star trail

[denniskee]

pie say, thought you shooting sunrise, so call you @ 0530hr.

yup, clear sky, the canel difinitely a very good place to shoot star trail, as long as its a moonless night.

 

[Ian]

any suggestions to prevent lens fogging? we also had this problem towards dawn.

I dont want to stand there for full 2-3hr, using lens blower to blow the lens to prevent condensation.

remember reading something about wrapping the lens with tower or something.

The most effecient heating method is to make up a chain of resistors that will give you around 3-5W of heat dissipation, that is more than sufficient for a typical camera lens of 72-77mm diameter. Powering it from a pack of NiMH batteries will give you ample power for the night. If you are really keen adding a simple voltage control circuit or PWM controller will give you better battery life and allow you to match the amount of power to the dew point and so on.

Heat packs etc produce too much heat and lead to excessive temperature differential in the lens that can result in focus issues due to the exapnsion and contraction of the lens elements.


A bit about star trails
Stars appear to rotate around the celestial poles at roughly 1° per 4 minutes, or 15° per hour. Using a longer lens will reduce the apparent angular coverage of the sky and thus make your trails appear longer. The drawback to longer lenses is you are more likely to suffer image quality issues unless you have a rock steady tripod and there is no wind/breezes etc.

Ian

 

[denniskee]

thanks Ian, for your valueable input. :thumbsup: