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Posts Made By: Dick Jacobson

May 21, 2010 06:28 AM Forum: Equipment Talk

What's it called?

Posted By Dick Jacobson

I suggest you browse the McMaster-Carr ( web site, they have pictures and names for all sorts of obscure mechanical components.

October 5, 2010 06:08 AM Forum: Reflectors

Periscopes on Newtonians eliminate ladders

Posted By Dick Jacobson

I replaced the prism diagonal at the top of the periscope with a mirror. This eliminated most of the false color. There is still a small trace of color visible. This could either be from the telephoto at the top or the refractor at the bottom. My guess is that it's the telephoto, which is more than 30 years old and was probably built before low dispersion glass was available. I plan to replace it with a larger and newer one.

November 26, 2010 06:24 AM Forum: Telescope Making

My custom build 14" Sphere Dobson

Posted By Dick Jacobson

Very nice work, but from the picture it appears that the scope cannot reach the horizon. What is the lower limit altitude angle? I would think you would need more than a half-sphere to reach the horizon.

February 13, 2011 07:47 AM Forum: Binoviewers

19mm or 24mm panoptics?

Posted By Dick Jacobson

I bought 24mm Panoptics because their field of view (aperture stop) almost exactly matches the binoviewer, so you get the widest possible field. I'm very happy with them. Haven't tried 19mm so can't tell you how they compare.

May 5, 2011 06:34 AM Forum: Equipment Talk

Re: Comparison of 2" diagonals

Posted By Dick Jacobson

Prism diagonals can add false color in fast optical systems. I don't know exactly where to draw the line but I saw obvious color on bright objects when I used a prism in a f/4.5 telescope, although it was still usable.

June 4, 2011 10:00 AM Forum: ASTRONOMY

New Supernova in M51

Posted By Dick Jacobson

I believe it had faded to 14.5 or less by Friday night. I was at a star party with mediocre transparency and seeing. I saw it at least half the time in my 20", couldn't see it in a 12.5 but some others said they saw it. It was easy to see in a 30".

August 27, 2011 08:37 AM Forum: After Dark

Comet C/2009 P1 Garradd and M71

Posted By Dick Jacobson

I did observe the comet and M71 in the same field (about 1/2 degree apart). A gorgeous sight, the two objects about equal in brightness.

September 2, 2011 05:56 AM Forum: Eyepieces

ES 120 degree fov eyepiece coming out

Posted By Dick Jacobson

Amazing! Where will it all end? A glass dome that shows you a 360 degree field if you climb inside?

I think the manufacturers have gone beyond practical limits in terms of size, weight, and price. On the other hand, this would go very nicely with my new 100-degree 14mm...

September 12, 2011 06:02 AM Forum: Mounts


Posted By Dick Jacobson

It depends on the type of telescope and mount. If you have a Newtonian on a German equatorial mount, a tripod sometimes creates problems because the lower part of the tube tends to bump into the tripod legs. Otherwise, a good sturdy tripod with wide legs is a good choice and probably somewhat easier to transport than a pier.

January 12, 2012 05:53 AM Forum: Equipment Talk

C14 binoscope project

Posted By Dick Jacobson

Pardon me for being negative, but why not a 20" and a binoviewer? Same light gathering power and much simpler. The only real advantage I can see to a binoscope is at low magnifications where you can get a wider field of view without exceeding the maximum exit pupil.

I would love to have a 14" binoscope but can't justify the money to buy one or the time to build one. Good luck, it should be a fascinating project!