Ok, that sounds like a good place for it. I was trying to figure out why the tube was reading warmer than everything else.
Now that I think about it, maybe the tube reading is good and the mirror temp reading is a couple of degrees too low. As the mirror cools it might be warming up the tube with no fans there to move the air away. Hard to see where else the heat is coming from to warm the tube up like that.
Next experiment is to test out the fan i have superglued to the middle of the mirror. I reckon that the secondary shadow should cover this area and wont affect my viewing.
Cloudy here today and no doubt tonight, so the temp drop wont be as dramatic, but i hope to test out the fan tonight.
there is a little ledge at the base of where the clamps screw in. I glued it there.
I am going to move it around the other side because when i tilt the scope, it now hangs above the mirror. I am thinking that this is not good if the glue gives way. I have tried this superglue before and it comes away from metal with a solid tap with a chisel
The mirror is a bit dirty hee hee, but I will wait a fair while until i get the courage to clean. I have done an alright job with the cheapie ep's i have, but not a good enough job on the mirror.
Homework...mmm, there's always the Bird approach - "if it don't fit, drill more holes".
To be serious for a moment, I think the opinions are divided about where the fan should be - some people say on the back of the tube, and some say on the side of the tube like where you have it, or even down a bit so it's blowing/sucking partially onto the side of the mirror.
Where most people agree is that if you have a passive fan arrangement then you're better off sucking the hot air out of the tube. The computer case and power supply manufacturers worked that out many years ago.
I've experimented with fans sucking the layer off the mirror. It created a cyclonic effect in the OTA....the column of air in the OTA rotated as it was sucked down past the mirror, & you could see the effect at the eyepiece. Good stuff Dave, good to see your experiments.
Dave, I've been inspired by your efforts and I now take a digital thermometer outside with me when observing. It's just measuring ambient, but it gives a good indication of how well the scope will perform. Once the temperature does not change much more than about 1/2 degree in 1/2 hour, the views are getting good.
The thermometer itself appears to be limited in relative accuracy to not much better than 1/2 degree. E.g., it can keep jump back and forth between say 12.2 and 12.7 degrees without displaying any values in between, but at other times it will show values between; like after I take it inside... The odd jumps and flat bits on your graphs might be due to inaccuracy in the measurements.
