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Posts Made By: dan hilts

January 14, 2010 05:54 AM Forum: Telescope Making

Re: virgin teflon source

Posted By dan hilts

The original design by John Dobson used records on teflon for bearings. There are better materials but obviously, records worked well enough to start the reveloution.


January 29, 2010 06:47 PM Forum: Telescope Making

Re: Measuring Secondary

Posted By dan hilts

The name size of an elliptical diagonal refers to the side to side or minor axis measurement. The longest dimension is referred to as the major axis.

hope this helps,

January 29, 2010 06:50 PM Forum: Off Topic Discussions

Re: Just in case you're bored.

Posted By dan hilts

I'm not THAT bored.


February 28, 2010 08:05 AM Forum: Prayer Line

Prayer for my wife

Posted By dan hilts

My wife joined me in Florida after WSP2010 and we had a few days to see some of the sights of Miami and the Florida Keys. When we returned home she went to the doctors for abdominal cramps due to suspected gall stones. Complications from a diagnostic procedure have left her in the hospital, unable to eat and in a great deal of pain. She has had two blood transfusions in the last 48 hours. She has never been sick before and is very scared as I am. Please include her in your prayers.

God help my wife to find some comfort, end her suffering and give her the strength to have faith that all is unfolding as it should. Amen

May 13, 2010 08:38 AM Forum: Eyepieces

Re: Too much $$

Posted By dan hilts

Yeah, that sounds a little off but since the seller has a number of eyepieces for sale in that range, perhaps he simply got confused when he was setting up the ad. Why not drop him a note with your observation and see what happens? He may appreciate it.


September 8, 2011 07:33 AM Forum: Landscape Photography

Spider webs!

Posted By dan hilts

We had some high humidity lately and the morning mist softened the bright sun to make these webs standout. Not great photography but an interesting subject.


August 7, 2012 05:14 PM Forum: Equipment Talk

Re: another pic

Posted By dan hilts

Nice clean up job!


August 18, 2012 10:22 AM Forum: Eyepieces

Re: Blackened lens edges question

Posted By dan hilts

I am of the opinion that most of the time it is inconsequential.

Blackened edges are suppose to reduce the amount of scattered light from the lens edges. In a properly designed eyepiece, the lenses and their holders should be sufficient diameter to pass the light rays without any light hitting the edges. There shouldn't be any scatter. A properly sized and positioned field stop is important to reduce the amount of stray light entering the optics and will help to prevent scatter.

Yes there may be times when a bright star or other object is right at the edge of the field of view and creates some glare that makes it pass the field stop. Under these circumstances the whole field could be awash with stray light, not just the edges of the lenses. I doubt that you would notice the difference between an eyepiece with blackened edges versus one without under these viewing conditions.

Point your scope at the daytime sky while you look through it. Can you see the edges of the eyepiece lenses? That will give you a pretty good idea how much you will see any reflection of scattered light from the lens edges.

Just my 2 cents worth.
Lots of folks will disagree.


September 23, 2012 07:07 AM Forum: Refractors

Re: Scope on another site: (Buyer beware)

Posted By dan hilts

He didn't get away with it over there either.


June 23, 2005 09:55 AM Forum: Telescope Making

Should a chamfer affect sagita depth?

Posted By dan hilts

Hi Marcin


No, if you do the math you'll see it has very small effect.


The chamfer will reduce as you grind but a 2mm chamfer is quite a large amount to disappear. The chamfer is required to keep the edge from chipping out on the face of the mirror due to tiny stress points caused by variations in the size of grits. It also helps to prevent damage if you should accidentally knock the edge during routine handling. As you grind, make sure the chamfer does NOT disappear. You may have to touch it up a bit, much less as you move to smaller grits. IMHO, 1mm is lots during fine grinding and if it reduces to 0.5mm towards the final stages, so much the better.


During rough griding, you can use a straight edge and a suitable piece of wire for a guage. You don't need precision. You can also get a good estimate of the focal length by measuring the distance to the best focus of an image of the sun. The wet glass will cast an image, poor but usable. When you get beyond the hogging out stage you can get a pretty good measurment using the image of the sun. If you want to get it really close, set the mirror up on the test stand and use the knife edge. Add a drop of dish soap to the water you wet the mirror with and it will stay wet long enough to make a good measurement. Don't struggle for perfection as the focal length will shorten a fair bit during the 120-400 grits. You can control the change by working TOT to lengthen, MOT to shorten.

have fun,