COLD WEATHER PERFORMANCE Last updated: 31 January 2003

Subject:	ETX-105 Cold weather issue
Sent:	Tuesday, January 28, 2003 16:36:46
From:	simo55@rcn.com (Simonich)
Here is an Email discussion I had with Dr Clay.  You may add it too your
site if you wish.  [read from the bottom]

 Dave
----------


Fantastic and thanks for the update!

Clay
----------------------------------------
Dr. P. Clay Sherrod
drclay@tcworks.net
Arkansas Sky Observatory
MPC/cbat Obs. H43 / Conway
MPC/cbat Obs. H41 / Petit Jean Mountain
www.arksky.org


  ----- Original Message ----- 
  To: Clay Sherrod

  Hi Dr Clay -

  Well I gave  the scope the acid test tonight, or should I say freeze
  test.  As soon as I got home tonight I moved the scope outside.  3
  hours later I went to do some observing of Jupiter.  The views were
  much much better, even at high power.  Extreme cold does take the
  scope that much longer to cool down.  Tonight it was 2 degrees F when
  I finally went out.   I used the scope in purely manual mode, and
  while noticeably stiffer everything still worked smoothly.  Actually
  the scope cooled down so much that when I brought it in after I froze
  up the condensation formed and immediately turned to frost.

  Thanks again for your advice, and I'll forward your advice to Mike to
  post on his site.

  Dave
      ----- Original Message ----- 
      To: Clay Sherrod

      Thank you for your quick reply.  I'll try to be more patient an
      let the scope cool down longer.

      Dave
        ----- Original Message ----- 
        From: Clay Sherrod

        Hello Dave...with temperature extremes like you are experiencing
        I doubt that you are going to get good views at all for three
        reasons:

        1) air unsteadiness, worse when the temperature is coldest;
        2) tube currents; you must allow at least two hours for your
        scope to cool down to ambient temperature;
        3) the 26mm eyepiece is horrible for sharp images; Meade used to
        provide good quality Plossls, but they are very poor now....the
        26 is the worst and has much flaring around the edges.

        I think the cold sky conditions are your key here....NOT the
        telescope.  When the seeing is that bad, just back off and enjoy
        deep sky low power objects like nebulae, clusters and
        galaxies....or some of the new comets!

        Clay

          ----- Original Message ----- 
          To: drclay@tcworks.net

          Dear Dr. Clay -

          Recently I have been noticing that on bright stars like
          Sirius, I am getting some flaring, and last night which was
          very clear and steady here I am barely able to see any detail
          on Jupiter, or the Cassini division on Saturn, even with my
          26mm eyepiece.  THe  scope is a year old now and I know that I
          was getting crystal clear views of the planets when it was
          new.  The strange part is that I seem to be seeing decient
          views of nebulaes like M42 & M43.  Could it be because they a
          fuzzy by nature so I am not noticing the difference?   The
          only other detail that may be worth mentioning is that it has
          been very could out this way lately.   It was 8 degrees F out
          when I came in last night.

          I would appreciate and thoughts you may have on this.

          Thanks, 
          Dave

Subject:	Cold weather scope usage
Sent:	Thursday, January 30, 2003 5:02:24
From:	AlanM@peoplepc.com (Alan McDonald)
To:	simo55@rcn.com
I saw your thread on cold weather performance with Dr. Clay, and I
thought I'd add a few thoughts for you to consider, since I live in
Michigan and deal with cold weather a lot as well:

1) When plastic gets that cold, it gets really brittle.  Be very careful
with it because the plastic will have very little flexibility or impact
strength.  Be careful not to bump it or stress it, because things that
are OK at room temperature can lead to cracks at very cold temperatures.

2) When the meniscus gets that cold, your breath will condense and
freeze on the lens on contact.  The eyepieces also can freeze up just
from the vapor coming off your eye and face.  Your session will be
pretty much over at that point if you don't have a dew remover gun (you
can switch eypieces when they freeze).  A dew shield helps quite a bit
too.

3) When done, I take my hard case outside and pack the scope (being
careful not to breath on it so the icing stays to a minimum) and
eyepieces in it, and close it all up before bringing it inside. I leave
the case closed for at least 12 hours so that the scope can slowly warm
up, and then take it out so that it can finish warming and drying.  By
doing this, I get none of the icing and condensation on the scope that
you observed.  I try to avoid the condensation, because I expect that
the drips that form could enter the tube, thereby increasing the
humidity in the tube during storage (and maybe fogging the primary
mirror on the next cold observing session).

As a general rule, I try to avoid observing sessions when it is much
below 20 degrees F, as I think it is just too hard on the scope to keep
sending it through those severe thermal swings - but I might just be
overly cautious on that one.

Alan

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