GSO RC Secondary Mirror Centring

[E_ri_k]

Hi, does anyone know how to adjust the centre position on the secondary mirror in the GSO RC's? Have a look at the photos. To me it only seems like these screws would allow for the assembly to be removed, not adjusted?

Any thoughts?
Erik

[Paul Haese]

What size RC do you have? If you have a 10" and above you can buy a centring ring which fits on the back of the scope. It will centre the sensor to the existing optical line and negate the need for trying to do what you are discussing.

[Joshua Bunn]

Even if the secondary isn't centered over the primary?

[Paul Haese]

It might be the case Josh that this secondary is not centred properly but I am more inclined to think that a centring ring is what is needed here.

[Joshua Bunn]

Put a laser in the focuser and see if it hits the secondary center dot. Be sure to rotate the laser somehow while keeping it collimated with the focuser. Then you will know if it's not centered, if you don't already. This may not be such a good idea though it your focuser isn't square to the mechanical axis of the scope, something tells me the focuser tips and tilts with the collimation of the primary, but this can be adjusted separately.... is this correct?



You may be right Paul.

[E_ri_k]

Hi Paul, its a 10" The problem is when I rotate the focuser collimation is lost. Long story short but I have only now been able to see properly through my TAK scope, and the spider assembly is off centre.

Wont the scope still be out of alignment, even with this centring ring?





Thanks Joshua, sold my laser hehe! I can quite clearly see through the TAK collimation scope that the secondary is not sitting right. Plus when I rotate the focuser the centre spot shifts quite considerably off centre, then back again.

[Joshua Bunn]

So when you rotate the focuser, if you had a laser in there, would it rotate around the center spot with the center spot staying concentric in the circle? Can the focuser be collimated separately?

[Paul Haese]

No the centring ring is designed to sort out any misalignment to the camera. It works well.

[E_ri_k]

Yeah ok, I'll have a look at it then. Thank you :) However do you know how the secondary can be adjusted?

[Paul Haese]

The secondary is not designed to be moved in that way. So you need to get the primary lined up with the secondary and the secondary pointed down the baffle. From there you need to line up the optical centre with your sensor with the collimation ring. It will move the secondary into the centre.

[E_ri_k]

Thanks Paul, before I lash out, I know I can adjust the tip tilt on my focuser. Might try that and see if it is enough.

[Scheimfluge]

Hi Paul.

You are very knowledgeable about the RC 12" Serrurier Truss Telescope thank you for all your efforts and input and tests on describing all aspects of this instrument. I have recently installed the Kendrick dew heater into the secondary mirror and I forgot to measure the spacing from the spider vanes to the back of the secondary housing, could you please tell me the exact spacing.
Thank you
Geoff

[Paul Haese]

Actually the best thing you can do is measure the total mirror separation. From the centre of the primary to the centre of the secondary. Using a tape measure, gently touch the surface of the mirror with the end of the tape near the baffle on the primary and measure to the start of the secondary baffle. Add that distance to a measurement from the centre of the secondary (which should read about 64.5mm). The total distance between both mirrors should read 687.89mm. That will give you the exact separation required.

[Scheimfluge]

Thank you Paul for the info.

Geoff