In an ongoing attempt to determine how and why the focus of the
F717 can fail I have been working on a theory based on observation
that the laser assist mode works differently than the regular focus
mode. I believe the camera in laser assist mode actually looks for
the laser, and not just the contrast of the scene that is augmented
by the laser. So if the camera can't see the laser, but the scene
otherwise has enough contrast to focus, the focus will fail until
the camera can see enough of the laser to focus.
This is how I have come to the conclusion.
Note: If anyone can see a fault in the test, please, suggest a
different test. This is very interesting to me, and I would like
to get to the bottom of it.
I setup a focus target in a low light situation. The camera
settings were the same for all tests except for the focus assist
mode (f/2 - 1 second - ISO 100). The cameras lens was exactly 1.2
meters from the focus target. The camera was also on a tripod and I
used a remote control to trigger the camera. I half pressed the
shutter on the remote control to auto-focus and then slid the focus
selector to manual to readout the distance, then I fully pressed
the shutter to take the picture.
1st picture:
laser assist off - reported distance 1.3 meters
2nd picture:
laser assist on - reported distance 1.2 meters
3rd picture:
laser assist on, but the beam was blocked - reported distance 4 meters
The only thing that changed in the focus assist images was the beam
being block. The lighting remained the same, and the existing
contrast of the target, which was enough for the camera to focus on
with the focus assist off, was now not enough to focus on with the
laser beam diverted. This tells me the camera is actually looking
for the laser and ignoring the existing contrast in the scene.
I was also surprised to see the .1 meter reported distance
discrepancy and I can only surmise it is the result of using two
different focusing procedures by the camera, one for scene contrast
detection, and the other for laser only contrast detection.
It would be interesting to see what an F707 would do with this
test. Does it behave the same way as the F717? I don't have one
anymore, so if anyone would like to give it a whirl, I am sure
there are others that would be interested in the results.
--
Shay
My Sony F707 Gallery:
http://www.shaystephens.com/portfolio.asp
My F717 Observations:
http://www.shaystephens.com/f717.asp
