A few beginner questions

[rahulvictor]

Hey guys, just getting my hands into cinematography. I was wondering about a couple things dealing with how much light should be let into the camera, so to speak.

First, if somebody could tell me what that white, half-dome thing is DPs use to gauge light that would be great. But my bigger question is how do DPs come to conclude that, for example, a shot should be f/4.0 as opposed to say f/5.0 or something (I understand that the DP/Director wants something specific visually within a shot, but say if its a brighter scene, what brings them to a specific number...trial/error? arbitrary? something else?)

I know this all probably sounds terribly amateur but I figured someone here would know...thanks!

 

[KKeller]

The white dome you are talking about is a light meter.

Briefly: To set iris a skilled DP will use his tools (light meter with film, scopes and monitors with video) to determine best exposure level. A DP knows what lights to choose for the desired output. They select a specific light and place it at a set distance to get what the exposure they want. ND filters on the camera can also help with fine tuning. Knowledge just comes with time and experience.

 

[Cassius]

Light meter. Look it up. Not really needed with digital cameras in my opinion.

Exposure is a collection of three elements: sensitivity of the stock, aperture, shutter speed. Shutter speed is somewhat limited in moving images, but has the same effect that it does in still photography. It can make a scene choppier or with more motion blur. Sensitivity has a trade off, as higher sensitivity tends to mean more noise/grain, depending on film or digital. Aperture is what you're talking about, which also affects depth of field and lens performance. Most lenses perform best in the middle of their range as far as sharpness goes. The more closed down a lens, the more depth of field you get. Focal length also decides depth, but adds to perspective differences with the background. Between f4 and f5 (which isn't a full stop, look those up) the DoF difference is there but minimal. That change would more likely be fine tuning the exposure.

 

[j1clark@ucsd.edu]

Hey guys, just getting my hands into cinematography. I was wondering about a couple things dealing with how much light should be let into the camera, so to speak.

First, if somebody could tell me what that white, half-dome thing is DPs use to gauge light that would be great. But my bigger question is how do DPs come to conclude that, for example, a shot should be f/4.0 as opposed to say f/5.0 or something (I understand that the DP/Director wants something specific visually within a shot, but say if its a brighter scene, what brings them to a specific number...trial/error? arbitrary? something else?)

I know this all probably sounds terribly amateur but I figured someone here would know...thanks!

Meter's are calibrated to give an exposure setting on the camera that produces a 'middle grey' value.

Using that information, the camera can be set such that if there is a 'middle grey' value in the scene, it will be reproduced on film at the required density.

There are several reasons why even in the digital age, one should meter the scene. First off, in order to control 'the light' one has to know what is being 'seen' by the camera. So, if one wants a 'high contrast scene' but still be within the camera's ability to capture the light values, meter reading will indicate that. In a case where the scene is complex, as in lots of different values ranging from 'high' to 'low', a 'spot meter' is prefered. If the scene is low complexity, or one is attempting to get an overall reading of the light, and incident meter is useful (the meter with the white dome..).

I tend to spot meter reading.

Certain digital cameras have assists for getting an exposure 'right'. The simplest is 'zebra' patterns on areas of the frame where the intesity has exceeded the sensors ability to render the image. Some people don't bother with meter readings, and just watch the zebra patterns, stop down the aperture, or add ND filters until they 'go away'... That works if one is running down the street following a news event... but does not do well for 'dramatic narrative' film making, where part of the art is creating lighting effects under control.

In regard to digital filmmaking with the usual 'entry' level prosumer cameras, special attention needs to be directed to what the camera can render, and not exceed its limits. Many 'first' films fail in this regard. The image is murky, or highlights are blown out, and shadows blank black. To get a 'film noir' look takes knowing the camera response, and lighting appropriately... which means metering the scene...

 

[KKeller]

...which means metering the scene

I am sure a lot of people will agree with me on here. With the digital video metering as pretty much useless. A meter will only give you information on what is entering the lens. With a digital camera, once the light hits a sensor it goes through too many processes to make metering an accurate tool. With each setting change the ISO rating of a digital camera varies too much to be precise. Which is why things such as Waveform monitors, vector scopes, histograms, etc. are so crucial in the professional digital video world. These tools give data after the fact, data on what is actually being captured.


(Using "accurate" and "precise" correctly amuses me.)

 

[Steve Laramie]

I personally never go without a meter especially with a RED. I like to read contrast ratios and color temp.

 

[j1clark@ucsd.edu]

I am sure a lot of people will agree with me on here. With the digital video metering as pretty much useless. A meter will only give you information on what is entering the lens.

Using the various monitor functions that a camera may allow someone to set things up when the camera is in place. Now perhaps I'm wrong, but on still shoots, and the few moving picture shoots, that I've setup, I spent perhaps 1-2 hours seting up the lights, if it was a situation I had not setup for, and all the while I was able to meter the values, and get the ratios I wanted, or could live with...

Once that's all setup, looking at the scopes on the camera, (the only one I've used to date that had them 'built in' was the Panasonice HMC150, and I only recently got CS4 Production Premium with On Location (don't know if it works with USB based cameras....) and my Firewire based DVX100A is SD, so I probably will not be using that much in the future...), anyway, once everthing is setup, looking at the wave form does give the operator 'the best' of what someone can do with the camera...

I will note, that probably a meter that reads out in Footcandles is probably better for video.

However, as for 'well the various processing make using a meter nearly useless'... Well, that's a matter of opinion... anything can be calibrated, and if one takes the time, one can come up with a set of effective ISO values for various gains. It is done all the time for still cameras. I will conceed that digital video camera manufacturers seem to take pains to make the initial starting points 'obscure', in their attempt to bandy about low illumination sensitivity.

But that is not unlike what one had to do in the ancient days of 'real(tm)' film... manufacturers ISO ratings were notoriously 'off' from real world use. And one had to basically 'know' how to compensate, and that 'knowing' came from testing...

 

[Davdo]

Light meters are very valuable with video, though perhaps not so great/easy for finding your stop.

On-camera LCD's suck and the good production monitors are usually in one place, by the camera. If you're a DP on a small crew, chances are you're one of the folks that's going to have to actually adjust the lights. Having a light meter on hand while doing this let's you adjust contrast ratios and such without having to run back to the monitor with every change. Also, if you don't have a pro monitor, it's a lot more accurate than eyeballing it on the little flip-out screen. Sure, you can turn on the spot meter function on certain cameras and move the camera around getting readings but that is a P.I.T.A. Also, if you're shooting with multiple cameras and/or multiple subjects, a light meter can ensure even and consistent lighting between subjects.

~~Dave