Re: [APML] Camera testing

["Michael Barlow" <mikeba@rochester.rr.com>]

Kent.. Stupid me should have thought of that, just using a star test with
the heartman mask.  But knowing me even if I find that absolute sweat spot
I'd probably still look for some way to better it.  Thanks Kent, and I will
do this.

Jason,  Those patterns on Norman's site look very familiar.  I may try the
USAF 1951 and maybe even one or two others just for shi*s and giggles.  And
as mentioned above, should I have thought of it to begin with, the heartman
mask and star test is probably all I do need.

Thanks everybody,
Michael A. Barlow

----- Original Message ----- 
From: <KGKIRKLEY@aol.com>
To: <mikeba@rochester.rr.com>
Sent: Thursday, February 24, 2005 3:28 PM
Subject: Re: [APML] Camera testing



In a message dated 2/24/05 2:08:36 PM, mikeba@rochester.rr.com writes:


> First, Kent.. Once you mentioned the focusing aids I realized I
> miss-typed. In fact I have a heartman mask for the LX90 but I haven't used
> it but once or twice. I shouldn't have mentioned Focusing directly as much
> as flaws in focusing.. I used a magnifier to focus on the Moon once and
> still came out slightly out of focus enough that the guy who scanned it
and
> used to do this all the time with his photo's pointed it out to me, that
it
> could have been focused a bit better. So that makes me think that there's
a
> ~possibility~ the focusing screen could be off just enough that when it's
> focused in the view finder it's not focused at the film plane, or there
> could be other reasons. Which gives me the idea that if I had a good day
> time pattern to work with I might be able to figure this out. It might
even
> tell me if the film it self isn't seated right and it's getting curled up
> slightly giving me more vignetting then there should be, or many other
> possibilities. I believe my only problem with setting such a test up would
> be the pattern, what would be best? Something with perfectly strait lines
> would help in many ways, I know I'd have to find something with good clean
> and clear lines but I can't think of any other possible parameters or
other
> patterns to find other flaws with the system.
>

I don't think a 'test pattern' will help you.
I've been a professional photographer for 30 years and have sometimes used
optical test charts to test my lenses, but this was at relatively close
distances and not at infinity where telescopes are used.
Achieving critical focus in astrophotography is more difficult that people
believe.
In fact, it's usually the last thing a beginner will consider.
I don't think your problem is the screen or film seating.
Judging, from what you said (above) I would first suggest attempting to
focus
on a very bright star, like Sirius, using the Hartman mask (two or three
hole?), using your eye thru the 0M1 viewfinder. When you see multiple stars
it's
out of focus, when one, it's focused. You could take a series of short
exposures, refocusing between each and have the film developed, then check
to see how
they look and if they are consistent.

Kent Kirkley

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