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Posts Made By: Mike Hosea

July 13, 2006 01:02 AM Forum: Eyepieces

Re: Ye old Pan 24mm

Posted By Mike Hosea
Greg Nowell said:


I don't know if this is what we call "pincushion" but holy mama. It is the most dramatic eyepiece distortion I have ever seen.

[snip]

To my mind, this puts the very modest XW 20 field curvature, which in some instances is not even readily detectable, in a proper perspective.

Yep, that's pincushion. I'll offer a different "perspective". First, I found the distortion noticeable but not so bad as you describe. The distortion in a Panoptic 24 makes it less than ideal for panning around, but the problem stops being obtrusive in DSO observation when you stop panning and start observing. To me, the field curvature of the XW 20, on the other hand, is an unsolvable, perpetual nuisance in faster scopes.
--
Mike

February 10, 2008 07:54 PM Forum: Eyepieces

Re: Fair price on a used EDMUND RKE ?

Posted By Mike Hosea
It's been more than a few years now since I bought a few from Edmund, but my 4 year-old recollection is that their idea of a "shipping and handling" charge was less than fair, so perhaps that needs to be taken into account.

BTW, I just checked the Edmund website. Says $57.50 each, without shipping.
--
Mike

February 26, 2008 04:55 PM Forum: Eyepieces

Re: Outer Edge smoothness

Posted By Mike Hosea
John Meiners said:
My concern (have not had a chance to view a bright object like the Moon or Jup.) is that the anomaly will manifest itself when light hits the edge. Would not be apparent when viewing lets say a double star with black sky as a backdrop..

John, I don't remember much about the 8mm RKE that I had many years ago, but I've had a couple of 15mm's, and both had a razor sharp field stop. IIRC, one of them even cut me. The problem with that is exactly the sort of thing you describe, as burrs and irregularities are common. Most manufacturers opt for more of just a bevel rather than a knife-edge, as the effect on the light path can be the same and yet anomalies of the field stop edge are far less likely. If this is what I think it is, you shouldn't worry--there will be no deleterious effects. You can potentially fix it if the burrs are weak enough, say knock them off with the shaft of a Q-tip, but it should be an entirely cosmetic matter.
--
Mike

August 15, 2009 05:01 AM Forum: Eyepieces

Re: Masuyama worth more than $300 ???

Posted By Mike Hosea
john raymond said:
In the auctions the 5mm Masuyama is already over $300 bid.

What gives?

And the reserve isn't met. Worth is in the mind of the buyer. Probably it's a collector thing, not a practical thing. At least I hope that's what it is. Like nearly all discontinued, high-quality eyepieces, Masuyamas do have an enthusiastic minority following.

January 28, 2010 03:28 AM Forum: Eyepieces

Re: Last weeks eyepiece auction ???

Posted By Mike Hosea
There are no completed auctions for Celestron/Vixen eyepieces in January that come up in the search. I'm sure you're thinking of the Tele Vue 17mm Plossl:

http://www.astromart.com/auctions/details.asp?auction_id=5561



April 3, 2002 08:58 AM Forum: Equipment Talk

Adding stability to a dob mount

Posted By Mike Hosea
I can't remember this mount too well, but I would try rebuilding it using Titebond or TiteBond II wood glue on the joints and adding some additional screws to make sure the joints are solid. If an additional "crossbar" support is possible without limiting scope movement, then that is worth a try also.
--
Mike

April 10, 2002 07:22 PM Forum: Equipment Talk

What's the difference between a Mak and an SCT?

Posted By Mike Hosea
Mechanical differences really need to be discussed with respect to each IMPLEMENTATION of these designs, and mechanics vary quite a bit within the collection of MCTs. For example, the Intes MK-66 and MK-67 Maksutov-Cassegrains have the same basic optical design (if not the same exact design), but the mechanics are very different. The MK-66 incorporates a moving mirror focusing mechanism (like most SCTs) while the MK-67 focuses "refractor style".

Optically, there are a number of Maksutov designs (e.g. some with aluminized spot secondaries and some with separate secondaries), but the main significant optical difference is the corrector design. With the Mak it is a spherical meniscus (concave on one side, convex on the other) lens and with the Schmidt it is a complicated aspherical curve. Mak correctors are typically thicker and heavier, and are correspondingly more expensive than the mass-produced Schmidt correctors. I think the Schmidt correctors would be more expensive, though, if it were not for the invention of a particular manufacturing process for mass-producing them.
--
Mike

April 10, 2002 09:58 PM Forum: Equipment Talk

Portable, convenient mount

Posted By Mike Hosea
Richard,

Now it seems like the AZ3 mount ought to work for that little scope. I had a Celestron version of that mount that gave fabulous stability with a Tele Vue Ranger.

That mount wasn't good enough for the Intes MK-66 Deluxe, and it was this that sucked me into ATM-ing. TThe telescope and mount are sold now, but you can see what I did for the MK-66 in the photo below.
--
Mike

April 12, 2002 07:58 AM Forum: Equipment Talk

Eyepiece Parfocalizing

Posted By Mike Hosea
http://www3.bc.sympatico.ca/gwolanski/PARFRING.HTM

I've never used these, though. Instead I use 1.25" rubber slip-joint washers from the plumbing section of a hardware store and/or o-rings, whatever it takes to get close. For 2" eyepieces I stretch the 1.5" rubber slip-joint washers. Another trick for 2" eyepieces is to cut hunks of 2" ABS or PVC pipe. You can hold it on with a slip-joint washer.
--
Mike

April 13, 2002 05:52 AM Forum: Telescope Making

Determining eyepiece focal length

Posted By Mike Hosea
Put it in a scope of known focal ratio and measure the exit pupil size. Multiply this measurement by the focal ratio. Voila!
--
Mike

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