Spider Vains

[johnkirkpatrick]

OK I had my secondary out today and am collimating it.. Following AB guide The spider vains should be of equal length. mine are all at 115mm each. Through the focuser the secondary should be central but through my sight tube its not its to far to one side. I have had it pretty much bang on but the spider vains had to be made to different lengths to achieve this.. I have not started collimating the secondary yet till I have it centred under the focuser.

Do I stick to equal length's or stick to the un-equal lenghts?

[Doc]

Equal lengths I would say.

[johnkirkpatrick]

thats what i thought, but how do i get it central without movung the vains?

[johnkirkpatrick]

If i apply a small amount of force to the whole focuser and flex it slightly then I can get it bang on, let go and it just springs back to being off again

[Doc]

What do you see through your sight tube?

Can you see the whole secondary and your three primary mirror clips?

This is what I would do.

1. keep vanes equal length and place secondary holder into tube and tighten vanes

2. When mirror holder is tighten make sure three little collimation screws are tight and loosen of centre screw a little until mirror becomes loose.

3. Place sight tube or collicap into focuser

4. Move secondary mirror around until you can see all three primary mirror clips and secondary mirror looks circular not oval.

5. Tighten centre screw.

6. Undo the three collimation screws

7. fiddle with the three screws until donut on primary is centered in either collicap or laser.

8. Tighten collimation screws.

9. Recheck if you can see mirror clips, secondary is circular and donut is in right place.

Thats secondary done only primary to do next.

[xboxdevil]

You will need to adjust the three collimation screws on the front of the spider, have a play and you'll see the impact of tightening / loosening them, this will move the mirror reflection that you are looking at left/right/up/down.

[johnkirkpatrick]

thanks guys, I can get all the above. but my main problem is that when looking through the sight tube not looking at the reflections is that i can see the secondary is oval and i can see the 3 mirror clips and the dohnut is central but the secondary is not perfectly central under the focuser. The space between the secondary and the edge of the sight tube is not equal, its to far to one side.

[Jason D]

Check the squareness of your focuser. The alignment relationship between the focuser and the spider vanes is important. If the spider vanes are centered and the focuser is squared then you should have the proper relathioship.

Jason

[spaceboy]

Hi John, Glad to see you've finally made the leap in to collimation Did you have the secondary out because you flocked your tube?

I'll be honest and I hold my hands up if I'm wrong but as long as you have your spiders at equal length and you center inward, outward your secondary then you need not worry. I know what you are experiencing as I have the same with my Explorer 200 and I have had no problems with my views. AB dose mention that some scopes may have an offset on the secondary and I think this is the case here. My star tests are OK and the only thing I have ever had an issue with was that the star test showed that the secondary wasn't square on IE: not round but oval. As long as you can make out the primary clips and your spiders are all equal length along with the diameter of the tube I don't think you will have any problems.

SPACEBOY

[johnkirkpatrick]

Hey SB, no, no flocking yet was just wanting to get the hang of the crazy world of collimation so i took it out and put it back in lol, Well why not? I live in scotland!!! rain rain rain...... oh wait ... and more rain..

Still waiting on flo stocking the flocking paper.

[johnkirkpatrick]

@ Jason.. I dont have a clue how to square the focuser? or even check that it is..

@Doc thanks for the check list very handy..

[xboxdevil]

It's probably a combination of a slight rotational error, and the angle of the secondary mirror. I would loosen the main bolt and the three collimation screws and manually adjust the mirror (angle and rotation) so it looks central then start to tighten things up.

Good luck!

[Jason D]

@ Jason.. I dont have a clue how to square the focuser? or even check that it is.

Squaring the focuser means adjusting the focuser in such a way to ensure:

1- Its axis intersects the OTA axis

2- Its axis is perpendicular to the OTA axis

There are several methods to accomplish the above. Can you google it.

If your focuser does not include adjustment screws, you can shim it.

Jason