Dobsonian Fan Experiment III

Hello all,
I performed another experiment, this time with our new Explore Scientific 10 Dob (Isaac) to see if using a stock rear-mounted fan improved visual clarity at high magnification. This is my third experiment attempting to highlight a phenomenon known as a "Boundary Layer" and to see if a stock rear-mounted fan disrupts it at all.
I recently conducted a similar experiment using an Apertura AD10 (Carl) using it's stock fan here: • Dobsonian Fan Experime...
Since then, Carl was donated and we are now using an Explore Scientific Firstlight 10" Dobsonian. As this is a new telescope, I wanted to repeat the first experiment as best as I could before moving forward.Isaac did not come with a fan and so I had to attach one. To do this I followed this guide: www.fpi-protostar.com/bgreer/...
The fan I am using is a Noctua 120mm supported by elastic bungees.
The Hypothesis:
Even an acclimated 10" telescope mirror will release heat at a slower rate than the ambient temperature drop throughout the night. As the night cools, the 10" mirror will not cool at the same rate and the slowly escaping heat from the mirror's surface will create a "Boundary Layer" above it.
As light travels into the telescope it must pass through this boundary layer, causing a distortion to the incoming light. This is due to the differences in air density within the telescope. Light passes through empty air faster than dense air. Thus, incoming light will not reflect evenly off the mirror and will make details at high magnification "dance" for the observer.
Supposedly, using a fan to assist with cooling and creating an outward flow of air for the heat to escape should cause the boundary layer to be disrupted and even blown away. This should make details remain more steady, so long as the fan doesn't also cause vibration.
My goal here was to identify that a boundary layer indeed exists moments after a telescope has been acclimated. To prove to myself that my mirror really is radiating heat as the night cools. And to see if using the fan made any difference to the distortions at all.
The Camera Experiment:
On February 14th, 2023, I let Isaac acclimate for 1 hour using a custom-rigged rear-mounted fan starting at 22:00. Before use, the telescope was collimated and all the accessories were acclimated for 30 minutes.
The accessories used were a Explore Scientific Reflex Finder and a ZWO ASI 120MC Planetary Imaging Camera. The reason I used this camera is twofold: One is because it is a cheap and popular camera used by many amateurs. My hope is that if one wished to repeat this experiment, it wouldn't be overly expensive to use the exact same equipment.
The other reason I chose the 120MC is because it has a small sensor and when used with the ES10 Dob the field of view is similar to 250x with an eyepiece. This is considered "high power" or "high magnification" according to this article: www.telescope.com/Telescope-P...
I set up the telescope on a patch of grass and aimed at Polaris, the North Star. Since Polaris stays relatively stationary all night long, it allowed me to have a stable source of light to analyze all of thermal distortion patterns without having to continuously touch the telescope. To better analyze the distortions, I de-focused Polaris until I saw the shadow of the telescope's secondary mirror and its four supporting beams. With Polaris de-focused, the slow moving waves of heat within the telescope were revealed to me.
I recorded two videos of the distortion patterns using the ZWO ASI120MC, both with the fan on and off, roughly two minutes apart from each other.
With the fan off I noticed subtle waves of heat slowly moving across the mirror. With the fan on, the waves of heat are virtually gone and I only see a smooth, circular motion of the air within the telescope. This at least concluded (for me) that a stock-rear mounted fan does make a difference to the movement of thermal distortions. That the fan is actually doing something!
Any insight into what we are actually seeing in these videos would be helpful. I am not certain if the waves of heat I see are actually coming off the mirror, the secondary mirror or coming from the grass the telescope was set on. All I see is that the fan changes the directional flow and structure of the thermal distortions within the telescope.
I am still working on a thermometer to attach to the mirror itself to prove the mirror is still acclimating to the outside temperature. This will be implemented in future experiments.Sources: skyandtelescope.org/astronomy...
The next experiment will be with Polaris in focus.
Clear skies!