Problems with dew-band and dew/frost prevention on Esprit 120

[old_eyes]

This is probably and idiot question with a very simple answer, but I am having trouble keeping my Esprit 120 objective clear of dew/frost.

Last night was clear so I was imaging away happily, monitoring progress from inside the house, when suddenly the subs went bad on me as if the sky had suddenly clouded over. It wasn't that, but when I went to investigate I had what initially looked like dew on the objective, but turned out to be a fairly substantial layer of frost. This despite having the dew-band operating at its usual setting.

The ambient temperature wasn't that low (-2C), but there was quite a lot of moisture in the air.

I turned the dew-band up to maximum but it did not clear the frost in a reasonable time. My first thought was that the dew-band had failed, but I check this morning and it was working. I used a temperature probe to measure the temperature under the dew-band and it was 6 degrees higher than the edge of the lens cell on the scope. So I wonder whether the heat input from the dew-band is being transmitted effectively to the lens cell. There is quite a gap on the Esprit 120 between the inner surface of the dew shield and the body of the scope.

Options are:

1. Whack the dew-band up to maximum and keep my fingers crossed.
2. Add a second dew-band.
3. Extend the dew-shield with some foam camping mat.
4. Change the position of the dew-band. At the moment it is wrapped around the dew-shield at the position of the lens cell. perhaps it would be better at the base of the dew-shield allowing better conduction to the body of the scope and thus the lens.
5. Chalk it up to unfortunate weather conditions and live with it. It is the first time I have actually seen frost on the lens.

I am using the Lynx Astro 4-port dew controller together with Lynx Astro dew bands on main scope and guidescope.

Any advice from other Esprit 120 users, people who have fixed similar problems, or experts on dew prevention gratefully received.

old_eyes

Edited January 21, 2023 by old_eyes

[david_taurus83]

I have the Esprit 100 and usually leave the dew controller to manage the power of the dew bands (Pegasus UPB) and never have issues but if it's cold and frosty I always override it and switch them on full power. It's the only way to be sure!

[old_eyes]

That's the easiest thing to do, and as I have a couple of hours possible this evening I will try that. 

I think I was worried that if the dew-band was set too high it might contribute to convection current in the dew-shield. But that is probably far less likely than dew/frost!

I don't have automatic dew-heater controllers, but I have been thinking about a Pegasus UPB for other reasons, so may check that out.

[Guest]

I run multiple dew bands on my dob. The trickiest one to get right will always be the one on the OTA.  You have no way to know exactly how much heat to apply.  For my environmentals here in Ohio i run the main band around 30 or 40 percent most of the time.  On heavier dew nights that might go up to 50 percent.  On nights that i a certain that i will run into frost i will run at 75 percent for a bit and start backing down to where the dew or frost ends before the focuser and secondary mirror.  This works well for me. 

[old_eyes]

52 minutes ago, Mike Q said:

I run multiple dew bands on my dob. The trickiest one to get right will always be the one on the OTA.  You have no way to know exactly how much heat to apply.  For my environmentals here in Ohio i run the main band around 30 or 40 percent most of the time.  On heavier dew nights that might go up to 50 percent.  On nights that i a certain that i will run into frost i will run at 75 percent for a bit and start backing down to where the dew or frost ends before the focuser and secondary mirror.  This works well for me. 

Thanks.

I must confess that up to now I have tended to set it and leave it, and so far with few problems.

Clearly I have to be more active.

[Guest]

6 minutes ago, old_eyes said:

Thanks.

I must confess that up to now I have tended to set it and leave it, and so far with few problems.

Clearly I have to be more active.

Yeah its not just plug and play.  There is a lot of monitoring that will get you to where you need to be.  The cool thing is you make a dope chart of where you are nightly and you can develop a trend and narrow down where you need to be 

[bosun21]

3 hours ago, old_eyes said:

I turned the dew-band up to maximum but it did not clear the frost in a reasonable time.

The dew bands are not really designed to defrost your objective or whatever. They are best used preemptively to ward of the dew and frost. If it’s dew then at the first sign of it turn the bands up to about 50% unless more is required depending on the severity of the dew. You will learn to fine tune the correct setting yourself. With actual freezing conditions and frost deposits I run mine at maximum BEFORE any has settled on my objective or corrector plate. Good luck 🍀 

[newbie alert]

Have it on full and I have it a little Infront of the cell as you want it heating the air rather than the cell itself... Never personally had an issue with my esprit 

[Guest]

3 minutes ago, bosun21 said:

The dew bands are not really designed to defrost your objective or whatever. They are best used preemptively to ward of the dew and frost. If it’s dew then at the first sign of it turn the bands up to about 50% unless more is required depending on the severity of the dew. You will learn to fine tune the correct setting yourself. With actual freezing conditions and frost deposits I run mine at maximum BEFORE any has settled on my objective or corrector plate. Good luck 🍀 

That depends on the system.  My Orion system will "dew" just that. Hahahahaha, but you are spot on, its better to use preemptively 

Edited January 21, 2023 by Mike Q

[old_eyes]

Thanks for the advice and comments everyone.