Interpretation of collimation pictures

[Corpze]

Hi, I would really like to hear your thoughts of the images I have attached.
The scope is a 10" f4 native and with my reducer it is f3,4 which i think have nothing to do with this really.
The laser collimator is a 2" Hotech with crosshair and it is collimated itself.
The laser dots are well aligned but as you can see on the picture taken through my chesire, it seems that the secondary is not properly aligned.
According to my own thoughts, it is a rotation issue - as the reflection from the primary is well aligned in X -axis (horizontal) but not in Y-axis (vertical)
How much of an impact would this have on the final results through a 3" Corr/red to a atik 460ex with a 17mm diagonal chip?

/BR

[CraigT82]

Are you using a 2" to 1.25" adaptor when putting the Cheshire in? Could be some error introduced by that if so.  I always had trouble getting laser and Cheshire to agree, until I got a howie glatter parallizer and used both laser and Cheshire in that. 

I'm not sure how this would affect images, possibly vignetting at one side of the image?

[Corpze]

37 minutes ago, CraigT82 said:

Are you using a 2" to 1.25" adaptor when putting the Cheshire in? Could be some error introduced by that if so.  I always had trouble getting laser and Cheshire to agree, until I got a howie glatter parallizer and used both laser and Cheshire in that. 

I'm not sure how this would affect images, possibly vignetting at one side of the image?

Yes it is a 1,25" to 2" adapter, but both is using their rubber compression rings, so in theory, it should be dead center.
I Will look into the howie glatter ones!

[Ricochet]

Are you collimating the secondary using your Cheshire first? If you ignore the reflection of the primary and just look at the secondary it is too low. You can raise it using the secondary collimation screws but if the second step of aligning it with the primary takes it back to that same position then I think you need to adjust the spider vane lengths. 

Of course, that assumes that the laser is accurate. I bought a Hotech but found that the self centring was not consistent and I could not get repeatable results with it. These days I just use a Cheshire and collimation cap as the batteries in my cheap laser (for barlowed laser method) need replacing. 

[Corpze]

16 hours ago, Ricochet said:

Are you collimating the secondary using your Cheshire first? If you ignore the reflection of the primary and just look at the secondary it is too low. You can raise it using the secondary collimation screws but if the second step of aligning it with the primary takes it back to that same position then I think you need to adjust the spider vane lengths. 

Of course, that assumes that the laser is accurate. I bought a Hotech but found that the self centring was not consistent and I could not get repeatable results with it. These days I just use a Cheshire and collimation cap as the batteries in my cheap laser (for barlowed laser method) need replacing. 

I have collimated both with the laser and cheshire several times, and each time, after checking with the cheshire, i get rotation error och the secondary (confirmed that it is rotation)
I have now laser cut metal shims to be able to rotate the secondary. (it is the three-legged version from telescope service)

The laser collimator is collimated.

[dweller25]

Good advice from Ricochet 👍

Edited October 10, 2019 by dweller25

[alacant]

Hi

I think it more accurate to use a Cheshire sight tube with cross hairs (CST) for (all of the) collimation, but essential for the position of the secondary. Once the latter is in place, leave it. You can then use your laser to tweak the primary mirror, although even then it's just as quick with the CST.

FWIW, for our 8" f3.9, the CST is the only economical only way we've found to get consistency corner to corner over aps-c 

As always, never forget the collimation misunderstandings.

Cheers and HTH

Edited October 10, 2019 by alacant

[johninderby]

I thought I had the secondary set up properly until I used a TS-Optics Concentre to check it. Then I realised just how poor a Cheshire sight tube and collimation cap were for the initial setting up of a secondary. Looked perfect through the Cheshire but not through the Concentre. If only that tool wasn’t so expensive but it does the job too perfection.

 

Edited October 10, 2019 by johninderby

[CraigT82]

5 hours ago, Corpze said:

22 hours ago, Ricochet said:

Are you collimating the secondary using your Cheshire first? If you ignore the reflection of the primary and just look at the secondary it is too low. You can raise it using the secondary collimation screws but if the second step of aligning it with the primary takes it back to that same position then I think you need to adjust the spider vane lengths. 

Of course, that assumes that the laser is accurate. I bought a Hotech but found that the self centring was not consistent and I could not get repeatable results with it. These days I just use a Cheshire and collimation cap as the batteries in my cheap laser (for barlowed laser method) need replacing. 

I have collimated both with the laser and cheshire several times, and each time, after checking with the cheshire, i get rotation error och the secondary (confirmed that it is rotation)

I used to get the same kind of error on my 200p when using hotech and site tube together. Basically came down to variable clamping by my cheap1.25" adapter I think.  I was certain the the secondary was centred in the tube (by measuring vane lengths) and also with the centreing under the focuser by using the site tube (which may actually have been off due to tilt), however the Hotech never agreed. 

In the end I ditched the hotech and bought both a parallizer and a glatter tublug (which I use with a cheap laser). Now my method is to:

1) use site tube to centre the secondary under focuser and set rotation to show three primary mirror clips evenly. I never use a laser to set the secondary.

2) use tublug with laser to set primary. (The tublug has basically a fancy way of  doing the barlowed laser method)

 Using this method has worked perfectly for my f6 and f7.4 newts. However I appreciate your fast newt will be much more demanding

I guess my main point is that you need to be sure that your two collimation tools are being held in exactly the same way in the focuser.

Hope you get it sorted quickly! 

[johninderby]

After adjusting the secondary with the Concentre the Hotech worked perfectly and I got a perfect textbook star test afterwards. It seems that the Hotech does require a good quality focuser to get good results though.

[Corpze]

Thanks for all input guys

I had a session in my obsy starting over from scratch.

1. measuring the spider vanes, got the secondary holder centered to 1-2/10th of a millimeter.
2. Insert cheshire and got the rotation of the secondary correct, however, i recognized that the focuser was not centered to the secondary (or so i thought) - it turned out that the secondary was not glued to the holder as precise it could be, it was off by a couple of millimeters. I hope that this not will cause any issues (70mm minor axis) 
3. changed the cheshire to the hotech laser collimator and checked everything and indeed the error between the cheshire and laser was much lesser than before.
4. with the laser turned on, i corrected the tilt of the focuser so that the laser beam hit the center mark of my primary.
5. adjust primary to hit the center mark of the laser collimator.

6. repeat cheshire procedure, even more fine tuning of the secondary (because of my adjusted focuser)
7. insert laser collimator and yet again adjust tilt on the focuser tuning in the laser dot to the primary center mark.
8. adjust primary mirror again (we are now in the region of just tenths of millimeters...

9. Put back camera, adjust focus and got it down to 3" fwhm with alot of humid in the air and a primary mirror not even close to ambient temp (looks promising)
10. Clouds rolled in.
11. put a "snus" under my lip and wait out the clouds.
12. found a gap in the clouds, shot apr. 20 images and measured them with ccd... aprox. 2% tilt, just a couple on arc seconds collimation off.

Conclusion - as a newbe on newtonians (have been photographing with APOs for almost ten years) i might have found a workflow that actually gets me somewhere.
And this was done with a diy cheshire (drilled a hole in a 1,25" cap)
I have now ordered a concenter eyepiece.