thanks Gary, Erick Geoff and John
what I have found on the net for a larger secondary is somewhere around 2-3 watts but being only 2-1/2" I think maybe 1-2 watts.
I thought about the light shield but being a imaging newt it will result in vignetting on the DSLR. So I might stick with a heater..
But having a fan to cool things down would serve to keep the dew away as well...good idea
I have been thinking about a cool down fan for sometime but just havn`t got around to doing it..
cheers