New Mirror Cooling Simulator software

[Satchmo]

A great new piece of software from Robert Houdart who brought us the mirror edge support calculator. Makes it easy to study where the margins of performance lie for your mirror over different amounts of temperature change during your observing session. The online help is excellent.

http://www.cruxis.com/scope/mirrorcooling.htm

[davidpretorius]

top find mark,

i will read with interest!

[KISA]

Awesome Mark, thank you very much. I've been looking at setting up cooling on my primary but have been unsure if it would be worth the effort. This has given me the answers I was looking for. Cooling here I come. :D

Thanks again,

Markus

[davidpretorius]

Hey Markus, Bird is just down the road at Murrumbateman, ,he is a leading expert on primary mirror cooling.

[iceman]

Bird and Markus are friends already :)

[davidpretorius]

bugga, now where is that embarrassed smilie gone????

[bird]

Thanks Mark, I'll see if I can find Roberts email address - I've got lots of cooling graphs that he might find useful.

It's interesting to look at the examples he's chosen to illustrate the software - seems like he's left out one important graph, "mirror with fans in dropping ambient" that would show that even fans are not enough if the ambient is dropping 1.5C or 2C per hour, probably the most common event for many of us.

eg here's last nights graph from my home, you can see that ambient was dropping very quickly!

update: I found his email address and sent him an email.

cheers, Bird

[bird]

ps, looking over my graphs from the last couple of years I reckon you have to factor in a temperature drop of between 1.5C and 3C per hour from sunset through to midnight. After midnight things tend to be reasonable stable (but not always) until just before dawn when the temp will often plummet another 2 or 3C very suddenly - eg look at this graph from this morning (follows on from the graph above). Look what happens to the ambient when you get within an hour of sunrise!

cheers, Bird

[davidpretorius]

yes, i get at least one degree drop around this 5.30am to 6 whilst imaging jupiter this apparition

[KISA]

Certainly no need to be embarrassed :thumbsup:, and you're right, Bird is certainly the man to talk too. We have discussed the topic, but have been unsure if my primary would need additional cooling as it's a lot smaller than his and might not suffer the substantial delay in natural cooling that his does.

Originally I was going to attach temp sensors over my scope to determine if I needed cooling so in that regard the simulation program has certainly made that task a lot easier.

From your experience Bird, what temperature difference between the primary mirror and ambient has been enough to noticeably affect image quality and warrant cooling?

[davidpretorius]

at high mag, 1/2 a degree either side of ambient is the target

[iceman]

I'd agree with David, based on my experiences too.

[KISA]

Thanks guys, that puts me in an interesting position. From using past temperatures and my primary mirror specs I end up at spot on 1/2 a degree behind a dropping ambient temperature. So is it worth it??? :shrug:

[Satchmo]

I'm guessing that to work out the correct setting for the cooling co-efficient setting for a current rig, its only necessary to attach a digital temp probe to th eback of the mirror and measure ambient as well. Given knowledge of the mirror material type and thickness one should be able to monitor everything for a number of hours , draw a gragh , then play with the cooling co-efficient setting until a match to your data is obtained?