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Re: (meteorobs) Oct 15 Observations ZAYGE

In a message dated 96-10-17 02:39:01 EDT, you write:

<< Actually, George, I got a great deal on a 1960s vintage Miranda Sensorex
 that I use for my astrophotography (don't much enjoy the daytime kind, but
 I have friends who are real shutter bugs). Anyway, it's all manual, and I
 use a 15' cable release with it. I was just curious about whether you were
 doing shorter exposures (like 15 mins), and if so, how you were tripping
 them from the top of your observatory! (Like, maybe with a 50' cable
 release?! :>)
 
I do have a 30 foot air actuated cable release, but I don't use it because I
still have film advancing and polar alignment to do. For awhile last summer,
I had a spectrograph set up down below as well with that cable release. The
plan was to keep the bulb in my hand and whenever I see a bright meteor of
about -3 or brighter, I was going to squeeze the shutter open with hopes on
catching at least a portion of the meteor to obtain meteor spectra. I think
the plan is still good, but got to be a hassle beyond what I want to put up
with. I still will try it during the peaks of major showers such as the
Leonids, Geminids and Perseids where the effort will be more worth it. But
for any night observing, it's too much. I also will be running my chart
recorder during the Leonids and Geminids to see if my solar cell set up to it
is workable. I tried it last month, but nothing bright passed in front of it.
I did note an increase of the crescent moon registering...I'm hunching that I
can get at least -6 fireballs to register and perhaps go down to about -3.
This is also something that I'll only be using during major showers...the
Leonids, Geminids and Perseids. I might be able to do better than that, if I
can figure out why when I have the two solar panels hooked up in it's most
sensitive mode does constant screwey things on the chart recorder. 
 
 >>Anyway, you answered my question: you do 20-30 minute guided exposures
 instead. But NOW I'm curious about something else: why is it that guided
 exposures allow for longer exposures? I'd figure that fogging and other
 stray light problems would actually be WORSE with guided than unguided
 exposures: is that not so?<<

Lew, I think film fogging has become a great big "boogey man" for no real
reason. I use exclusively Black and white, so it may be different for color.
 I can't say that guided versus unguided will have various degrees of
fogging. I've done unguided mainly by accident on occasions. Last Summer I
did a 4 hour unguided exposure for the fun of it with another camera out in
the field. I was trying to compose a windmill and some trees with the star
trails. The negative was dense but not "bullet proof"..dot it was certainly
useable.  With my guided camera, I sometimes get an exceptional polar
alignment that allows me to make 1 hour exposures without any star trailing
with a 28mm lens.  I haven't seen any fogging to cause any concern.  I have
made perfectly normal prints from these. From my astrophotography days when I
used hypered 2415 film, now fogging became a concern, but usually not from
the exposure.  That fogging seemed to be due to not processing right away or
warm temperatures negating the hypering process. This is all of course from a
very dark location. If you notice most of the black and white photos in the
various astronomy magazines, their exposures can go up to 3 hours...but more
normally around 90 to 120 minutes. I see no fog effects with these to worry
about...actually that goes for color as well.  Of course the amount of light
may be different due to various f/stops being used.  With my 28mm I use
f/2.8. This is relatively fast when compared to most photos in the magazines
that are probably using anywhere between f/4 to about f/10.  I can safely say
that I have good negatives at least after an hour of guiding.  As for
worrying about stray light..dot it's all a lesser problem than I thought. I use
to be concerned about the headlights of cars driving by affecting my
exposure(about 100 feet away). But after a few years of this and Bob backing
his car with it's tail lights literally only a few feet from the camera when
he comes in to join me, I think I've only noticed once or twice any possible
car light problems on any negatives.  It's the airplanes that torks me.
 
>> Or is it just that you can do longer exposures because the field doesn't
 change so much? (An important point I've neglected in my photography so
 far!) Is it just because camera FOV is easier to determine with a guided
 exposure, or is the analysis of unguided images actually too hard with
 longer exposures?<<

I use guided exposures for a variety of reasons. Mostly for personal
preference. I prefer to see the sky looking like a sky rather than a lot of
star trails.  Also, when I get a meteor in the field, it's easier for me to
figure it's path...ie begin and end points. Analysis of unguided images is
done routinely by some, but I believe the longer the exposure, the more
uncertain these points become and yes I would think more difficult.  unless
you know almost exactly where the camera was pointing, you may not be able to
know what 6 stars to get a good fix on.  As a routine, I always list
approximately where my camera is pointing for each exposure...even then the
print sometimes looks foreign. The sky looks different due to the addition of
many stars you normally don't see
 
>> Thanks in advance,
 Lew
 
 PS: BTW, George, keep healthy! Those marathon 6 hour sessions y'all are
 always doing must really wear on you after a while, especially in the cold!
  >>

Oh! I feel fine this morning. I will be observing tonight. 
George Z.
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