Jump to content

Focus motors + vintage lenses?


Recommended Posts

Hey all,

I'm currently assembling a set of canon rangefinder glass from the 60's and was wondering if it would be considered a bad idea to use them with follow focus motors like as a preston or a tilta nucleus paired with follow focus gears such as these: https://www.simmodlens.com/followfocusgears

Would it be possible to damage the helicoid focus system with the torque of the focus motor pulling focus on the adapted gear?

Thanks in advance!

 

Link to comment
Share on other sites

  • Premium Member

I would say that there is a very good possibility of damaging the internal parts of the lenses. I use the Preston full time and I have experienced the wear and tear of the motors on vintage lenses. They’re simply not robust enough for the torque of the motors. 
 

G

  • Like 1
Link to comment
Share on other sites

  • Premium Member

Even the lower-cost focus options are pretty insistent these days. I have a PDMovie Remote Air Pro 3 system here, which can be had for under £1k motors and all. I am personally unable to hold on to the gears with my hand sufficiently to stall the motor without risking the gear teeth tearing my skin. It's perfectly capable of pushing the gears out of mesh on at least some kinds of lenses, potentially leading to damage on the gears, lenses and mount. For this reason it's actually impossible (or at least desperately ill-advised) to use the automatic setup features, which rely on finding the end stops of the lens. They won't. They'll bend something.

Yes, this is a horribly missed feature in the firmware, but anyway.

These lower-cost systems are of course most likely to be used with the least-ideal lenses and mounts which are least able to stand the punishment.

Link to comment
Share on other sites

  • Premium Member

I spend a lot of time repairing or modifying lenses because of motor damage, but the reality is this is how modern filmmaking is done. 

It depends on the lens design, but generally the damage is to things like end stops, iris pins and increased wear to the helical. Often I find holding screws have loosened, which causes play in the body or drive systems, and can damage screw threads if left unchecked. Weak mount systems like you often find on stills lenses are also problematic - they tend to shift with motor direction, causing focus errors and eventual wear or damage to the mount itself.

So what to do? A few suggestions can help mitigate damage:

If a motor system has varying torque settings, use the lowest setting that still turns the ring. As Phil mentioned, cheaper systems often have only one, super strong setting. Avoid these if possible.

During the calibration phase hold the rings (without damaging yourself) to try and dampen the force of the motor slamming into each end stop. 

Don’t use clamp-on matte boxes with vintage lenses or any lens that telescopes as you focus. These add weight to the front of a lens and put strain on the helical threads. The motor then effectively acts as a grinding tool, wearing away the thread and causing focus play and image shift.

Make sure the lenses are periodically serviced with fresh grease. This helps reduce the thread wear that forceful motor driving causes. As soon as grease gets contaminated with dust or dirt, it acts more like an abrasive than a lubricant.

If a focus ring is very stiff to turn, have the lens serviced. A motor driving a stiff focus is putting strain on the entire lens. If play develops in a gear ring, have it serviced. Screws may have come loose and a motor slamming into end stops will damage the screw holes.

If a lens doesn’t have hard stops at the ends of the focus travel, if it feels spongy or sticks, be very wary of using a motor. It may be possible to have a lens modified with hard stops.

Avoid using motors on the iris ring if possible. Invariably the iris is driven by tiny transmission pins that are very easy to break, and sometimes the iris mechanism itself is the end stop, meaning a motor will drive the mechanism to its limit and potentially destroy an iris.

  • Like 1
  • Upvote 2
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...