Mars:7/27 refractor vs. reflector

A friend came over the other morning @ around 0415 to do some Mars observing.
Mars was about 45 degrees above the horizon. He used his 8" newtonian and I used a 6" F8 refractor w/chromacor.
We set up on the deck and looked over the roof of my house. I set up a least a half hour before he arrived.
We planned to observe with similar magnifications for comparison.The atmosphere was stable, the sky was clear, &the jet stream was nowhere to be found.
We expected his reflector to need time to cool down, but were surprised to find how wrong we were! Regardless of magnification, the refractor never seemed to settle down. The images blurred, danced, & never stabilized in the refractor while the reflector produced steady, sharp images, with detail. This was counter intuitive and surprised us both (particularly me.) I thought refractors generally don't have cool down problems. Has anyone else experienced this or have any ideas about how to deal with it? thank you, Bill

[QUOTE]Bill Barrett said:

A friend came over the other morning @ around 0415 to do some Mars observing.
Mars was about 45 degrees above the horizon. He used his 8" newtonian and I used a 6" F8 refractor w/chromacor.
We set up on the deck and looked over the roof of my house. I set up a least a half hour before he arrived.
We planned to observe with similar magnifications for comparison.The atmosphere was stable, the sky was clear, &the jet stream was nowhere to be found.
We expected his reflector to need time to cool down, but were we surprised to find. How wrong we were! Regardless of magnification, the refractor never seemed to settle down. The images blurred, danced, & never stabilized in the refractor while the reflector produced steady, sharp images, with detail. This was counter intuitive and surprised us both (particularly me.) I thought refractors generally have cool down problems. Has anyone else experienced this or have any ideas about how to deal with it? thank you, Bill

Could have been hot air trapped inside the tube, or cold air.

Chas

Local hot-spots on roof (vents, etc.)?
"set up on the deck and looked over the roof of my house"

Was the Chromacor and diagonal also in the scope and
cooled for the half-hour? Also, half-hour might not
be enough depending on temperature swing.

We wondered about the heat being given off by the roof, but it didn't seem to bother the reflector. I was sure to have the chromacor in the scope when I set up...that might have been the problem(?)
Someone suggested that some warm air may have been trapped inside the tube. There are 4 baffles and the entire inside of the tube is flocked. So, maybe for cool down, I should try having the end cap off & chromacor out so air can circulate inside the tube.

Since the original post I have had 2 more sessions with Mars, and have had much better success. Prior to observing, the scope was mounted cap off, lens down,and was allowed to cool for about 30 minutes. This really helped. The images were much more stable, with excellent surface detail, and a bright white polar cap. I could not have asked for more.
Thank you, Bill