Bolex and HMI lighting

Roy Brown · August 18, 2004

Well I got my film back from my Bolex shoot (see earlier Post) and exposure was dead on. However one or more HMI lights flickered badly. I had thought the HMI's were flicker free but one must not have been. In order for this not to happen again what can I do in the future. Is it as simple as making sure the HMI's I rent are designed to be flicker free at any shutter angle? I would be using a Bolex or a Eclair NPR.

BTW The Video from the Panasonic DX100 in 24P mode did not have any flicker present. On a comparison note the film showed so much more detail that flaws unapparent on the video were glaring on the film. For example Skin complexion, Dirty windows, Imperfections in the paint of the location. The colors really popped with the film and were more subdued on the video.

Tim Carroll · August 18, 2004

Roy,

What model Bolex were you using. The reason I ask is that we shot a short last year with a Bolex EBM and the whole film had flicker, and it turned out not to be the lights. It turned out that our EBM had an intermittent shutter bounce.

That may be why the footage from the DVX100 looked okay.

-Tim

Roy Brown · August 18, 2004

What model Bolex were you using. The reason I ask is that we shot a short last year with a Bolex EBM and the whole film had flicker, and it turned out not to be the lights. It turned out that our EBM had an intermittent shutter bounce.

That may be why the footage from the DVX100 looked okay.

Its possible but I have shot several rolls of film with it using just daylight or Tungsten lights and the footage was great. Also you could clearly see the light flicker in the scene. The flicker varied a lot from scene to scene depending on the light positions.

Roy

Tim Carroll · August 18, 2004

Which model Bolex were you using, and what did you have the shutter speed set to? Was it crystal synced at the speed you had it set? If it was a Bolex with a variable shutter angle, what was that set to? All those variable could effect what you see in the footage.

If you are using a spring wound Bolex, shutter bounce is probably not an issue, but variable shutter speed as the spring winds down could be. If you are using an EL or EBM or REX 5 or SBM with the Bolex motor, but no crystal sync, you could also be getting variable shutter speed, as the regular Bolex motors can vary quite a bit.

If you were using an EL, EBM or the motorized REX 5 or SBM and a crystal sync, and you are getting flicker, I would shoot a test in daylight and see if it goes away. Or test it with a strobe by removing the lens, firing the strobe at the shutter (while you are running a test roll of film through the camera) and freezing the shutter blade half way through the frame. When we did that, we could visibly see the shutter bounce or sink about every second or so.

What we found when we investigated our camera is that no one is really sure which part of the electronics goes bad that leads to the intermittent shutter bounce. Bolex just replaces most of the circuit boards to fix the problem, which can run up to I think $1500 to have it done by the factory. Since they are not sure which components go bad, they are also not sure when and how they go bad. So just because your earlier footage was fine, does not mean your camera has not developed the problem.

The other thing is that your camera could be fine and you have a bad light and the shutter speed you had the DVX100 set at did not pick up the bad light. I just would investigate the issue with the Bolex before you shoot any more critical film projects with it. The intermittent shutter bounce is unfortunately not an uncommon problem with those cameras.

Hope that helps,

-Tim

Roy Brown · August 18, 2004

I was using a Spring wound Bolex with the shutter open. 135 degrees? I thought the flicker was constant and seemed to be from one of the three lights. I really need to learn more about HMI's. Are some HMI flicker free at all shutter angles or are they set to be flicker free at a specific film speed and shutter angle. Does the camera need to be running at crystal 24fps or will the spring wound motor running at lets say 23.5 to 24.5 fps go out of sync with the light? Thanks for the responses

Roy

Tim Carroll · August 18, 2004

Roy,

I have never used HMI's. Mitch or David or one of the other folks can probably answer your questions better when it comes to HMI's.

-Tim

Sam Wells · August 19, 2004

Even electronic ballasts can bite you.I don't have a safe speed chart at hand that would apply to 135 degree shutter. (there must be one online somewhere).

A spring wound Bolex may not run at a constant speed even if it looks constant enough for tungsten or sun light. They also may not run at the marked speed, it's a mechanical governor on the motor, they wear and the cameras have a tendency to run faster than the speed indicated.

-Sam