Fluttering time-lapse with the A99/Ziess 24-70

Started Nov 29, 2012 | Questions thread
sybersitizen Veteran Member • Posts: 8,215
Re: Fluttering time-lapse with the A99/Ziess 24-70

I wrote about this flickering problem doing time-lapse video with a KM5D back in 2007 and came up with an explanation and a solution, summarized here:

I did discover something during these projects that I wasn't really looking for, and didn't like finding... I noticed an obvious flickering effect in the video. The frames weren't uniformly exposed... the sunlight was obviously constant during the sequence. The only variables left were the shutter speed and lens aperture.

The lenses I used... (Konica Minolta 50mm f/2.8 D Macro and 18-70mm f/3.5-5.6 D) are auto-aperture lenses. Even when used in manual mode, these lenses close down only for the length of the exposure, then re-open and await a command from the camera to close again. Obviously, there is some margin of error in the camera/lens system that closes the diaphragms. The variation has presumably been there all along, but it is so slight (maybe 1/4 stop) that I never noticed it in any still images. It becomes readily apparent with a series of images shown in quick succession. This is unfortunate, because the flickering really detracts from the viewing experience. Holding down the camera's depth-of-field button while shooting doesn't solve the problem.

Happily, there is a workaround: when attaching a lens, stop turning it just before it 'clicks' into place. The camera will think no lens is attached. Only manual focusing will be possible, but that's not a problem. The aperture can still be adjusted within a limited range, depending on how far the lens is turned - and it will stay put for every shot.

A similar solution is to use some other manual focus, manual aperture lens rather than an A-mount AF lens.

This assumes that you retain full manual control of aperture, shutter speed, ISO, and focusing during time-lapse work. If you allow any kind of autoexposure or autofocusing, you're inviting flickering or focus changes.

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