A quick question on collimation

[woodmeister]

I decided to recently check all parts to see if my telescope was correctly collimated. Spider vanes are equal, secondary looks centred and round ect. My Cheshire crosshairs line up with the primary center spot and the peep hole from the Cheshire.

However I noticed that all 3 mirror clips are not all equally in view. One protrudes out more than the other. Is this wrong and will it affect my views?

[Floater]

I'm far from being an expert but, in lieu of responses from those who are, what scope do you have?

My understanding is that some scopes are more forgiving than others.

You will get a definitive answer, I'm sure.

[Charic]

...........a slight tweak may be in order. First I would align to Polaris and de-focus, checking the accuracy of the rings formed in the Airy disk. If their concentric, I`d leave the mirror clips alone. As Floater requests, what telescope? My 8" (the clips are all visible). But if the Airy rings are concentric, just ignore the clips and enjoy the views.

[Charic]

And just checking is always the best way, rather than just diving in.

[woodmeister]

I own a 8 inch skywatcher skyliner dob f/6. When I put the star fairly out of focus the shadow looks centred and the rings look fine. If I just throw it ever so slightly out of focus it looks slightly off to me but that might be me thinking it is when it is really small. I can see all the mirror clips at first but when I rack the focuser out the one closest to the mirror disappears first. The airy disc is the rings that appear around a focused star right?

Only other point is that on the other side of focus does not look the same which I think is spherical abberation but that would be for a different post.

[Charic]

...........is there anything here that may help. http://www.backyardastronomy.com/Backyard_Astronomy/Downloads_files/Appendix%20A-Testing.pdf

Note its word of warning. The Star test is sensitive. 

[stepping beyond]

You're secondary should be just off center to allow the correct angle for reflecting back  to the focus tube.. There plenty of videos on youtube on this subject.

[jetstream]

Racking the focuser out should not cause the image to change, this may indicate focuser alignment issues. Try collimating with the focuser at the same height as the EP's need- to minimize the effect.

[woodmeister]

...........is there anything here that may help. http://www.backyardastronomy.com/Backyard_Astronomy/Downloads_files/Appendix%20A-Testing.pdf

Note its word of warning. The Star test is sensitive. 

Lol I have that book. My star seems to look fine when It is defocused to 5 waves, the secondary looks to be in the centre of the star though the atmosphere always sucks. the edges of the airy disc seem broken in places.

 When viewing through my Cheshire the secondary looks like it points slightly off toward the primary so that sounds good.

Just to note about the spider vanes. The spider vanes opposite each other are of equal length, but all the spider vanes are not equal.

[WaveSoarer]

The alignment sounds good to me.  The clips on my 200p aren't fully symmetric on the mirror and they aren't a good indicator for the alignment of the secondary. If you have a Cheshire then you don't need to use the clips anyway. With my scope I can't get the focuser in far enough to see the clips with the Cheshire in place and I would need a colly cap for that. You can do everythiing you need with the cheshire so don't worry about the clips.

[Moonshane]

It sounds like your secondary is not central in the drawtube. Personally I would start the process again from stage 1 - ensure the secondary is round and central in the drawtube / end of the cheshire. These threads may help

http://stargazerslounge.com/topic/197640-collimation-and-star-hopping/

http://stargazerslounge.com/topic/186348-collimation-tip/

[woodmeister]

Cheers for the links. I will have another look at the end of the week.

[woodmeister]

I collimated today and put the scope outside so I could try check if my efforts paid off. blumming clouds roll in so I can't check. This hobby sometimes .

Does it matter that my spider vanes are not all equal? both opposites are the same length but there is a 1mm difference between the 2 sets.

[jetstream]

I wouldn't think so as long as the sec looks round and is centered under the focuser.

[nicoscy]

I collimated today and put the scope outside so I could try check if my efforts paid off. blumming clouds roll in so I can't check. This hobby sometimes .

Does it matter that my spider vanes are not all equal? both opposites are the same length but there is a 1mm difference between the 2 sets.

As long as the secondary is equidistant from the OTA then you are ok. Use a ruler for this. Also, another tip to help you see what is going on with the secondary, is to get a white A4 piece of paper and stick it in the OTA opposite the focuser. It will make use of the Cheshire easier.

[woodmeister]

Yeah I use a yellow piece of card to cover the primary and blue opposite the focuser to help increase contrast between the secondary and the edges.

I use a home made colicap to check the centering of the secondary and rack the focuser out to roughly where my 7mm gets focus to check. Then I slide in the Cheshire to check if the primary centre spot is in the middle of the crosshairs by adjusting the secondary. Then I line up the peep hole of the Cheshire in the middle of the primary by using the primary.

Just making sure I do nothing wrong.

[nicoscy]

This covers collimation with a Cheshire pretty well:

http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

I stopped using a Cheshire once I switched to Howie Glatter Laser and Tublug. Much faster and the results always agree with the Cheshire...

[woodmeister]

It just dawned on me that I might have not been able to get all my spider lengths the same as I might have over tightened on 1 axis and pulled it in on itself. And not slackened off enough when I readjusted to let the open end unwarp. I best get the tape measure out and check if it is round.