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

[Larry]

Chris,
Your mechanical shield or a full skirt may be what I will wind up with too. 
I have a particularly bad occasional situation which needs resolving on pool 
lights next door which are 7 or 8 feet below my camera lens. I am not sure 
how close it is to being direct lighting and how far below true horizon they 
are located. Those lights and other luminous points are well illustrated in 
a fireball shot at:
 http://cams.seti.org/sentinel/v20090326_210854.18.jpg
I do not want to do anything about these lights until my measures are 
completed.

Finished the transit work today and will start gathering information 
(measures) on exactly how far from the Sentinel image circular edges true 
horizon is located when the camera is properly aligned to zenith and has a 
very minimal amount of clipping (but equal) in the North & South direction. 
Hopefully that clipping will not be above true horizon.

Below true horizon measures will be taken with a precision digital level 
mounted on the transit aimed at objects at the circular edge of Sentinel 
photographs in a daylight shot.

That info. will help make reporting to AMS a bit more accurate and give 
others decent reference points too on their Sentinel photographs for true 
horizon and below.

Sunlight & contrast is the secondary objective. Any gain in that is worth 
the effort.

Hemispherical mirrors will be considerably more difficult to measure. They 
can see far below the horizon I noticed before during some tests. My mirror 
system is down for modifications at present.

YCSentinel



----- Original Message ----- 
From: "Chris Peterson" <clp at alumni.caltech.edu>
To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
Sent: 2009/06/14 06:35
Subject: Re: (meteorobs) Improving the contrast of all-sky camera 
&mirrorsystems. Chris?


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.)

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