Click here if you are having trouble logging into the forums
Privacy Policy |
Please read our Terms
of Service | Signup and
Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User
Oregon Don
member
Reged: 08/25/09
Posts: 28
Loc: Southern Oregon, USA
|
|
I have the Celestron Skymaster 15x70 binoculars. I haven't used them in quite awhile but looked through them tonight and can't get stars to focus to a nice pinpoint. They flare inside and outside of focus, which I understand is coma. Any way to correct this or is it just a function of inexpensive binoculars.
--------------------
10" Hardin Dob
5" Orion 120 Refractor
Homebuilt 6" Dob
Orion ST80
Celestron 70mm Binos
|
daniel_h
sage
Reged: 03/08/08
Posts: 485
Loc: VIC, Australia
|
|
I understand coma is a newtonian flaw in which the edge stars are blurry - it isn't a problem of a refractor. the skymaster's don't have a great reputation though for sharpness or good quality control. what were the viewing conditions like - what is the focus like during the day?
--------------------
regal 10x42, 10x50ultras, 15x70 ultras, 20x80
Oly e-500, vixen 100/1000 with 0.965"/1.25",
2 old sturdy tripods for the bins (slik & velbon)
zeiss f5.6 refractor/lens (under construction)
|
GlennLeDrew
Pooh-Bah
Reged: 06/18/08
Posts: 1298
Loc: Ottawa, Ontario, Canada
|
|
Coma isn't limited to reflector telescopes. It is a defect found in refractor optics as well, and normally rears its ugly head *off-axis*, if the optic is properly aligned.
If you're seeing an aberrated image on-axis, and it's not attributable to astigmatism in your own eyes, then something is significantly out of alignment in the bino. I've all too often seen cases where, in order to achieve collimation, a bino must have significant tilt introduced into the prism train. This can be the source of your problem. (Not to mention other possible defects to be found in a quickly-produced, inexpensive instrument which can receive only so much attention lavished upon it during the quality control process.)
I have examined several of these Celestron 15X70's, and a couple have been deplorable regarding optic train alignment, *even if well collimated*.
--------------------
Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Home-made Mk II RA bino, using interchangeable objectives and eyepieces
My Gallery
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
|
BillC
on a new path
Reged: 06/04/04
Posts: 2238
Loc: Washington, USA
|
|
COMA in refractors is increased with Shorter ratios (binos are about f/3,5 to f/4.1, with the really big units going to f/6) and increased aperture.
Cheers,
Bill
--------------------
William J. Cook, Chief Opticalman, USNR-Ret.
Founding Editor, Amateur Telescope Making Journal
20-year vet. of Captain's Nautical Supplies, Optics Dept. Mgr.
Optics Machanic, WG11-3306, Ft. Lewis, Tacoma,WA
Yata, Yata, Yata . . .
|
|
13 registered and 9 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: 131
|
|
|
|
|
|
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
[Re: 