Collimation Query + Photo

[cybernautic]

Hello

Can someone take a look at this photo below and let me know what I'm doing wrong. I've aligned the secondary mirror using a collimating cap so I can see the three mirror clips. So far so good. Then I insert the Cheshire collimator to try to align the primary mirror.

The thicker straight black lines are the crosshairs on the Cheshire. The thinner ones are the spider vanes which, according to Astrobaby's guide, I should ignore. What bothers me are the two dots in the centre. The circular dot is the mark on the primary mirror. The solid dot is the hole in the Cheshire, right? What doesn't the Cheshire dot line up in the centre of the Cheshire crosshairs? I just don't understand it. Does it mean I need to realign the secondary mirror? I can align the primary so that the two dots overlap, but they're still miles away from the Cheshire crosshairs. I think something's off but I'm not sure what!

Any advice would be appreciated!

[Spec-Chum]

Hi buddy. Your secondary is still out. The crosshairs on the Cheshire collimator should be in the middle of the doughnut on the primary.

Sort that and the primary should be a doddle.

Sent from my Nexus 4 using Tapatalk

[cybernautic]

Hi buddy. Your secondary is still out. The crosshairs on the Cheshire collimator should be in the middle of the doughnut on the primary.

Sort that and the primary should be a doddle.

Sent from my Nexus 4 using Tapatalk

Wow, thanks for the quick reply! Should I align the secondary using the Cheshire then? Or go back to the collimating cap? The colimating cap doesn't have crosshairs so I'm not sure how I can get it aligned unless I use the Cheshire

[Spec-Chum]

If you can see the mirror clips then its roughly in the right position but the tilt is out.

This is corrected by using the three grub screws on the secondary.

Loosen one, tighten 2 until aligned.

Don't worry about the primary until the crosshairs and doughnut align.

Sent from my Nexus 4 using Tapatalk

[Spec-Chum]

Sorry didn't answer your exact question.

Use the Cheshire from this point on. The collimation cap is mainly to get all the primary on view, which you've done.

For the record I don't use a cap at all, only a Cheshire.

Sent from my Nexus 4 using Tapatalk

[cybernautic]

Thank you so much. I'll have another go and report back in half an hour or so

[wookie1965]

Use this site it explains it better and helps because it shows you how to block out all the other mirror images so it is not as confusing, your secondary is out get that centralised first showing a full circle then using the three collimation screws tilt it to show your three mirror clips.

http://www.schlatter.org/Dad/Astronomy/collimate.htm

[bambuko]

What I found confusing at first, was that you can see both the cross-hairs in the cheshire and their reflection in the secondary.

I take it that you are supposed to disregard actual cross-hair and look at their reflection on the secondary?

BTW - if I am not clear in explaining, I will take cybernautic's picture and point at both.

[bambuko]

That's what I mean:

Highlighted in red are actual cross-hairs and in green their reflection in secondary.

[cybernautic]

OK, how does this look as far as the secondary mirror is concerned?

[wookie1965]

That looks better. That is how it is supposed to look. hard part is done now make sure your collimation screws are just tight then as long as you dont bang your tube (OTA) you will not have to adjust this again.

[cybernautic]

OK, this is after I've aligned the primary mirror (photo below). What bothers me is that the silvery circle in the centre isn't aligned within the black circle even though the black dot is aligned with the crosshairs of the Cheshire. How does it look as a basic collimation? (no wonder my sister bought binos instead!)

[wookie1965]

Thats ok there is always a bulge at that side.This page is taken from Moonshane`s notes on collimation as you can see at the top it says the lobe an the right is correct.

[cybernautic]

Thats ok there is always a bulge at that side.This page is taken from Moonshane`s notes on collimation as you can see at the top it says the lobe an the right is correct.

Is that ok even with a relatively slow f6 tube?

[wookie1965]

Yes its perfectly fine. Do a star test next just to check when we have clear skies but that looks perfect from the picture.

[stargazerslivingroom]

Thats ok there is always a bulge at that side.This page is taken from Moonshane`s notes on collimation as you can see at the top it says the lobe an the right is correct.

Could you post a link to these notes, please?...I can't find them.

Thanks

Steve

[wookie1965]

Could you post a link to these notes, please?...I can't find them.

Thanks

Steve

Yes here you go http://stargazerslounge.com/topic/160336-peak-star-party-2013/page-36 post 716

[Jason D]

Yes here you go http://stargazerslounge.com/topic/160336-peak-star-party-2013/page-36 post 716

You can click on the post# (in this case post # 716) at the top right corner of the post then copy the link

http://stargazerslounge.com/topic/160336-peak-star-party-2013/?p=2067463

The above link will take you directly to the post of interest

Jason

[stargazerslivingroom]

Yes here you go http://stargazerslounge.com/topic/160336-peak-star-party-2013/page-36 post 716

Great...Thanks for that. My! That was buried; no wonder I couldn't find it!

Thanks

Steve

[cybernautic]

I did a star test earlier before the full moon drove me inside. It seemed fine. I had a circle of light with a dark hole in the centre and I could just make out the mirror clips.

[wookie1965]

If you just go out of focus you should see concentric rings like this

http://popastro.com/documents/PA_jan-mar2009_p12-13_telescopetopics_startesting.pdf

[Moonshane]

Please note that the schematics are Jason's (used with his generous consent) not mine. It's looking a lot better now.

[wookie1965]

Please note that the schematics are Jason's (used with his generous consent) not mine. It's looking a lot better now.

You say that in your notes don't you.

[cybernautic]

If you just go out of focus you should see concentric rings like this

http://popastro.com/documents/PA_jan-mar2009_p12-13_telescopetopics_startesting.pdf

I thought I should see concentric rings but I don't. I'm seeing something more like this (not my scope):

Should I use it on a brighter star? I tried it on Altair (I think) but with the full moon it was pretty faint.

[wookie1965]

I thought I should see concentric rings but I don't. I'm seeing something more like this (not my scope):

Should I use it on a brighter star? I tried it on Altair (I think) but with the full moon it was pretty faint.

Im not seeing your image just a red circle with a hand in it.