50mm Stellavue finder - how can I tension the focuser?

[[1ponders]]

I've had a Stellavue 50mm finder for quite some time now and while it has lovely optics the helical focuser has always been a bit of a problem. Firstly it has always been very stiff to focus, so much so I had to be careful focusing that I didn't throw out the finders alignment with the main scope. Secondly, even though it was stiff to focus if i left an illuminated reticule (with pulse illuminator) in it, the weight of the illuminator off to the side would gradually rotate the focuser so next time I looked it was out of focus.

Recently I decided to try the finder as a guidescope, so out came the turps and I pulled the focuser apart, cleaned it out and regreased with Supalube. Slick and smooth focusing now. Too slick and smooth now with no 'stiction' to resist gravity.

Short of getting a grub screw put in, can someone suggest a means of tensioning the helical focuser to reduce (eliminate) focus shift? I could put in a heavier grease but then i'd be back to 1st base. I have also considered a rubber O ring, at the base of the focuser but that would only solve the problem in one direction.

thanks

[Waxing_Gibbous]

Its Achilles heel.
I have one too. Short of a grub screw, try Teflon tape (that white stuff that plumbers use). The pink version is "stickier" though.

[scopemankit]

can you fit a grubscrew with a teflon tip or insert?

[[1ponders]]

Thanks for the feedback Peter and Chris. I think the grub screw might be the answer. I'm make sure its tastefully done and very understated . ;) wouldn't want to mar it seductive beauty.

Only those that have had a SV finder would know what I mean :lol:

[gbeal]

Why not focus it, and then tape it up, as the focus doesn't need to be changed once set. I used an O ring, and it fixed the sloppy focus on a finder.
Gary

[[1ponders]]

I've thought about an O ring Gary, its fairly unobtrusive/ I thought about taping it up but I couldn't do it, there has to be some standards. :D

[h0ughy]

duct tape and velcro?

[[1ponders]]

Even I couldn't use Velcro on it Dave, and duct tape is just ....tacky :P

Really its the one aspect that is a poor design, relying on the viscosity of the grease to manage tension on the focuser. Shame really. I think for the time being I will use the tape idea until I can either find an O ring or take it in to get tapped.

[Graham W]

Try the stellarvue groups on yahoo or email Vic at Stellarvue

[peter_4059]

I got a nice piece of red gaffer tape for mine

[Brundah1]

Paul,

Thanks for sharing, maybe a bit of "chinese precision", both my F50M & F60M are not affected - as yet.

I agree like Williams Optics etc., these are not products to butcher!
Perhaps the main offender is the mass of the Rigal pulse illuminator - but I doubt you will bin that unit!

Since you have dismembered this beautiful object, suggest applying silicone grease (Dow Corning DC- 4 is the aviation version). Its a bit like Vasolene, but slicker and never dries out. MDS:

http://www.dowcorning.com/applications/search/products/Details.aspx?prod=01903128&type=PROD&country=AUS

BTW this is the best electrical moisture barrier bar none!

David

[hotspur]

I just bought a Borg 'finder guider scope) its 50 mm and all the bits came in cute little boxes-putting it together was like a 'optical meccarno set',the helical focuser can be;it appears-be bought separately its very fine in focusing-it may well fit your finder-not sure if there is a Borg agent in Australia-I do not think there is-mine came from States-well worth it.

[ausastronomer]

Hi Paul,

I have the 50mm Stellarvue straight through finder on my 14" SDM. I dont have a problem with the focus moving and I have the illuminated reticle gadget dangling off the side of it. Maybe I just got lucky.

It does have excellent optics.

Cheers,
John B

[[1ponders]]

Hmmm :confuse3:, vaseline, now there's something I didn't think about. :D I'll have a look locally to see if I can find anything similar David. There is hardly any weight in the illuminator, its lighter than those little metal ones that used to come with illuminated reticules. Very light.




I'll have a look into that Chris if I can't solve it simply. The focus thread on this though isn't all that fine, but definitely something to consider.




they really do have lovely optics John and the helical focuser makes it ideal for a guide scope. At least I'm getting plenty of ideas here. I'll start with the simplest and cheapest and then work my way up til I find something that works for me.