star testing collimation

[planetdnb]

hi all,

have been playing around with collimation recently. I can get it pretty spot on with the Cheshire collimator but star tests are proving to be an issue. I have tried on a handful of occasions in differing conditions but always seem to suffer atmospherics. I always aim high up in the sky and allow plenty of cool down time but I get a hazy moving glow round the outer ring when out of focus.

is this normal?

[Beulah]

Yes it is.

I have star tested nearly every time I've observed; and only had one occasion where airy rings were present - just barely....

Our British skies are often too turbulent.

[perrin6]

but I get a hazy moving glow round the outer ring when out of focus.

is this normal?

If the outside of the image is 'woolier' inside focus than outside it, the mirror has a turned-down edge (like mine)

Alan

[Doc]

I don't think I've ever seen rings in my 16", I'm beginning to think they don't exist

[planetdnb]

thanks for the info guys, just to be sure we are talking about the same thing I found an image online that looks similar to what i see

Its the top row that best represents what I see. This outer woollyness appears to move around in hazy like motion.

Thanks

[planetdnb]

lol. thinking about it that image just confirms to me that I am seeing the effects of turbulence!

So we are not blessed with good enough atmospherics to perform star tests in this country!

[callisto]

Can't remember when my star test showed an image like the bottom one, Well not in the U.K. anyway LOL.

[planetdnb]

thanks. i will give up on the star tests and just trust in my collimation eye piece!

[Perryellis]

The top set of images are very similar to what I get. what I notice as well, is that when you de-focus very slowly the rings look like they suddenly catch fire...I was quite impressed with that actually!