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Posts Made By: Doug Peterson

March 26, 2005 05:56 AM Forum: Equipment Talk

Celestron 130 Mak collimation--success

Posted By Doug Peterson
The knob is plastic and pressed on, there is no set screw. It must be carefully wedged off using a screwdriver wrapped with tape to prevent damage to the plastic housing. Inside are the usual push pull screws with melted wax seals, the wax does not prevent adjustment. Unlike Synta, the flip mirror is attached only to the housing so it is not in the way.

April 1, 2005 01:59 AM Forum: Equipment Talk

Celestron C130 vs Orion 127 Mak?

Posted By Doug Peterson
The Orion 127 is the superior scope. I have both, I had to test two to get one good Celestron 130, even then I had to collimate it after partial disassembly that is not in the manual--see my earlier thread. The Orion is much lighter, has no plastic, and mine has excellent optics. On the other hand the recent sales prices on the 130 are pretty cheap, and if you get a good one, it could be a bargain.

April 19, 2005 03:34 AM Forum: Equipment Talk

A question about Cave Telescopes - please

Posted By Doug Peterson
I sold my 10"F7 in excellent shape, original dual axis drives, for 1700 a couple years ago. This business about red Herring mirrors is controversial, as was he, and I think frankly overblown. Mine didn't have his name on it and the mirror was absolutely superb.

April 24, 2005 06:34 PM Forum: Equipment Talk

Replacement Focuser for Synta

Posted By Doug Peterson
William Optics has a drop-in replacement, the same apparent crayford as on their own scopes.

Synta itself uses a crayford on its APOs, I do not believe it is available separately.

More interesting is the Moonlight crayford, which has collimation capability, which should come in handy for people with the chromacor.

June 25, 2005 06:23 PM Forum: Equipment Talk

Wavefront error question

Posted By Doug Peterson
The wavefronts are cascaded, which is to say they can add or cancel along the optical axis, across their 2-dimensional apertures point by point, depending on whether the errors lead or lag. Typically there will be some sort of averaging. But no exact predication can be made without interferometry.

July 10, 2005 11:33 PM Forum: TeleVue

Diaoptrx

Posted By Doug Peterson
I just obtained a 1.0 diopter Dioptrix and have tested it with the Nagler 31 and FLT 110mm, 4.8mm pupil. It works! It is amazing to see low power stars look like they do at high powers.

As has been pointed out, the astigmatism at nighttime may differ from the daytime prescription that uses a stopped down portion of the cornea. This would not be the case if the eye was otherwise perfect. In my case however, the correction for pure astimatism is just about dead on. However, I too have a slight flare, i.e., not astigmatism and therefore not corrected. Nevertheless this is a small issue compared to the overall improvement.


September 18, 2005 05:36 AM Forum: Equipment Talk

University optics 2.8x Klee Barlow

Posted By Doug Peterson
After discussing the Pretoria eyepiece, and some coma correcting eyepieces of his own, Dr. Buchroeder comes to the Klee:



Excerpted from RTMC 88 proceedings

A Nearly Perfect Eyepiece For Newtonian Telescopes

R.A. Buchroeder, PhD

"Fortunately, there is an alternative. Heinz Klee from South Africa designed a beautiful three-element, coma-correcting barlow lens which is now available from University Optics and is known as their 3x Barlow. It is superbly corrected for its own abberations and that of any Newtonian primary, which cannot be said for any cemented doublet barlow, which comprise the majority of Barlows on the market. We find that the residual field curvature of this 3x barlow comes close to compensating that from many of the Plossl types that have a 26mm focal length. The combination gives a coma-free, long eyerelief, superbly corrected flat-field eyepiece with about a 9mm focal length, and with more eyerelief than the same eyepiece used alone! Similar good results are obtained with shorter focal length eyepiece combined with the Klee barlow, but of course the eyerelief is less. The Klee barlow is curious and advantageous also in its extremely short length, whereas most barlows on the market are long and unattractive."

September 18, 2005 06:00 AM Forum: Celestron

Optimal Back Focus for C14

Posted By Doug Peterson
For a C8, I once calculated the depth of focus is about 8 inches, i.e., 1/4 wave of spherical abberation for a perfect system is generated by moving the focus from nominal +/- 4 inches. The C14 should be similar. Since no system is perfect, it implies that the best corrected position could be found by trial and error using the star test.

October 17, 2005 01:00 PM Forum: Refractors

8" F6 ED Travel Star Refractor

Posted By Doug Peterson
Just answered my own question:

http://www.drapell.com/

Joseph Drapell

October 17, 2005 05:41 PM Forum: Equipment Talk

Whats the story on Chromacor availability?

Posted By Doug Peterson
Update, John Hopper is answering emails. He is a class act and very helpful.

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