Hello to all,
I have a question on material of dew shield.
There are commercially available dew shields that are made of metal, polymer and fibrous material almost exclusively. And all of them function well to a certain extend. I would like to find out which is the more effective material of dew shield given all factors are equal?
Without further evidence, my gut feel is incline towards poor thermal conductor as the better option, however i might be wrong as metal dew shied are prevalent.
Hence, anybody who can shed some light on thermal properties of the material with regards to dew prevention would be appreciated.
Thank you in advance.
Matthew
Material of Dew Shield
scopes pointing towards to cold dark skies loses heat thru radiation. the main purpose of the dewshield is to prevent the scope from seeing so much of the cold dark skies. based on this alone, any material would serve the same purpose, as long it can shield the scope.
but i read somewhere else, the dewshield is suppose to allow dew to condense on it, so that the air will be less moist when it reaches the scope. how true this is, i have no idea.
personally i feel that one shouldn't be too concerned about the dewshield, since it can only help prevent dewing and not completely stopping it. even with a dew shield 2x the diameter of the aperture, dew continues to settle on the lens. the only way to completely stop dew would be using a heater. either in the form of heat packs, or those electronic version.
~MooEy~
but i read somewhere else, the dewshield is suppose to allow dew to condense on it, so that the air will be less moist when it reaches the scope. how true this is, i have no idea.
personally i feel that one shouldn't be too concerned about the dewshield, since it can only help prevent dewing and not completely stopping it. even with a dew shield 2x the diameter of the aperture, dew continues to settle on the lens. the only way to completely stop dew would be using a heater. either in the form of heat packs, or those electronic version.
~MooEy~
-
weixing
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Hi,
Looking for a dew shield for your Vixen VMC200L??? I think the AstroZap Dew shield is quite good, the material seem quite resistance to heat loss and seem to be able to absort some of the moisture in the air in the dew shield, thus minimize the dew.
Yes, open tube design of the reflector and the Cassegrain had less dew problem than close tube design, but it still had dew problem. The most common problem is not the primary mirror which sit deep in the tube, it is actually the secondary mirror that will dew first. That's why those expensive teleport have a built-in heater behind the secondary mirror... no money to buy a built-in heater secondary holder
Have a nice day.
Looking for a dew shield for your Vixen VMC200L??? I think the AstroZap Dew shield is quite good, the material seem quite resistance to heat loss and seem to be able to absort some of the moisture in the air in the dew shield, thus minimize the dew.
The heater/heat pack version is only useful to SCT/MCT and refractor. It won't be useful for those who have a reflector or a Cassegrain telescope which is a open tube telescope.personally i feel that one shouldn't be too concerned about the dewshield, since it can only help prevent dewing and not completely stopping it. even with a dew shield 2x the diameter of the aperture, dew continues to settle on the lens. the only way to completely stop dew would be using a heater. either in the form of heat packs, or those electronic version.
Yes, open tube design of the reflector and the Cassegrain had less dew problem than close tube design, but it still had dew problem. The most common problem is not the primary mirror which sit deep in the tube, it is actually the secondary mirror that will dew first. That's why those expensive teleport have a built-in heater behind the secondary mirror... no money to buy a built-in heater secondary holder
Have a nice day.
Yang Weixing
"The universe is composed mainly of hydrogen and ignorance."
"The universe is composed mainly of hydrogen and ignorance." Thanks Mooey and Weixing
Both of you have made a few good points.
In the field, i am usually equip with OTA electric heater, dew shield, heat packs, 12v hairdryer, enough to keep the worst dewing condition at bay. Hence it not so much of an issue for me.
What I am interested to know is the empirical answer (to satisfy curiosity more than practical reasons). Given different materials of the same form factor, which dew up the objective first and which one last? Of course, it would lead to us to conclude why, but that is secondary importance to my question.
Thanks
Matthew
Both of you have made a few good points.
In the field, i am usually equip with OTA electric heater, dew shield, heat packs, 12v hairdryer, enough to keep the worst dewing condition at bay. Hence it not so much of an issue for me.
What I am interested to know is the empirical answer (to satisfy curiosity more than practical reasons). Given different materials of the same form factor, which dew up the objective first and which one last? Of course, it would lead to us to conclude why, but that is secondary importance to my question.
Thanks
Matthew