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Posts Made By: dan hilts

September 3, 2006 07:13 AM Forum: Telescope Making

Long focus mirrors?

Posted By dan hilts

<>

The difference between the best fit parabola and a spherical surface on an 8" F20 mirror is only 0.011 waves error. You could never reliably measure this, let alone work to it.
A good sphere should do.

clear skies,
dan

September 4, 2006 01:04 PM Forum: Refractors

OTA Diameter

Posted By dan hilts

Mark,

I think all the Chinese produced 120mm scopes use a 4.5" tube. While this may not be ideal it is what has been done. I agree that the tube is a little small since there is no room for a baffle in the front section. However with the dew shield in place, there is little chance of glare from this point unless you have the moon in the edge of the field of view.

Orion used a 100mm tube for their 80mmED model and some folks have complained that it feels too big. Compact has become fashionable.

clear skies,
dan

September 4, 2006 03:08 PM Forum: Telescope Making

Yet another ronchigram question

Posted By dan hilts

Micheal,

Here's a link to the pretty good site for the basics of Ronchi test interpretation. It should answer your questions much better than I ever could. Enjoy!


http://www.users.bigpond.com/pjifl/ronchi_interpretation_basic.html


dan

September 4, 2006 03:12 PM Forum: Refractors

double double

Posted By dan hilts

Itz,

I have bad eyes but a pretty good memory. Here's a link to a recent discussion on this exact topic.

http://www.astromart.com/forums/viewpost.asp?forum_post_id=452307&poll_id=&news_id=&page=

September 7, 2006 12:49 PM Forum: Beginning Astronomy?

Quick Question on the Difference between Longer/Sh

Posted By dan hilts

The shorter scopes with the longer focal lengths are compound scopes. The primary image from the mirror is magnified by a curved secondary mirror and this magnification is what gives it the long focal length. Here's a link to a quick explanation with diagrams. Also note that just about everyone of the telescope manufacturers have a section on their web sites that is dedicated to beginners. Google 'Telescope types' and take a look. The pictures are worth more than simple explanations.

http://www.wvp-consulting.com/astronomy/othertelescopes.html

November 6, 2006 06:59 PM Forum: Telescope Making

Table on rear of dob

Posted By dan hilts

I like it. It's a good idea. Of course, I would modify it just a little with a couple of holes to securely hold some eyepieces. Maybe a lid to keep the dew off them when not in use.

Classical music only on the CD player.

clear skies,
dan

December 1, 2006 11:27 AM Forum: Refractors

Need help from the straight thru experts

Posted By dan hilts

<>

Why not? You have nothing to loose.

good luck,
dan

December 29, 2006 03:30 PM Forum: Solar System Observing

Saturn Ring Observations

Posted By dan hilts

Kevin,

Check out the picture in this post from a discussion some time ago.


http://www.astromart.com/forums/viewpost.asp?forum_post_id=437156&poll_id=&news_id=&page=


happy holidays,
dan


January 11, 2007 06:23 PM Forum: Eyepieces

GSO 15mm and 20mm superview 1 1/4" eyepiece

Posted By dan hilts

James,

I tried both these eyepieces when they first came out and wasn't impressed even at F15. If I recall images were kinda soft and not nice and crisp. I had pairs of each so I don't think it was just a bad sample.

I have a GSO 20mm on the shelf and just tried it out in a home-brew 80mm F5. The closest thing I had to compare it to is a 19mm Gary Russel wide field that I picked up new a couple of years ago for $45. It's pretty cloudy out here so all I could do was look around at some distant lights and a radio tower a few miles away. The 19mm was noticeably brighter and provided a much cleaner view. Images were soft only at the extreme edges. The 20mm showed soft images in the outer 30% of the field with extreme distortion at the edge. It was also a lot darker which seems very strange. I don't think you'll like it at F5. Also note that any dirt on the field lens of the GSO 20mm will show up badly as it is almost in focus.

good luck,
dan

January 12, 2007 03:59 PM Forum: Beginning Astronomy?

APO vs. ACHRO

Posted By dan hilts

Darryl,

Check out the two photos in this thread and see for yourself what the difference looks like.

http://www.astromart.com/forums/viewpost.asp?forum_post_id=425706&poll_id=&news_id=&page=

clear skies,
dan