Telescope Reviews: Testing for collimation

Click here if you are having trouble logging into the forums

Cloudy Nights - Official Forums of the 2009 International Year of Astronomy

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User

You are not logged in. [Login]

Entrance · Main Index · Search · New user · Who's Online
FAQ · Calendar

Equipment Discussions >> Binoculars

Pages: 1 | 2 | (show all)

EdZ
Professor EdZ

Reged: 02/15/02
Posts: 12569
Loc: Cumberland, R I , USA42N71.4W

Re: Testing for collimation new

[Re: Mr. Bill]
#2010210 - 11/26/07 12:58 PM

Quote:

Thanks, Rob

Never saw that one....looks like I'm retreading well worn ground.

The difference I see between my use of the Cheshire and the one mentioned in the Zen thread is that I cover the objectives and thus can examine both the alignments mentioned and also the alignments of the objective lens with respect to each other because of their internal reflections.

These are not seen if the objectives are left uncovered because the light washes out the internal reflection images.

The Cheshire is a very simple and well-known test for checking a refractor. It is especially useful for refractors like the CR150 which has 3 push-pull screws for adjusting the tilt of the objective lens cell. The cheshire is used only to confirm the objective is centered and not tilted. The aperture must be covered, just as you would when testing a refractor. (Barry Simon described this test about 4 years ago.) The Cheshire will show a correlation between a tilted objective, which produces out-of-center disk reflections, and astigmatism.

edz

--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21

Post Extras:

Mr. Bill
Carpal Tunnel

Reged: 02/09/05
Posts: 2759
Loc: Just passing through.....

Re: Testing for collimation new

[Re: Mr. Bill]
#2010458 - 11/26/07 02:57 PM Attachment (32 downloads)

Here's the right barrel....the bright reflection (actually the Venn intersection of two lens reflections) is off center the center dot of the objective reflection (the small circle offset at 12:30).

This barrel shows astigmatism due to wedging (optical axis not coaxial to mechanical axis).

Edited by Mr. Bill (11/26/07 07:51 PM)

Post Extras:

Mr. Bill
Carpal Tunnel

Reged: 02/09/05
Posts: 2759
Loc: Just passing through.....

Re: Testing for collimation [Re: Mr. Bill]
#2010484 - 11/26/07 03:09 PM Attachment (32 downloads)

The left.....notice that the objective reflection(smaller circle at 2 o'clock) has the dark dot almost covered by the brighter internal reflections off the elements; they are almost perfectly stacked. This side shows good extrafocus patterns, in spite of the greater offset of the overall objective reflection from the eyepiece barrel centerline of the big circle (Cheshire ep.)

--------------------
10x50 Fujinon FMT-SX binos
15x70 AP binos + Paragon p-mount
Oberwerk 100BT 45 degree + Hercules fork mount
120mm f/5 Orion achromat + Moonlite focuser
140mm f/5.7 Vixen NeoAchro Petzvel refractor
150mm f/6.5 Antares achromat
150mm f/8 homemade achromat....EE Barnard MW Sweeper
8 inch newt with f/5 Swayze mirror
10 inch f/4.7 Orion newt + Paracorr
15 inch f/5 Discovery split tube
35mm Pan, 26mm Nagler, 17mm Nagler, 13mm Ethos, 8mm Ethos

Member IDA

Edited by Mr. Bill (11/26/07 06:58 PM)

Post Extras:

Pages: 1 | 2 | (show all)

Extra information

9 registered and 19 anonymous users are browsing this forum.

Moderator: EdZ

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled

Thread views: 2189

Jump to

Home

Cloudy Nights Sponsor: Astronomics