Eclair ACL flicker (technical)

[Boris Belay]

[Gregg MacPherson]

Hey Boris,
Glad you came. I continue...

In terms of what is observable on the neg or scanned frame, I'm assuming that there is more than one kind of flicker. I have to try categorising them...

1)  Even exposure across each frame, but variation in brightness in alternate frames. A 2 frame cycle.

2) Variation in brightness across the  frame, with brightness to the  L and R alternating. A 2 frame cycle.

3) A shadow on the top corner or side edge of the frame, on every second frame.

4) Scattered light from a leak in the body. Not sure what that looks like. 

Anyone, feel free to add to this list, or remove one if it is fictitious.

Type 1 flicker, I don't get yet how it could be  due to mis-timing. If the mirror sweeps into frame while the shutter is open should we not have some variation in neg density across the frame...?

Type 2 flicker, makes sense that it is the mirror and shutter out of phase. Mis timing. I don't know what all the possible variants could look like.

Type 3 flicker,  with the mirror at positions A,B, let's call them the "dwell" positions, if the mirror partly shadows the aperture there must be a dark area every second frame, no? The only explanation I can come up with is the link rod length.

Beyond that,  I still wonder about elasticity in the system, and resonance. At the very least we need the opinion of someone who was solving flicker with new rubber drive couplers in the 80s, 90s.

Is there a reason why Aapos N16 mirror dwell positions are so asymmetric? Is that common, or has someone fitted a S16 link to that camera? The dwell positions favour a S16 frame.

I'm speculating a lot. Perhaps we should start with simple but precise observation of one particular case, and try to find an explanation. Aapo swears that his sample frames have even density across the frame, and alternating density, a two frame cycle. Does anyone have an explanation for that?

And so it continues...
 

Edited October 24, 2023 by Gregg MacPherson
spelling and context

[Gregg MacPherson]

More puzzling things.
The small drawing on one of Boris' pages that shows the mirror, shutter and the driven link rod. It's a schematic like mine, with the mirror spindle and MIN83E orthogonal to the drawing plane. It looks like it shows the effective mirror radius.

I assumed for now that it was to scale and copied it into 2D CAD. I discovered that the position of the driving ball end on 83E was not plausible if the mirror was in its dwell position (A). The dwell position for the mirror would be 23deg further to the left. So I think the drawing is not to scale...ha. There's a pdf here that will print the image 1:1 at full size or 100%.....

ACL mirror, shutter, rod, 83E copied to CAD from maint docs.pdf

 

 

[Gregg MacPherson]

13 hours ago, Gregg MacPherson said:

.......I'm speculating a lot. Perhaps we should start with simple but precise observation of one particular case, and try to find an explanation. Aapo swears that his sample frames have even density across the frame, and alternating density, a two frame cycle. Does anyone have an explanation for that?.....

I think we need to be precise about what phenomena we are observing. The word flicker perhaps masks several discrete phenomena. In an ideal case we might observe them in isolation and find causes. In real life, one or more may present in concert, making observations more difficult. 

Does anyone have ideas about  Aapo's case? I'm tempted to challenge him on the neg density (brightness), the lack of variation across the frame. How was that measured. Not because I disbelieve him, I just want a bit more precision.

Regarding resonance in mechanical systems. The oscillating frequencies of separate elements /assemblies can resonate to give extreme elastic deformations. It can happen with aircraft during design/development. Example..(normally a fatal error, but not in this case)

  https://youtu.be/kQI3AWpTWhM

The obvious element in the camera that could allow large variation in angular velocity is the rubber drive coupler.

Edited October 24, 2023 by Gregg MacPherson
more words

[Heikki Repo]

4 minutes ago, Gregg MacPherson said:

Does anyone have ideas about  Aapo's case?

It's not really Aapo's case, the footage is mine and I have that particular ACL right there on my desk ? I can send you the footage Gregg if you want to inspect it too.

[Gregg MacPherson]

50 minutes ago, Heikki Repo said:

It's not really Aapo's case, the footage is mine and I have that particular ACL right there on my desk ? I can send you the footage Gregg if you want to inspect it too.

Oh I see. Please send it if it's easy, or put it in your Dropbox etc. But I don't have much skill with digital to examine the frames carefully.

Gregg.

[steven jackson]

I just ran a test roll on a recently acquired super16 ACL, converted by Visual Products that has been modified with a 144 degree shutter.  For what its worth, I've owned a number of ACL cameras and have always done a lubrication service on them myself and I've never had any experience with flicker on any of my standard 16 cameras.  I decided to set the camera on a tripod and shoot out of the window onto a full sun cityscape scene and test all of my super16 compatible lenses, running from a 5.7mm Kinoptik to a 300mm Nikkor.  When I first got the footage back, I noticed some really faint flicker, so I just assumed it was throughout the roll, but when I looked at the footage again, I realized that with certain lenses, there was no flicker!  The lenses that had zero flicker were the 5.7mm Kinoptik, a 16mm Zeiss Distagon,  Schneider 25mm Cine-xenon, Schneider 28mm Xenon and Schneider 35mm Xenon.  I also use the 16mm-35mm lenses on an Arri IIc.  (I tested 13 lenses in all--- one 12.5-70mm Angenieux zoom, the rest were primes, 4 of which were Nikon F lenses, 85mm, 105mm, 180mm and 300mm.  The other lenses in the test were a Schneider 16mm cine-xenon, Schneider 50mm cine-xenon, and Schneider 75mm xenon ).

From this experience, it would seem that flicker can actually be related to the optics being used. I had a look at the mounts on the lenses to see if there was any relation to them either being chrome or painted black and the answer is no.

Edited December 22, 2023 by steven jackson

[Aapo Lettinen]

47 minutes ago, steven jackson said:

I just ran a test roll on a recently acquired super16 ACL, converted by Visual Products that has been modified with a 144 degree shutter.  For what its worth, I've owned a number of ACL cameras and have always done a lubrication service on them myself and I've never had any experience with flicker on any of my standard 16 cameras.  I decided to set the camera on a tripod and shoot out of the window onto a full sun cityscape scene and test all of my super16 compatible lenses, running from a 5.7mm Kinoptik to a 300mm Nikkor.  When I first got the footage back, I noticed some really faint flicker, so I just assumed it was throughout the roll, but when I looked at the footage again, I realized that with certain lenses, there was no flicker!  The lenses that had zero flicker were the 5.7mm Kinoptik, a 16mm Zeiss Distagon,  Schneider 25mm Cine-xenon, Schneider 28mm Xenon and Schneider 35mm Xenon.  I also use the 16mm-35mm lenses on an Arri IIc.  (I tested 13 lenses in all--- one 12.5-70mm Angenieux zoom, the rest were primes, 4 of which were Nikon F lenses, 85mm, 105mm, 180mm and 300mm.  The other lenses in the test were a Schneider 16mm cine-xenon, Schneider 50mm cine-xenon, and Schneider 75mm xenon ).

From this experience, it would seem that flicker can actually be related to the optics being used. I had a look at the mounts on the lenses to see if there was any relation to them either being chrome or painted black and the answer is no.

I believe the size of the back element and the relative position of it (how close it is to the mirror) might affect the flicker. so the geometry of the lens might be what affects it more than the colour/material of the mount.

the geometry affect the angle of how the light rays converge from the lens to the film plane and also how much spill there is to the out-of-frame areas and from which direction/angle the spill comes from

[Duncan Brown]

With access to a high speed camera now, I thought this might be a fun place to post this:

 

Duncan

[steven jackson]

Looks perfectly timed to me.  Thanks for sharing this.

 

[Duncan Brown]

It does show why converting an ACL to S16 is so fraught with potential problems though - they cut all that timing SOOooooo close.

I'd have to remove the whole front of the camera to see whether we see any of the proposed bounce/bend/stretch at the end of the motion, to explain why an extended or repositioned mirror can slap the camera body even though statically it doesn't reach.

Duncan

[steven jackson]

3 hours ago, Duncan Brown said:

It does show why converting an ACL to S16 is so fraught with potential problems though - they cut all that timing SOOooooo close.

I'd have to remove the whole front of the camera to see whether we see any of the proposed bounce/bend/stretch at the end of the motion, to explain why an extended or repositioned mirror can slap the camera body even though statically it doesn't reach.

Duncan

Makes a strong case for the 144 degree shutter. 

 

[Dom Jaeger]

Here’s a Bosher S16 conversion where he doesn’t change the shutter angle,  the mirror clearly moves in front of the gate before the shutter.

 

 

[Heikki Repo]

1 hour ago, Dom Jaeger said:

Here’s a Bosher S16 conversion where he doesn’t change the shutter angle,  the mirror clearly moves in front of the gate before the shutter.

 

 

I have a Bosher converted ACL that has the shutter close perfectly before the mirror moves. But: this is the camera that originally had the light leak issue through the lens mount (Bernie solved the light leak).

Apparently the two things are interconnected - Les shaved so much stuff of the camera body that the mirror has enough space to take a longer time to travel from side to side. Thus the mirror never moves over the gate when it's open.

My second S16 modified ACL by Bosher originally had the same characteristics minus the light leak. Alas, it would give a small *ding* sound every other frame - the mirror was hitting something inside.

I sent the camera to Les for further shaving of the body and finally received it back without the mirror hitting the insides - alas, the timing is now problematic and there's slight flicker in the corner. So, Les fixed it by just changing the mirror trajectory - I can confirm this by comparing the two S16 ACLs side by side.

 

[Kamran Pakseresht]

I was discussing the flicker issue with Paul from Visual Products - here is what he had to say:

Quote

In regards to the flicker issue, If motor and gear train are not perfect and there is any flutter or bounce in the system it can manifest. Also, there is such a fine line in regards to synchronization between the focal-plane shutter and the oscillating reflex viewing mirror in that if not timed perfectly will cause flicker on the one side of frame, every other frame. It shows up ever so slightly with certain backgrounds visually as well as on IRE in video transfer if off. If not addressed, becomes more pronounced in any conversion that widens the film aperture at all. I have always had to modify the oscillating reflex viewing mirror assembly to clear the frame properly on these when doing conversions... On S-16 mods, I have to take 2mm off the operator-side and on U-16 mods, 1mm off each side.

[steven jackson]

5 hours ago, Kamran Pakseresht said:

I was discussing the flicker issue with Paul from Visual Products - here is what he had to say:

My ACL is a Visual Products conversion yet I still get flicker when using certain lenses, even though they cover super16.  I have found that my arri lenses for my 35mm camera offer the best results and no flicker.