which new focuser?

[starman345]

I recently bought a new Hotech to collimate my Skywatcher 10". The red dot was quite a ways off the donut on the primary so I adjusted the allen head screws on the secondary until the dot was in the middle. All was fine until I focused in or out with the focuser wheel, with the hotech still in place I noticed the laser dot moves outside the donut from one side to the other depending on which way I adjust the focus. I figured some slop that might be adjusted out but now I dont' think that is possible, I took the focuser out of the scope and notice someone(previous owner probably) had put tape on the inside of the focuser tube to take up the slack but it really doesn't help.

Keep in mind here I"m new and probably have some of the terms of the scope wrong so feel free to correct me. BTW, the scope is about 5 yrs old according to the previous owner and I think the focuser is probably stock.

With all this in mind, I'm am thinking of buying a better focuser, something that will hold collimation while focusing but am not sure what to get. I'm thinking that at some point I would like to take some pictures of the moon and whatever else comes to mind with my Nikon D50 dslr so what focuser do you think I should get for a replacement that could handle my camera?

I've read a bit about the Moonlite models, they seem to get rave reviews.

So, am I correct in thinking I even need a new focuser or are there some hidden screws that can adjust the slop? If not can anyone offer an opinion on what might be a good option for a new focuser for my Skywatcher 10" dob? Thanks

[johninderby]

You can adjust the standard focuser to improve things a bit but it'll never be as good as even an inexpensive replacement focuser.

Telescope House sells their Revelation crayford for £89.99 and it's actually quite a decent focuser, and a big, big improvement over the standard one. Great budget buy.

I can recommend the Baader Steeltack crayford, just as well built and smooth and precise as the Moonlite and has the same weight handling capacity. It's also cheaper than the Moonlite. Telescope Service does a curved base that will work with the Baader and a 10" dob if you don't want to use the standard base that comes with it.

John

[acey]

The way round slop is to use a Cheshire. My understanding was that the Hotech is meant to get round slop with its self-centering adapter. If that isn't doing the job in the Skywatcher then will it do any better in a replacement focuser?

I wonder if the focuser isn't properly squared to the tube, in which case some washers under the fixing bolts might sort it.

I can see why ultra-fine focus adjustment may be necessary for imaging, and I can see that massive load-bearing capacity is necessary if you're going to apply a massive load, but when using my eyeball I find that the Crayford on my Skywatcher Flextube works well enough, and the rack-and-pinion on my previous dob was fine too. I wouldn't replace a focuser because it doesn't give satisfactory results with a laser collimator - I'd replace the collimator.

[astromerlin]

The standard SW focuser does have adjusting screws although you will have to look hard to spot them as they are so small. You will find the easiest one just in front of the focuser locking screw.

I've adjusted mine just to the point of not getting any stickiness through the travel. Even so I still get a small movement of the laser spot but this will not be a problem as long as you get to focus in one direction only, collimate so you are spot on when you focus in or out if you prefer.

BTW, I've just ditched my cheshire in favour of a home made laser, my eyesight could not cope with squinting down the thing.

[starman345]

Thanks for the replies everyone, I think after playing around some more with the focuser and not being able to get rid of the slop and reading that the skywatcher focusers aren't top of the line anyway, I'll probably just get a replacement. I"m just too picky to put up with it the way it is.

The Moonlite is quite highly rated so I'll give those people a call and see if they can advise me which of their models will work well with my scope.

Thanks for the suggestions and advice, I"ve learned so much from this forum:)

[Moonshane]

I never use my laser for the secondary anymore. I tend to use a collimation cap for that and the the barlowed laser for the primary BUT I have also recently started using a Cheshire collimator with much the same results and less 'worry' about whether the collimator is itself collimated

[ollypenrice]

Hang on, this is a Dob? It is not really suited to much astrophotography however well collimated it is. If this is your main intention the new focuser might not be a great investment?

Olly

[starman345]

Olly, yes its a 10" dob, I understand from reading here that its not an imaging scope but I was hoping to get a shot of the moon maybe with my camera but its not really important.

No, the main intention is to get rid of the slop, when I focus in or out it is annoying to feel the focuser shifting in the focus tube (or whatever you call it). I can look inside the telescope tube((secondary mirror end) and observe the focuser tube moving side to side when I turn the focus wheels, so I don't think the Hotech is in any way at fault here when I can see the movement with my un-aided eye.

I found 4 small phillips head screws that seem to adjust tension on the rack and pinion but adjusting them doesn't seem to effect the slop. There is a larger thumbwheel screw on the opposite side of the focuser that I think is responsible for adjustiing slop, if I do it up tight, most of the slop is gone but now I can barely move the focuser wheel as its so tight. The thumbwheel screw bears on a piece of plastic that pushes on the side of the tube.

[Moonshane]

the 'slop' adjusters are more likely to be tiny grub screws within the wall of the drawtube (usually on the top). they have been on my own stock R&P focusers anyway. they usually work pretty well although I have changed both of my focusers for dual speed crayfords which make a massive difference to enjoyment and critical (visual) focus.

[starman345]

Thanks Moonshane, I'll try to attach a few pictures so people can get a better idea of what type of focuser I"m talking about....picture is worth 1000 words

[Moonshane]

I think there's a grub screw hole in front of the locking thumbscrew in the pic one up from the bottom? there might be another on the other side of this. if they are in there use a thin allen key and you may be successful?

[Moonshane]

BUT I have replaced my focusers with £100 approx dual speed crayfords and there's no comparison.

[starman345]

Aha, I see that little [removed word], so tiny it had eluded me, I just went and had a look under the lights and there it was. Observant of you Moonshane to notice that in my blurry picture. I don't have an allen key that small, a trip to the hardware store is in order, thanks. I'll report how I get along.

[Moonshane]

I reckon that fiddling with this will make a noticeable difference.

helps when you are looking for something specific and know it's there

the thumbscrew is useful too, especially when seeing is 'in and out'. stops you constantly fiddling with it once you 'hit' focus.

[Moonshane]

just on focusers generally. personally although I have not used one, based on the comments of others the Moonlite are really superb, light, accurate and 'trendy'. BUT if you need a focuser for visual use and the odd moon and even planet pic (which is all you'd do with the dob - unless you mount the OTA on a very expensive mount) then the £100 approx dual speed Skywatcher and similar focusers are really quite excellent. the rough (i.e. approximate!) focus might not be as good as the Moonlites etc but it gets you there and the 10:1 focus really is wonderfully smooth and accurate.

I'd certainly recommend this one Skywatcher - Dual-Speed 2” Low Profile Crayford Focuser for Skywatcher & Celestron Newtonian Telescopes and this one Antares Antares dual-speed Crayford focuser for Newtonian telescopes I have both. If I had to recommend one it would be the latter. for both you'll need at least a 50mm extension tube. they both come up used on here too every now and again for about £85 and £70 respectively.

[Hypernova]

I think it would be worth noting that the Antares crayford that Shane linked to is identical to the TH Revelation model. Both just rebranded GSO but the Revelation is £26 cheaper.

[Moonshane]

nice one Tom

I hadn't realised this. that's a serious bargain.

[yeti monster]

It's pretty much the nature od a rack and pinion drive, in what ever application, to want to wander to the left going one way and to the right going the other way. Without precise bearings to keep everything in alignment, this is what you will get and the more it becomes worn, the worse it will become. Also, as the mesh between the rack and pinion wears, just at the point where you most use it, i.e. at prime focus, you'll be inclined to tighten things up a little, introducing further wear.

The beauty of the Crayford is that it relies on friction between the operating shaft and the flat of focuser drawtube. This is where it gets its smoothness from.

[wulfrunian]

I've got the SW dual-speed crayford on my 10" dob. Trouble is, it was too low profile for my eyepieces, and so I have to use an extension tube. I get the same issue with this when collimating, the laser dot is in a very different position depending on the focus position. I too am toying with the idea of upgrading the focuser.

[Moonshane]

I've got the SW dual-speed crayford on my 10" dob. Trouble is, it was too low profile for my eyepieces, and so I have to use an extension tube. I get the same issue with this when collimating, the laser dot is in a very different position depending on the focus position. I too am toying with the idea of upgrading the focuser.

this is the main reason I am now using a collimation cap for the secondary and cheshire for the primary - if I used the laser for the primary then I always barlow it which gets around the focuser slop/movement issue as you are collimating to the shadow of the donut and not the dot itself which is diffused by the barlow. no need to change your focuser.

[acey]

My main gripe about the stock low-profile Crayford on my Skywatcher is nothing to do with slop or collimation, but rather the lack of internal baffling. I sorted this by lining the drawtube with Protostar and adding a ring baffle at the bottom - this cuts a lot of stray light that was reaching the eyepiece, and makes a big difference.

[Moonshane]

My main gripe about the stock low-profile Crayford on my Skywatcher is nothing to do with slop or collimation, but rather the lack of internal baffling. I sorted this by lining the drawtube with Protostar and adding a ring baffle at the bottom - this cuts a lot of stray light that was reaching the eyepiece, and makes a big difference.

this will be the first thing I do when I buy some flocking material for my tubes.

[aussi skywatcher]

Hi, I have just fitted a dual speed GSO focuser to my 8" dob and I cant believe the difference it has made to my viewing - obtaining prime focus is so much easier - we had clear skies for a while last night and I tried it our on Jupiter - was amazed how much detail I could obtain but the icing on the cake was being able to view Uranus for the first time and resolve it as a perfect blue disk - fantastic! I was also pleased to find the new focuser has helped considerably in collimation - no slop anywhere in the system now. Looking forward to more clear skies - for once here in Australia we have had a long run of cloudy nights (and days).

Cheers Paul

[starman345]

Thanks for that Aussi, I too have been looking at the GSO models, can anyone say how you determine how long an extension I would need to make any replacement focuser work with my 10" dob? I notice there are low-profile GSO focusers and "regular" GSO focusers, how do I know which I should get? Seems to me I read something here in the past about measuring the existing focuser travel and going from there, trouble is, I don't quite have my head around what I need to do with the numbers.

I finally located an allen key to adjust the grub screw on my focuser but I think Yeti Monster described my situation quite well, the darn thing is just worn beyond adjusting.

[aussi skywatcher]

Hi Starman, I got the regular focuser - nicely built and very smooth - I fitted it to my 8" skywatcher and found the "hole" in the scope was bigger than the base of the GSO focuser. I made up a plate to cover the larger hole and mounter the new focuser on that. The base of the GSO is 90mm square with hole at approx 70mm but worth the effort. On the subject of extension tubes I bought a 35mm (the skywatcher one wont fit!!!!) but to determine it was ok I made up a cardboard tube and kept cutting it down until I got the length that suited all my eyepieces. Have fun - I did