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Posts Made By: dan hilts

November 2, 2005 03:14 PM Forum: Telescope Making

Now Here is a Newtonian!

Posted By dan hilts

That scope would be huge, The prime focus image of the moon would be 4" in diameter. You're gonna need some new eyepieces,

clear skies,
dan

November 8, 2005 01:53 PM Forum: Eyepieces

Re: Safety undercuts

Posted By dan hilts

<>

You only have to back the screw out until falls on the grass and you loose it in the dark. A royal pain.

dan

November 16, 2005 05:36 PM Forum: Reflectors

8" SCT Vignetting with a 50mm EP? HELP!

Posted By dan hilts

Alan,

The dark circle sometimes seen is the shadow of the secondary mirror in the exit pupil of the scope. Under the right conditions it can be seen with any obstructed scope, Maks, Newts, SCTs etc. Naturally, it isn't there with unonstructed scopes such as refractors or off axis reflectors.

The exit pupil from the eyepeice is actually a small image of the objective of the scope and includes the diagonal or secondary mirror shadow and the spider assembly etc. The size of the exit pupil is dependant on the power the eyepiece gives in the scope and for the combination you are considering, (50mm eyepiece, 2000mmFL = 40X), the exit pupil is about 200mm/40 =5mm. (size of the obj / mag).

In that 5mm circle of light of the exit pupil is the central dark circle which is the image of the secondary mirror. If the central obstruction in the scope is about 30% by diameter, then the dark spot in the centre of the exit pupil is about 1.5mm. At night when your eye is well adapted to the dark, your large eye pupil receives all the light from the objective and you will probably have no problems. In daytime, when your eye pupil is much smaller (maybe as small as the dark spot) you will see black outs if you position your eye right on the dark shadow in the exit pupil.

So yes, in your scope, it's a pretty good bet any low power eyepiece is going to give you blackouts if you want to do daytime observing. No, you shouldn't have trouble with star gazing at night when your eyes are dark adapted and your eye pupil is much larger.

There is another problem with some eyepieces that creates blackouts appearing from the sides of the view,(called kidney beaning because of the shape of the dark shadows). This can occur when the eye is not placed at exactly the correct distance from the eyepiece. Some eyepiece designs are worse than others in this respect and rubber eyecups help to alleviate the problem by assisting with the correct placement of the eye.

hope this helps,
dan

December 17, 2005 09:11 AM Forum: Eyepieces

In-focus question

Posted By dan hilts

<>

Most barlows require some amount of in-focus to work. Just how much depends on the barlow/eyepiece combination.

December 29, 2005 05:28 PM Forum: Equipment Talk

Orion focuser modification

Posted By dan hilts

Floyd,

I have also modified this type of focuser for improved performnace. I found the Synta style focusers on refractors could be adjusted for reasonable action but they would not hold adjustment with any use. The set screws that adjust the slider were too small and pointed and the slider material would easily distort and flow around the point of the screw. It didn't take much weight in the tube to create a lot of slop in the adjustment. Eventually the set screw was buried so far into the slider there was no possibility of adjustment.

I removed the set screws and drilled and tapped the existing holes in the housing for a 6X32 screw. I also obtained some dog point set screws that have a very blunt dowel shaped end. I then modified the slider by carving a channel to carry some small washers where the set screws fit. The intent was to mate the washers to the end of the dog point screws and distribute the load over a larger surface of the slider material. The sides of the washers had to be ground down a little to fit better. (I suppose the slider could be drilled with a fostner bit to accept the washers.)

The end result is an adjustment that holds way better than the original and I can now use the heavier eyepieces and diagonal I have without ruining the alignment on the focuser. It's not perfect and still needs to be tweeked periodically but is much, much better than the original.

clear skies,
dan


January 18, 2006 10:08 AM Forum: Beginning Astronomy?

Explaination of refrator terms please??

Posted By dan hilts

I am not aware of any short answer that would be adequate. You could try Roger's web site for a detailed technical description.

http://alice.as.arizona.edu/~rogerc/


dan

January 19, 2006 08:36 AM Forum: Equipment Talk

Mounting a very light scope

Posted By dan hilts

Lee,

If it were mine, ideal solution would be a 60mm clamshell with a 1/4 x 20 thread to mate with the photo head. Or, a 1/4 X 20 mounting block to accept a pair of 60mm rings would also work.

have fun,
dan

March 10, 2006 10:42 AM Forum: Telescope Making

Small scope, 6"? Go for it!

Posted By dan hilts

Hey Mike,

I certainly agree with what you have said regarding your little scope. It is a fine performer and you really do seem to enjoy it. No, it's not in the same leaque as a much larger premium scope but I do recall the views of M42 through your scope at WSP2005 and they were pretty darn pleasing. If it were my scope, I'd be proud of it.

I had some medical issues that kept me from WSP2006. From the picture it sure looks like you had some pleasant weather.

best regards,
dan

March 13, 2006 10:46 AM Forum: After Dark

What did I see?

Posted By dan hilts

I saw something similar at WSP2005. Someone explained that it was probably space junk such as old satellites or lost rocket stages tumbling in orbit. The blinking is caused by the sun's reflection off various panels as the object tumbles. It was further explained that the height of the orbit can be calculated by the apparent motion across the sky. When the object appears to move slowly, it is way out there.

clear skies,
dan

March 17, 2006 10:35 AM Forum: Telescope Making

Re-coating objective lens

Posted By dan hilts

Before you can recoat a lens, you will first have to remove the original coating. There have been a number of threads on these forums regarding the stripping of damaged coatings on lenses. Typically you would have to grind off the old coating and repolish and refigure the glass surfaces. It's not a simple task. If you can find an easier method, folks would like to hear about it.

clear skies,
dan