(meteorobs) Improving the contrast of all-sky camera &mirrorsystems. Chris?

[Leo S]

Hi Larry,

Larry wrote:
> Hello Leo.
>
> It seems you are pursuing very challenging work in daylight lightning.
>   
It's actually not too hard to do. Certainly no harder than trying to 
capture daylight meteors. At least lightning is fairly predictable 
compared to meteors. I think that apart from that, in essence, the 
problems of trying to capture daylight lightning and fireballs are more 
or less the same, the biggest problem being contrast between the event 
and the sky (once the triggering issue has been overcome).

> There is a possibility that very large(not small) industrial IR domes where 
> the camera is distant from the surface of the dome itself at the radius 
> center might work for that. Those domes are used in Casino's but are a bit 
> "pricey".
>
> This would allow more latitude in sensitivity and threshold adjustment. I 
> lost a daylight fireball test camera using this method due to internal metal 
> or PVC sweating even though it was heated on a timer during the night and 
> was sealed from ambient moisture. The CCD substrate itself failed I believe 
> because slow oven treatment did not bring it back.
>   
Yikes! Perhaps a small PC fan for ventilation might prevent this from 
happening again? The dome does sound like a good solution if you can 
overcome these problems though!


> If you can post some lightning strikes or your personal research results I 
> think it would be quite interesting to the group. Certainly I would like to 
> see what you can image.
>   
Previously I would just set up the camera so that the sky was slightly 
under exposed, and then rapid fire in the hope of catching the 
lightning. I got a few pics by doing this, but I wanted to avoid wearing 
out the shutter as much as possible. You can see previous attempts here: 
http://www.btinternet.com/%7El.stachowicz/pics/weather.htm

Last year came across a blog detailing how to build a photo-sensitive 
trigger using a mini-computer (see: 
http://www.glacialwanderer.com/hobbyrobotics/?p=16 Scroll down for 
someone else's daylight lightning pics using the same device) which I 
built, and I did not get an opportunity to test it in a real storm until 
yesterday. This is the trigger I built:
http://farm4.static.flickr.com/3205/2882095025_e9d564cdce_o.jpg

Unfortunately, by the time I had set up the trigger yesterday, the storm 
had almost petered out, but I did manage to catch the last strike that I 
saw. It's not a great shot, but it proves the trigger works as it 
should. The exposure was 1/1600 of a second, ISO 200 @ F3.5
http://www.btinternet.com/~l.stachowicz/pics/other/YX9J3301.jpg


> Yes on the mechanical shielding. I will study that issue now. I do need to 
> keep certain fixed lights on my horizon as Azimuth alignment markers, which 
> assures me no changes have occured with the cameras North alignment during 
> my routine servicing.
>
> YCSentinel
>   

I was thinking you might be able to get around this problem by cutting 
notches or drilling holes in the appropriate places in the shield, so 
that just the lights that you need shine through, but it might be a bit 
fiddly to get right, although you could always patch up a hole if it was 
not quite in the right place.

I think a better idea might be to install a couple of small LEDs on the 
shield edge that you could then use to align the camera. You would have 
to make sure the shield was well and truly fixed in place though. 
Otherwise, it might be an even better idea to install LEDs on some other 
object that is fixed, and you have access to, or if there is none, you 
could fix a pole or two that would be just high enough to elevate an LED 
into your FOV.

Leo