[APML] Re: Star Measuring WAS: Horsehead and Pleiades testshots with 6x9 camera/OAGand BRC

["Jim Janusz" <jjanusz@dc.rr.com>]

Now this is interesting.  I have attempted to measure stars on my TP
negatives but my measuring engine is rather low tech.  I have a calibrated
loop from EDSCORP.  It's calibrated in inches and only goes to .005 as the
smallest circle.  I regularly have stars that fit within the .005 circle
which I estimate are .004 inches.

You math wizards can help here.  If 10 microns is .0254 inches then I
regularly get stars of ~ 20 microns.  My F7 scope should be capable of ~ 9.5
microns so I expect seeing and halation are causing the difference.  There
are smaller stars on the negative but they are not fully exposed so I don't
count them.

Using this low tech method results are repeatable.

Help or comments?

Jim


----- Original Message -----
From: "Gene Horr" <genehorr@texas.net>
To: <astro-photo@seds.org>
Sent: Thursday, December 20, 2001 5:54 AM
Subject: Re: [APML] Horsehead and Pleiades testshots with 6x9 camera/OAGand
BRC


> > How do you measure star diameters on negatives? I tried with a measuring
> > microscope, but could not get consistent results
>
> Apparently the same thing.  I borrowed a microscope that has an EP with a
> reticle with measuring marks.  You count the ticks then look up the scale
> at whatever power you are at.  It had a very high price tag and the owner
> claimed high accuracy, but I can't vouch for that myself.  I can still go
> back and test the instrument, but how would one do that?
>
> Gene Horr
> genehorr@texas.net
>
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