Iris/Aperture pulls

Started by JohnBarlow, October 25, 2013, 04:53:40 PM

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Manual Exakta lenses on the Canons have the neat feature of being able to perform aperture pulls by pressing the button on the extended arm which is on the lens. This can also be operated by a shutter release cable allowing the lens to open up or close down in an instant.

When pulling aperture on the Canons the Auto ISO tends to overshoot or undershoot.

Light a scene to F2.0 ISO 100, pull aperture to F5.6 ISO 800 -- the Auto ISO undershoots by going dark first and then levelling out to correct exposure.

Light a scene to F2.0 ISO 100, pull aperture from F5.6 ISO 800 to F2.0 ISO 100 -- the Auto ISO overshoots by going bright first and then levelling out to correct exposure.

I would like to see a feature in ML to remove this undershoot/overshoot behavior by essentially increasing the damping or time constant in the Auto ISO controller.

Please let me know if this useful feature can be implemented.

best, John


Tried enabling gradual exposure?


A step change would be awesome ....

PS Sorry I should add that the purpose of Aperture pull is to quickly increase/decrease DOF. So it is a kinda focus pull but via aperture.


Indeed, gradual exposure won't work with a fully manual lens; it needs a Canon lens so it knows when you change the aperture.

Some really old versions had an option to tweak the time constant, but I don't remember anyone using it, so it was removed. May be worth digging through the code to see if it helps. The relevant code snippet is LVAE_ISO_SPEED = some_value.


Will this value affect the damping?, if not the overshoot will still be present?