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Posts Made By: Alan French

May 23, 2006 07:47 PM Forum: Refractors

Np127 vs Tmb 130 f/6 vs TOA 130

Posted By Alan French
nick tsakoyias said:

And the winner for visual use is in your humble opinion is?

Too close to call. It's probably not worth fretting about too much. Which one has the most features you want?

Clear skies, Alan

May 31, 2006 08:40 PM Forum: Astro Binoculars

Canon 15x50 is battery usage

Posted By Alan French
Have you verified that the IS feature does actually shut itself off?

Clear skies, Alan

June 2, 2006 12:56 PM Forum: Solar System Observing

Projection Solar Viewing

Posted By Alan French
I used to do solar projection with my little 60mm Unitron all the time. It came with a projection screen, but I eventually made one where the screen itself was shaded more effectively.

I always used to eyepieces that came with the Unitron, and never had any problems. A friend of mine did manage to melt a cheap plastic Kellner he used. If you stick with a modest aperture, keep the Sun centered, and avoid very long periods of projection you are probably unlikely to fry an eyepiece - but an inexpensive eyepiece dedicated to the task might not be a bad idea for peace of mind.

At one convention I attended, a gentleman had a rotating screen to project the Sun on. That worked pretty well, but he later gave it up for a well shielded non-rotating screen.

When I used solar projection at public events, I was very careful to stay with the scope all the time, and never left it unattended. Kids can be quick and often do unexpected things (kiss a 35mm Panoptic, for instance).

Clear skies, Alan

June 5, 2006 01:16 PM Forum: Eyepieces

....What is so grand about a NAGLER eyepiece

Posted By Alan French
Berry Nellums said:

"...descent Binoviewer.

Thanks
Berry

For observing while going downhill? wink

Clear skies, Alan

June 8, 2006 01:03 PM Forum: Refractors

How do these compare?..... Roland?

Posted By Alan French
Kurt Endres said:

Mating element aside....How do the FPL-53, FPL-51 and OK-4 Glass types compare?

The Ohara catalog (FPL53 and FPL51).....
http://www.oharacorp.com/swf/catalog.html

The LZOS catalog (OK4).....
http://www.lzos.ru/en/glass_nocolor_cat.htm

Clear skies, Alan

June 8, 2006 10:34 PM Forum: Telescope Making

Glass Transiition phase - Old mirrors/lenses

Posted By Alan French
Russ Swaney said:

Livescience article (http://www.msnbc.msn.com/id/13208990/) talking about new research into the ideal glass transition phase, mentions that "old, handmade windows that over the years have grown thicker at the base, as the molecules have slowly flowed downward due to gravity."

Could this happen to a mirror or lens if left in one positon too long??


If glass flowed even a little, those old Clark objectives would be junk by now instead of commanding $2000/inch or so. Obsidian is a volcanic glass, and there are arrowheads and scrapers made from obsidian that are thousands of years old, and they are still nice and sharp.

Clear skies, Alan

June 12, 2006 04:12 AM Forum: Reflectors

C6

Posted By Alan French
Magnus Ahrling said:

Hi
Iam seriusely considering purchasing a C6.
Anyone in this forum who owns this C6?
If so what do you think of it........
Thanks,
Magnus

Magnus,

Are you asking about the new Celestron 6" SCT, or something else?

Clear skies, Alan

June 18, 2006 03:14 PM Forum: Equipment Talk

Re: Naglers & Schiefspieglers & f/3.5?

Posted By Alan French
John Biretta said:
[SNIP]
Next lets talk about size and weight. Whats your comparison scope? Lets compare apples and apples -- un-obstructed, apochromatic systems for planetary observing. An 8" F20 Schief is about 60 pounds and 68" long. A nice 8" F9 TMB APO refractor is 68 pounds and 65" long. Pretty similar.
[SNIP]

It's not really oranges and oranges. The f/9 APO would be a lot more versatile than an f/20 instrument.

A Schief is an interesting project, but I think there are better choices for most folks. I'd take a 10" f/6 or 7 Newt over an 8" Schief. In my experience, the press about Schiefs has been a bit more enthusiastic than their actual performance seems to warrant (although I continue to watch for them).

Clear skies, Alan

Clear skies, Alan

June 19, 2006 02:56 AM Forum: Telescope Making

Room temp carbon dioxide glass- for real (see link

Posted By Alan French
I got the final ")" included....

http://news.bbc.co.uk/2/hi/science/nature/5083222.stm

Clear skies, Alan

June 19, 2006 02:00 PM Forum: Eyepieces

Re: threats to the validity of eyepiece comparison

Posted By Alan French
I agree with Jon when he writes "eyepieces are just not that big a deal." Most quality eyepieces work just fine on-axis, and the big bucks go into a wider field of view. Of course, the folks selling eyepieces have to convince you they have something "special," so some folks wind up in an endless search for the "perfect" eyepiece.

I agree with Texereau when he wrote "The astronomer's hopes are almost wholly tied to the size and quality of the objective." The eyepiece is far less important, and there isn't a lot to gain here.

With the limited number of clear nights we have here in upstate NY, I am not inclined to devote time to eyepiece comparisons. (Folks are welcome to borrow any eyepiece I am not using to make their own comparisons, however.)

Clear skies, Alan

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