Parfocal Zooming

There is not many good and reasonably priced electrical zoom lenses, so why not use a servo.



It is not a perfect solution. Servos are designed to move fast to given position, more smooth operation would be preferable for zooming. Also servos can be a bit noisy. I guess there is a reason the video lenses with electrical zoom are expensive, really expensive. They are also parfocal, i.e. they keep the focus while zooming.

Testing with Canon EF 24-105mm f4. it is not parfocal by design, there is quite a lot focus shift on range 24 - 60 mm, but why not correct it electrically. Notice how the focus moves when zoomed. it is correcting the focus.



Well it does not quite make the Canon EF 24-105mm f4 equal to some 20 000 euro + video lenses, but I am pretty happy with he result. Absolutely makes it much more usable for video work and especially useful for gimbal work.

Note: The controller on these videos has a special modification, pressure sensitive elements for zoom control. More information about the basic version of the controller below.