4 replies to this topic

[Overtime]

Months ago I purchased a older Celestron FirstScope and now I am noticing it is a bit hard to keep in accurate collimation.

Why you say? One reason is a very slight focuser drawtube wobble. The focuser feels fine when using it but it's very hard to keep in alignment. Is there a way to adjust it? Or rebuild it? Or is it normal? Just replace it? It seems I have many things that I want to do to this scope to make it better. I guess that's what happens when you purchase used merchandise. Oh its a 4.5 inch x 900mm scope if that matters.

[deSitter]

For a long (f/15) refractor, misalignment of the focuser tube is an annoyance, but causes no issue unless it is REALLY whacked.

 

Such issues are usually handled with slippery material (e.g. teflon) between the housing and the tube. Possibly those have fallen out during previous maintenance.

 

-drl

[aeajr]

I don't have your scope, but based on what you are describing it sounds like there is too much space between the draw tube and the outer tube.  I would look to build up the draw tube with some tape to tighten up this sloppy fit.  Figure out which way you want to adjust it, or if you want it to stay even down the center of the focuser tube.

 

Depending on how much you need to build up you can use a teflon or other low friction tape.  You could try scotch tape or electrical tape as a first test, or something similar that will give you an easy slide surface.  You probably don't want to add friction so you won't want a tape with a rough surface unless the focuser tends to slide in or out while you are using it.  

https://www.amazon.c...,78&sr=8-9&th=1

 

https://www.amazon.c...78&sr=8-10&th=1

Edited by aeajr, 01 September 2024 - 01:15 PM.

[Starman1]

Months ago I purchased a older Celestron FirstScope and now I am noticing it is a bit hard to keep in accurate collimation.

Why you say? One reason is a very slight focuser drawtube wobble. The focuser feels fine when using it but it's very hard to keep in alignment. Is there a way to adjust it? Or rebuild it? Or is it normal? Just replace it? It seems I have many things that I want to do to this scope to make it better. I guess that's what happens when you purchase used merchandise. Oh its a 4.5 inch x 900mm scope if that matters. celfocB.jpg

The 2 screws on the back of the focuser press the pinion gear into contact with the rack on the drawtube.

Tightening the screws will reduce the slop, but will also make the knobs harder to turn, so there is a fine line between tight enough and too tight.

And if the drawtube is plastic instead of metal, tightening the pinion gear will crack the teeth on the rack.  So be sure it's metal before you tighten the screws.

Inside the focuser (accessible from the bottom, there should be a couple plastic slides the drawtube moves up and down on.  The pinion gear presses the drawtube against them.

They might have shifted or gotten lost, so look in to see that the focuser is sliding on the slides inside the focuser body.

[Overtime]

For some reason the replies didn't show up on my notifications at the top of the forums. I just happened to look and see some posts. Earlier after I thought I wasn't going to get a reply and seeing the skies were looking clearer I took it upon myself to shim the drawtube between the tube and the housing with 4 tooth picks and some regular tape to hold them in place on the draw tube. It seems better but not what I would call perfect. I also re-collimated and took note it' less wobbly for now. I wonder if it will hold up? BTW I put wax on the toothpicks to give it some lubrication.

 

I didn't know that tape aeajr suggested. I might have to try it. 

Anyone know if they sell rebuild kits for focusers?

 

I am considering buying one off Amazon but that will take quite a bit to make fit. It looks like the drawtube is too long so I will have to shorten it ( shorten the drawtube then shorten the adjustment rack) also others in the reviews said they had to enlarge the drawtube hole a bit and drill new mounting holes ( my old one has 3 screws the new ones have 4 ).