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Posts Made By: Mike Hosea

February 14, 2005 11:15 PM Forum: Eyepieces

Plossls vs Naglers

Posted By Mike Hosea
I think both scopes used had slow f-ratios. For planetary purposes, simpler designs do tend to work better, or at least as well, in that circumstance. With fast scopes, however, there can be a different story, at least when a quality Barlow is not also used. Many people still prefer the simpler designs in fast scopes for less scatter and the benefit that gives to contrast, but the simpler designs may also represent a compromise in sharpness due to their inferior levels of correction. Generally, when used in a fast scope, the simpler designs require that the planetary detail be centered and stay centered, and this is best accomplished with a GEM. With Dobs, tracking is required. Even with an equatorial platform, precise centering and perfect collimation are required in fast Dobs for the simpler designs to keep up in sharpness (i.e., without a Barlow to slow the system).

March 12, 2005 06:22 AM Forum: Eyepieces

Speaking of astigmatism...

Posted By Mike Hosea
Astigmatism is common from corneal defects with large exit pupils. The aberration is caused by a spoon-shaped lens surface rather than a spherical one, and it occurs at the edge of field of many eyepieces because this is the shape that the light cones encounter as they pass through the eyepiece at an angle. People don't expect this from everyday experience, but if you have your eyes dilated you can probably see, as I do, a substantial amount of aberration when a wide swath of the cornea plays a role in photopic image formation. It's possible that your implants are playing a role, but it could easily be just normal corneal imperfections. As you have observed, the smaller the exit pupil the better.
--
Mike

April 1, 2005 06:08 PM Forum: Eyepieces

Eyepiece Re-Coating?

Posted By Mike Hosea
No, never heard of such a thing. I'd be concerned about the stripping process, particularly for cemented groups, but I'm just guessing.

If anybody knows, these guys know:

http://www.siriusoptics.com/

--
Mike

April 23, 2005 04:45 AM Forum: Eyepieces

Nagler 7 or Nagler 5?

Posted By Mike Hosea
Bill,

I agree.

...

Oh, well, I have both 7mm and 5mm Type 6's. I guess if I had to pick one of them in your shoes, I'd pick the 5mm, but there's reason I have both, and I use them both. If you want something to use when seeing is below average, then maybe the 7mm would be better, but my thinking is that below average seeing is less important than average or better, so when I have to leave a hole somewhere, I choose to leave the hole for the conditions that will be less satisfying anyway.
--
Mike

May 13, 2005 01:20 AM Forum: Eyepieces

32mm UO Konig?

Posted By Mike Hosea
Yeah, in an f/10 SCT I think you'll like it. I included this eyepiece in my Burgess SWA and Meade QX review on Cloudy Nights.
--
Mike

May 13, 2005 11:06 PM Forum: Eyepieces

New EP I just could not refuse it!

Posted By Mike Hosea
I had both the 14mm Meade UWA and the 14mm Pentax XL for awhile. IMO, it's not the equal of the 10.5mm and shorter XL's in faster scopes due to field curvature. It's better than the 21mm XL in this regard, but still not nearly as flat as teh 10.5mm. I liked the 14mm Meade UWA better, although it's hard to complain about the quality of the 14mm Pentax XL. What I really would have liked, and still would like, is a a Pentax implementation of the 14mm Meade UWA design, with Pentax coatings and attention to baffling and other build detail.
--
Mike

May 14, 2005 11:02 PM Forum: Eyepieces

Coma corrector doubts. How does it work ?

Posted By Mike Hosea
Andre,

A coma corrector reduces coma. Unfortunately coma is just one of the aberrations that leads to poor performance of eyepieces in fast telescopes. The Tele Vue Paracorr will also reduce field curvature (when the edge is out of focus even though the center is in focus), but other aberrations are not corrected. Unfortunately, the problem with cheap eyepieces in fast scopes is not coma, rather astigmatism, and a coma corrector will not fix that. For example, in your BO SWA 32mm in an f/4.7 Newtonian there will be coma, field curvature, and astigmatism at the edge of field. Using a Paracorr will reduce coma and field curvature, but it won't help with astigmatism. Using an f/8 or f/12 scope instead will reduce all three aberrations. Where coma correctors make the most sense are with expensive eyepieces that have very little astigmatism even in fast scopes. Then, the Paracorr makes a big difference because it is correcting all the dominant aberrations at the edge of field.
--
Mike

May 23, 2005 08:11 PM Forum: Eyepieces

Antares W-70 EPs

Posted By Mike Hosea
I had a 5.7mm W70 not long after they came out. I had problems with glare from an unblackened spacer (hopefully fixed in later models) and bright green coatings. I assumed at the time that the coatings were par for the eyepiece, but much later (a year after selling it, I think), I learned that some (most?) people got much better coatings. With both of these things fixed, the only other complaint I had was sperical aberration of the exit pupil. The eyepiece was comfortable to use on DSOs, Jupiter, and Saturn, but daytime and lunar observation revealed a tendency to kidney bean. The eyepiece was still usable then, but not by a wide margin. On the positive side, to the best of my recollection, the usual edge-of-field aberrations--field curvature, astigmatism, and lateral color, were as you have described.
--
Mike

June 17, 2005 04:03 AM Forum: Eyepieces

Where is your Televue made?

Posted By Mike Hosea
Here's what I can recall owning over the last few years.

20mm Plossls (2, both Japan)
15mm Plossl (Japan)
8mm Plossl (Japan)
24mm Panoptic (Taiwan)
9mm Nagler T1 (Taiwan)
18mm, 14mm, 12mm, 10mm, 8mm, 5mm, 4mm, 3mm Radians (Taiwan)
3-6mm Nagler Zoom and 2-4mm Nagler Zoom (Japan)
12mm,17mm Nagler T4 (Taiwan)
16mm Nagler T5 (Tawian)
11mm, 7mm, 5mm, 3.5mm, 2.5mm Nagler T6 (Japan)
1.25" 2x Tele Vue Barlow (4, all Japan)
1.25" 3x Tele Vue Barlow (Japan)
1.25" 2.5x Powermate (2, don't recall)
1.25" 5x Powermate (don't recall)
2x Big Barlow (don't recall)
1.25" 2.5x Barlow (Japan)
26mm, 21mm, 17mm, 10.4mm, 7.4mm Plossls (old style, Japan)

June 22, 2005 08:56 PM Forum: Eyepieces

what about the new UO O.P.S. Orthos?

Posted By Mike Hosea
So far reactions have been mixed. A very experienced observer noted an internal reflection (which is not normally a problem with the Abbe design) and didn't like them overall, at least with Jupiter as a test target. Another observer seemed to like his results with Saturn. I guess the first question to ask is whether you bother with so-called contrast filters for planetary observing already. If not, I would try a similar Sirius thread-on filter before buying an OPS (I assume there is one available). If you love the results thread-on filter, you might want to try the OPS to see if you can eek out some more contrast, but it's debatable whether that would be the result given the increased danger of internal reflections. No way to know without trying.
--
Mike

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