Is there any way of getting finer focussing control?

[JOC]

When I've used things like microscopes the focus controls have a coarse focus knob, which if you are clever can often be sufficient, but they have also had a fine adjustment knob for the very accurate focus of the objective which requires lots more movement for a small amount of adjustment allowing for a finer control of the focus unit and the object in view.  Can you get such things for telescopes and could my telescope have one fitted please?

[Cornelius Varley]

There are types of dual speed Crayford focuser that have a 10:1 or similar fine focus. You will probably have to replace the entire focuser depending upon your telescope.

[steppenwolf]

A replacement dual speed focuser would probably be the best option but have a quick look at this thread for a different solution if you fancy trying a little DIY.

[Dave In Vermont]

Here's an example of what is called a Crayford 10:1 Dual-Focus for putting on as an upgrade to what comes with a scope. I just swapped out a few of mine. The difference is night & day.

 

 

They come in different models for different telescopes.

Hope this helps!

Dave

[Alan White]

Hi JOC,

As the others have said, yes they are available, either change of complete focuser or upgrade one wheel.
I take it that the one fitted is already a single speed Crayford.
365Astronomy do a Lacerta upgrade wheel unit., here is the link.

http://www.365astronomy.com/Dual-Speed-1-10-Microfocus-Upgrade-Kit-for-Skywatcher-Crayford-Focusers.html

I have used both single and dual speed and depending on how much finesse you can provide, have found  most single speeds ok in use, I actually rarely use the fine wheel on my ED100 dual speed as I have it licked using single speed, but many of my Eyepieces are parfocal.

[Cosmic Geoff]

I had this problem when I acquired a f5 Newtonian reflector with a single speed rack & pinion focuser.  Instead of buying a complete new focuser which would have cost as much as I paid for the whole OTA, I bought a helical focuser thingy from China which cost me about £20, and does the job nicely. It's actually sold as a focuser for guidescopes etc IIRC.  One end has the standard 1 1/4" eyepiece holder with grip band, and the other has a T-thread, which screwed into an adaptor I got by re-using the 2" to 1 1/4" adaptor that came with the scope.

If that's not clear, I posted about this about 8 months ago and you may be able to find it.

[Knighty2112]

This is the dual speed Crawford focuser that came with my 200P-DS when I had it, so should be a straight swap with the original focuser to give you finer control. Worked very well on the scope when I had it. 

https://www.firstlightoptics.com/skywatcher-focusers/dual-speed-crayford-1252-inch-focuser-for-skywatcher-explorer.html

 

[Dave In Vermont]

I wanted to get a Crayford for my older 200mm F/4 Rich-Field (old term for today's 'Astrograph') Newtonian. But it was only made for a 1.25" focuser. And I wasn't about to perform surgery on the tube. So I got a single-speed Crayford to replace the old R & P focuser.

I needn't have worried. The single-speed Crayford was excellent! As Alan reported above, the single-speeds have very nice 'finesse' on their own.

Enjoy -

Dave

[JOC]

Ooo....that's great thanks one and all, I think I might look into all these solutions and see what might work best.  According to the advert for my scope it has a Dual-Fit 1.25"/2" Crayford Focuser - so it seems it is just the single-speed focus unit - I have been finding that when I use my camera on the zoom mode to focus it in that I find myself knowing it could be more focussed, yet feather light touches on the existing unit seem to go one way or another.  I was hoping that a little more control might provide what my short stubby fingers don't seem to achieve. 

[Ben the Ignorant]

Simply increasing the wheels' grip and/or diameter is worthwhile, too. Rubber wheels for toy cars are said to work very well. My f/5 dob has a very smooth (taiwanese GSO machining, great!) single-speed crayford but at f/5 the super-grippy rubber coverings I added make fine focus decidedly easier.

The extra diameter is only 4mm, not much change here, but the rubber from old-fashioned binox objectives sticks to the skin much, much stronger than the finely ribbed aluminum wheels, which I realize were slippery, in retrospect. And the things look like they were put there at the factory.

[Dave In Vermont]

" Ooo....that's great thanks one and all, I think I might look into all these solutions and see what might work best.  According to the advert for my scope it has a Dual-Fit 1.25"/2" Crayford Focuser - so it seems it is just the single-speed focus unit....."

If your scope can handle 2" eyepieces, then you can get a 10:1 Dual-Focus Crayford to fit. The thing with mine was that it couldn't fit the dual-speed as it had a tube that won't fit a 2" drawtube.

Up to you -

Dave

 

[iapa]

3 hours ago, JOC said:

When I've used things like microscopes the focus controls have a coarse focus knob, which if you are clever can often be sufficient, but they have also had a fine adjustment knob for the very accurate focus of the objective which requires lots more movement for a small amount of adjustment allowing for a finer control of the focus unit and the object in view.  Can you get such things for telescopes and could my telescope have one fitted please?

There is a retrofit Dual-speed Crayford 1.25/2" for Skywatcher Explorer

and also a lower profile Skywatcher Dual-Speed Low Profile 1.25/2" Crayford

With are dual speed, and bot have a 2" to 1.25" eyepiece adapter.

Skywatcher's focus motor fits these.

[JOC]

Thanks all, at the moment with regards simplicity and cost I am tending to be drawn by the Lacerta solution - not as much dismantling involved - as you know I am not big on dismantling things that work (more than happy to if they don't - nothing to lose), but plenty to lose if you stop something working!

[ronl]

The Lacerta works quite well, and it is very easy to fit, I had one for a couple

of years before upgrading the whole focuser, which is superb, but the Lacerta

Is a very good improvement, well worth the money.

[Dave In Vermont]

One warning:

If you replace the focuser - don't lose the little screws that hold it onto your telescope. The upgraded focusers don't come with those and you're expected to attach the new one with them!

This can save you a trip to a hardware-store.

I'll leave you with a photo of my re-tooled ST80 w/ 10:1 Dual-Focus Crayford. Note the large wheel on the fine-focus knob. I can just about fine-tune the focus with this larger-wheel by breathing on it!

Dave

 

 

[Waldemar]

That is a nice solution, Dave!

I had not seen those before, or did you make it yourself?

[Dave In Vermont]

1 hour ago, Waldemar said:

That is a nice solution, Dave!

I had not seen those before, or did you make it yourself?

Hi Waldemar -

That wheel is a nice 'BLING!' factor from ScopeStuff here:

http://www.scopestuff.com/ss_fsm1.htm

But you could use the lid off of a tin of peanut-butter. And people have! ScopeStuff is worth packing a lunch for exploring. Jim, the owner, is a great guy with an amazing inventory. I don't know how he keeps track of all the astro-goodies he stocks. Actually - never mind the lunch. Pack a sleeping-bag & tent. And if you meet up with a British Expeditionary Force, ask them to call home You can get lost in there!

Have fun -

Dave

[MARS1960]

On 6/8/2017 at 13:06, Dave In Vermont said:

Hi Waldemar -

That wheel is a nice 'BLING!' factor from ScopeStuff here:

http://www.scopestuff.com/ss_fsm1.htm

But you could use the lid off of a tin of peanut-butter. And people have! ScopeStuff is worth packing a lunch for exploring. Jim, the owner, is a great guy with an amazing inventory. I don't know how he keeps track of all the astro-goodies he stocks. Actually - never mind the lunch. Pack a sleeping-bag & tent. And if you meet up with a British Expeditionary Force, ask them to call home You can get lost in there!

Have fun -

Dave

Nice one Dave, i've just emailed them about one for my ED120, cheers.

[SonnyE]

I already have a dual speed Crayford focuser on my ED80T CF telescope.

But after adding Tekky Dave's electronic focuser, I'm in Nirvana!

Super fine focus control, in a no touch electronic focusing system.

But then, I am a Borg.

 

[Waldemar]

resistance is futile...