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Posts Made By: Bob Polcyn

November 27, 2004 02:16 PM Forum: CCD Imaging and Processing/Solar System

Having trouble posting images

Posted By Bob Polcyn
Hi all --

I've reoriented Wes Higgins' image of Schroter's Valley to match the orientation in Rukl's plate 18 and can't get it posted. This is my first attempt to post an image. The image I'm trying to post is a JPEG -- have to be doing something wrong but can't figure out what. Help!
Thanks.

Bob Polcyn

May 7, 2006 12:54 PM Forum: CCD Imaging and Processing/Deep Sky

Star testing

Posted By Bob Polcyn
Hi all --

I've never been able to get comfortable with star testing my Dob. In a well collimated newtonian scope the defocussed star image is supposed to be a bright central spot surrounded by nicely concentric circles. But the view I see varies big time as my eye moves with respect to the eyepiece. What am I missing? HELP! And thanks.

Bob Polcyn

May 8, 2006 12:26 PM Forum: Equipment Talk

Rifle scopes as finders

Posted By Bob Polcyn
Hi all --

There are a lot of riflescopes out there with low to high price tags. Some have illuminated reticles. Are they practical for astro use?

Bob Polcyn

May 25, 2006 08:49 PM Forum: Deep Sky Observing

Deep sky with binoculars

Posted By Bob Polcyn
Hi all --

I've had a difficult time relating what I see thru my binoculars (16x70's) to sky atlases. I have Sky Atlas 2000.0, Bright Star Atlas 2000.0, The Cambridge Star Atlas and the Edmund Scientific Mag 6 Atlas. With all, the problem is the scale of the images -- too much sky which makes small star fields too cramped to be useful.

For what it's worth, I've just discovered that I can come close to what I see with my binocs using Starry Night Pro by setting star magnititude to7.7 and verticle field size to 4 degrees.

My skies are fairly dark, not great. Anyone who tries this will have to find their own star mag settings.

Has anyone found another technique?

Bob Polcyn

August 11, 2006 04:46 AM Forum: Telescope Making

What size tube for a 6" mirror?

Posted By Bob Polcyn
Hi all --

I'm about to build a scope around a 6" f/6.5 mirror. Are there advantages to 7" or 8" tube diameters which would make one preferable?
Thanks for any help with this.

Bob Polcyn

August 21, 2006 12:52 PM Forum: Telescope Making

What size secondary for a 6" f/6.5?

Posted By Bob Polcyn
Hi again all --

It's decision time for the secondary mirror to be mated with my Mark Harry primary. With a 7.5" diameter tube, a 1" secondary would be an easy match but a .75" secondary is doable with some creative focuser design. Secondary obstructions by diameter would be 16.7% and 12.5% respectively.
The question is, would the smaller secondary bring enough contrast improvement to be worth the extra trouble?
Any help will be appreciated.

Bob Polcyn

December 27, 2006 05:19 AM Forum: Equipment Talk

A 16" f/2 Newtonian?

Posted By Bob Polcyn
Hi all --

I bought a 16" spherical mirror which has a radius of curvature of about 35". It has a 4.25" center hole. I bought it as a tinker project and am wondering what I should expect if I have the mirror ground to a parabola with the same 35" focal length. A 4" secondary would cover the mirror and place focus just about right. I'm guessing that there'd be a lot of edge coma, but how good could I expect image quality to be otherwise?
Or would a Cassegrain approach be more likely to produce decent images? And where would I look for a Cass. secondary?
Funds aren't limitless but I wouldn't mind spending some money and time if there was reasonable prospect for success.
Thoughts/ideas? Thanks for any help.

Bob Polcyn

May 24, 2007 04:31 AM Forum: Astro Binoculars

Nikon 20x120's

Posted By Bob Polcyn
Hi all --

The few Nikon 20x120 binocular reviews I've seen (Cloudy Nights has two) make them sound like a perfect large aperture system if you can get past the price (~ $5,500). Does anyone have experience with them? And where might a used pair be found?

Bob Polcyn

January 25, 2008 07:29 AM Forum: Astro Binoculars

Use of a doubler with binoculars

Posted By Bob Polcyn
Hi all --

Things have been quiet here for a while.
Most binoculars have a fixed single magnification which is fine as far as it goes. But Swarovski sells a 'doubler' which is (I assume) a 2x scope designed to piggy back onto one of the eyepieces of a binocular pair. Does anyone have experience with one of these?
They're a bit long, not to mention expensive and perhaps awkward to use. But are they effective?
Thanks for any response.

Bob Polcyn

May 10, 2009 12:13 PM Forum: Digital SLR AstroPhotography

Finding focus with a Newt

Posted By Bob Polcyn
Hi all -- Finding afocal focus with refractors seems to be fairly straightforward but with Newtonian scopes, not so easy. I don't want to tackle moving the primary mirror forward to achieve focus. The only thing I've found so far is shooting thru a Klee barlow (2.8x) which of course increases the effective focal length of the scope and narrows the field of view. Are there any other solutions for afocal work?
Thanks for any help.

Bob Polcyn

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