscrew them?

Thank you:)

[starguest]

That's the SCT scope right?

I've read people just change the 3 screws in the small front secondary and get Bob's Knobs which are exact replacements but have a head you can easily grip instead of using a screwdriver. What you need to do with those is change 1 at a time to keep the secondary in place. I haven't seen anyone mention the back end where the primary is, are there collim screwsd there?

[roger94]

It's a newtonian:)

[John]

Bob's Knob's do some for that scope:

Celestron C8-N, C10-N

[Moonshane]

rule 1. always replace one at a time. that way nothing bad can happen.

you can buy the bobs knobs which are purpose made but I would establish what size the threads are. they may be M4 for the secondary and M6 for the primary. if this is the case you can use readily available thumbscrews off ebay or Astroboot at scopes n skies to replace them very cheaply.

can you post some pics of the primary cell so we can see what sort of fitting you have? might be able to advise further then.

[The Warthog]

Why do you feel you need to replace the existing screws?

My C6N has a push-me pull-me system for collimating the the primary; I.e. two different size screws at each adjustment point, one which moves the mirror up the tube, and one which pulls it down the tube. It was invented by a sadistic ****. Still, if I needed to replace them, I would take out one of each, take them to a hardware store, and pick up screws the same size.