(meteorobs) OT. -Profiling the Sandia Sentinel Camera's vision.

[Larry]

The following measurements were found. The methods of arriving at this data 
will be explained below.

The out-of-focus circular fringe area in the Sentinel cameras photographs 
was measured to be 5.8 degrees BELOW true horizon at its first edges. 
(-5.8). The actual fringe in focus could be a -6.3 but cannot be confirmed 
without refocusing a Sentinel camera.

True horizon (-0.9 actual degrees) is located close to the 10 degree circle 
on a linear Altitude scale of my own design fitted to an Azimuth scale and 
made public.

The Azimuth scale I constructed for general public use on Sentinel photo's 
with a later added Altitude scale contains errors in altitude at lower 
elevations due to what I believe is logarithmic compression of the lens. 
This was anticipated at the time of the construction of the linear degree 
circles. At 30 degrees elevation it is quite close, not more than 1.5 
degrees error, measuring no more than 31.5 degrees maximum on a planet or 
bright star at 30 degrees per an older astronomy program called Skyglobe. 
Above 30 degrees the scale is quite precise and is accurate for all intents 
and purposes for a camera aligned to zenith.

At the present time with this public scale fitted to Sentinel images, the 
outside edge portion of the Azimuth scale is measured to be at a minus 0.9 
degrees of true horizon. (-0.9). That bottom portion is scaled 10 degrees as 
a linear scale circle. It was necessary to use this Azimuth-Altitude scale 
to perform the measures as clearly defined fixed points were not available 
in the North-South direction for the Transit.

The transit was leveled at the lower edge portion of the Sentinel camera 
fish eye lens.

Altitude measures were taken with a precision digital level attached to the 
transit as it deviated away from the fish eye lens in new azimuth 
directions. Controlled tilting of the transit was measured for below horizon 
fixed points. The points used were: Camera lens, Roof top edge in S.E., amd 
Roof gutter edge, all located below the true horizon but within the photo 
vision of the camera. The gutter edge is located at the edge of the 
out-of-focus camera perimeter. Local porch lights are slightly below that 
edge and can be seen by the camera occasionally. This suggests -6.3 is very 
close for the maximum below true horizon aperature of the camera.

These measures are very close but not precise due to out of focus targets 
being used to compare to the Sentinel image taken this morning. If this 
information is of some interest or use by others besides myself,  the task 
is made worthwhile. Others may want to make their own measure to confirm or 
argue what I have found to be a workable.estimate.

YCSentinel
(Too tired to check language or spelling.)