Originally posted by jamesm007 When you have SR off or on it uses data from the Hall Sensors to keep the platter square. These same Hall Sensors will read when the body of the camera applies any amount of force that may lag the sensor platter. This is what makes it work while panning with SR off.
...
Remember the sensor platter is rolling on ball bearings.
The Pentax SR has two control loops:
1. an outer control loop reading the gyros which can be switched off.
2. an inner control loop forcing the sensor to shift into the exact position as required by the outer control loop. It can't be switched off as otherwise, gravity alone would make the sensor "fall down".
This second, inner control loop is using hall sensors. Also, the sensor isn't on ball bearings. By all means, the inner details of the
second (inner) control loop should
not be mentioned in a discussion about SR. It doesn't help to understand things. I.e., it is counterproductive in order to understand what happens during panning. The entire inner control loop is best understood by thinking about a motor which can accurately move the sensor to any position the (outer) SR control loop determines. The only exception to my rule was when we tried to determine possible causes of excess shutter-induced blur with the K-7. That's not our topic here. From now on in this thread, I will not mention the inner control loop, the hall sensors, the linear motors etc. anymore.
Because the SR gyros measure angular velocities (
not accelerations!), the firmware theoretically can determine the camera to be panning. However, I am unsure if it does. AFAIK, nobody studied this yet.
In LV and when rotating the camera, I believe to see that the image moves to the sensor border and then stays there. To "crawl back" to neutral if rotatation stops. The sensor being driven to the edge is a perfect way to "support" panning as it leaves SR with only one degree if freedom. So, in video and LV, I would say that panning and SR do nicely cooperate.
In normal mode, I am not sure though. The SR motor has enough power and time to compensate for the panning rotation in a short enough exposure. One could measure this with a motorized panning head programmed to follow a known target like a race car on a track. It may then be that SR causes more blur on the car and less blur on the track.
Alternatively, it may be that the firmware detects panning. In doing a pano, I repeatedly turn the camera, stop, take a photo, turn again, etc. It is in this mode that leaving SR on can give me blurred photos. If I pull the trigger each time immediately after turning what I call "doing a power pano" (doing a pano in the most rapid possible succession to "freeze" the scene as much as possible). Whether the SR cannot cope with sudden changes of movement or only tries to detect a panning, I don't know ...
Anyway, what I tried to say above: when doing a power pano, switch SR off.