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Dew Strap Placement

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#1 wsuriano

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Posted 27 January 2010 - 02:14 PM

I just ordered a dew controller and dew straps for my imaging scope and guide scope. Both have built in dew shields that I have extended fully. So, where do I put the straps? Just behind the end of the dew shield on the OTA? Or do I put them on the back of the dew shield itself? Or part way out on the dew shield? Does it matter?

Bill

#2 sailor70623

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Posted 27 January 2010 - 02:17 PM

Put them right where the lens is. The idea is to warm the lens, not the inside of the scope. Depending on where your dew shield sets, it may be on the dew shield, or just below it.

#3 John J

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Posted 27 January 2010 - 02:37 PM

I mounted mine at the very back end of the fully extended dew shield, just before it tapers down to the ota. This will still heat the objective and the air in front of it enough to prevent dewing / frosting.

JJ

#4 Midnight Dan

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Posted 27 January 2010 - 04:05 PM

All the dew heater manufacturers recommend placement just behind the front cell of the OTA, on the OTA body itself.

-Dan

#5 Kenny2004

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Posted 27 January 2010 - 09:33 PM

Probably best results would be on the OTA and not on the dew shield. You want to make sure the heat gets dissipated to the lens. If you put it on the dew shield then the heat will be mostly concentrated mostly there and also create hollow heat trap around the front objective lens within the housing of the dew cap. Not very effective for dew moisture prevention.

#6 wsuriano

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Posted 28 January 2010 - 08:36 AM

Thanks guys! That really helps.

#7 coutleef

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Posted 28 January 2010 - 09:25 AM

All the dew heater manufacturers recommend placement just behind the front cell of the OTA, on the OTA body itself.

-Dan


Like Dan wrote. It works wonders for me in dew country.

#8 gnowellsct

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Posted 28 January 2010 - 07:15 PM

Put them right where the lens is. The idea is to warm the lens, not the inside of the scope. Depending on where your dew shield sets, it may be on the dew shield, or just below it.


This isn't the way it works. The lens is typically isolated from the cell, and heating the cell is a near impossibility in any case. When you do heat the cell, because the lens usually has a cork shim or some other insulation from the cell, the way you are heating the lens is by heating the air behind the cell so that it rises to the cell.

This is horribly inefficient. Correct placement is on the tube behind the lens so that the warm air in the tube rises to heat the lens.

May sound awful but that's the way it works.

Greg N






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