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Posts Made By: dan hilts

January 15, 2007 01:25 PM Forum: Beginning Astronomy?

Essential resources for the beginning astronomer

Posted By dan hilts
I am a big believer in binoculars.

Given a simple star map and a pair of hand held binoculars, many of the Messier objects can be identified and some, like M33, are easier to find for the first time in binoculars than in a scope. True, you can't see the separate stars in a globular cluster through binos but you do get a better idea of relationships in a given portion of the sky. Even an inexpensive pair of binos can add a great deal to the experience, especially under dark skies. I have several pairs including some very nice older Japanese 7X35 binos that came from yard sales for less than $10 each.

I would rather leave my maps at home than forget my binos.

clear skies,
dan

January 31, 2007 07:45 PM Forum: Telescope Making

Re: bubble cavity between mirror blank and tool

Posted By dan hilts
Robert,

I suspect there may be nothing wrong at all. If you had good contact once, you shouldn't have lost it with a 1/3 stroke, COC. Any possibility you are using a little too much water and trapping an air bubble that can't escape?

I would work a few good wets of the 120, MOT. For each wet, once you've done a few strokes, pause the grinding and attempt to slide the bubble off the edge by carefully sliding the mirror sideways. Once the bubble breaks, rotate the mirror to reduce the bubble and return to grinding. Maintain the 1/3 COC stroke.

Once the mirror starts to form a good sphere the bubble shouldn't form up as quickly and it should certainly be smaller. You may need to experiment with the volume of grit and water to get the consistency right but it shouldn't take long. Work MOT, spread about 1/2 teaspoon of 120 in the centre of the tool, add a few drops of water, and start the grinding. Adjust as needed to get smooth grinding that doesn't mud up too quickly or wash the grit out too much.

You can tell the feel of a mirror with poor contact to the tool. It binds and grabs as you move it through the stroke. With good contact, the mirror moves much more smoothly without any jerkiness at all and it doesn't take a lot of pressure to complete a stroke.

keep at it.

dan






February 1, 2007 05:25 PM Forum: Off Topic Discussions

Re-entry Heat

Posted By dan hilts
Hi Lee,

I'm certainly no expert on this subject but I think the discussions are entertaining. I am sure there are some trained physics folks around here who know far more than I.

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As long as these private ventures stay within the atmosphere they will not reach speeds that will generate the same heat that a space vehicle experiences during re-entry. However, they may get hot during flight. According to Wikipedia, "the SR-71 Blackbird jet could fly continuously at Mach 3.1 while some parts were above 315°C (600°F)." Of course, once outside the atmosphere,(in space) there is no heating due to the friction of the air.

It is my understanding that the heat of re-entry results from converting the kinetic energy of the space vehicle to heat. This is what provides the necessary braking action to slow the vehicle. It could be done with a rocket engine prior to re-entry but it would take a similar amount of fuel to slow the vehicle as it did to accelerate it in the first place. Also keep in mind that if a space vehicle is not moving forward, it is going to fall straight towards the earth. That might make the landing a little tricky.


dan

February 2, 2007 12:27 PM Forum: Equipment Talk

Any opinions on the Oberwerk 20x80 Lightweights?

Posted By dan hilts
I can't speak about the weight but I do believe that 20x is not hand holdable.

I had a pair of 16X50s for a number of years and though they could be held they were very much better on a mount; even a simple pole made them much more useable. As soon as a little fatique sets in, it is almost impossible to steady the view without some sort of brace. And it's very difficult to see any detail in the skies with even a little vibration going on. I can remember standing beside a tree so I could hold the 16x binos against the tree trunk to stop the shakes.

20X80's need a mount.

clear skies,
dan

February 9, 2007 04:36 PM Forum: AstroMart FAQ

OH CANADA

Posted By dan hilts
<>

But that's still less than what it costs to ship that same eyepiece inside Canadian borders. Go figure, eh?

dan

February 16, 2007 05:01 PM Forum: Telescope Making

Bonding plywood panels

Posted By dan hilts
I now have a good selection of clamps but in the past I have used concrete blocks/bricks or a box of books to put weight on some panels. In a real pinch, go to Home Depot and purchase a couple of bags of play sand. They could be returned for a refund when you're done with them but that's not my style.

have fun,
dan

February 21, 2007 07:07 PM Forum: Refractors

Refractor vs. Binoculars.

Posted By dan hilts
Paulo,

You could start with this posting by Ed Zarenski.

http://www.astromart.com/forums/viewpost.asp?forum_post_id=398075&poll_id=&news_id=&page=

clear skies,
dan

February 26, 2007 12:21 PM Forum: Telescope Making

What Do Amateurs Do For a Living?

Posted By dan hilts
I test software applications and develop test plans. Basically, I spend my time finding fault with other people's work, or planning to.

dan


March 6, 2007 06:09 PM Forum: AstroMart FAQ

How do I search closed auctions?

Posted By dan hilts
When you are on the auctions menu page there is a seach box in the upper right area. If you don't know the auction number you can select the advanced search and enter parameters to define the query. Results will include closed auctions.

dan

March 18, 2007 12:15 AM Forum: Beginning Astronomy?

Barlow and field of view Posted by Mike Alexander

Posted By dan hilts
Larry,

There is a simple trick that seems to be seldom used but can be very helpful in changing the power of a barlow lens. The magnification of a barlow is dependant on how far the eyepiece is placed from the barlow lens so if you change this distance, you can change the magnification. Increase the distance to increasae the magnification.

A simple extension tube can be used to increase the power of a barlow. Orion sells a 1.25" extension for less than $20.00. Another way to get an extension is to obtain an inexpensive barlow and remove the lens. You often see no name barlows for $15 or so here on Amart. With a couple of different length extensions you can use a 2X barlow at 2.5X, 3X, or any other magnification you want.

Here is a link to a web page with all the details of how to use extensions with a barlow.

http://www.atmsite.org/contrib/Carlin/barlow/

clear skies,
dan

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