UVEX Collimation

UVEX Collimation

Postby Tom Love » Mon Dec 02, 2019 4:28 am

I had difficulty collimating my UVEX, but left it for a while because I have been busy collecting data with the Alpy. But now there is a run of bad weather I'm back to trying to sort the UVEX again, in anticipation of decent weather in a week or so. Hopefully.

The problem is that I get a nice spectrum on one side of the slit, but it degrades as it goes to the other side. It's not a camera focus alignment issue (I rotated the camera 180 degrees and found that the image was consistent, nor does it improve as you move past focus). It's not a slit issue (I reinserted the slit rotated 180 degrees, but the image orientation stayed consistent, with the widening at the top).

I have removed and reinstalled both mirrors, which appear to be sitting nicely in their mounts, with the mounts well seated in the printed holders, which in turn are nice and flush against the inside of the case. The grating holder is also flush against the inside of the case, so hopefully everything is nicely lined up in the same plane. Tweaking mirror position doesn't seem to help.

I removed and reinstalled the cylindrical lens.

So I'm not quite sure what is causing the problem. Any ideas very welcome!
Attachments
uvex1.JPG
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Martinborough, New Zealand. Alpy, RC12
Tom Love
 
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Re: UVEX Collimation

Postby Ibrahima » Mon Dec 02, 2019 8:00 am

Dear Tom.

What is the F/D of the telescope you use with your UVEX? Christian explains here http://www.astrosurf.com/buil/UVEX_project/ (section 5.3)
that the size of the sharpness area decreases with the F/D number of the telescope.
Your spectra looks in some aspects like that shown by Christian with a F/5 telescope, except that Christian's spectra is symetric.

I hope this will help you.

Best regards,
Ibrahima.
Ibrahima
 
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Re: UVEX Collimation

Postby Thierry Barbier » Mon Dec 02, 2019 4:28 pm

Dear Tom.

Really weird this picture!

Is the image centered on the camera?
I think of a decentering of one of the mirrors, or the diffraction grating in vertical.

Try to tilt the network a little (a small wedge under the grating position lever) or tilt the second mirror on its support (without forcing).

I have an uvex, and work at F / D 4.5 without any problem. I see very little astigmatism on my images.

Regards,
Thierry
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Re: UVEX Collimation

Postby Christian Buil » Mon Dec 02, 2019 8:07 pm

Dear Tom,

Your problem comes from the inclination of the grating in its support (I agree the Thierry B. message concerning the grating tilt). This is a very classic UVEX problem (the grating holder is too flexible). Try to tilt the base of the grating support with adhesive tape on one edge and on the other edge (0.1 to 0.3 mm thick). You can also act on the back of the grating back surface.

In your situation, it is necessary to slightly scroll down the image so that the maximum finesse lines corresponds to the center of the slit image (see on the UVEX website).

Apart this slight problem, easy to correct, I have the impression that your spectrograph is correctly adjusted.

Can you tell the F/D of your telescope ?

Christian Buil
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Re: UVEX Collimation

Postby Tom Love » Tue Dec 03, 2019 2:57 am

Thanks Thierry and Christian - I will try playing with the grating orientation.

At this stage the setup is on a bench, with the Alpy calibration unit on the front but not attached to a telescope. I will be hanging it off the back of a 12 inch F8 GSO Ritchy Chretien.

Best wishes,

Tom
-------------------------------------------------
Martinborough, New Zealand. Alpy, RC12
Tom Love
 
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Re: UVEX Collimation

Postby Christian Buil » Wed Dec 04, 2019 2:06 am

Thierry, une petit remarque et question à propos de ton commentaire sur l'usage de UVEX à f/4.5.
Il s'agit d'une ouverture assez limite et le spectre de pleine lumière est relativement réduit. Cela dit, ça m'intéresse si tu peux montrer un image ou deux à l'occasion faites dans ces conditions (type de télescope ?), genre spectre du fond de ciel de jour et lampe spectrale d'étalonnage si elle est pleine pupille. Ces questions car je complète un dossier sur UVEX et je cherche des témoignages d'utilisateurs qui l'exploite avec des télescopes bien lumineux.

Christian Buil
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Re: UVEX Collimation

Postby Thierry Barbier » Thu Dec 12, 2019 5:55 pm

Christian, pas un brin de ciel actuellement (l'alsace ça n'aide pas !)
Une image faite à travers le Newton CT8 (200/900) avec lampe à économie d'énergie; Uvex perso équipé de la fente miroir 200/23 (je n'ai gardé que la partie fente 23µ (il doit y avoir un verre à traverser en plus ! :
(Mon capteur est super sale; et pas fait de flat...)

Image
La même en fit ICI

Une autre dans les mêmes conditions avec lampe halogène (grille pain 500W)
Image
La même en fit ICI

And for Tom an image of neon directly from Uvex :
Image
Thierry Barbier
 
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