I emailed Bird about this the other day, and I noticed Dave P also brought it up in a different thread so I thought it's worth a thread of its own for discussion.
After seeing Anthony's piece of art in action at Snake Valley, it's made me much more aware of how the mirror temperature can adversely affect the image. What I'd been blaming on bad seeing, could (in some instances) be bad temperture differences between the mirror and the surrounding air.
Seeing on Anthony's laptop, the difference in the image when the mirror was not an ambient, versus when it was after he'd had the cooling system running, was significant.
So of course it's now in my mind as a next project - to cool my mirror. However baby steps are in order, as I don't have the time or the skills to get it all done quickly.
So the first step is to monitor the temperature of both the mirror and the surrounding air, to at least log the differences and so I can see visually (through the eyepiece and via imaging) what the differences are when the temperature difference is great, what the differences are on hot vs cold days/nights, etc.
Anthony has 2 sensors measuring the temperature of the mirror, and 2 measuring the ambient temp, and feeds them into his laptop for graphing. That's where I'd like to start.
Obviously stage 2 is the actual active cooling - to bring the mirror temperature down. I'll worry about that bit later.
So Anthony, any pointers you can give (that we can all share in
) regarding a setup like that.. such as:
1) The type of sensors to use
2) Where they are placed on the mirror and where they are placed for ambient
3) How you stuck them on
4) Feeding the data into the laptop
5) Graphing the data
PS: I use Windows
I imagine Dave P is going down the same train of thought, so hopefully between the two of us (and anyone else who may be following suit) there might be a nice how-to article as a result.
Thanks for any advice and help.
- very impressive! I guess this setup is easier to implement for a newtonian with access from rear compared with cassegrains (even mine which is open at front is sealed at rear). Had a thought though that perhaps some useful data could be created for these scopes through experimentation and then relating experimenal results back to real-time log of temperature just on the outside tube surface (avoiding need for cable to intrude into the scope etc). In other words setup/attach sensors temporarily on mirror, inside tube and outside etc and then expose the scope to a range of temperature profiles, recording the results. From this it might be possible then to come up with some "scope-specific" data to predict when a mirror's temp would be close to ambient air temp simply through extrapolation of the outside tube temp profile. Nowhere near as accurate as a real-time inside/outside measurement setup as you have, but probably a lot more accurate - and specific to the users scope -than the simple rules of thumb many of us would use now (eg stick SCT outdoor for at least 1hr prior to us etc).
I guess how useful this approach would be might depend a lot on the local environment too - how stable and consistently temperature typically varies at one's prime observing location (eg. my backyard), by how much and how quickly. Brisbane might be a bit milder/predictable in terms of night time temperature variation than many other areas - I'm guessing here!
