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Posts Made By: dan hilts

May 5, 2009 07:36 PM Forum: Refractors

collimating a TV Pronto?

Posted By dan hilts
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I have always thought there is no real point in a telescope light path where the image suddenly is in focus. The out of focus condition gradually disappears as the light rays come together at the focal plane and then gradually disperse as they go beyond.

I think some folks see the snap into focus as their eyes quickly adjust to the image as it is focused with the end result that it appears to be a snap. But that is a combination of the telescope being focused and their eyes responding. The eye will adjust and see sharp images either side of the ideal focus, some folks do this better than others. Some like me, never see sharp focus.

I could be wrong. I'd like to hear more knowledgable people commment.

dan

May 25, 2009 07:05 PM Forum: After Dark

Shuttle landing

Posted By dan hilts
It's a great way to start the day!

A few years ago my wife dragged my sorry butt down to Orlando, Florida, to visit Disneyland. We arrived too early to check into our hotel and I didn't want to waste a day pass for Disney on a completely unorganized day so we headed over to Cape Canaveral. Just my luck, Atlantis showed up. It was pretty impressive to see and it is amazing just how much of the ship is scortched by the heat of re-entry. My wife really enjoyed it too.

clear skies,
dan

June 11, 2009 03:08 PM Forum: Telescope Making

Large aperture, long focus dob without the tube?

Posted By dan hilts
If there is no weight on the rod, why use one? Replace it with a laser.

This is looking like an observatory instrument with the upper cage actually being mounted on the dome at the opening. The dimensions of the dome would have to match the size of the scope to allow the secondary to be always in the right spot for the primary which would be mounted at the centre of the whole thing.

I'm thinking it would be much easier to build a fixed scope and use a moveable flat to trace the sky. Anybody got a 25 inch flat for cheap?

dan


June 26, 2009 03:23 PM Forum: Eyepieces

First 1.25" ocular you purchased?

Posted By dan hilts
The first real eyepieces I purchased were the Edmund RKEs back in the very early 80's. Prior to that I only had salvage from junked binoculars and projectors. I think I got the RKE 28mm first, followed quickly by the 15mm and 8mm. I still have them. At the time I bought them they were each worth more than half of what I paid for rent each month. Today, half of the monthly rent for that same apartment would easily buy a Nagler,(or two). How things have changed.

clear skies,
dan

July 20, 2009 04:43 PM Forum: Landscape Photography

Great Saltpeter Cave

Posted By dan hilts
I like big old caves. I've been through several in New York State and in Virginia but I've never made it to Kentucky. Nice photos. Thanks for sharing.

dan

August 4, 2009 05:16 PM Forum: Eyepieces

Eyepiece starters for a 8" SCT

Posted By dan hilts
In slower scopes like SCTs, I still like the Antares 32mm wide field Erfle. It is affordable, useable and offers nice wide field views. It is also fairly light for a 2" eyepiece. The 40mm is no where near as good.

dan

August 4, 2009 08:14 PM Forum: Eyepieces

A neutral density or polarizer filter?

Posted By dan hilts
A variable polarizer is at least two sheets of glass and four surfaces. Going with the theory that less is best, I would choose a fixed ND filter if I had to use anything at all. 13% is not a whole lot of reduction. Keep in mind that you can always up the magnification to reduce the brightness. Doubling the power cuts the brightness by a factor of 4, way more than 13%.

(my 2 cents worth for free!)

dan

August 14, 2009 04:33 PM Forum: Eyepieces

Flat field and/or Camera Projection eyepieces

Posted By dan hilts
I don't see why you would need to use two eyepieces. One should do the trick. Alternatively, get a nice pair of matched achromats and make your own relay lens to fit the distances and aperature you need.

good luck,
dan

August 25, 2009 08:16 PM Forum: Telescope Making

Telescope Conversion from Tube to Split to Truss

Posted By dan hilts
I think the most difficult part of the design is getting the balance right. There are procedures published to let you get the work down step by step and end up with a smootly working assembly.

dan

September 11, 2009 02:01 AM Forum: Equipment Talk

Am I an SCT Guy or not ?

Posted By dan hilts
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With tracking an object will stay centered in the field indefinitely with only minor adjustments. Just how long it will stay without adjustments depends on how good the tracking is and how well the alignment was done but definitely long enough for relaxed viewing.

Without tracking one has to deal with the drift which is at the rate of 3.98 minutes per degree of sky. If you can calculate the true field of view in the eyepiece, you can determine how long an object will take to drift across the view. At 300X, a 50 degree eyepiece will have a true field of approximately 300/50 or 1/6 degree. It will take an object about 1/6 X 3.9888 minutes or 40 seconds to drift across the view. Folks with Dobs like to use wide field eyepieces because they don't have to struggle as much to keep objects in the view.

hope this helps,
dan

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