Kovas Flicker in Footage
Posted 29 June 2006 - 12:48 AM
I've shot 2 projects with my Konvas 8M. The first was a commercial. No problems whatsoever.
My 2nd project was a short film. During telecine, we noticed a slight flicker throughout the footage. It's not enough to ruin the footage, but you can see it if you look for it. Especially in static shots.
HMI flicker - In the 1st project we used newer, flicker-free HMIs. In the 2nd project we shot with older HMIs with magnetic ballasts.
The telecine was somehow to blame.
There is a phase problem with my shutter and movement.
I had the telecine done at different places for these 2 projects, but the one that had flicker was actually the more expensive and prestigeous of the 2 telecine houses.
Anyone else experience this?
Posted 29 June 2006 - 04:45 AM
I picked up a loaded 8M package from a DP in Florida a few months ago. It has a modified motor crystal sync up to 50fps, done by Slo-Motion in CA.
The flicker can have a few sources.
What speed of shooting you use ? What frequency had main power ? 60 hz 59.9hz ?
The first problem can be on synchronization of camera speed and main power frequency.
This is synchronization very important for HMI lighters with magnetic ballast, because, HMI lighters generate
short pulses of light with double frequency of main power.
The electronic ballast have more wide square pulses and had of less influence.
The second idea.
We don't know technical side of modification of motor. If you send me image from inside of motor ( need open lid of motor, unscrew 4 screws) i hope, i can give you additional information.
But, If you use speed more 25 fps, the 17EP-16 APK motor, with original electronics or with modern electronics, need battery with voltage more 12 v., need 16..18 v battery.
But, i must underline for other user of 17EP-16 APK motor with original electronics, the high voltage battery , more 12 v, can destroy voltage regulator of original electronics, that's why need set additional voltage regulator for chips.
The next idea.
The mechanism of Konvas cameras to design for use of normal speeds 24, 25 fps.
This is mechanism not design for high speeds, that's why, the volume of stability of frame can be not too high for high speed mode.
And, the mechanism of camera must have very good balance.
But, you told, what you have good qulaity first footages and a some problem on second footage.
I think, the balance of camera not change between first and second footages, but, can change of lubrication.
The vibration of not balance mechanism can influence on quality of footages too.
The mechanical condition of fiml magazines can influence on qulaity of footages too, if the gears of magazine had jammed point.
What i think, At first, need check mechanism of camera detailed, check motor, service of mechanism,
and test camera on flicker again.
But, i think, this is problme of synchronization of camera speed and HMI lighters with magnetic ballast and main power frequency.
A many years ago we had some problem with Konvas + 17Ep-16 APK motor and HMI lighters with magnetic ballast. We design of special device for generate speed of camera from a frequency of main power.
The motor had AC adapter, take a frequency synchronization from main power and adjust of speed of motor for this sync frequency.
Posted 22 October 2006 - 05:57 PM
1. Did you use the same motor on both jobs? Fluctuations in exposure can be caused by mechanical problems with the motor, like missing rubber couplings on the drive shaft, worn motor bearings or anything else that causes heavy vibration.
I just had the same problem when I used my spare motor (15EPPS instead of 17EP) on a shooting, all 15EPPS footage had visible flickering in telecine. Worn bearing = uneven rotation = exposure fluctuations.
2. Did the problem occur with different mags or with the same one?
3. Sorry to repeat myself from other postings, but have both camera and mags been lubricated properly during the last year? Can you turn the main gear coupling (motor taken off camera) with the tip of your index finger?
Just my 2 cents...
Edited by Christian Appelt, 22 October 2006 - 05:59 PM.