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Posts Made By: John Wilson

March 9, 2008 06:19 PM Forum: Eyepieces

Brandon 32mm field stop question

Posted By John Wilson

Hi Doug.

Call it insanity but I've had at least 3 32mm Brandons. Two of them, an aluminum-sided one from the 50s or 60s and a black one from the 60s (both flat-tops), had field stops. I had another flat-top from the 70s that apparently did not. I've never owned one of the more recent variety with the rubber eye cup so I can't comment on that design.

Hope this helps,
John

April 21, 2008 09:27 AM Forum: Pictures of Me and My Telescope and........

Joshua Tree the morning after...

Posted By John Wilson

Hi... Could I ask you about that rugged-looking chair you use? Is that home made?

Thanks,
John

January 29, 2009 01:39 PM Forum: Equipment Talk

It had to happen..bifocals

Posted By John Wilson

Hi Ivan.

I've worn trifocals for a number of years and have found them OK for observing. They're not graduated and sometimes the "line" separating the different portions gets in the way. But then all I do is move my head a little and the problem disappears. I would expect bifocals to be OK, too.

John

June 18, 2010 12:52 PM Forum: Eyepieces

field stop measurement for eyepiece fov-works?

Posted By John Wilson

Hi Greg.

Several years ago, I asked David Nagler about the differences you get between the fs-based calculations for tfov and the afov-based calculations. If I'm quoting him correctly, he said that the formula tfov = fs * 57.3 / focal length is the correct calculation for tfov. It's not an approximation. The division of afov by magnification is the approximation. The reason is that different eyepieces with the same true field can have different apparent fields, depending on how light rays converge on your eye after traveling through the various eyepiece elements.

John

July 19, 2010 09:26 AM Forum: Eyepieces

September 24, 2010 01:09 PM Forum: Eyepieces

Clave 45mm 2" value?

Posted By John Wilson

Hi Fred.

I haven't seen this particular focal length in a while but other 2" Clave's have been advertised in the past few years from high 300s to low 500s. I guess what you asked would also depend on condition and, to the extent you could determine it, its vintage.

Hope this is helpful.

John

October 31, 2010 07:14 AM Forum: Zeiss

CZJ Micrometer problem

Posted By John Wilson

Hi John.

Baader Planetarium has a pretty good knowledge of Zeiss stuff. I had an AS 80/1200 OTA that developed a problem with its helical focuser. After exchaging some e-mails with Thomas Baader, I shipped them the focuser and they did a good job of fixing it (though not cheaply!). They might be able to help with your micrometer.

Best,
John