Re: [APML] Frost on the ST-4. was: ST-4 values?

["bert katzung" <katzung1@home.com>]

Hi Shekhar:
The frost problem doesn't have anything to do with the external temperature;
it's the frost that builds up inside the chip chamber window due to the
cooling of the chip. Even at 70 deg F air temperature, the chip is being
Peltier-cooled to a much lower temperature and if there's moisture inside
the chamber, it will either dew up the window or actually freeze on it. I
have a newer ST-4 that I use in the SF Bay Area and I went through exactly
this set of symptoms a year ago. When I looked at the window (60 or so
outside temp) there was frost on the inside.

After I baked the dessicant ring, the problem went away. It was my
understanding that SBIG will supply dessicant rings for the older ST-4s on
request; you should ask them.

Now I start the ST-4 as soon as I start setting up. Just before inserting
the nose piece in the eyepiece barrel, I look at the chip with my flashlight
to make sure there's no sign of frost. Hasn't recurred, but if it does, I
know there'll be no guiding that night.

Bert

Bert Katzung
katzung1@home.com
www.astronomy-images.com

----- Original Message -----
"Shekhar Borde" <shekhar@prodigy.net>
said:
> Thanks, but I am pretty sure it's not frost.  I live in California <g> and
> I have seen this problem when it's 70 degrees outside.  Anyway, my
> ST-4 unit is quite old and doesn't have a dessicant ring.  I think SBIG
> added that later.
>
> I have never really had any problems with mine -- I've just wondered why
> it won't saturate even with the brightest star.
>
> Shekhar
>
> > Be sure the window isn't frosted over from the inside. The dessicant
needs
> > to be removed and baked occasionally, I did mine every year when I had
an
> > ST4. If it frosts up, even a little, the brightness readings get lower.
This
> > was one way I would notice that it was time to bake the dessicant.
> >
> > Steve...
> >
> > swalters@att.net
> > http://astrophoto.home.att.net
> >



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