Small Dome Amateur Observatories - Downsides
Stone, Jack G
Liam – Rolando has a point.
I have noticed that after time – the heat convection from my body does warm up the dome.
Most time I left the door open, but still heat rises.
Rolando – The dome just looked kool according to my wife. Footprint for a roll-off will require presidential approval.
So other option is a flip top roof.
The other aspect is that it kept the stray light off from the sides – I’ve attached some images for reference.
From: email@example.com <firstname.lastname@example.org> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 1:47 PM
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
A person inside a small amateur dome emits a lot of heat that escapes thru the dome slit. That ruins the image.
Some of my experience with domes…
One way to offset the issue of heat in a domed observatory is to use an air conditioner during the day, set to the expected temperature at night. At night, the dome and air are already the same temp and the only real difference is humidity/dust in the air. This can be very expensive/impractical in colder climates like Illinois, but in some warmer locations it isn’t such a bad idea and can make for better images. In Texas this is how some people would handle the problem, and at the HET they keep the telescope freezing all winter to reduce the heat currents at night; the workers there all have to wear big coats all day even when inside.
On Behalf Of uncarollo2 <chris1011@...> via groups.io
Your questions are always welcome in this group. They need to be specific so that people who have done something similar can comment.
When it comes to observatories, I only know roll-off roofs and their peculiarities. I have two of them now, one here in light pollution-city and one in a very dark site in Hawaii. We also have a remote observatory in Chile at 7000ft in the Andes mountains at Las Campanas. each one has their own issues and strengths, but with the right equipment, they can all do a super job.
As far as Domed observatories, I have only limited experience. They don't work for me because I like to be with my scope when imaging and most domes are too crowded. I also don't like the fact that the instruments (and observer) have to exit their stored heat out thru the dome slit, the same opening thru which the scope has to acquire images.
Sorry – I did not mean that in a negative manner.
I’m just so impressed when someone has successfully tackled the LP challenge.
I worry that my questions would seem really dumb questions that I should know – hence my reluctance.
I did post a question regarding Observatory planning and available software.
But I never got a response ☹
Story is that I purchased a spanking new AP1100 GTO4 – and the observatory I have seems like a very tight fit. So a year later it sits unused.
So how can one make an assessment without models or ??? I tried simple geometry, but there is always something amiss in the 3D element.
Like the dome drive track and motor mount etc….. The motor is rather ancient still works, and dialed in steady incremental rotations using my servo tester.
So now I’m thinking of selling the current one, but which one will fit, support my 14” Edge with HS etc… and not stand out like the statue of liberty.
Rather low profile as well.
Any thoughts or considerations would be welcomed.
As for the LED lights – Lenhance Extreme – but that would limit my targets – Any other thoughts?
I have tons of questions!!!
Also I’ve search on CN as well, and found a couple of others who restored their Boyd Observatories.
Bring your questions up here in the user group. That's what we are for, not just for analyzing problems.
Rolando – You give me hope! I will ping you later, I’ve been somewhat apprehensive for the past few years.
Finally the city replaced the MV with LED – guess what they must be 1million lumens – enough to bring daylight to my backyard.
Tips and tricks if you allow me to bug you.
My "backyard' (AP observatory) is in a heavily light polluted area in an industrial park with large malls, gas stations, fast food joints etc, all competing for brightest lights in the neighborhood. The narrowband filter blocks a lot of that sky light, otherwise i would get a white frame with a luminance filter in a 1 hour exposure.
I think you know more about this than I do. But here's what I think:
In order for stacking to actually show the faint details, it has to be a little above the noise floor and then stacking (or averaging) lowers the noise floor so that the coherent signal pops up. If there are no photons that were caught above the noise floor then averaging will do no good: zero == zero no matter how you average.
That's why your long exposure caught enough photons above noise floor from the faint bits to show up. Your backyard must be much darker than mine, because as you increase the exposure time, noise also goes up as well, so at some point the noise is going to dominate and increasing the exposure time doesn't buy you anything.
Yes, higher read noise of course, but interestingly the amount of faint detail is also higher in the 1 hour exposure. Perhaps the detail is there in the stacked image, but buried in read noise.
I don't know how this would relate to CMOS cameras, but CCDs is a different animal. I'm going to try adding several 1 hour exposures if skies permit and see how much faint Ha I can dig out of my light polluted skies.
This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.
Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.
Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:
As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.
Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled: