Using a stills light meter as cine light meter

[Evan Andrew John Prosofsky]

Hi there!

 

I have a film shoot coming up shortly on the SR3, but I dont have a cine light meter, I have a stills one. Difference being-I cannot adjust for frame rate with the stills meter.

Questions:

1. Would anybody be able to help me do the math to find out necessary f/stop conversions? 2. Does anybody know how reliable the internal light meter in the SR3 is?

 

Thanks so much,

Evan

[Adrian Sierkowski]

Evan, for a film camera you can set your still meter for 1/50th of a second (or 1/48th if you can, which is the shutter speed for a 180 degree shutter such as the SR3 normally has @ 24fps). If you can't do 1/50th of a second you can get away with 1/60th setting on your meter as it's close enough.

I've never used the internal meter on my own SR3.....

 

The formula to figure out shutter speed from frame rate is as such:

 

Shutter Speed = (Frames Per Second *360)/Shutter Angle. For the SR3 @ 24fps and 180 it would look like this:

 

48=24*360/180, the 48 stands for one 48th of a second, or 1/48.

 

If we were shooting the SR3 at 48fps the formula would be this:

 

96=48*360/180

 

make sense?

[Evan Andrew John Prosofsky]

Evan, for a film camera you can set your still meter for 1/50th of a second (or 1/48th if you can, which is the shutter speed for a 180 degree shutter such as the SR3 normally has @ 24fps). If you can't do 1/50th of a second you can get away with 1/60th setting on your meter as it's close enough.

I've never used the internal meter on my own SR3.....

 

The formula to figure out shutter speed from frame rate is as such:

 

Shutter Speed = (Frames Per Second *360)/Shutter Angle. For the SR3 @ 24fps and 180 it would look like this:

 

48=24*360/180, the 48 stands for one 48th of a second, or 1/48.

 

If we were shooting the SR3 at 48fps the formula would be this:

 

96=48*360/180

 

make sense?

Hi Adrian,

 

Thanks for the formula. Yes, on the stills light meter I can select 1/48th of a second. But the thing is, like I said, there is nowhere to input frames per second. Doesn't this change the exposure? 24 pictures a second is obviously different than one picture (photo still) a second. So what I need to know is how to account for this. I guess I'm still confused, sorry

[Chris Keth]

Hi Adrian,

 

Thanks for the formula. Yes, on the stills light meter I can select 1/48th of a second. But the thing is, like I said, there is nowhere to input frames per second. Doesn't this change the exposure? 24 pictures a second is obviously different than one picture (photo still) a second. So what I need to know is how to account for this. I guess I'm still confused, sorry

 

To figure out exposure, you only need 3 pieces of information: speed of the film, shutter speed, and aperture. Two of those things work exactly in motion film as they do in still photography.

 

 

The framerate is part of the necessary information to calculate the shutter speed. Someone with a meter that has a cine mode can input the shutter angle and the framerate and have the shutter speed calculated for them. You need to input the shutter speed so you just need to know how to calculate that when you know the shutter angle and framerate and that's what Adrian gave you.

[Adrian Sierkowski]

Even though the film is moving what you want to focus on is how long each single frame is exposed for, same as a still camera-- the shutter is open for a finite amount of time, same as in a still camera. The difference is that in a cine-camera how long the shutter stays open also depends on how fast the film is moving, as Chris points out. As you can see, the higher your frame rate, the quicker the shutter opens (1/96h of a second for 48fps -v- 1/48th of a second for 24 fps).

It gets slightly more complicated when you realize film cameras can have shutters which are "shaped," differently, which in common parlance is known as having some shutter angle (e.g. 180 degrees, 172.8 degrees, 90 degrees) which will effect the shutter speed without necessarily effecting the frame rate. For example a 172.8 degree shutter @ 24fps would give you an opening of 1/50th of a second as opposed to 1/48th of a second. Not a big difference, but important for certain situations (Such as shooting in Europe to avoid flicker).

[Evan Andrew John Prosofsky]

Even though the film is moving what you want to focus on is how long each single frame is exposed for, same as a still camera-- the shutter is open for a finite amount of time, same as in a still camera. The difference is that in a cine-camera how long the shutter stays open also depends on how fast the film is moving, as Chris points out. As you can see, the higher your frame rate, the quicker the shutter opens (1/96h of a second for 48fps -v- 1/48th of a second for 24 fps).

It gets slightly more complicated when you realize film cameras can have shutters which are "shaped," differently, which in common parlance is known as having some shutter angle (e.g. 180 degrees, 172.8 degrees, 90 degrees) which will effect the shutter speed without necessarily effecting the frame rate. For example a 172.8 degree shutter @ 24fps would give you an opening of 1/50th of a second as opposed to 1/48th of a second. Not a big difference, but important for certain situations (Such as shooting in Europe to avoid flicker).

 

Thankyou everybody for helping me clear this up. My shoot today would have been very stressful without said information. Always a pleasure getting help from cinematography.com

 

Evan

[Patrick Cooper]

Yea, 1/48th of a second is about right on many of the Arriflex cameras (running at 24 fps.) I believe the Bolex H16 utilizes about 66th of a second running at the same frame rate. Regardless of what shutter speed you settle on with your stills light meter, I would recommend changing the asa setting to a lower one on the same meter if you are shooting on negative film. Negative films benefits from a just a little bit of overexposure. One thing you want to avoid with negative film is underexposure - it leads to an increase in grain, weak blacks and unpleasant colours overall. About half a stop, or two thirds of a stop of overexposure should be fine. Alternatively, you can keep the asa setting on the meter the same as the film stock and just remember to open up the aperture two thirds of a stop from the recommended reading. On the other hand, if you are shooting on reversal film, then your exposures have to be spot on.

[Brian Drysdale]

Hi Adrian,

 

Thanks for the formula. Yes, on the stills light meter I can select 1/48th of a second. But the thing is, like I said, there is nowhere to input frames per second. Doesn't this change the exposure? 24 pictures a second is obviously different than one picture (photo still) a second. So what I need to know is how to account for this. I guess I'm still confused, sorry

 

The exposure time is the same for stills and cine. Each 24 fps cine frame is exposed at 1/48 of a second, which is half of 1/24 - the other half being used to move the film for the next frame. It's basically taking a lot of still frames one after the other.