5 replies to this topic

[lsintampa]

This is my first run at collimation of Mt RC6 using a laser collimator.

 

Did a bench alignment then some star test tweaks.

 

Here is my last test shot.

 

Is it out of focus enough?  Any other notes?

 

I still get a bit of vignetting and egg shaped stars so I know it's not correct yet.

 

 

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[Tapio]

I believe it's too much out focused. And it's not concentric.

Is it a center star in field.

Vignetting is normal (which flats will take care of), and egg shaped stars - do they show in short exposure (like 5s) and are they overall in frame or just corners ?

[lsintampa]

I believe it's too much out focused. And it's not concentric.

Is it a center star in field.

Vignetting is normal (which flats will take care of), and egg shaped stars - do they show in short exposure (like 5s) and are they overall in frame or just corners ?

It is the star Elnath and zoomed way in.

 

The star test was only a 2 second exposure, and there were no other stars in the FOV.

 

My target images where I see egg shaped stars (after tweaking the secondary, are all the same all over the frame.  They all are pointing in the same direction (the tip of the egg shape being the pointer) regardless of where they are in the frame.  I was doing 30 second exposures and my guiding was like average of around .6 total rms.

[WadeH237]

The star is far too out of focus to really evaluate collimation.  If you get much closer to focus, I assume that it'll will become obvious that the 10 o'clock position will be brighter than the 4 o'clock position.  Note that as the star gets closer to focus, it will likely saturate.  You will probably need to either shorten the exposure length or pick a dimmer star.  In my opinion, just about any naked eye star will be too bright to finish collimation.  When I collimate with a camera, I am usually using stars at magnitude 9 or 10.

 

Also, the center spot is not a star.  It's a part of the diffraction pattern called a "Poisson Spot", and it is normal.

[Spaceman 56]

In my opinion, just about any naked eye star will be too bright to finish collimation.  When I collimate with a camera, I am usually using stars at magnitude 9 or 10.

thanks for this info Wade.  

 

Is this dependant on the F Ratio of the scope, or do you think its application is more general ?

[WadeH237]

Is this dependant on the F Ratio of the scope, or do you think its application is more general ?

It's not a hard and fast rule or anything.

 

The important point is that you pick a star that is not close to saturation, even in perfect focus.  It just turns out that I usually end up on a mag 9 or 10 star.  I don't do anything to choose a star of a specific magnitude.