Why no firmware update for Sig 50mm Art?

[Mt Spokane Photography]

I'm seeing quite a few people who are having no problems, so maybe it really isn't an algorithm problem, but, as has also been suggested in other threads, a quality control issue, some inconsistency of the motor assembly or circuits.

There are enough complaints about the AF on the 35mm Art for me to know that I'm lucky with mine, as it has been as reliable as my other lenses, and often wide open within a meter of the subject.

In any event, those of us craving a great 50mm with reliable AF have to either gamble or grumble.

This is entirely possible. The camera sends a coded signal to a lens to focus at say 27 ft. The lens then is supposed to do that. In order to accomplish this, there is a resistor with a wiper or wipers that move as the lens moves (This is analogous to the volume control in a old radio). There is a table in the rom of the lens electronics that correlates the resistor reading to distance, so the lens moves very quickly to where the correct resistance value is found. The lens calibration dock basically gives corrections to the value.

However, a dirty resistor (like a dirty volume control in a old radio) can cause a lens to hunt. If the quality of the wipers is poor, they may make poor contact with similar results.

Here is the zoom locator brush from a 100-400mm L. The focus indicator is similar, but wraps around the circumference rather than front to back. Its the same principle. If one of those fingers bends, breaks, or gets dirty, strange info is sent back to the camera.

 

[YuengLinger]

Thanks, Mt Spokane. This is a great explanation of how AF works and what might go wrong. Much appreciated.