Astromart

August 6, 2006 12:55 PM Forum: Telescope Making

Tools Tools Tools

Hi Bill --

Ain't life great! Tools are wonderful.

Bob Polcyn

August 12, 2006 12:51 PM Forum: Telescope Making

What size tube for a 6" mirror?

Thanks to all for responses. I decided to split the difference when I found a source for phenolic tubing which has an ID of 7.512". The source is Red Arrow Hobbies. The tubing has the same wall thickness as Protostar's phenolic offering and telescoping tubing is also available (OD of 7.512"). Red Arrow, by the way sells the tubing for use in the making of amateur rockets.
I'll have to tweak the fits of spider and primary mirror cell -- should be a fun project.

Bob Polcyn

August 21, 2006 08:47 PM Forum: Telescope Making

What size secondary for a 6" f/6.5?

Posted By Bob Polcyn

WOW! Amateurs should have such resources as you guys. And they do! You've given me a lot to think about.

I still don't understand the illumination loss issue though. My eyepieces all reach focus within 15mm of each other, so I don't need a lot of focusser travel. If any of them is focussed, why am I not going to see all of the mirror? I don't doubt the numbers coming out of the sources you've provided, I just don't understand why the losses are there. Could someone recommend a source for info?

Again, thanks.

Bob Polcyn

August 24, 2006 04:16 AM Forum: Telescope Making

What size secondary for a 6" f/6.5?

Posted By Bob Polcyn

Hi again, all --

My internet provider had some big problems which prevented my getting back to this thread until now. I'm really appreciative of all of your responses and have decided to go with a 1" quartz secondary from Protostar (along with a curved spider). I had a great phone chat with a very helpful gentleman at Protostar (never got his name) about this thread and he contributed a new insight to the 'illuminated field' issue. His info is that if a Barlow is used, the formulae which indicate decreasing field illumination with decreasing mirror size aren't as important because of the proximity of the field side of the Barlow to the secondary mirror. He said that it's possible to demonstrate the greatly increased field by looking (no eyepiece) down the focusser with and without the Barlow.

Astronomy is wonderful -- no end to interesting stuff.

Bob Polcyn

August 29, 2006 01:16 PM Forum: CCD Imaging and Processing/Deep Sky

M33 after more data -- It looks like fireworks!!

Posted By Bob Polcyn

Your image is all the more interesting because it includes much more of the outer margins of the galaxy than most images. I just Googled Triangulum Galaxy and most don't go nearly as deep. -- spectacular!

Bob Polcyn

September 22, 2006 12:37 PM Forum: Equipment Talk

How Big Should the Secondary Be?

Posted By Bob Polcyn

Hi all --

Something may be missing in this discussion. During a phone chat with a very knowledgeable person at Protostar I was told that secondary size isn't an issue if a Barlow is part of the optical path. The Barlow greatly expands the view of the primary (this can be verified by looking down the empty focussing tube and then with just a Barlow inserted). This makes me wonder if the same isn't true for widefield eyepieces used without an added Barlow. I haven't tried to check this out.

Bob Polcyn

September 24, 2006 12:44 PM Forum: Deep Sky Observing

Hercules M-13 Question?

Posted By Bob Polcyn

Hi John --

Your son asks good questions. M13 is definitely outside of the galactic plane but is still part of our home galaxy. Most globular clusters are above/below the galactic plane also. Dmitri's link will bring you to a program I recently downloaded and like a lot. The inexpensive program adds a whole new dimension to what we can learn about the location of telescopic objects. -- great stuff.

Bob Polcyn

November 2, 2006 03:42 AM Forum: CCD Imaging and Processing/Deep Sky