Sorry, I meant M 13 (I must have been in a gun mode with the m16 reference). -----Original Message----- From: Ann Blanchard Sent: Tuesday, April 08, 2008 10:43 AM To: 'Utah Astronomy' Subject: RE: [Utah-astronomy] Comet Boattini Great, thanks, I'll await your information. We have a Celestron CPC 11. The binoviewer I looked through I believe belonged to someone named Fisher? at the Gravel Quarry with his large Obsession scope, looking at M 16. It was so beautiful, it was almost like swimming in the stars! -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Tuesday, April 08, 2008 10:30 AM To: Utah Astronomy Subject: Re: [Utah-astronomy] Comet Boattini Hi Ann, thanks for the good wishes, it's good to be back on my hobby lists and good to hear from you. It's been a hectic winter. Still under the weather but back at work part-time, a little more each day. I haven't had a chance to use my bino-viewer yet. Like binoculars, it appears that many of the lower-cost units are all made by the same Chinese factory and then branded for retail sale, so one is likely as good as another unless spending thousands. Once I try it out, I'll let you know how it works and who's model it is. Hopefully soon. I can say that even for a "budget" unit, the fit and finish is very good. Years ago, a friend bought one and it quickly became apparent that the telescope you use the viewer with is just as important as the viewer itself. They require a lot of back-focus (or "In" travel), mine needs 4 inches (100mm), or 2" with an included Barlow lens that is used as a relay lens. 4" of back-focus is typically not achieveable on a fast Dob/Newt unless built into the design, and even if it is, significant vignetting will result. It takes a narrow-angle light cone to get all the way through a bino-viewer without vignetting and f/4 or f/5 probably won't make it unvignetted. Since the total throughput of the telescope is halved for each eyepiece in the bino-viewer, the larger the aperture, the better. No bino-viewer seller recommends them for deep-sky use because of this. Most advise using them for lunar, solar (with proper filtration), and planetary use, and some for the brighter DSO only. Telescopes such as the Ealing and 32" at SPOC are ideal for bino-viewers, since there is more than enough back-focus without having to resort to the Barlow transfer lens (which doubles the magnification and further cuts brightness by a factor of 4), as well as oodles of aperture. Even the Andy scope is probably large enough for good results with a bino-viewer. All three have long f-ratios that are ideal for unvignetted throughput with a bino-viewer. Larger Schmidt-Cass scopes (8" and up) are good candidates for use with a bino-viewer. Plenty of aperture, lots of back-focus, and a narrow (f/10) light cone. Long-focus, large-ish refractors as well, say 6" and up, and not much faster than f/8, as an estimate. That's not to say that you won't be able to coax an image from a bino-viewer with other types of telescope, but the view may not be optimal. Also, Patrick has pointed out that they are not the best for group viewing, like regular binoculars, due to individual variations in interpupilary distance and differential focus between left and right eyes. Too much fussing between each and every viewer. The bino-viewer is probably best kept in the accessory case during public star-parties. That's about all I can give you now, but as soon as I've had a chance to use it under the stars, I'll let you know my impressions with this particular unit. On Tue, Apr 8, 2008 at 8:11 AM, Ann Blanchard <a.blanchard@ugs.utah.edu> wrote: Hi Chuck, Just wanted to say I'm so glad you're back on the list and hopefully feeling better! If you have time, can you let us know what kind of bino viewers you bought and if you've had a chance to try them yet? I've seen in past NOVAs several binocular reviews you did, besides talks at some SLAS meetings--any opinions on what are the better bino viewers or what to avoid? Thanks! _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com