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Re: (meteorobs) Dewing problems.
Thanks Debbie and Ed,
I hadn't heard of waterproof paper for outdoor use. I'll check with the
office supply place here and see if they have any.
WRT the camera, I can wire up something and battery power it. It comes
to mind that I could make a foam collar to go around the lens and silicone
seal a network of resistors to the inside of the collar. I should contact
the kendrick people and see what one of their heater elements would cost, it
would be more reliable in the end.
Thanks for the suggestion on the synchronous motor driven chopped
shutter. I may be to that point for next year. I just completed my barn
door tracker and found it works reasonably well with about 3 Kg of cameras
on it. I've been working with a 6X7 format Koni-Omega camera along with a
35 mm SLR.
I was out again last night for a couple of hours with my kids. Activity
from when we started watching (about 03:40 UTC) seemed to start better than
the night before but was pretty slow by the time we quit (around 04:45 UTC).
I was messing around with the cameras but my 11 year old daughter kept her
own count.
Ron (in Gander, NF)
----- Original Message -----
From: Ed Majden <epmajden@home.com>
To: <meteorobs@atmob.org>
Cc: <rlthompson@thezonedot net>
Sent: Monday, August 13, 2001 1:41 PM
Subject: (meteorobs) Dewing problems.
> R. L. Thompson wrote:
> >
> > 1) I lost some good shots because the camera objective dewed up.
> >
>
> You can make a chain of resistors and wrap them around a lens shade.
> Feed a voltage to this chain, increasing the voltage in incriments until
the
> resistors just start feeling warm, (not hot), to the touch. This should
do
> the trick. I use a power resistor fed with a/c voltage from a variac.
You
> can also use a light dimmer switch available from home building suppliers.
> We do this for the convex mirror on a Sandia All-sky camera. If you use
a/c
> power to do this make sure your connections are well insulated to prevent
> shock. (BE CAREFUL) Always start at the lowest voltage level, adjusting
it
> until the resisters just feel warm. Dew cap heating devices are also sold
> by atm telescope sellers. Kendricks, comes to mind. They make them for
> camera lenses and up to 14 inch Schmidt Cassegrain telescopes. Probably
> larger, now!
> You can also increase the length of your exposures by using a
> synchronous motor diven chopping shutter. You can select different on/off
> ratios for this purpose. The direct cameras used at the now closed
> Meanook/Newbrook Meteor Observatories in Alberta, Canada, used a ratio of
2
> off and 1 one but 1 to 1 is okay also. This not only provides you with
> apparent angular velocity of the meteor, single station estimated height
> information if you can identify the meteor with a particular shower, and
> also lets you increase your exposures by 2 to 3 times before film fogging
> becomes a problem. Chopping ratios of 10 to 60 times per second have been
> used. For small format cameras 10 to 20 times per second is a good
choise.
> Hope these suggestions help!
>
> Ed Majden
>
>
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