From: "Tim" <tjp314@pacbell.net>

Date: November 23, 2005 6:04:52 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: What about the dragonfly 2?

Alan:

I've seen that too.  And I can see tube currents by throwing the planet out of focus and 

watching the plume up the side of the tube and off the secondary (turns galilean satellites 

into pollywogs).  Interestingly, I don't see tube currents induced by the dew heater.  

Similarly, I don't see them with my 6" Jaegers.  I think that this is because I don't have 

anything inside the wooden tube with widely different thermal properties to provide a heat 

source, and the tube is closed and the air doesn't move (for the most part).

-Tim.

--- In Astro_IIDC@yahoogroups.com, Alan Friedman <alan@g...> wrote:

On Nov 22, 2005, at 8:43 PM, Tim wrote:

P.S.  Alan.  I bought a Kendrick dew heater with the basic controller 

a couple weeks ago,

and next to the Robofocus, I find it's the most useful accessory I've 

added so far.  I set it at

the lowest setting, which kept dew off the optics the whole session, 

and the seeing got

"good" and stayed that way for a couple hours.  Before, I had to 

equilibrate again between

"blow drier events", and in reality must not have achieved it before 

the corrector dewed up

again!

Hi Tim - A dew heater is a very important accessory - but I use it 

mostly if I will be out for many hours or up all night at a star party. 

At home imaging sessions I usually set the alarm and get up for an hour 

or two. I set up my my equipment ahead of time and leave it covered. My 

10" mak has a long dew shield - I have a foam "blanket" that I wrap 

around the dewshield - not pretty, but it usually works just fine for 

one to two hours. I hate to bring heat into the equation for high 

resolution imaging. Though I haven't seen it myself, I've heard stories 

of folks noticing the heat plume deformation in the image from a hand 

brought close to the incoming light.

best,

Alan