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

[1ponders] (Paul) · #1 15-02-2011, 04:47 PM

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 (Peter) · #2 15-02-2011, 11:58 PM

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 (Chris) · #3 16-02-2011, 12:16 AM

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

[1ponders] (Paul) · #4 16-02-2011, 07:39 AM

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

gbeal · #5 16-02-2011, 07:51 AM

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] (Paul) · #6 16-02-2011, 08:05 AM

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.

h0ughy (David) · #7 16-02-2011, 08:18 AM

Quote:

Originally Posted by [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

duct tape and velcro?

[1ponders] (Paul) · #8 16-02-2011, 08:30 AM

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

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 (Graham) · #9 02-03-2011, 07:07 AM

Try the stellarvue groups on yahoo or email Vic at Stellarvue

peter_4059 (Peter) · #10 02-03-2011, 07:32 AM

I got a nice piece of red gaffer tape for mine

Brundah1 (David) · #11 02-03-2011, 09:39 AM

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/applicatio...OD&country=AUS

BTW this is the best electrical moisture barrier bar none!

David

hotspur (Chris) · #12 02-03-2011, 01:52 PM

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 (John Bambury) · #13 02-03-2011, 02:02 PM

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] (Paul) · #14 02-03-2011, 04:12 PM

Quote:

Originally Posted by Brundah1

Paul,

T
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/applicatio...OD&country=AUS

BTW this is the best electrical moisture barrier bar none!

David

Hmmm

, vaseline, now there's something I didn't think about.

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.

Quote:

Originally Posted by 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.

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.

Quote:

Originally Posted by 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

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.