Scopes dripping wet

Hi,

I met a group of observers who drive 2 hours out of the city to watch
the night
skies. One of them told me that in all observing sessions, they always
end up with
dripping C8, AP, TV scopes.. meaning not just the lens are wet but also
the tube
because of the coldness. I wonder if you get your scopes wet everytime
you
watch. How many percentage of observers got their scopes wet when
viewing
at night? Is there statistic in astro mag or study about it?

I'm asking this because for those really cold observing place. Maybe
certain
scopes must be avoided such as oil triplets to avoid water getting
inside
the oil or 4 element lens to avoid water being trapped that can't be
reached
by heater? In this case, reflectors that can be cleaned easily is
preferable to
refractors? Any articles about this?

Mango

Some nights things remain dry as a bone, other nights things end up
dripping. I think most of the answers you're looking for will be found
by searching through dew-busting topics.

I don't recall seeing anything specific about which scopes, or which
parts of scopes are more susceptible to damp.

I'll add a data point. I have a Meade LX200 with the standard Meade
finder. After a particularly wet session (everything dripping) the
finder got wet inside despite having a heater tape wrapped around it.
This caused internal fogging on the next couple of uses but easily
fixed by removing from the scope and leaving on the radiator for a
couple of days.

Cheers
Beats

On 30 Dec 2005 00:58:26 -0800, justbeats wrote:

After a particularly wet session (everything dripping) the
finder got wet inside despite having a heater tape wrapped around it.


I have the cheap little 6 x 30 Meade finder on my 12.5 inch dob. I keep
the finder capped at both ends except for the few seconds it takes to look
through it to grab an object for the larger scope. The lenses of the
finder never dew up when this is done.


--Martin

Mango wrote:
How many percentage of observers got their scopes wet when
viewing at night? Is there statistic in astro mag or study about it?

98% admit to it and the other 2% are probably lying.

Mango wrote:

[Some observers] told me that in all observing sessions, they always
end up with dripping ... scopes, meaning not just the lens are wet but
also the tube because of the coldness. I wonder if you get your scopes
wet everytime you watch.

Not every time, but except for those times that I just go out and look
half an hour at some small, discrete target or event, it's mighty rare
that the tube of my telescope *isn't* wet to the touch at the end of an
observing session -- or, at this time of year, covered with frost.
Any respectable scope is designed to handle this. I wouldn't
recommend leaving a scope out in the rain, but a little water
on the outside of the tube is nothing to worry about.

However, I rarely let my telescopes' objectives get wet, and when
I do, it's usually a sign that I've done something wrong. If you use
a refractor or a catadioptric, you really need to take positive steps
to avoid condensation on the objective unless you observe only
in ultra-dry conditions. For a refractor, a good long dew shield is
usually sufficient for a couple of hours, but catadioptrics typically
need electric heaters to keep the dew off. As a rule, Newtonian
reflectors are nearly immune to dew because the objective is
buried way back at the bottom of a long tube that acts as an
ultra-effective dew shield.

It's hard to imagine getting a refractor objective so wet that you
have to worry about water getting between the elements. You
would be unable to view through the scope long before that
happened.

- Tony Flanders

Tony, you wrote, quote:

Any respectable scope is designed to handle this.
======================================
Not true Tony. What do you call a "respectable Scope?"

Any respectable scope can, and will fog, have interiors get soaking wet,
and a hell of a lot of damage can occur because of this.

I'll give you an example about a "very highly respectable scope", an
$11,000 Astro-Physics 10" Maksutov, that is Roland's own personal scope.

Yes, at one Astrofest Star Party, Roland was using his Scope into the
wee hours of the night, He probably capped up, and covered the scope
somewhere around 2am-3am, or so.

The next morning upon removal of the cover (Probably a Desert Storm
Cover) inspection of the scope revealed that the entire Corrector's
internal surface was sopping wet. Why? Just like a cold glass of
Lemonade on a warm day, the cold scope was subjected to the warmer
daytime air.

Was this a fault of the Scope, or Roland's? Absolutely not. This state
of the art scope has every cutting edge optical, and mechanical
advantage, yet due to certain weather conditions, and not having the
advantage to get the scope off it's mount, and bagged, and brought into
a warm dry room, instances like this where you are "roughing it" out in
the boonies, cannot sometimes be avoided.

One would not have to worry about condensation occuring between elements
in an Oil Spaced-Contacted Objective Lens, but it can occur to the inner
surface of the inner lens (Surface R-6 of a triplet) And no doubt
internal condensation can occur to an Air Spaced Doublet, or Triplet
Design Refractor.

To ignore it, and say to one's self, that "Oh it will go away if I just
put the scope by the Radiator in the house" is surely wrong.

Mold, and Mildew, caused by Moisture, can, and will attack an Optical
surface's Coatings, destroying them, regardless of who applied them, or
what type.

I'm very certain after that Star Party, Roland quickly stripped his
scope, and cleaned that BK-7 Corrector on his Mak.

While it seems no one yet has addressed what to do about it I will. Yes
it is preventable in virtually all cases.

Before ever bringing a scope into a warm house, cap all optical
surfaces, and bag it in a Plastic Garbage Bag while it is still outside.
Tie, or tape up the bag tightly.

If it is a long Refractor, such as my 5.2" F-12 Apomax, use two bags if
you have to, one at each end. Let the scope warm up for at least a few
hours till the scope reaches room temperature before revoving the bags,
then let the scope finish "airing out" before it is stored back into its
case.

The one instance though where this method is not going to work, is when
the scope is already covered in a coating of frost, or moisture.
Bagging it will only trap it.

The addition of an acessory like the DDCAP Dessicant Plug for the
Focuser, sold by Particle Wave Technologies, and also Astro-Physics, is
a very worthy add on to any Closed Tube Scope, and will help insure that
moisture will not be sitting inside an Optical Tube

While it is a bit harder to have Open Tube Reflector's Mirrors
condensate, it does happen, and the unaddressed-neglected moisture can
also damage Reflective coatings if not properly, and quickly addressed.
Mark

If it is a long Refractor, such as my 5.2" F-12 Apomax, use two bags if
you have to, one at each end. Let the scope warm up for at least a few
hours till the scope reaches room temperature before revoving the bags,
then let the scope finish "airing out" before it is stored back into its
case.

I have found that even a short bag over the dewshield/lens, and another
short bag over the entire focuser (with a DDCAP in it), with 2 rubber
bands
on each end sealing the bag to the scope, works great.

Sure, moisture condenses all over the outside of the tube assembly for
a while, but the bagged ends stay dry.

I have found that even a short bag over the dewshield/lens, and another
short bag over the entire focuser (with a DDCAP in it), with 2 rubber
bands
on each end sealing the bag to the scope, works great.
Sure, moisture condenses all over the outside of the tube assembly for a
while, but the bagged ends stay dry.
======================================
Exactly. Provided the OTA doesn't look like a piece of swiss cheese, no
way can the mositure enter the scope at the center of the tube. It is
as you say, the ends of the OTA that need to be shielded for all
practical purposes of keeping the optics themselves dry.

If it was a quite long, large 225mm F-9 TMB or larger Refractor, you
might be hard pressed finding a long enough bag/bags to seal/protect the
entire OTA anyway.

Now if it's a smaller-shorter scope, such as a Televue Pronto, C-8,
C-11, or the like, there's no problem at all covering-sealing the entire
OTA (and even Forks/Drive Base) in a bag.
Mark

Mark D wrote:
I have found that even a short bag over the dewshield/lens, and another
short bag over the entire focuser (with a DDCAP in it), with 2 rubber
bands
on each end sealing the bag to the scope, works great.
Sure, moisture condenses all over the outside of the tube assembly for a
while, but the bagged ends stay dry.
======================================
Exactly. Provided the OTA doesn't look like a piece of swiss cheese, no
way can the mositure enter the scope at the center of the tube. It is
as you say, the ends of the OTA that need to be shielded for all
practical purposes of keeping the optics themselves dry.

If it was a quite long, large 225mm F-9 TMB or larger Refractor, you
might be hard pressed finding a long enough bag/bags to seal/protect the
entire OTA anyway.

Now if it's a smaller-shorter scope, such as a Televue Pronto, C-8,
C-11, or the like, there's no problem at all covering-sealing the entire
OTA (and even Forks/Drive Base) in a bag.
Mark

Mark. If a pronto for example is not sealed in a bag after
observations.
Does the condensation reach the inner surface of the lens behind the
front? When this happens. Do you have to open the lens cell and
clean the lens behind. Or does condensation only occurs at the
front element? I'm asking this because if I'd get the FC-100 and
the fluorite being uncoated at the back. I couldn't wipe it with any
clothe because uncoated fluorite being soft, it can leave mark
permanently. For example if you touch the rear fluorite uncoated
element with your fingers. It would leave permanent fingerprint mark.

Mango