Night sky images?

[fractonimbus]

How to break the bank: buy the Rolls Royce camera they're using at Siding Spring Observatory

Axis 221 network Camera with Pentax lens

From Mount Stromlo's tech people: "It uses a SONY HAD CCD and sums up many de-Bayered frames after dark, it is fitted with a fast fixed focal length lens."


See: http://www.amazon.com/Axis-221-Night-Ne ... B00083Y57I
and
http://www.axis.com/products/cam_221/

This is a *bad* discovery. And even worse. they have lots of other cameras.

DN

[Gina]

WOW! That's some beasty!!

[Gina]

Has anyone seen anything about avoiding sensor damage from the sun in "all sky" cameras? I've looked at various cameras that use the Sony HAD CCD image sensors and all warn against letting the sun shine into the lens as the sun's image will damage the sensor and lead to failure. The Sony sensors seem to be recommended for low light applications. The articles I've read refer to using CCDs for astrophotography attached to telescopes and used at night. I've always heard that special equipment is required to have the sun within the view. I was thinking of using a physical shutter if I make an "all sky" night camera system. This would require some sort of automatic control.

OTOH I would like to have a daytime "all sky" view, in colour, to show clouds, but that's another matter. I'll make do with the more usual webcams.

[fractonimbus]

The Siding Spring 'Axis' camera does not point at the sun ever, so that's consistent with the advice you read. OTOH, the All Sky camera nearby, which picks up starlight, also looks at the sun all day, without damage. I don't know what sort of sensor it uses, but it's quite old, so the chances are it's a CCD.

DN

[Gordon-Loomberah]

... OTOH, the All Sky camera nearby, which picks up starlight, also looks at the sun all day, without damage. I don't know what sort of sensor it uses, but it's quite old, so the chances are it's a CCD.

I should be able to find that out, and also I think at least one of Rob McN's meteor cameras has the sun in its FOV during the day, although it isnt imaging then... I think they are Mintrons, but will check.

EDIT- update.
details of the camera at the APT:

It's pretty crude, but very reliable, and has now been running for a
decade or so non-stop with practically no maintenance. In essence
it's GSTAR-EX analog low-light b/w TV camera with Pentax wide angle
auto-iris lens. Details of GSTAR-EX current camera versions may be
found at...

http://www.myastroshop.com.au/guides/gstar/index.htm

...including a very satisfactory looking fish-eye lens.

The video signal I plugged into an no-brainer Axis video server.
Current versions may be found at...

http://www.axis.com/products/video/vide ... /index.htm

[Gina]

Details of GSTAR-EX current camera versions may be
found at...

http://www.myastroshop.com.au/guides/gstar/index.htm

...including a very satisfactory looking fish-eye lens.

Very nice! Somewhat over my budget though, pity.

[fractonimbus]

details of the camera at the APT:

Thanks, Gordon. Very interesting.

DN

[Gina]

The first low-lux camera I ordered has arrived - direct from China! This has the 1/3inch SONY Exview HAD CCD which I think was the one someone modified for long exposure. Link here :- http://www.dinodirect.com/1-3-SONY-Exvi ... P&AFFID=51. Now I must find those details of how to provide long exposures

I've had it apart - bit of a "Chinese Puzzle"!!! But once I'd got into the dome case it all comes apart very easily - just a few screws. I think the lens is a standard board camera lens and I have a 2.1mm focal length one of these I can use. Current lens is 3.6mm I think. There was supposed to be a user manual with it but I didn't find one!

It's not waterproof but I think it should be reasonably easy to seal the dome case. They quote a maximum humidity of 85% which is pretty low - we often get humidity above this. Maybe I could completely seal the case and put a bag of silica gel inside with the camera. I don't want to heat it as that would increase the sensor noise level.

[Gina]

Been browsing this thread again and following the links. This seems to be the article I had in mind :- http://www.qcuiag.org.uk/LONGEXPOSURE/JGVideo/index.htm

Jon's modification produces a video camera with a 'bulb' exposure function. A switch is fitted for the modification that makes and breaks a connection between pin 5 on the control chip and the pad of pin 5. The result of this modification is that when the swich breaks the contact, the camera starts integrating a long exposure. When the switch then makes the contact, the camera downloads the long exposure frame as the first frame of a normal stream of video frames. All of the video session is recorded on video tape which can then be jogged, frame by frame to find the long exposure frame and then capture it via a capture card.

I wouldn't be recording on video tape, of course, but a video capture card and XawTV probably.

[fractonimbus]

Now that looks interesting... Presumably one would use a timer and a CMOS switch to do the exposing. Ideally software to set the time interval.

DN

[Gina]

Now that looks interesting... Presumably one would use a timer and a CMOS switch to do the exposing. Ideally software to set the time interval.

DN

Yes, I would think so. I'd probably use a "1-wire" chip to control a CMOS switch. It all needs a lot of thinking about and some research - an interesting project!

[mcrossley]

For a similar project I wrote a script that controlled the exposure time, it just calculated the average signal level per pixel on a captured image, and then halved/doubled the exposure until it was within an acceptable range. Once within range it went back to capturing an image once a minute. That was with a software controlled camera though.

Edit: found the script, but it's not much use unless you have the control program - MaximDL - which is expensive and designed for astro-imaging, but does control dSLR cameras too.

AutoImage.vbs.txt

I wrote the script for capturing fisheye all sky images, and it seems to work quite well when I tested it at sunset into darkness.

[seabreeze3]

The first low-lux camera I ordered has arrived - direct from China! This has the 1/3inch SONY Exview HAD CCD which I think was the one someone modified for long exposure.

Hi Gina,

I don't have any experience with dinodirect. Have you done much business with them? I was looking at the various cameras available and some look rather interesting for a great price. They have a waterproof dome which is intriguing. I've got a PTZ indoor wireless IP cam which, if I could weatherproof it, would serve multiple purposes, including night sky.

[Gina]

This is the first time I've used DinoDirect so this camera is my first experience. If you use courier delivery or add insurance to standard delivery they give you a tracking number so you can see how far your package has got. Delivery seems reasonable so far, considering the goods come from China.

Just been trying the camera. It's not quite what I thought. It's colour/mono depending on the light level. The sensitivity seems about that of the non-night adapted human eye - the picture shows random noise rather than going dark. That might be because it's a CCTV camera rather than a webcam. The angle of view seems to be 90 degrees or a bit more, as supplied. Resolution appears good on my 15" monitor.

So far I've only got it connected with a short lead so testing has been limited. The video lead is terminated with a BNC socket/female whereas my other CCTV cameras have plugs/male connectors, so the video connection is a bit of a bodge as I lack the right connector/adaptor. I was hoping to get it outside to see what it made of night-time. I'll see if I can sort things out tomorrow. I may also try it on our HD TV rather than the old 4:3 standard res TV I use as a CCTV monitor.

[Gina]

I've now set up the camera looking out of the lounge window pointing south and covering the same view as my weather webcam (MS Lifecam Cinema). Well about the same horizontal coverage but a lot more vertical (this CCTV camera has a 4:3 image sensor - the Lifecam is 16:9). The CCTV camera shows quite distinct fish-eye distortion of the image. It's also definitely more sensitive. When the Lifecam had gone dark the CCTV camera was still showing daylight. Now the Lifecam is showing about 3 distant street lights whereas the CCTV camera is showing many more streetlights and some lights in houses in a village just over a mile away. I think it would show a lot more if the video frames were to be integrated. There's a hint of more detail but difficult to see for the noise. I'm dying to see how much better the Super HAD sensor will be with 10x the sensitivity of this one (allegedly).