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

[Chris Peterson]

My camera does not capture more than a 180° field. Certainly, the Rainbow 
lens doesn't get you 20° below the true horizon. My actual horizon is a few 
degrees above the true horizon in spots because of hills, but I have not 
found any need to use a physical mask. I have a logical mask in the software 
that prevents false triggers from areas of the image that don't show sky.

One of my cameras is installed at a school in a location where car 
headlights from the parking lot can hit the dome. These lights aren't 
visible to the camera directly, but the light on the dome can generate false 
triggers. I've got a mechanical shield installed in that case to shadow 
those lights. The shield isn't visible in images because it is out of the 
camera's FOV. A shield like this is always useful if you are in a situation 
where you have a significant direct light source hitting your dome.

I start/stop my cameras when the Sun is 6° below the horizon, so I'm not 
concerned with sunlight hitting the dome at sunrise or sunset.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message ----- 
From: "Larry" <ycsentinel at att.net>
To: <meteorobs at meteorobs.org>
Sent: Sunday, June 14, 2009 12:42 AM
Subject: (meteorobs) Improving the contrast of all-sky camera & 
mirrorsystems. Chris?


> Picked up a commercial builders transit today with a broken tripod leg 
> which
> I intend to use to determine (true) horizon. This has started my thinking 
> on
> the faults of both all-sky camera lenses and mirror systems.
>
> Your thoughts on the following comments Chris would be appreciated.
>
> 1) Both all-sky fisheye lenses and mirror systems capture the light from
> distant terrestrial objects on an "apparent" horizon which is FAR BELOW 
> the
> actual true horizion. This includes rising and setting Sunlight saturation
> at important fireball recording hours.
>
> 2) It appears that our systems see & photograph somewhere around 20 
> degrees
> or more below the true horizon. (I have not measured that yet).
>
> 3) Our practice has been to "Mask" all of this unwanted light from
> triggering our systems. But I do not believe this is the best approach
> because it does nothing to help the camera sensitivity which is based on
> contrast. Street lights that are close are a separate issue if they are
> above the true horizon or even close to the true horizon.
>
> 4) My thoughts are that we should be BLOCKING the light below the true
> horizon or maybe blocking all light more than 5 degrees or so below that
> true horizon to improve the operating contrast of our cameras by reducing
> the stray light, artifacts, and saturation that inhibits contrast.
>
> 5) A circular black ring, paint stripe, or similar application should be
> placed around the dome or mirror with a height just below or at true
> horizon. Masking should be only employed for lighted objects above the
> elevation selected for blocking if no steps are taken to specifically 
> block
> those too.
>
> This approach may significantly improve our camera sensitivities and/or 
> the
> early evening, early morning, working hours.......
>
> YCSentinel
> (P.S. thanks for your classified thoughts earlier.)