Star test with eye piece???

[IanL]

Collimation

Which eye piece to do a star test with?
Reckon it’s better to do a collimation star test with a high power eye piece.
Say some like a 12mm rather than a 20mm.

Ian

[davidpretorius]

I always use my 5mm LV vixen......it has the best glass in it......... a radian would be better of course.

[IanL]

Cool Dave I'll dig out the 3 or 5 mm radian.
Just to awaite clear sky's
Cheers
Ian

[davidpretorius]

Originally Posted by Ian Law

I'll dig out the 3 or 5 mm radian.

http://legault.club.fr/collim.html

this is a great read for when you are ready for star test.

I started with 6mm series 500's then bought a 5mm LV vixen from asimov and was amazed at the improvement in diffraction rings and then in june 2007, i got to look through a 6mm radian and by habit focussed in and out and my jaw dropped at the quality of the diffracition rings during focussing.

Iwould have said I originally got a 100% improvement over the cheap series 500, then another 100% improvement with the borrowed radian.

[ausastronomer (John Bambury)]

Hi Ian,

If you are just trying to defocus for the purposes of checking the scopes collimation, anything over 10X per inch of aperture is more than enough. If you try to go too high under poor seeing conditions the fressnel rings just go to mush and you defeat the purpose of what you are trying to do. When you defocus for the purposes of checking collimation it is important to go both inside and outside focus and check for consistency on both sides of focus.

When you are star testing the telescope for the purpose of evaluating the quality of the optics, you should use much higher power. Something in the order of 25X per inch of aperture is appropriate. Importantly, you need superb seeing conditions, a properly cooled telescope and a good quality eyepiece to star test it for optical quality.

Cheers,
John B

[IanL]

David / John

Thanks for the reply.

I use a Tak mewlon 180 and have installed Bob Knobs on the front of it to replace the Allen screws and awaitng some clear nights to collimate it and test.

By the looks of the weather here in Brisbane it might be a while yet.

http://mirror.bom.gov.au/products/IDR503.shtml

Many thanks
Ian