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Lens dew heater


daz
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Looking for a bit of a sense check here .....

Have now (finally) got what I think are the correct resistors 4.7 ohms and I think they are 0.5 watts.

So the plan is to make a chain of 6 of these and connect via a fused plug to the 12v output from the power pack.

This gives me the following:

12v

25.28 - 31.02 ohms resistance (based on 10% tolerance)

0.48 - 0.39 amps

4.6 - 5.7 watts

Is this enough power, or too much?

How hot will the resistors get, do you think?

Any input appreciated before I go and melt something vital!!!

Cheers

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... it's for my SLR camera, 50mm lens.

The plan is is afix the chain to a short cardboard tube to wrap round the lens

Just use a longer black cardboard tube and you aren't likely to need a dew heater.  (Its about how much air is held stationary in front of the objective; the tube should project at least the diamater of the objective). 

Steve :)

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It'll be with you tomorrow Daz - post willing.

As with all hoods for wide-zooms, its too shallow to act as a dew-shield on its own but it can be extended so long as you accept that it will vignette at the wide setting.

Steve :clouds1:

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