newtonian focussers

[Solanum]

I found the original focusser in my GSO Dob to be rather inprecise in use, so I replaced it with a GSO 10:1. However, I find that with moderately heavy eyepieces (I'm not talking 2" monsters here, just anything more than a Plossl) I find that if I adjust the tension screw so that the tube doesn't fall back in under the weight of the eyepiece then the 10:1 only works in one direction (inward).

Is there a simple fix for this? Alternatively, should I be looking at a better focusser (nice though it would be I'm not in the market for a feathertouch/moonlite etc. Are something like the JMIs reasonably priced and worth buying?

[jjjnettie]

There should be one, maybe 2 adjustment screws on the underside of the focuser. One, when tightened, fixes the focuser so it doesn't move. (handy for astrophotography)
The other adjusts the tension so the focuser moves in and out, it's this one that needs to be tightened a little.

[Solanum]

Yeah, I know. That is what I'm talking about, I wasn't clear enough. If I tighten the tension screw enough to prevent the eyepiece falling back in when I touch it, then the fine adjustment focus knob will only work in one direction (the rough adjustment focus is fine), which makes it useless.

[stephenb]

I find that in my 8" Newt with a BinTel/GSO low profile 10:1 focuser, it takes a bit of fiddling but I can generally get them 'fine tuned'.

If you wanted to upgrade, I can vouch for both Moonlite and Feathertouch. Exceptional! Ask anyone with an SDM Dob (err.., not me). I think they all come with Feathertouch focusers.

hoo roo

Stephen

[CoombellKid]

I had a GSO low profile 10:1 focuser on my 16". The focuser mounts so
that it is horizontal to the ground. Even then I found it struggled as most
of my ep's are 350gm+. When I brought a 31mm T5 it became almost
useless with too much slop that I couldn't remove. The fine tuner was
non-existant, and the rough focus would more or less grind and jerk
under the weight. So I ditched it and upgraded. Was looking at Moonlite
but then along came a deal on a Feathertouch. Haven't looked back :thumbsup:

GSO focusers do ok, until you start using heavy ep's. No matter how I
tried to adjust it it just wasn't up to the job.

Cheers,CS

[PeterO]

Its a fairly easy thing to fix, I,ve done it to a few Synta style focusers, in step eleven of the link below just put a little more pressure on the reduction asjusting nut. Depending on how much you tighten it (within limits of course so that the reduction assembly still rotates) you will then be able to adjust the tension knob quite tight for heavy loads.

http://www.agenaastro.com/Articles.asp?ID=179

[Solanum]

Looking at some prices I see that the Moonlite's aren't more expensive than the JMI ones and obviosuly have a very good reputation. Is there anything in between the $125 GSO and the $400 Moonlite etc. that I should know about?

[Solanum]

Hey thanks for that link. I'll try going through those steps before trying to locate some cash for a new focusser!

[CoombellKid]

I dont think you could go wrong with a moonlite. But never used one
myself that I can remember.

I had to modify two things to install my feathertouch. Enlarge the
focuser hole in the focuser board. And the baseplate mounting screws
had 2mm smaller foot print.

Cheers

[Solanum]

Hey, success! At least in my living room. Taking out the spindle and tightening that nut now lets me put my heaviest eyepiece in and the fine focus still works in both directions. Now if I ever get a clear sky again I'll be able to test it for real.

Thanks.

[erick]

I've had no problems with my 10:1 GSO focusser with a 35mm Panoptic - 700+g. Sounds like I'm lucky - my focusser is already well adjusted?