GSO RC8 collimation issue

[glend (Glen)]

I have priced the replacement focusers, the Starlight and Moonlight are both going to cost around $500 USD plus shipping . If i bought direct from Moonlight in the US I could get it delivered for $600 AUD. The Baader Steel Track and adaptor is a lower cost option at $450 AUD landed but it seems to be exactly like the GSO rail focuser that I have on the RC08.
I use the exact same GSO rail focuser technology (newt version) on my 10" imaging newt and have never had a problem with focuser flex/sag on that scope with my heavy cooled DSLR (and it's a non-rotating scope so sometimes the camera is hanging at very severe angles).
I am having a real problem justifying spending half again the cost of what the RC08 cost me to buy a replacement focuser. Altair Astro advise on their website re the RC08 that the standard GSO linear rail focuser:

... will handle a DSLR or CCD camera, and a light weight filter wheel perfectly well, and is adequate in most imaging situations. Note this focuser has the Linear Bearing upgrade, and will outperform most Taiwanese dual speed focusers, both in rigidity and pulling power. It is perfectly adequate for a DSLR/CCD camera and light weight filter wheel.

I will take what steps I can to improve the stock focuser first.
So I have stripped down the stock focuser and tightened up the rail bearing screws (which seemed fine anyway) and firmed up the pinion shaft that presses against the rail - its all now tighter than my 10" newt focuser. I can not force any sideplay in the focuser rail nor up/down sag/flex that I can detect.
Reading old threads about this subject suggests that the bevel and stop ring placement on the focuser flange mount might be a source of bad fitting so I checked that as well and made sure the stop ring was in the best position to be pushed against by the locking bezel. I can't really do more to QA the stock focuser.
A new round of star tests will now be done at various mount attitudes looking for indications of sag/flex.

[Ausrock (Chris)]

Glen,

What model F'touch will suit your scope?

Chris

[glend (Glen)]

Originally Posted by Ausrock

Glen,

What model F'touch will suit your scope?

Chris

Chris,

FTF2015BCR-A20-271 is the product number I believe. Starlight store says $500 USD plus shipping if purchased direct.

[Ausrock (Chris)]

I have a 2015BCR on my C9.25. If it would fit your RC I think I could spare it long enough for you to try out and see if it solved your problems.

Chris

[glend (Glen)]

Thanks for the offer Chris. I would still need the GSO RC adaptor flange. I have a Moonlight on my iStar refractor and could use that as well to test but same problem, I need the adaptor flange.

[Ausrock (Chris)]

Aaahhh........now I understand the "A20 271".......that had me buggered as to what it meant earlier .

[glend (Glen)]

I will see if I can get the Moonlight GSO RC adaptor flange, that should be a low cost test option, then I can move my Moonlight focuser onto the RC. The draw tube on the refractor focuser is too long for the RC but it should not matter for testing, and can always be changed if needed for permanent duty.

In the meantime I will test with the tightened up GSO focuser.

[glend (Glen)]

I caved in and bought a TAK Collimation Scope and 2" adaptors today from Teleskop-Express (best price I could find that had stock and they will ship UPS tomorrow). I figured it was either that or sell the scope - guess I have to keep it now.

[Paul Haese]

Originally Posted by glend

I caved in and bought a TAK Collimation Scope and 2" adaptors today from Teleskop-Express (best price I could find that had stock and they will ship UPS tomorrow). I figured it was either that or sell the scope - guess I have to keep it now.

Glad you finally caved. These Tak scopes are great. Click on the link below for instructions on Tak scope use.

I cannot find the video by Ken Crawford anymore. That was really easy to follow.

http://www.rcopticalsystems.com/supp...ollimation.pdf

If you get stuck, let me know, but I did the collimation on my scope in 5 minutes the very first time I used a Tak collimation scope.

Something to be really wary of though. When you get all the big rings concentric, looks for some really tiny thin rings in the centre dot. Those rings will be white and very small and are illuminated with the torch light on the tak scope illuminator (white disk). You can only see those if the torch is squarely centred on the white disk. Those rings show the inside of the tak scope. You get them centred by using camera collimation ring. It is critical that you get those really well centred.

Procedure wise you should get the secondary centred first, then the Primary. If either are too far out you will need to do an iterative process to get that sorted. Then do the tiny rings in the centre. The secondary position might change a bit after that, so adjust the secondary again and then finally tweak the tak rings.

Then do a star test. I have collimated a few guys scopes for our society (I am the instruments officer for the Astronomical Society of SA) in recent months and got the collimation so good that a star test reveals an ever so slight tweak if at all. The more particular you are with the tak scope the better the results you get.

[LewisM]

Originally Posted by glend

I caved in and bought a TAK Collimation Scope and 2" adaptors today from Teleskop-Express (best price I could find that had stock and they will ship UPS tomorrow). I figured it was either that or sell the scope - guess I have to keep it now.

'bout time - stubborn bugger

[Paul Haese]

Found the video

http://www.rcopticalsystems.com/supp...imation_V3.wmv

[glend (Glen)]

Thanks Paul. I had been using Stephen Kirk's utube three part RC08 collimation instructions and feel its very close now. The TAK Scope is another tool for better precision and may save me some time in the future if I stay with RCs.

[glend (Glen)]

Still waiting for the TAK Scope to arrive, but messing around today with the stock focuser alignment, trying to work out why one side of the collimation ring has so much tilt to get the laser centred on the secondary spot, I stumbled on the reason : One of the extension tubes (the one that I had the focuser mounted on) had paint on the anodised bevel surface where the focuser engages to the tube. The paint was the material used to coat the the inside of the extension tube and had run on one area of the bevelled surface creating a non-symetrical bevel. This probably would not have mattered if it was not the extension that I used to attach the focuser. The fix, I hope, was to sand the paint off the bevelled face. This allowed the tilt to be near equalised.
Anyone buying a GSO RC with these extension tubes should inspect the bevelled surface if using the stock focuser.
Have to wonder what the next surprise will be.

[glend (Glen)]

All collimation problems now resolved with a perfect star test with camera load and no apparent focuser sag at various attitudes - and still waiting for the TAK scope to arrive

Once the TAK arrives I will double check everything but I swear it will be a cold day in hell before I ever mess with that primary setup again.