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Posts Made By: Lorne Johnson

January 9, 2006 12:19 AM Forum: Eyepieces

Siebert modified-Orthos

Posted By Lorne Johnson
You might want to look at cloudy night reviews, someone compared the Siebert standards with the expanse, and the Sieberts came out on top. You can also call Harry Siebert, and talk to him, he's very helpful, and does not want to sell people anything they won't be happy with. I have used a number of his eyepieces, and none of them have been poor (Harry's machining has improved a lot). I have a Siebert barlow and 2 inch observatory eyepiece that are a permanent part of my collection. I also have a couple type 6 Naglers that I am very fond of, TV plossls, an Ortho, and a couple of Monocentrics.

January 10, 2006 02:30 AM Forum: Telescope Making

Seeking advice on 17.5" Dob

Posted By Lorne Johnson
Floyd's advice is very good. I would only add that there are a number of kits on the market as well that might form a compromise between cost and sweat equity. There are links to some of them from rfroyce.com also see tscope and Dob parts.

January 12, 2006 02:11 PM Forum: Deep Sky Observing

NH/VT observing locations?

Posted By Lorne Johnson
Welcome to New England, Jim. I'm about an hour south of you in Putney VT. We tend to get sky that is dark enough by turning off the lights here (the veil visible with no filter). West Lebanon will be a bit more of a problem, but you should be able to find dark sky with 20 minutes of home.

The Hillsborough site, mentioned above, is probably good, although it's a bit of a "You can't get there from he'ar!"

Stellafane is a great place to go for the convention, but it is located just above a prison, that turns off their security lighting (or much of it) for the convention.

January 20, 2006 11:40 PM Forum: Eyepieces

Which eyepiece should I purchase?

Posted By Lorne Johnson
I have rarely been able to go above 250 in Southern VT. 150 to 230 is usually it. That's with a quality 8 inch DOB, but I don't remember my times with the 16 inch doing any better on power. It's generaqlly atmosphere limited.

January 25, 2006 08:32 PM Forum: Equipment Talk

14" Tscope

Posted By Lorne Johnson
Thanks Larry. I'm looking into building a T-Scope kit with a Royce conical mirror pretty seriously, so the feedback is useful.

February 20, 2006 05:04 PM Forum: Maksutovs

Mak correctors

Posted By Lorne Johnson
Hopefully Roaland will indeed jump in here.

My understanding is that Mak correctors are thick, one piece, and spherical on both surfaces. It also corrects the aberration of a spherical mirror, so the primary mirror is also spherical. I believe that the thickness of the corrector is designed to make this happen. The entirely spherical surfaces are supposed to make them easier to grind and test to close tolerances.

It certainly works well on my little Mak-Newt.

March 5, 2006 10:22 PM Forum: Beginning Astronomy?

reflector/refractor, planetary-wise

Posted By Lorne Johnson
This really depends on the quality of your dobsonian and how well it is set up. A high quality 10 inch f5 dob (such as the Teleport) with a 1.86 inch secondary (or even 2.14) will give excellent planetary views. It has considerably more resolving power than 4 or 5 inch refractor, even an APO refractor.

The closest SxS comparison (to what you're asking) I've done was between a D&G 5 inch f12 achromat, and an 8 inch f 5.7 with 1.56 secondary dob (Mike Spooner optics). So both scopes were of high optical quality. The dob walked all over the D&G in good seeing and thermal equilibrium. A similar comparison was made between high end scopes on Ed Tings web site with similar results. T Scopes gets excellent results at f 4.7.

This does not mean that you shouldn't get a refractor, a smaller apo is very portable, equalizes very quickly, and gives beautiful views.

March 7, 2006 10:01 PM Forum: APM

TMB80/480 vs TMB80/600

Posted By Lorne Johnson
I do not claim personal experience with these. I believe that Markus has noted that some people prefer the 600 as it will reach higher power for planetary viewing without resorting to very short focal length eyepieces or barlows (and tiny exit pupils). I suppose that it would also be more forgiving of eyepieces, but f 6 is hardly a real problem either, These would not appear to impact your intended use, at least very much.

March 21, 2006 12:51 AM Forum: Eyepieces

So, how many have the Siebert Observatory EPs?

Posted By Lorne Johnson
I have the Siebert 36 mm observatory eyepiece. I found it to be quite competitive with the 35 mm panoptic that an observing friend owned. Stars stayed as pinpoints quite as well, and the field stop is certainly wider than the panoptic.

Jim's observations may wind up hurting my enjoyment of the eyepiece, but I have not (yet) had his negative experiences with it. I should note that with the eye shield off it has significant reflection issue, and with the eyeshield on I have had no trouble with balckout.

Unfortunately, or perhaps fortunately, I no longer have access to a 35 mm panoptic to compare it with. When my friend had his 16 inch f 6 dob, we used the Siebert in it a lot because the Panoptic required rebalaning. I put a retaining ring on the barrel to make it parfocal with TV eyepieces.

April 16, 2006 01:53 AM Forum: Eyepieces

Comparing Performance On Naglers - For You, Floyd!

Posted By Lorne Johnson
Thanks Chuck!

I read a comparison of the 20mm type 5 and the 22mm type four that found the 20V clearly had better through put than the 22.

Did you look at through put specifically?

Lorne

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