Best focuser upgrade, crayford vs motorised?

[barees63]

Hi All,

I dont like my focuser.. I have a standard GSO R&P focuser and I find it is quite stiff and hard to get optimal focus, especially since I have to tweak it, wait for the vibration to stop, tweak it again and so on.. the movement seems quite coarse also so it is fiddly to get it to perfect focus without overshooting. So, I'm thinking (once the dust settles on my recent purchases) I might upgrade it, I was wondering what your opinions are on moving to a crayford style focuser vs motorising the R&P? From the little research I've done it seems Moonlite focusers are a good option fo a crayford at around USD300, but I saw someone advertising in Australian S&T a motorised focuser kit for R&P focusers for AUD95.. has anyone gone the motorised route? comments? On the face of it the motorised option would appear to be good from a vibration standpoint?

[[1ponders]]

Hi Bruce. Why not do both :D

If your R&P is giving you trouble have you tried pulling it down, cleaning out the glue grease, regreasing and reassembling. You might find that that makes quite a bit difference to start with. If it's really bugging you then a crayford style focuser is very sweet to use. You probably won't even need motorising.

There are quite a few "crayford" style focusers around, moonlite and feathertouch (mmmmmm feathertouch arggghhh :P ) being right up near the top of the list (don't forget JMI as well). Have abit of a look around but both Bintel and Andrews (and I'm sure other Aussie shops) can supply crayford style focusers quite cheaply. Play with it for a while, then decide whether you want to motorise it. You would come out paying a lot less than for just a moonlite. Mind you if you get a two stage moonlite you mightn't want to motorise.

[iceman]

I got the moonlite CR2 for my 10" GSO dob, and I love it. I had to drill new holes to install it, but it came with a template and mounting kit so it was no drama. Details here (http://www.iceinspace.com.au/?moonlite).

The moonlite CR2 is lovely, the 8:1 ratio on the slow mo knob is just right.

I've also motorised it, DIY style - details and pics here: http://www.iceinspace.com.au/forum/showthread.php?t=2116

I only use the motor when i'm doing imaging, because it's crucial that there's zero image shift so you can actually see what you're focusing. For visual stuff, using the slo mo control is good enough.

[barees63]

Maybe I should, the other day I noticed the 4 small screws that hold the little silver plate underneath were almost dropping out, I tightened them and it's been much stiffer since then, but if I loosen them I'll lose them..

Would a motorised Crayford be better than a motorised R&P? I thought given the same stepper resolution there would be no real difference?

[Starkler]

Those screws has plenty enough thread on them to adjust the tension without fear of loosing them.
If after a cleanout and adjust of the r&p you're still not happy ( I wasnt), I recommend you try a crayford. I have the gso one and im happy with it. It fits the same mounting holes as the standard r&p.
In short I would avoid complexities like electric focusers as it detracts from the main beauty of using a dob, simplicity and freedom from wiring and gadgetry :)

[janoskiss]

The basic $99 crayford from bintel or andrews are a very good upgrade from a R&P, but still quite stiff, especially with heavier eyepieces. If you want to be sure collimation stays spot on, again, you've got to keep a fair bit of tension on it with any eyepiece and it ends up quite stiff. (There is no image shift but quite a bit of sag without the tension up.) There is some backlash in the pinion shaft but not in the focuser barrel itself. You do get what you pay for, but in this case for $99, perhaps a bit more even. I haven't tried to pull it apart and try to improve on it. Maybe one day.

[Starkler]

Interesting, I run mine with the tension screw fully loosened and have no issues with sag or backlash, even with a 31mm nagler in a barlow hanging out of it :shrug:

The only way I can see a crayford having backlash is if the focus knob isnt tightened properly on the focus shaft.

[janoskiss]

It's not the knob, it's the shaft itself. Roger from Bintel diagnosed the problem and it has to do with the shaft not being fully supported at the sides only in the centre, about which it can pivot. But as I up the tension there is less and less movement in the shaft and consequently less backlash.

Re sag: I can push upwards on the end of the focuser barrel and the whole thing lifts up until it goes clunk against whatever supports there are in there. Maybe a tweak on the top screws is needed but I haven't touched them yet.

PS. for the record, Roger did not sell me the focuser with the backlash problem, the last one at the time in the Melbourne shop. But I got impatient and excited when the price dropped to $99 and ordered one from Sydney, which has the same issues.

[[1ponders]]

I noticed the same thing with Nightshifts dob Steve but I don't recall it in jjjnetties. Wonder what's going on there. :confuse3:

[janoskiss]

Paul, I tried two Crayfords at Bintel one in a box one on a scope. The one in the box had "pinion" shaft backlash but an evenly machined "rack" surface. The one on the 10" Dob had no backlash, but uneven tension: it would get stiffer the further out it got. And my new one has backlash and a sloppy barrel without the tension way up.

So QC does not seem to be best with these cheap Crayfords. But that's to be expected for a $99 focuser, I guess.

[anthony2302749]

Hi
Try this modification on the GSO Craydfords (follow link http://www.helixgate.net/ed80mods.html) it is for the ED80 but should also work for the GSO's

[OneOfOne]

I put a Crayford from Andrews onto my 8 inch a few months ago. The focusing is much smother now and one turn of the Crayford produces about half the tube movement as the old R&P that came with it. The mounting flange that came with it was exactly the right size for my tube, which saved a lot of work. However, I was not happy with how the focusing mechanism is attached to the flange - two grub screws on either side of a shoulder. I have subsequently machined (having a lathe in the garage is handy) a ring to attatch the two parts together with several screws, as a result you could hang a car or Nagler off it (whichever is the heavier!).


I have also attached a small geared electric motor to the shaft and a couple of batteries etc. for a total cost of about $20.

the main problem I have found with the focuser is that sometimes it slips, and won't move the focus tube up or down (depending on which direction it is facing). I may need to do some more work on it some time, but at the moment it works great! No shaking, and easy to adjust.