Err... W= (V x V) / R = (9.6 x 9.6) / (8 x 5.6) = 2Wyour design only draw 0.2 A (1.76W) which is too low to generate enough heat.
Hmm... 4.8W... will it be too high?? Anyway, will try out using slightly less resistance, but first need to get some 1W rating resistors first.you should consider using a 12V Gel battery pack or use 10 NiMH batteries instead and reduce the total resistance from 45 to 30 ohms.
that should give you 0.4A (4.8W). A 4AH Gel pack should give you about 9-10 hrs while the Sanyo 2500mAH NiMH battery should yield about 6 hrs.
Hmm.. how you measure the temperature on the lens?? Quite uncomfortable in putting sensor on my lens to measure it temperature. Also, as what I mention, I can't feel the heat in the dewshield without putting the lens cap on for a while and also can't feel any heat on the dewshield itself.Hmm.. have you measured the temperature of the lens? A temperature increase of 1 to 2 deg C over the ambient temperature is usually sufficient to prevent dew formation. You also know that too much heat will generate tube currents. If you need to measure your tube temperature I have the sensors. Let me know when you are free!
Anyway, will review my dewshield design again after it go through a few observation session.
Thanks and have a nice day.