AllSky cameras (round 2)

[admin]

After a bit of a break, I've decided to have another go at all sky imaging. I stopped last time because the previous camera housing seemed to let in water in heavy rain and in spite of several attempts to seal what I considered to be the likely ways the water was getting in, I never managed to fix it...

So, new all-sky housing from my friend Jason at All Sky Optics . I'm a bit of a difficult customer, since I wanted a set up that I could use with a variety of different makes/models of camera, rather than just one single camera. That means that instead of having a single camera cradle permanently fixed into the mounting, I have a range of them which I can stick in (and remove, with care) using UHB tape.

Here's the new setup attached to one of the runoff rails of the observatory (low enough to be missed by the roof!)

PXL_20230807_185843894 (Large).jpg (344.16 KiB) Viewed 12355 times

The enclosure has a built in dew heater ring around the camera mount to keep the dome clear. I've also added some silica gel sachets inside the box to keep the internal humidity low - every little helps.

Currently I have an Altair 224C camera mounted in the system with a 2.1mm lens. The choice here was determined by a number of factors...

* No need to have a really wide field of view because my sky view is limited by house, trees, etc
* Cannot use a mono camera as I have a security camera nearby that has an IR illuminator
* A relatively square sensor (4:3) works better than a widescreen sensor like the 290C
* Have to choose a camera with a 12.5mm (CS) mounting - larger sensors often have a 17.5mm (C) mounting, meaning short focal CS lenses cannot be used.

I have also been tweaking SharpCap just a bit to help support the all-sky use. The very latest SharpCap 4.1 (4.1.10949) contains two new features that help make this set up easier to run

* Option to allow saving from RAW8 to compressed WMV video.

Why? WMV makes for nice compact recordings, but cannot record RAW data directly as the compression would destroy the bayer pattern. However, if you run the camera in RGB mode then it is hard to get rid of the hot pixels without dark frames, and you can't use darks as the exposure varies (auto exposure). So... Run camera in RAW8, set Dark Subtraction to 'Hot Pixel Removal only', set save format to WMV (having turned on the option to allow this) and SharpCap will do the hot pixel removal on the raw frame then debayer and save to WMV.

* Command line option '/runsequence' to start a sequence automatically when you run SharpCap

This is added for being generally useful, but particularly because I intend to use the sequencer tool to automate the captures (previously I used python scripting which was less user-friendly).

Currently I am using this sequence

Code: Select all

SEQUENCE
    LOOP 100 TIMES
        WAIT UNTIL EVENT CivilDusk
        CAMERA OPEN ALTAIRGP224C
        TARGETNAME AllSky
        LOAD PROFILE "AllSky RAW8 to WMV"
        DELAY 10
        CAPTURE START
        WAIT UNTIL NEXT EVENT CivilDawn
        CAPTURE STOP
        CAMERA CLOSE
    END LOOP
END SEQUENCE

The sequence will wait until dusk (no wait if already later than dusk), open the camera, load the camera settings and start capturing. Then it will wait until dawn (civil dawn, not sunrise), stop capturing, close camera and wait for the next evening.

Camera settings that are being used are as follows (the important ones only included)

Code: Select all

Output Format=WMV file (Lossy Compression, *.wmv)
Colour Space=RAW8
Auto Gain with Auto Exposure=Up to 1600
Auto Exp Target=70
Frame Rate Limit=1 every 30 seconds
Analogue Gain=1600
Exposure=36.585s(Auto)
Hot Pixel Sensitivity=15
Subtract Dark=Hot Pixel Removal Only

Here the Altair camera is set up with auto exposure (which goes up to 60s) and auto gain (configured to allow up to 1600 - that is 16x - gain). Also the frame rate limit of 1 every 30 seconds keeps the video rate vaguely constant as the exposure changes. Might change that to 1 every 60s later.

I guess after all that I ought to share some video... Not the clearest of nights, and youtube has rather messed up the stars in places, but you get the idea



cheers,

Robin

[Buckrogers]

This is awesome Robin and I will try this on the weekend with my all sky camera. I have an ASI224MC with a fisheye lens.
Couple of questions though, how long did you leave this run? All night? You say it's better to do 1 sequence every 30 secs?
Also how much disk space did this take up? Love the bubble idea

[admin]

Hi,

yes, it's an all night run - the sequence is set to start at the end of civil twilight in the evening and stop at the start of civil twilight in the morning (that's when the sun is 6 degrees below the horizon at each end).

The limit to a maximum of 1 frame every 30 seconds keeps the video rate roughly constant through the night - otherwise you would get *lots* of frames for the start as the sky darkens and the exposure is short, about 1 per minute through the night and then lots again in the morning.

If you save to WMV then the output file is pretty small - 10 to 20 Mb. If you did the same but saved to SER then you would be up in the Gb range I think.

cheers,

Robin

[Buckrogers]

Hi Robin,

So I used the scripts you provided and they worked out perfectly but I only got a 25 sec video? Is that normal It was a cloudy night and this was just a test run but each step worked one by one.

[admin]

Hi,

yes, that's about right - SharpCap sets up the video for a faster frame rate than real time, so the whole of the night gets compressed into about 30s of watching. You didn't want to watch it in real time, did you ?

cheers,

Robin

[Buckrogers]

Hi Robin,

lol definitely not just wanted to make sure I didn't do anything wrong. One question when you select RAW 8 and WMF, did you select Debayer on or off?
I have clear skies tonight so will be running this maybe I'll catch something cool

[admin]

Hi,

you need to set RAW8, WMV output, Debayer on.

cheers, and clear skies!

Robin

[admin]

Hi,

just an update or two...

* Update to SharpCap 4.1.10970 to get WMV files that you can seek/pause/rewind/step frame by frame in

* Don't use the Altair 'Auto gain with Auto Exposure' function - I have found that when enabled the autoexposure will reset moderately often to very short (<1ms) and then build up again to the right exposure. This inevitably ends up with black frames in your all sky video. I have now turned this off and set the gain to 1600.

cheers,

Robin