GSO Focuser/Collimation Question

shane.mcneil · #1 06-10-2009, 08:33 AM

Hi

I recently bought a GSO 10" with the 10:1 crayford focuser. Regarding collimation, do I need to make sure that the focuser itself is at right angles to the tube/primary mirror?

If so, how do I make the adjustment? There are screws all over the focuser including two grub screws and I wouldn't know which to start with.

Many thanks for your help.

Shane

toryglen-boy (Duncan) · #2 06-10-2009, 09:27 AM

Quote:

Originally Posted by shane.mcneil

Hi

I recently bought a GSO 10" with the 10:1 crayford focuser. Regarding collimation, do I need to make sure that the focuser itself is at right angles to the tube/primary mirror?

If so, how do I make the adjustment? There are screws all over the focuser including two grub screws and I wouldn't know which to start with.

Many thanks for your help.

Shane

Hi Shane

If the focuser isnt at a right angle to the tube anyway, then i would be concerned.

i wouldnt worry too much about the focuser just now, you will probably find that jsut doing the optical alignment is all you need

erick (Eric) · #3 06-10-2009, 10:54 AM

Well, be careful of those two grub screws. If you leave them loose, the whole focusser body can come out of the base plate. You can use these to allow you to rotate the focusser body to a more comfortable angle, if you want. It is probably worth while loosening them and checking that the focusser body is sitting, hard down and flush in the base plate, then tightening them up again.

shane.mcneil · #4 06-10-2009, 06:34 PM

Thanks for that. I figured that a focuser would be designed to be at right angles. Don't know why you wouldn't. But I read on a thread somewhere that the first step in collimation is to make sure the focuser is at right angles to the tube.

Thanks again for your help.

Regards,

Shane

bmitchell82 (Brendan) · #5 07-10-2009, 12:43 PM

... Do be careful that it is not tilted dispite what the others have said. recenlty i had all sorts of issues with my 10"... bloody tilted focuser. Though if you have just purchased it, you shouldn't have to worry about this just a simple colmination routine should see you good!

Easy way to see if your focuser is tilted is to look though a ceshire ep, rack your focuser in and out. watch the image of the 45 deg cut away(should look like a silver circle with a black dot in the middle. if it changes then its tilted to some degree start fiddling and rectify the problem.

shane.mcneil · #6 07-10-2009, 12:47 PM

Thanks for that Brendan. I'll check it. I only have a laser collimator at the moment but plan on buying a cheshire style. May I ask which one you have and if you are happy with it?

Regards

Shane

bmitchell82 (Brendan) · #7 07-10-2009, 01:05 PM

well mine is just a cheapie Skywatcher one and ive learnt how to use it very well. but you can spend any amount you want on them. Though do buy one sooner rather than later as a laser isn't the best unless you have purchased one thats quite expensive aka 200+ range. its always good to check with another tool to cross referance that your collimation is correct. not so important for visual extremely critical for astro photography.

Starkler (Geoff) · #8 07-10-2009, 06:18 PM

The focuser axis being square to the tube isnt absolutely critical. What is important is the focuser axis intersecting the centre axis of the ota. This means your focuser could be tilted toward the top or bottom of the ota and it wouldnt matter at all because you would align the secondary mirror to compensate.

You will know when its correct because the spot of your (perfectly collimated) laser will be hitting the centre of the primary and not moving when you rack the focuser in and out.

bmitchell82 (Brendan) · #9 07-10-2009, 08:07 PM

very interesting as if you look at it if your focuser is tilted enough it will make a big difference, trust me when i say this as i had egg stars on one side of focus and those egg stars rotated 90 degrees on the other side of focus, and i had 3 senior members of ASWA looking at my scope, with a Astrosystems Barlow/laser Autocollminator, and Cheshire ep's all collminating my scope. the laser reterned perfectly to the focuser as did the doghnut of the barlow laser for the primary... the laser prooved useless in detecting this abberation. not that it happens to everybody but something to be aware of when using newts