Seeing impact of imaging in a Dome

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AJ132
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Seeing impact of imaging in a Dome

Post by AJ132 »

I have an 8' Explora-Dome with a permanent pier that I use for nighttime imaging. I purchased my first solar scope last year (Lunt LS80MT). I tried solar imaging a few times from inside the dome, but the seeing each time was terrible. I am curious what the is the impact on Seeing when solar imaging inside a Dome vs imaging on a stand alone mount outside the dome? I know that the sun heats up the dome through out the day causing it to radiate heat, but not 100% sure if the Dome is causing the poor seeing or if the seeing was just bad in general.

I am looking at making some changes to my mount in my dome and wondering if I should keep the old mount so that I can set it up outside the dome for solar imaging. I am curious if anyone here has solar imaged both inside and outside a Dome and noticed any differences?

Thanks in advance for the helpful info.

Andrew J


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Re: Seeing impact of imaging in a Dome

Post by marktownley »

Hi Andrew,

You're going to have to give us a few more clues here - what time were you observing in the dome? Was it summer/winter etc?

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Re: Seeing impact of imaging in a Dome

Post by Bob Yoesle »

I have no direct experience with domes as of late. But I do see the dome is fiberglass.

I would bet the outside seeing is better. I would imagine the fiberglass would be a good source of stored thermal energy, which would negatively affect the seeing immediately through the opening.

The solution for all solar observatories is to use "cool roof" paint materials that have both high reflectivity and high emissivity.

I've used Henry 687 enviro-white (carried at Home Depot) with good success for my roll-off-roof observatory, and would consider this a must for a dome.


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Re: Seeing impact of imaging in a Dome

Post by christian viladrich »

As said by Bob, domes can have good or bad impact of day-time seeing.
During the day, the heating of the dome surface will degrade the seeing. A difference of 2°C between the surface of the dome and
the ambient air is sufficient to seriously degrade the image quality. You can check this with an IR thermometer.
Thus, iit is recommended to paint the surface of the dome in white. Professionals use titanium oxide or zinc paints because they help stabilize the surface temperature to the air temperature. This is explained by the combination of their high reflection coefficient (typically 84%), which limits the heating of the dome by the incident solar radiation (particularly infrared), and high thermal emissivity (typically 93%) which gives efficient re-emission of the heat accumulated by the dome.
A friend has a 435 mm (aperture) refractor in an aluminium ASH Dome. The dome is painted with titanium oxide paint. The seeing is quite good.
Still ... roll-off-roofs are preferable ;-)


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Re: Seeing impact of imaging in a Dome

Post by AJ132 »

Hi Mark.

Sorry, I forgot to mention that I primarily do solar imaging during the summer months when it is too hot to do nighttime DSO imaging. I live near Houston, Texas so it can get quite hot during the day. I try to do my solar imaging in the mornings before it gets too hot. The ExploraDome is constructed from UV stabilized polyethylene plastic. The dome itself is not painted. The tan color is "baked" into the plastic when it is made.
Last edited by AJ132 on Thu Feb 25, 2021 8:28 pm, edited 2 times in total.


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Re: Seeing impact of imaging in a Dome

Post by AJ132 »

So the feedback here so far has confirmed my suspicion that the reason I was getting such poor seeing last summer was at least partially due to the temperature differential between ambient and the stored energy in the dome. I am not in a position to switch to a ROR so it would seem that my Dome should be kept for nighttime imaging and for daytime solar I should move outside and setup a mount away from radiant heat sources. I just put down a deposit for an Astro-Physics 1100 GTO mount which will take over the primary mount position in my Dome. My current Mach1 will be then available for Solar, which I can setup out in the yard.


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Re: Seeing impact of imaging in a Dome

Post by MapleRidge »

Andrew...

The dome will treat yo better if you can image in the morning before it heats up as much as compared to later in the day, and ideally you have few heat sinks to start radiating heat after the sun warm the landscape up. A white dome and wall exterior is also highly recommended.

One other thing to look at is the colour of the observatory interior (dome or roll-off both). A nighttime setup with dark walls will heat up in the light of day and dark flooring isn't noticed in the dark but will add to the interior heat sink.

Just my opinions ;)

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Re: Seeing impact of imaging in a Dome

Post by AJ132 »

Thanks Brian for the feedback. I will definitely consider it. I think I would like to have the option to be able to use both the 80mm or the 100mm if the seeing is good enough for the 100mm.


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Re: Seeing impact of imaging in a Dome

Post by MalVeauX »

Heya,

Paint the outside of your dome with white paint that is meant to specifically not hold heat (reflect, high emissivity as Bob pointed out). Make sure ALL dew has been evaporated off and that it's dry. If you have active evaporation occurring, your seeing will suffer greatly. It needs to be dry and very, very white. I redid my observatory twice, to get materials on the outside that would not hold heat and would reflect heat via the paint I used. It made a world of difference.

Then see what time during the day is most likely your best seeing moments. Focus on those times when its most commonly supposed to be good.

Meteoblue has a nice predictive chart to work with as a starting point (plug in your location and look at astronomical seeing):

https://www.meteoblue.com/en/weather/we ... ca_4644585

Very best,


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Re: Seeing impact of imaging in a Dome

Post by AJ132 »

Hi Marty.

Thanks for the helpful feedback. I picked the tan dome color so that is would not draw unwanted attention from my HOA. If I paint it white I am afraid I might end up on the wrong side of the HOA Police. For now I think I will just try setting up my Mach1 out in the grass in my back yard and avoid shooting over any radian heat sources. I plan on relocating in a few years once my son graduates high school and plan to avoid HOAs like the plague so that I have more freedom on what I can and cannot do on my own land. Unfortunately, in mean time I have to play by their rules.

Andrew J


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