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LBN 576 - The Garlic Nebula

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Posts Made By: Alan French

July 6, 2006 02:37 PM Forum: Eyepieces

Barlow vs. high mag EPs

Posted By Alan French
As others have mentioned, the added eye relief of a longer focal length eyepiece is often appreciated. A barlow may actually push the eye relief out a bit farther. A Powermate will not change the eyepiece's eye relief.

There are alternatives to short focal length eyepieces with poor eye relief. The Pentax XLs and their newer XWs, and the TV Radians all feature 20mm of eye relief. Of course, they have a built in "barlow" at the bottom of the barrel - so I guess you are taking the same approach with these, although it is designed as an integral part of the eyepiece, which could be helpful.

Clear skies, Alan

July 6, 2006 11:22 PM Forum: Reflectors

Sky Designs

Posted By Alan French
Darian Rachal said:

I hope I have the name correct, but does anyone remember these Dobsonians? They were crude by today's standards, but a real step up from the Coulter closed tube Dobs. The first one I recall seeing was a 17.5"(?) owned by a vacuum cleaner store owner from Harlington TX, out at TSP, in the early '80s. The diagonal mirror was "glued" to a piece of dowel & adjusted by 6 bolts in a metal "spider of sorts".

Actually, they were very nice looking scopes for their time.

Darian,

Our club owns two 18" Sky Designs. One has been heavily modified and work is in progress on the second. I just got the upper cage assembly for a 15" Sky Designs from a friend today. It needs some work.

One of the biggest drawbacks to the design is the secondary adjustment. The secondary is mounted on a large wooden dowel, which is inside a larger thick walled tube. Screws through the tube go against the dowel for adjustments. Argh!

Clear skies, Alan

July 7, 2006 11:58 PM Forum: Telescope Making

How bad is 1/3 wave mirror?

Posted By Alan French
Robert Apruzese said:

Pretty darn bad.

I wonder. A mirror that is true 1/4 wavefront and nice and smooth actually works fairly well. Perhaps not quite "Pretty darn bad."

Clear skies, Alan


July 18, 2006 04:51 PM Forum: Telescope Making

All wood (almost) 6-inch

Posted By Alan French
Mark,

A lovely job. Do you keep it set up in the house?

Clear skies, Alan

July 18, 2006 06:28 PM Forum: Reflectors

Rain-X on eyepieces

Posted By Alan French
Darrell Hensley said:

Has anyone ever tried the rain-x anti fog on your eyepieces? I'm having trouble viewing for more than 3to4 seconds then fogging up due to such high humidity here in Kentucky.Before I tried it I wanted to check with you folks to see if it would harm the coatings.My arm is about to drop off from fanning it so often,so I bought a battery operated fan but I hate constantly having to stop viewing just to defog my ep's.Any input would be appreciated.Thanx,Darrell Hensley

I sure wouldn't put it on my eyepieces. I think you sound like a candidate for a Kendrick eyepiece heater - something that will warm the eyepiece slightly while not getting in your way like a fan does.

Clear skies, Alan

July 18, 2006 10:18 PM Forum: Refractors

Active cooling of scopes? Impractical?

Posted By Alan French
A refractor is a somewhat different creature. In a Newt the primary is way down in the bottom of the tube where it can not radiate well. In SCTs the mirror is closer to the front, but the tube is sealed.

A refractor objective is up at the top of the tube where it can radiate heat effectively, especially if you leave the dew cap off. I don't really see a need for active cooling.

Clear skies, Alan

July 22, 2006 04:23 AM Forum: Astro-Physics

New Product Announcement

Posted By Alan French
I notice that Anacortes has the 15x70s listed as "call or e-mail for availability." Hmmm.

I am glad mine are on their way.

Clear skies, Alan

August 15, 2006 02:42 AM Forum: Refractors

What are the challenges for making fast APO refrac

Posted By Alan French
I consider a wide field three degrees or better. If you play with the numbers, you'll find you can not get much aperture with such a wide field and get all the available light into your eye. A 150mm f/4 can provide a 4.4 degree field with a 2" 55mm Plossl or a 41mm Panoptic, but either case your eye will act as an aperture stop.

A 27mm Pan would provide a more useable 6.75mm exit pupil, which some folks could fit through their pupil, and would give a field of 2.9 degrees. Most of us older folks would not use the entire aperture.

Clear skies, Alan


September 19, 2006 01:24 AM Forum: CCD Imaging and Processing/Deep Sky

M27

Posted By Alan French
Wonderful!

Clear skies, Alan

October 6, 2006 03:03 PM Forum: Telescope Making

Installing Threaded Inserts

Posted By Alan French
Thanks for all the advice. I do have a drill press, so I will use it.

Clear skies, Alan

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