Lens VR unit IR leakage affects long exposures - cont'd.

Started Feb 17, 2008 | Discussions thread
SteveL54 Senior Member • Posts: 2,709
Re: Lens VR unit IR leakage affects long exposures - cont'd.

Marianne,

I ran tests on my D70 (more IR sensitive) and 18-200mmVR.

It turns out to get rid of the IR source both lens switches (VR and AF) must be off. If AF is disabled by the body's switch only - leaving the lens in M/A - then the IR source stays on. I suspect the folks reporting this problem with VR off and AF in manual position left the lens switch in the M/A position.

Here's a thread I restarted last night in the lens forum.

http://forums.dpreview.com/forums/read.asp?forum=1030&message=26820887

Marianne Oelund wrote:

In any servo system such as the VR unit, there must be a means of
position feedback to the control electronics. In various
applications, we typically find potentiometers, strain gauges, LVDT's
or RVDT's, and optical position sensors used for this. Apparently,
the latter are employed in the VR unit. These consist of a light
source, in this case an IR LED, and a phototransistor or transistor
array which uses the light from the LED to read physical position.
In the case of the 18-200 and 70-200 VR units, then, there must be a
small amount of leakage from the IR LED which is finding its way via
reflections, back to the camera's sensor.

Your suggestion that IR leakage from an optical position feedback sensor makes sense.

Steve

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