I managed to get this data earlier in the evening than the Lagoon Trifid image. I think there was some asymmetric heating that was causing astigmatism in the rear elements of the lens. This was due to the simple thermostat (pic below) shielding the heat from one side of the lens. I have ordered one with a thermistor sensor on a 2M lead. Even with this crude arrangment the lens temperature was constant to about plus or minus one degree C.
Large image 5MB
http://d1355990.i49.quadrahosting.co...9_05/musca.jpg
Bert