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halation due to B&W stock?


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#1 Ward Crockett

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Posted 11 October 2006 - 05:50 PM

I've posted this in the 16mm Only forum as well, but I've come across a theory related to filmstock.

We've been testing our Bolex EBM (modified for S16) by shooting black and white reversal (7266) and negative (7222). Our footage keeps coming back with a halation-like ghost image around highlights. See the attached pic. The weird thing is that it's a horizontal aberration. As far as I can tell, the ghosting does not occur vertically--difficult to tell, though.

I've come across some posts about black and white film not having rem-jet backing, and that cameras need to be optimized to run black and white due to differences in film thickness and anti-static coating (gate tension has to be adjusted).

Does this look like a halation problem to anyone? Particularly one that might be caused by that difference in black and white film? Do you think it would be worth testing a roll of color?

Thanks!
-Ward Crockett

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#2 Adam Frisch FSF

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Posted 11 October 2006 - 07:53 PM

This is a notorious problem with b/w film and pressure plates. Most metal pressure plates are shiny and this is why highlights (and generally bright scenes) get reflected back into the neg, as if from a mirror. It's very visible, even when you pan from a dark are to a bright, how much the 'bounceback' lessens contrast and washes out the neg, and it has ruined many a scene.

Another common situation, and asking for trouble, is when you're shooting through car windows (mainly from the outside in): the sky reflected in the window can rarely be polarized or otherwise removed, so you're in effect shooting through a giant bright filter that's flashing the film. It's bad enough on colour negative, but in b/w this gets doubly compounded by the fact that all this brightness gets bounced back into the negative again.

The way to avoid this is to shoot with cameras that have dark pressure plates. On most professional cameras you can order them with special b/w pressure plates that are black. If it's not available for your camera, it has been known that you can attach a thin, well-sanded piece of wood made out of Ebony to the front of the pressure plate to minimize reflections.

That said, your camera looks like it has horizontal stability problems - one can clearly make out a ghost image to the left. This is probably due to that the neg isn't traveling properly in the gate and not held firm laterally. All cameras tend to stabilize vertical movement somehow and trust that the railigs of the gate (or pressure plate, depending on design) take care of the horizontal. Check the play in the gate by moving some film sideways and generally inspect the railings, or ridges, designed to hold the film in place laterally. It could also be induced by poor vertical stabilizing - it's hard to tell. There seems to be some slight vertical instability present, as well.
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#3 Clive Tobin

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Posted 11 October 2006 - 08:57 PM

This is a notorious problem with b/w film and pressure plates. ...


The new Tri-X Reversal film has a quite dense dye undercoat which disappears in processing, in addition to the grey base, and should be about as immune to this problem as is color film.
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#4 Ward Crockett

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Posted 11 October 2006 - 11:32 PM

Thanks Adam and Clive.

My Bolex does have a black pressure plate, so it sounds like that's not the problem.

If you look closely, the ghost image actually appears on the right AND left sides of the person in the image.

I loaded some leader and tried to push it horizontally, but it seems solid to me. We looked at the film on a Vidette and saw that the film line is stable--doesn't seem to be a registration prob.

I thought it might be some kind of lens issue, but the ghosting doesn't show up in the reflex viewfinder. Maybe the viewfinder is too dim to pick up the ghosting?

And it seems like a lens reflection would produce more aberrant results.

Collimation issues don't cause problems like this, do they?

Clive, you're saying it's unlikely that it's halation problem. So it's probably not even worth testing a color film to see if there's a difference?

Thanks, guys. What a frustrating problem!
-Ward
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#5 Clive Tobin

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Posted 12 October 2006 - 09:56 PM

...Clive, you're saying it's unlikely that it's halation problem. So it's probably not even worth testing a color film to see if there's a difference?...


I'd guess not, but who knows.

Is there any chance you might have a crack in your reflex prism or lens element that could be giving a multiple image? That's about all I can think of.
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#6 Charles MacDonald

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Posted 12 October 2006 - 10:03 PM

I'd guess not, but who knows.

Is there any chance you might have a crack in your reflex prism or lens element that could be giving a multiple image? That's about all I can think of.


Thinking about the look, could it be a really weird ajacency effect in the processing? (althoigh that would be more likly to cause longitudinal problems. {I am thinking of the developer giving an edge effect where the exposure transitions from light to dark due to local exhastion. SOme Still developers actually use that sort of effect to increse apperent sharpness.

The granularity of having to use 100 ft to run a test is a disincentive to try colour film, but that would also have a differnet downstream process to cut that posibilty out.
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#7 David Venhaus

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Posted 12 October 2006 - 10:29 PM

From looking at the image, I agree that your problem doesn't look like normal halation. Halation usually looks much more like a diffused glow around brighter areas. You could check for yourself on the net of examples of halation in infrared photography, Kodak's b+w HIE infrared film doesn't have an anti-halation coating.
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#8 Dirk DeJonghe

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Posted 13 October 2006 - 12:30 AM

This looks like an optical problem in the lens or the telecine (registration) to me. Have you looked at the negative with a magnifier?
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#9 Dominic Case

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Posted 13 October 2006 - 01:40 AM

This absolutely looks like a double image caused by a crack or reflection or similar in the optical system. Don't know the camera well enough to go further, but I can say what it isn't . . . .

It's not an adjacency problem in processing: usually that's vertical and applies to extreme black/white edges most.

It doesn't look like unsteady lateral movement in the camera - though you'd need to run a number of frames to be certain of that .

It doesn't look like a halation problem at all.
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#10 Ward Crockett

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Posted 16 October 2006 - 11:25 PM

Thanks everyone.

We've had different rolls of footage transferred on different telecine machines at different labs--same double image.

So yeah, sounds like it's definitely either the prism or a lens element--the guys at the lab seem pretty sure that it's a lens issue. Unfortunately, we can't find anyone in Colorado to look at the lens. Any ideas? I imagine we'll end up sending it off to New York or California.

Thanks!
-Ward
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