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Posts Made By: Demetrios Papadopoulos

October 10, 2005 11:33 PM Forum: Equipment Talk

Damaged Optics - need help please

Posted By Demetrios Papadopoulos

I had a mishap with my Hardin 10" dobsonian. This has a Swayze refigured primary and protostar secondary.

While readjusting the secondary, I dropped the holder with secondary onto the primary! The secondary is not visibly damaged. The primary has 4 superficial scratches into the coatings, the largest of which is ap. 3mm x 6mm.

After the mishap, the star images are not pin point and have a small lateral flare when focused. With out focus in one direction the stars are tear shaped. With out focus in the other direction the stars have a concave, tangential line on the opposite side from the tear shape. I wondered if somehow the optics were pinched, and checked the primary mirror cell to ensure there was no pressure on the mirror.

Is the primary irreversibly damaged? Could the secondary be damaged also?

Thanks in advanced for your expertise.

I certainly have already learned a valuable lesson from this embarassing event. CAUTION, CAUTION, CAUTION WITH UNATTACHED OBJECTS ABOVE THE PRIMARY!!!

Demetrios


November 6, 2005 07:00 PM Forum: Equipment Talk

FOLLOWUP- Damaged Optics Need Assistance

Posted By Demetrios Papadopoulos

Last month I posted a thread related to accidentally dropping my secondary mirror and holder onto a Swayze 10" primary. Several of you gave me thoughtful comments and advice which were much appreciated. We considered collimation problems, damaged optics, etc.

Initially the mirrors did not appear damaged. Specifically, the secondary had no obvious scratches or cracks on the front and side.

Yesterday I removed the secondary from its holder where it was attached by silicone. Lo and behold the backside of the secondary revealed a large crack including ap. 1/4 of the mirror surface!

I learned two lessons from this mishap: 1) Always be careful with loose optics, and 2) Damaged optics can be tricky to diagnose.


May 25, 2008 01:44 PM Forum: Birding Optics and Photos

Spotting Scope Recommendations?

Posted By Demetrios Papadopoulos

I'm looking into spotting scopes for birding and other terrestrial viewing. I like the Pentax PF-80ED-A. It comes with a zoom eyepiece and will also be compatible with the Pentax XW eyepieces. Is it light enough for walking around out in the field? Is the angled eyepiece the way to go for more comfort? Are they any good at all for Astronomy with the Pentax eyepieces?

What about a good lightweight tripod?

Any commments or recommended alternatives will be appreciated.

Thanks,

Demetrios

January 24, 2005 02:35 AM Forum: Telescope Making

kydex-like plastic??

Posted By Demetrios Papadopoulos

I am at the same stage of building a 16" Dob, and I have the same problem. I am in the process of gluing 3 sheets of wood veneer together using contact cement. Then I plan to coat the inner and outer surfaces with polyester fiberglass resin to give it more strength. I then plan to line it with McMaster-Carr's black felt with adhesive backing. I hope it all works. I've used the black flocking material with superior results on another telescope.

Demetrios

September 5, 2005 05:08 PM Forum: Equipment Talk

Dew on primary-help please

Posted By Demetrios Papadopoulos

Tom,

Do you use a shroud? They absorb a lot of the dew. I've had 3 truss tube dobs and the primary has rarely been a problem. It's always the secondary and finders that dew up for me.

Demetrios

September 9, 2005 12:59 AM Forum: Reflectors

Bausch & Lomb Criterion 4000 - Advice?

Posted By Demetrios Papadopoulos

Steve,

I own one. I think you can get a much better quality telescope in a reflector on Astromart.

Demetrios

January 28, 2006 10:24 PM Forum: Telescope Making

Question about Hastings tubing

Posted By Demetrios Papadopoulos

Mike,

My Hastings 12" diameter tube has the roll going inward 1/2", making that end of the tube 11" in diameter.

Demetrios

April 28, 2006 06:55 PM Forum: Equipment Talk

Another fan module system for the Hardin

Posted By Demetrios Papadopoulos

Do these suck air down the tube, or blow air onto the mirror? What size mirror? It looks like a nice system.

Demetrios

January 20, 2007 08:41 PM Forum: Refractors

127ED Focuser Review

Posted By Demetrios Papadopoulos

Floyd, your review is very nice about the focuser.

I have always been displeased with the Meade stock focuser on this telescope with excellent optics. I tried the Cortolano two speed adapter and even the JMI motofocuser and did not like them either. The Moonlight looks beautiful but is too pricey for me. But I did use a Moonlight on my home built 16" reflector and am very pleased with it.

I ordered the Wyorock for my 127ED immediately after you had received yours before the review. I am looking forward to a nice focuser for a very good telescope.

Demetrios

May 23, 2008 12:07 AM Forum: Equipment Talk

Lightest Right-Angle Finder?

Posted By Demetrios Papadopoulos

I have been using a 6x30 raci finder from orion. It has been very useful with my 12.5 Portaball which needs lightweight stuff near the eyepiece. The field of view has been very acceptable to find most anything I desire.

Demetrios