:( :( :( what's next?

[Starkler (Geoff)]

Originally Posted by GUIDESTAR

Anyway, the sweet spot can be fixed in place at the center of your FOV by using the barlowed laser collimator method. I have one and i can make the collimation adjustments in less than 30 seconds.

What I dont see mentioned often with the barlowed laser is the importance of the secondary alignment. You must use the laser unbarlowed first and point at the exact centre of the primary. Any error here may be doubled at the target after reflecting off the secondary twice.

This will align the optical axis to the focuser axis. The importance of this is that a barlowed laser target is never close to the focal plane, which of course is the place where collimation is most important.

[EzyStyles (Eric)]

so a coma corrector will make this sweet spot bigger? i don't get the barlow laser method. if i move the primary collimation screws, wouldnt that put my collimation off? i tired putting a laser into a barlow, what i can see is just a big red rectangle.

[GUIDESTAR]

Originally Posted by EzyStyles

so a coma corrector will make this sweet spot bigger? i don't get the barlow laser method. if i move the primary collimation screws, wouldnt that put my collimation off? i tired putting a laser into a barlow, what i can see is just a big red rectangle.

The big red rectangle is only half of the collimation process. The next half is getting the shadow of the center spot marker back to the laser source.

Below is detailed description;

http://gmpexpress.net/~tomhole/blaser.pdf

The COMA corrector basically increases the diameter of the "sweet spot". Up to what extent would depend on the quality of the corrector. At some point it may be not enough to cover the CCD size of your camera. Will wait for your test results.



For Starkler:

Yes you are right. Alignment of the secondary is very necessary. This assumes that the magnified "red rectangle" (as Eric would name it) would hit the center marker of the mirror and the return shadow is right on the middle of the laser source.

[EzyStyles (Eric)]

thanks guidestar. i don't thik the barlow laser applies for my laser. My laser already has a primary centering screen but thanks anyway.

btw if you are the software developer for guidestar 1.1, what a remarkable software you have created.

[janoskiss (Steve H)]

Eric, the barlowed laser method will work with any laser that inserts in the focuser. You need a screen (paper sheet) at the end of the barlow, onto which the mirror projects an image of its centre spot. The screen should have a hole in the centre for the laser light to pass through. You align the mirror centre spot's image on the screen with the hole in the screen by adjusting primary mirror collimation screws.

Sorry if I'm not explaining it properly. It's easier to show than describe.

[EzyStyles (Eric)]

yep i sure get it. but the barlow laser way will be similar to looking at the laser light reflecting off the mid hole in the laser?

http://home.earthlink.net/~celstark/...ctures/lcc.jpg

[janoskiss (Steve H)]

There is an important difference which makes the barlowed laser method much more reliable than using the laser on its own:

It is insensitive to misalignment of the laser in its housing, and the housing in the focuser. You can loosen and jiggle around the laser in the focuser and the back-projection of the centre spot will not move. Its position depends only on collimation of the mirrors.

[EzyStyles (Eric)]

true .. hmmm might have to give the barlow laser another go. cheers steve.

Just received my Lumicon coma corrector today as the Vixen one didn't fit. thanks merlin. I have to return the vixen one. here's some shot with it in the camera with the modified t-mount + 2" barrel adapter and the baader uhc-s filter. should the filter be the last thing screwed in or the coma corrector? wil test this out on a clear night .. doesnt look like it is coming till the weekend though

[Striker (Tony)]

Thats fine Eric....I have the filter on the end after my Focal reducer...and when I use my Coma corrector on my 8" schmit/newt it will look the same as yours.
Except for the step down ring.