An Aid to Star-Collimation for a SCT.....FireCapture

[Craney]

Apologies if this is common knowledge to the cognoscenti, but I discovered it by accident last night and it was very useful, and I thought I would share.

Collimation...... oh I wish it was not an issue......but it is something that you really cannot avoid !  

Even if you think that your optical system is rock solid and will never shift... you still have to check  it to make sure.   

The general consensus is that no matter how you twiddle and tweak the adjustment screws in tandem with laser guided wizardry,  the ultimate test is to line up a bright star and slightly de-focus.  You should get something like this.......

Well....easier said than done when the star is wobbling about all over  the place. 

Large scale adjustments are easy to perform and their effect show up very easily in the image.  Alas, when the optical system gets ever nearer to perfect collimation , it becomes much more difficult to assess any slight skewing of that dark center circle from parallel concentric heaven.  

I have been trying to improve my planetary imaging recently with my C8_EdgeHD as the poor results I have been achieving cannot be solely down to the low altitude of the planets.

I was using FireCapture last night and as a consequence found a very useful tool to help collimation.

Firecapture has a feature called 'Auto_Align'  which tries to hold a wobbly and shifting planet in the centre of the FOV by image processing. ( it doesn't  control the mount  like auto-guiding).

I tried this on my de-focused star and found that it locked the image securely on the screen. ( I suppose it does look very similar to a round planet). 

Subtleties in the position of the central circle became much more apparent, and led to a loop of ever finer tweeking.

 

 

 

The image on the left shows a slight offset to the right, which was very difficult to spot without the 'align' feature.  The one on the right follows an adjustment and is slightly improved.   

The two dots are part of the alignment feature display.

An added bonus is the recticule is circular as well, which you can use to make sure everything is central by de-focusing the star just enough to touch the edges.

(Use the keys <ctrl-Left Mouse button> to move the recticule about the screen.... easier than moving the star !!!)

Well all in all it made the process a whole lot less painful.... I will not say "enjoyable".

I hope this helps.

Sean.

Edited August 10, 2020 by Craney

[michael.h.f.wilkinson]

HAdn't seen that feature in FireCapture, will certainly give it a spin

[Craney]

These are the two specific tick boxes to 'check'.