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It's an ED80 with the stock focuser. I think there is some astigmatism somewhere as my stars can be a little stretched and so I want to see if I can use a collimating laser to check if the focuser is in straight. (I'm also going to make a determined effort to get the spacing right between the FF//FR and the sensor, but that's another story). I can't see any threads that get into the detail of lining up the focuser with a laser.
If I put the laser in with the target bit facing up, then the red dot that bounces back off of the lens is slightly off centre on the target on the collimator. If I loosen the screws, turn through 90deg, retighten and look again, then the red dot is in a different place and so on all the way through 360 deg. I'm thinking that the red dot should be central (as when collimating a Dob that I used to have). Is that right?
It may be that the laser needs collimating, but I'm not sure how to do that.
Any advice on whether this approach is going to get me anywhere would be appreciated.
I thought I would share how I fixed my sloppy rack and pinion focuser on Skywatcher 130p.
The issue? When using or collimating the slop in the focuser would put the target or centre dot way out of line.
With the tube tilted downward I removed the 4 screws/nuts of the focuser to remove it from the OTA.
Loosen the lock and 2 adjusting screws, I used a small torx screwdriver as i did't have an allen key small enough.
Remove the 4 screws holding the adjuster bar in place, and remove the adjuster.
Note: Be careful to avoid the very sticky grease used on the drive!
Remove the draw tube assembly, remove the lock/adjusting shim located at the top of the main body.
There were 2 plastic shims 1 each side of the drive I removed both of them.
Thoroughly clean everything with degreaser and isopropyl alcohol except the drive itself.
I cut 2 plastic shims from food packaging, cleaned them, and using 50mm double sided tape I lined out the main focuser body. Be careful to cut to the correct size and shape before installing and don't cover the drive or lock/adjusting shim areas.
Next using teflon tape purchased from eBay I covered the draw tube exterior.
I then did the same covering the plastic shims in the main body.
It was still a little loose so I doubled the teflon tape at the top of the tube either side of the adjusting shim.
Next I added a plastic shim onto the adjuster shim and covered with teflon tape.
Put it all back together and almost no slack!
I can now move the focuser from fully in to fully out without the collomation moving out of the centre ring on the primary.
Complete success I think.
Having suffered for some while with broken teeth on my Tracelscope 70s plastic focuser rack; I finally got around to doing something about it.
First of all I cut a piece of aluminium (aluminum for our friends across the Pond 🇺🇸) the same size and dimensions as the plastic one on the focuser tube. Using the damaged one on the tube as a template, I marked out the replacement and began to file it down to size. Once this was done I copied across the positions of the valleys between the teeth onto the aluminium replacement. Using a manual mitre saw with a blade suitable for metal I cut the valleys. Some rough filing and the rack was almost complete. A hole was drilled at each end to receive a screw. I then cut off the plastic rack from the focuser tube, filed the cut flat and the glued and screwed the replacement into position.
Due to the rough hand marking, cutting and filing it is not 100% smooth running, but at least it gives me full travel.
A couple of pics:
Broken plastic rack (removed). New aluminium rack glued & screwed in place
I am selling my Moonlite installation kit for 8" newtonian focuser as shown here
The installation kit was fitted on my 8" dobson in Italy and used very little (it is essentially new). I no longer need it as the focuser now sits on my 12" dob.
New £58, my price: £40 (including RM 1st class signed-for). PayPal (pay as a friend) or direct bank transfer.
Also advertised on ABS.
Thanks for looking,