I have a Skywatcher 8" Classic 200P Dobsonion telescope, with the stock Crayford focuser that it comes with.
I find that it is a bit stiff to move the focuser wheels, so the image tends to shake for a second or two after focusing. This is fine for most things, but for getting a good focus on planets at high magnification it is a bit annoying, as the planet gets a fair way through the field of view while this happens.
Unfortunately, my stock lenses (10mm and 25mm, plus an entry level 2x Barlow), mean that I do have to change focus whenever I change lenses.
I understand that there will always be a bit of shaking when you touch anything on the OTA, unfortunately there doesn't seem to be a way to gently turn the wheels to minimise this at the moment.
From what I have seen on these forums and similar places, there are a few options here:
1) Motorised add-on to the focuser (Skywatcher auto focusing motor)
Good because you aren't touching the scope directly.
Also on special at my local astro shop, only $109 instead of $150.
Downsides are you are a bit locked in to using it all the time, need to disconnect the battery to stop it draining, apparently the controls aren't the greatest.
If I go down this route, I might upgrade the controller using the 4Tronix Focus RF Remote Control, which plus straight in and has better buttons and controls apparently.
2) Dual speed focuser
I'd probably go the Lacerta upgrade kit from 365 astronomy. 75 pounds, so probably around $160AU after conversion and delivery.
This would be easy to install, and let me have fine control.
My main worry is if the wheels would still be stiff, and so still cause shaking.
3) Trying to do some adjustments on the focuser myself.
Sounds like the stock focuser on the cheaper Skywatcher models is not the best.
I've read about people sanding down the flat part so it is actually flat, to get it to move better. Also about people taking out the default grease and putting in something different. I'm not sure that this would fix my specific problem though, some of these seemed to be about making sure the focuser held firm, which isn't a problem for me. My main worry here is making my focuser worse.
4) Replace the focuser entirely
I'm not really interested in this, the prices to get anything seem to be half the price of my scope. Maybe down the line.
My inclination at the moment is to go for the motorised upgrade, but I thought I would check in with some people who know a lot more about this than I do. Would I be passing up on an easy home fix? What do people think would be the best approach here?
Thanks Philip
I've attached a picture of the focuser. There is a big pin there that adjusts the tension. I can definitely tighten it so that it is very hard to move the focuser. But at the lowest setting it is still a bit tight.
First, I would wait for someone with experience of this particular focusser. Hopefully not long.
Depending on that, I would suggest loosening the 4 Phillips head screws just a quarter or half turn at a time, with the larger knob loose. If the whole starts working for you, then tightening the larger knob should then increase the tension nicely. If, of course, I am right about how it works together.
Chris, make sure that the locking thumb screw, the knurled thumb screw, is loosened off a bit when trying to change focus and maybe more importantly, loosen the grub screw directly under the focuser shaft, it may be a little too tight. 1/8 or 1/4 of a turn should be enough if it has been adjusted too tightly. That is the tensioning screw and is usually a thumb screw as well, at least on mine it is.
Thank you for the suggestions. I'd tried loosening the one big screw, to make sure the focus wasn't locked, but I hadn't considered loosening any of the others.
I'll give that a go (assuming no one else chimes in with drastically different advice).
As others have said, a bit of trial and error with both the locking knob and the 4 attachment screws underneath should give some sort of improvement. Having said that, I put the Lacerta dual-speed focuser on my 8" skywatcher dob several years ago, and it has been great - very smooth motion indeed, and only takes a few minutes to install. Treat yourself.
Whenever you take hold of the focuser you will transmit shaking. The best way to focus at high power is to attach a peg of some kind to the focus knob and gently push the end of the peg backwards and forward to focus. I'll see if I can post a picture of what I mean.
I used a short piece of aluminium tubing and tapped four holes around the circumference. Screwed in four shortened matching bolts to hold it in place and to just push on the tips to focus. Although this is on a dual speed focuser, I hope that you can see what I mean.
Have you tried just a small drop of WD-40 don't spray it of coarse but a small dab applied with a small child's painting brush or even a drop on the end of a tooth pick or similar.
Then just work the knob and let it penetrate the sticky parts
I would undo the 4 screws on the back, the grease inside might have gone hard, clean and re grease. Just be careful when taking apart, and reassembling!
These current Skywatcher Dobs are very affordable but Synta in the past few years decided to change from a dual speed focuser to single speed on all the range except for the huge Stargate, obviously to cut costs and hopefully increase sales. These SW Dobs and GSO Dobs years ago use to come standard with a Dual speed focuser ( I’ve had 8” and 10” non Goto and currently have a 2018 model 12” SW Goto Dob , all came with a Dual speed focuser )
A SW 8” non Goto Dob costs around $900 with single speed focuser. To buy a Dual speed focuser to replace the single speed will cost around $450 which absolutely ridiculous, half the price of the Dob !!!
How times have changed
These SW single speed focusers are cheap so you can’t expect the smooth buttery type roller action and fine focus control of a Dual speed. Also if you back off the tension screw slightly to allow it the move more freely and therefore more precise ( not bumpy ) there’s a chance that if you pop in a heavy eye piece and a coma corrector like a Televue , the focus tube may inadvertently drop and not support the weight.
The only way I know to improve these single speed focusers is to clean out the old grease with turps and re grease the rollers with lithium MOS grease. Then apply turtle car wax to the flat section of the focuser drawer tube and then wipe it off leaving a waxy film coating.
I’ve done this on a friends 8” and it did improve a bit but not substantially.
Like everything today you pay for what you get.
Good luck with it
Martin
I've had a look - those screws (other than the locking screw) are in very tight, and I am not sure if I can unscrew them without threading them.
This does seem to point towards this being the problem - if they are all in too tight, then it makes sense it is a bit harder to turn the wheels than it should.
I'm a bit wary of putting WD40 on it, I have heard it can get into the optics eventually if it gets into the focuser.
I've had a look - those screws (other than the locking screw) are in very tight, and I am not sure if I can unscrew them without threading them.
This does seem to point towards this being the problem - if they are all in too tight, then it makes sense it is a bit harder to turn the wheels than it should.
I'm a bit wary of putting WD40 on it, I have heard it can get into the optics eventually if it gets into the focuser.
You should be able to put a bit of WD40 on them without splashing it everywhere - maybe a bit on a cotton bud or something. Even if you were a bit heavy handed, I don't think you'd put enough on to ever have a chance of getting near your eyepieces, given that there's a fair bit of gear between those screws and the eyepiece, plus they're at the bottom of the assembly.
Hi everyone
I have managed to sort this out, thanks to all your help. Saturnine in particular was right on the money - I needed to adjust the small screw that was below the locking screw. It is a little recessed so I didn't initially realise there was a screw there. So I ended up wasting a bit of time trying to loosen the wrong screws.
I've been able to adjust this now, and the focuser moves much easier. I've made sure it isn't too loose, so the whole thing doesn't drop down when I put in an eyepiece.
