Light Leaks

Dear Friends,

I recently worked as an AC on a feature film shot here in India on super 16 Arri hsr3 using vision2 200T and 500T stock and prime lenses. We got the rushes back a while back and there was a problem with one of the scenes.

In one of the shots we let the sky burn out a lot. Now what has happened is that there is a light leak of the burnt out sky which was on the bottom of the frame onto the top of frame of the next frame which was a dark green tree.

I have personally experienced this problem during still photography especially while using wide lenses in shots in which the sun is just out of frame. The light leaks onto the next frame especially when one keeps the sun out of frame on the right.

The reason why this happens I think is due to internal reflections in the film itself that it spills onto the next frame as well as the light being so strong it passes through the anti halation backing and reflects back onto the next frame. Also I think its got to do with the angle at which the strong light enters the lens.

Am I on the right track?

This has been my reasoning I would appreciate it if all of you could share some of your experiences with this phenomena so that we could all understand it better.

I did search on the net. In most of the photography mailing lists they took it as something given, that happens, but what I'm looking for is a reason why?

Thank you

Manu Anand
New Delhi

Manu Anand wrote :

>In one of the shots we let the sky burn out a lot. Now what has >happened is that there is a light leak of the burnt out sky which was on >the bottom of the frame onto the top of frame of the next frame which >was a dark green tree.

This often occurs from light bouncing off the edge of the aperture plate and back onto the film -- so the source of light that you are seeing may well be in the frame just below/above the problem, rather than in the adjacent frame. It does tend to show when there is a great contrast between the top of one frame and the bottom of the next.

Older Aatons with chrome aperture plates were susceptible to this problem, which could he helped by filing down the plate a bit and angling the edge (bevelling it) slightly so light bounces away from the film.

Obviously, this problem is more common in 16/S16 and Techniscope, because of the lack of a fat frameline between frames.

Jeff "has had it in an Oxberry, too" Kreines

Jeff "has had it in an Oxberry, too" Kreines wrote:

>This often occurs from light bouncing off the edge of the aperture plate >and back onto the film...

We had the same problem with an ACL 1, which we fixed by dabbing flat black paint on the offending edge. Have to repaint it every few years.

Wade K. Ramsey, DP
Dept. of Cinema & Video Production
Bob Jones University
Greenville, SC 29614

>Obviously, this problem is more common in 16/S16 and Techniscope, >because of the lack of a fat frameline between frames.

Then it must also occur on Scope (Anamorphic) pictures, not much fat there either.

Kelvin Crumplin
Managing Director
Movielab & Multivision 235
101, Eton Road,
Lindfield,
NSW 2070
Sydney, Australia

Kelvin Crumplin writes :

>Then it must also occur on Scope (Anamorphic) pictures, not much fat >there either.

Yes, probably does, tho I haven't personally seen it so I didn't mention it.

No intent to slight 2-perf, ok?

Jeff Kreines

>Then it must also occur on Scope (Anamorphic) pictures, not much fat >there either.

And two-perf, Kelvin? Any spread into the frame would be twice as much in proportion to the frame height (compared with regular 4-perf anamorphic).

Dominic Case
Atlab Australia

Dominic wrote :

>Any spread into the frame would be twice as much in proportion to the >frame height (compared with regular 4-perf anamorphic).

If that were the Case, (ooppps, sorry Dominic) 2 perf film wouldn't be shot at all. One thing's for sure though our 2 perf cameras (all modified by us), has not caused any of these type of light leaks, to date anyway and I certainly wouldn't like to guess on the spot how much footage has travelled through them over the years.

I will be keeping my eye on this one, if I see the problem I might let you all know.

Good modification engineering could be a key factor here.

Cheers

Kelvin Crumplin
Managing Director
Movielab & Multivision 235

Kelvin Crumplin writes :

>If that were the Case, (ooppps, sorry Dominic) 2 perf film wouldn't be >shot at all.

It's not all that common a problem. So you might not have come across it yet.

Jeff "a signatory to the need to sign" Kreines

Jeff Kreines wrote :

>No intent to slight 2-perf, ok?

No worries Jeff, I know you didn't. You said Techniscope anyway, our system is called Multivision.

Cheers

Kelvin Crumplin
Managing Director
Movielab & Multivision 235

After being burned many times in time-lapse/stop-motion I choose to take the attitude that there is no such thing as a light tight camera, especially with these kinds of frame rates. So, I always take the simply precaution of covering the camera when shooting at less than 2 fps. I usually cover it just enough to keep direct light from hitting the body or mag. If you drape a piece of duvateen over the camera, this is almost a good as taping every single crack, crevice and hole.

Of course I still like to test the camera the day before the shoot. I have an entire ritual I go though to test camera and mag. By doing so, I identify where the leaks are (usually around the front of the door, and at the mag seat), and I know how long it takes for the leak to show up as fog on the neg, so I know how long the camera could be safely uncovered.

Don Canfield
Gear+Rose Motion Control
New York
www.gearandrose.com

Another way to check for light leaks is to load some unexposed stock in the camera either daylight or tungsten then get your MagLite and with the camera running shine it all round the camera body (around all of the seals of the mag is good) - if you are using tungsten stock put some CTblue gel around your MagLite and if it is daylight stock leave the MagLite clean - that way any light leaks will show up easily once it is processed as either very blue on tungsten stock or very orange on daylight stock - it is obviously more expensive and the results are not as instant than putting a lite in the magazine and looking for leaks but it might show up other problems (like the viewfinder not properly closing without pressure.)

Anna Carrington
Camera Assistant
UK