Software rack focus

[Steve Maller]

Originally Posted by Jon Fairhurst

Of course. That's how they provide autofocus to still photographers. The camera sends the signal and the lens has the motor.

Whoa. And duh. Of course. :-)
That's a wonderful feature. That alone may make me start using ML.
Thanks.

[Tramm Hudson]

Originally Posted by Tramm Hudson

I've posted a short video showing an upcoming Magic Lantern feature: software focus pulls. This is a demonstration of how smooth the software control can be with a very fine step size. It is doing 30 steps/sec in the video with a stepsize of 1 and speed of 1.

Now that my camera's batteries are recharged, I've done some more analysis and found that there are not separate stepsize and speed controls; instead it is a signed 16-bit value for the number of counts. Positive is a longer focus distance, negative is a shorter focus distance.

Here is a better video showing a range of speeds: Magic Lantern - software rack focus speeds

These were generated by selecting the different speeds from the Magic Lantern menu and hitting "Test rack focus". If I had thought about it, I would have written a short program to loop over the desired speeds and reset the focus to 0.85 m after each one. That way the video wouldn't have any edits at all and would demonstrate something approaching scriptability (in C).

The slow speeds work fairly well (although there is still an occasional hiccup), but since the AF motor seems to only run at full speed when commanded with PROP_LV_FOCUS, it is hard do a smooth, fast focus pull. The really fast pulls even over-shoot the desired 2.9 m distance. I'm hoping that there is another command that allows a selectable focus speed.

When focusing with the "focus by wire" 85 mm f/1.2 L, does it seem to have multiple smooth speeds or does the lens always jump to the new focus distance? If anyone has one that I can use for non-destructive testing near Charleston, or if you just aren't happy with it and want to trade it for my 85 mm f/1.8, you know how to reach me.

[Chris Barcellos]

Very nice, Tramm. Is this long term project or do you think this is coming to ML 0.1.6 ?

[Tramm Hudson]

Originally Posted by Chris Barcellos

Is this long term project or do you think this is coming to ML 0.1.6 ?

There will be some support for it in 0.1.6, but I'm not sure what the interface will be. It will likely be at the scripting level for now, until we figure out how to best expose it to the user.

[Jon Fairhurst]

My preference for simplicity is a script or series of scripts that can be triggered by IR. That lets people with gimbal rigs trigger measured focus pulls without upsetting the balance. This application is probably the most in need of a remote, no-tension solution.

Live use, with a knob, will take more tinkering...