Eclair ACL flicker

[daniel shetron]

Hey all,

Was hoping you guys could help diagnose what type of flicker I'm getting from my U16 ACL. I have been doing a lot of reading, and talking to Paul over at VP, (he did my U16 conversion and CLA'd the camera) and I am aware this camera has inherent issues with flicker, especially in backlit situations. What I am hoping to better understand is when certain backlighting will create flicker and when it won't. I haven't had the camera very long and only have  shot about 1,500 feet through it but can't seem to fully understand what situations to stay away from and what are acceptable. I've attached a link to a handful of shots that all have flicker, but some for reasons I don't fully understand.

 

Camera is an U16 ACL 1 with AZ Spectrum HD tap, I am running a 12V 4.5 amp NiMH battery I got from Du-All

 

Here  is a link to the clips with timecode burned in to better identify specific clips.

00:00 - 00:07 - I understand this flicker-sun crashing into the lens and lighting spilling where it shouldn't 

00:07 - 00:12 - Sun was high in the sky and was not hitting the front element of the lens. This situation is surprising to see flicker, its not bad but its still present.

00:12 - 00:19 - Sunlight hitting the front element and also the end of a 200' roll which was spooled down from 400'. Paul explained that the end of rolls can be problematic because the film has so much set in it that it can cause the pressure pads to be forced away from the gate and they also have a tendency to be flashed in the spool down process

00:19 - 00:25 - Sun was behind a cloud from my vantage point so not sure what created this flicker?

00:25 - 00:30 - Sun in the lens and also end of the roll. But this flicker was minimal, so again, not sure why sometimes its worse than others?

00:31 - 00:39 - Sun in the lens

00:39 - 50 - I don't think sun found its way into the front element of the lens on this shot. It was shot on a Schneider-Kreuznach Arriflex-Cine-Xenon 25mm which has the front element set back really deep and the sun was not in a position to get to the front element.

 

Any insight would be greatly appreciated. 

 

[Kamran Pakseresht]

I’d try shooting with a lens hood or a matte box to see if it makes a difference. I am curious if the lens you used is made for a larger format? Meaning a larger back element than a regular 16 lens? 

[daniel shetron]

Lenses used were the Schneider kreuznach arriflex 10mm, a Bell & Howell Angenieux 17-68 zoom (covers S16) and the 25mm schneider I mentioned above. Flicker is persistent even when using R16 glass.

Edited Monday at 03:24 PM by daniel shetron

[Matthew J. Walker]

Flicker in any form is incredibly annoying, especially for (presumably) a 16mm first-timer because it can be the result of so many different factors. I have experienced only a slight flicker a few times with 16mm film. The first time was due to cheap LED Christmas tree string lights and the second happened inside a restaurant, also a result of LED lights. My most recent flicker incident this summer lasted less than a minute of a roll outside under only sunlight while running at 150fps which, in my imagination, I attribute the to a low battery as I never found a reason otherwise and never experienced it since (Knock on wood). Nevertheless, for your situation, you must eliminate all other possibilities first such as frequency of the flicker, a faulty scan, or low camera battery among other things. The flicker should not the result of the sun because the sun is not running on electricity.

[Aapo Lettinen]

The acl has asymmetrical mirror swing and certain lighting conditions + lens + settings combinations may suddenly cause visible flicker, or not. 

Should not happen often/all the time though. If your camera visibly flickers all the time get the mirror timing checked. 

The acl is built that way to make it smaller. People are fine with it most of the time. But if it starts to give you trouble then get it checked and retimed or modified further to reduce the issue to acceptable level. If it is just one lens giving trouble then trade it to some other lens. If most lenses do that then it is the camera body itself

[Aapo Lettinen]

There is very simple way to determine if the cause is the mirror. The mirror swings to left for one frame and to right the next frame. So mirror flicker is every other frame slightly underexposed/slightly overexposed. 

If your scanned film shows this alternating higher-lower exposure on adjacent frames then it is the mirror. Open the scanned clip in resolve, slowly move forward frame by frame and look on the waveform scope if the waveform slightly jumps up or down the same amount every time you advance a frame forward

[daniel shetron]

Thanks Aapo--it would appear that every other frame is receiving slightly more exposure. The waveform scope confirms that. Just not sure why it's only sometimes and not consistent. Would that be a power issue if the timing is off? I would be fine with it if I knew what conditions to stay away from, but since it has happened in backlit, and non backlit situations, and with multiple different R16 and S16 lenses, not sure what to do.

[Aapo Lettinen]

24 minutes ago, daniel shetron said:

Thanks Aapo--it would appear that every other frame is receiving slightly more exposure. The waveform scope confirms that. Just not sure why it's only sometimes and not consistent. Would that be a power issue if the timing is off? I would be fine with it if I knew what conditions to stay away from, but since it has happened in backlit, and non backlit situations, and with multiple different R16 and S16 lenses, not sure what to do.

the mirror timing is kind of a matter of taste, has pros and cons how it is exactly adjusted and possibly modified when modifying the gate.

I think the most common issue with lenses is that the back element is relatively large and far away from the gate so that the mirror can mask the stray light inside the cavity more easily. so the asymmetrical mirror causes a "shadow" of the stray light which is slightly darker on every other frame when the mirror is on the camera right side, slightly closer to the gate and lightpath when the shutter is open. It is pretty much a matter of tons of testing and when finding a more problematic lens then deciding if wanting to use it anymore. but first maybe checking that the mirror is not badly out of sync, a technician can look your camera to see if it can be better than it is now.

Hard mattes should help a little with the flicker issue I think but would not eliminate it, maybe just saving a shot or two every now and then.

if being brave enough it is possible to diy adjust the mirror timing if wanting to just try different settings and fine tunings. A camera tech can do it better but it being like me who can't wait for cameras being shipped back and forth then it is interesting to try diy repairs 😄

these screws hold the mirror timing locked and one can fine tune it if loosening them carefully and altering the timing a little. Not recommended to remove any gears for larger adjustments because that will likely cause more harm than good and they are very time consuming to get back to correct alignment, the spacing and everything. So flicker fine tuning possible by those two screws, other stuff dont touch 😄 

[daniel shetron]

Aapo when you say "hard mattes" what exactly do you mean? 

I don't think I feel confident going in and adjusting any screws, last thing I would want to do is make anything worse. 

[Aapo Lettinen]

22 minutes ago, daniel shetron said:

Aapo when you say "hard mattes" what exactly do you mean? 

I don't think I feel confident going in and adjusting any screws, last thing I would want to do is make anything worse. 

mattebox hard mattes to mask out any out-of-frame stray light possible. might help a little

[daniel shetron]

 👍 Ah yeah ok, I wasn't sure if you were referring to some kind of internal matting that I was unaware of. 

[Duncan Brown]

From one of the other flicker threads in this forum, I posted a slo-mo video of the ACL mechanism in action.  You can see it's a very very tight dance between all the parts.  Works just fine from the factory but if you start widening the gate or moving the lens mount, the dance gets that much tighter, and I think the mirror starts coming into play rather than just the shutter.

 

Duncan

[Duncan Brown]

That other flicker thread:

Duncan

[daniel shetron]

Thanks Duncan, I read through those threads, very helpful. However, I just wish I knew which kind of flicker my camera is getting. Seems like my ACL has what Gregg MacPherson has labeled as flicker type 1.