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Have success in the collimation of your telescope !

Chapter 1 : Easy Collimation :))
Chapter 2 : Have success in your collimation "final phase"
Chapter 3 : Collimation with an artificial star (1)
Chapter 4 : Collimation with an artificial star, inside, outside
(inspired from Texereau)
Chapter 5 : Good Collimation with Astrosnap !

Chapter 1 : Easy Collimation with a camera or a webcam :))
as it is often difficult to be at the same time in front and behind one's telescope :))


(many surveillance cameras have a large sensor which facilitates the work especially at the begining when the optics are far from good collimation)

First rules :

use the same optical line than when you are observing
and wotk with a star not far from the object you want to catch
and above all wait until the telescope has reached thermal equilibrium !
Also if possible go to a location where seing is nice (avoid towns or at least prefer large lawns in front of the scope)

Here, our starting point (focal length is 7.5m !) as seen on the video monitor
using a low magnitude star (bright) as Vega, Altair...
This shows when out of focus.
It is easy to see that optics are not aligned !
Do not take care of the dust donuts, they don't interfere

This shows at best focus ...

A large sensor B&W surveillance camera is place after a 3x barlow behind the 10" LX200
No mirrors are interposed, they would make akward the movements description below !

For the work use the proper Alen with some white tape on it to find it better in the dark if fallen. Also you will see it better if you replace the cover at any moment, forgetting about it.
The first step is to verify that all screws are slightly tighten. If not do it otherwise the secondary miror would float around to much rendering collimation ephemerous !

Here is the disposition to adopt in order to succeed with the explanations below.
Place some white electric tape on the same radius as screw #1 where is the Alen wrench.
This screw by default will only affect vertical moves of the center of the star on the monitor.
The two others (#2, #3) will affect mainly horizontal movements + a bit of vertical movements.

Now at the rear of the scope, adjust visually the top plate of the camera
with the white tape put at the opening of the scope.

TAKE CARE : DANGER !
You must turn the screws only by a small amount (fraction of degree). On many scopes unscrewing to much will liberate the secondary mirrors which can then destroy the primary mirror when falling on it. REMEMBER : You do this collimation at your own risks only ! Please read beforehand your telescope instruction manual !

Here are the main movements generated on the monitor when adjusting screws #1, #2, #3

In order not to loose the star picture and also to improve collimation,
it is very important to recenter the star image
after each consequent turn of the wrench !!


Indeed the figure may look later uncollimated even if it is nicely collimated !

Above what will happen (small vertical moves generated by the #2 & #3 screw not shown)
on the monitor when acting on the screws.
For this setup, after personnal trials, I recommend using a magnification of
1 x diameter of instrument in mm.

Print this chart full page to post it aside the scope !

IMPORTANT NOTES:

2) when you get nearer from good collimation, you must "allmost not" turn the screws anymore :)
See this reference page : http://legault.club.fr/collim.html

3) Remember that the movements done to screws #2 & #3 generate some vertical movement easily corrected by turning screw #1 afterwards.

After a few min of work, reduce the size of the star image by focusing better and redo previuos steps. You should also diminish exposure in order not to saturate the screen (or choose another smaller star).

This is the aspect now with a higher mag star. At the eyepiece it is possible to see the Airy disk.
It is possible to go further only if the seing is good ! You would do the same procedure but now often at the eyepiece.

TAKE CARE : DANGER !
You must turn the screws only by a small amount (fraction of degree). On many scopes unscrewing to much will liberate the secondary mirrors which can then destroy the primary mirror when falling on it. REMEMBER : You do this collimation at your own risks only ! Please read beforehand your telescope instruction manual !

                                                  

Above what will happen (small vertical moves generated by the #2 & #3 screw not shown)
on the monitor when acting on the screws looking in the eyepiece !.
For this setup, after personnal trials, I recommend using a magnification of
1 x diameter of instrument in mm.
But when working inside the Airy disk use about 5 x diameter of instrument in mm (eg. 6mm eyepiece + 3x barlow for a 10" SCT).

Above : Aspect of circles near end of phase 2 collimation ...

Left near focus, right far from focus

Attention, this is not the Airy figure ! It appears only when perfectly focused by good seing !

Chapter 2 : final phase with the camera

Those Airy disk images are real ones ! They are taken with my 10" SCT Meade LX200 and show Vega.
An unmodified Vesta Pro (10fps, luminosity 100 and low gain) + a 3x Televue barlow have been used.

The 3 rather nice images of the central row (the only ones on the 1206 frames of a 2 min AVI)
are in good agreement with a level 3 collimation according to Thierry Legault
(see
http://perso.club-internet.fr/legault/collim.html )

On the contrary the thousand other images show important deformations
This explains why it is difficult to succeed at the eyepiece
!

My suggestion is then for T>125mm :


Step 1 : do the best collimation you can by eye using a barlow...
Step 2 : Make a 1 minute AVI of the Airy disk and look at it frame by frame (in VirtualDub)
or try to select the best frames as for a registration with Registax to see
what quality has been achieved when seeing is good for an instant
!

Also the % of rather good images (here about 5%) is a good indication of seeing !

 

 

Here is the result of the combination of the 13 best images with Registax.

.... to be translated later ....

Chapitre 3 : Easy collimation with artificial star
(Here methode 1... new one chapter 4)

LED garden bulb

Vesta eyepiece glued with hot glue and aluminium paper cap with a very small hole done with a needle.
Put some tape on batteries contacts when no more in use (execp if you recharge with sunlight !)
.

The DIY artificial star

It is very bright

You need to put the scope at about 15m

quality check : 80mm refractor, 6mm eyepice, the artificial star in in the round blue circle

What you get ...

QV Casio on tripod dehind the eyepiece

Chapter 4 : Easy collimation with Texereau inspired artificial star

The scope is placed near a very bright torch (could also be a small laser)

A stainless steel polished marble of 5-15mm is placed at about 20m and in the dark. During the day, put the marble inside a long carboard tube.

Very nice diffraction images are obtained

Here a short movie

 

If the bulb is very powerful don't play to long (joke !)

 

 

Chapter 5 : A good simple fast collimation
here with free version of Astrosnap

Center a star, use software guiding with limit detection and set the size

The red dot must stay staistically at the center of the unfocused star otherwise do some minor corrections

Also try to superimpose the image coming from the webcam with this software of Gilbert Grillot :
Mire de Collimation
( ask for it)

New : Collimation verification with Astrosnap and DMK21AF04.AS

Settings :

Telescope : TSC LX200 12", Televue 3x barlow, cooled for more than 7 hours
Astrosnap : Soft tracking activated (Axis sum), Zone 230 pixels, Minimal level detaction 140, Integration 10frm loop, 6 level Wavelet filters (-2000 424 2727)
camera : 640*480, refresh rate 3.75ms, 30.6ms exposure, 1023 gain, gamma 20, logarithm 155
Collimation sight adjusted

latest software available : Al's Collimation Aid !

Screencapture

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