Using a Light Meter for DV shoots

[John Astad]

Hi,

I was wondering if anyone in the forum has used a light meter when setting up their manual shots. I've been using the zebra pattern with success but what about a light meter for getting a general f-stop/shutter speed reading?

I have a hand held http://www.bowerusa.com/SP-lightmeters.html light meter that I used with my 35 mm camera and was thinking about putting it to use for DV cam shoots.

Question is, what do you set the ASA at on the light meter dial? Anyone have any ideas?

Regards,

John

[Dennis Hingsberg]

...okay you film guys are going to hate this, but forget ASA ratings, f-stops and shutter speeds.

1.) If you want a filmish look you definitely do not want to shoot on anything other than 1/60th for 60i, 1/48th for 24p or 1/50th for 50i (PAL) shutter speeds. Anything else will not allow you to use magic bullet, dvfilmmaker or other post film look softwares incase you have to.

2.) F-stop. For DV you want this as open as your camera will let you go given the light level of your scene. You definitely don't want to use gain in your camera to compensate either so lock this off to -3dB or 0dB.

3.) Depending on the settings in your camera, once you start seeing zebra stripes it could be too late and your highlights might be blown. You will only see this later when you are editing and it will piss you off. If you can adjust your zebra settings in your camera (like the XL1s or XL2) set it to something low like 75 so when you start to see them you don't have to panic too much.

4.) When using a light meter for DV forget film speed setting and work with contrast ratios instead. For DV you should use a contrast ratio of 4:1 whereas in film 8:1 or even higher is prefered. So basically if you meter your background light in your scene and it measures f2.8 you might want the key on your subject to be around f5.6. Your fill light can then be weaker than your key. This is easily accomplished by using a reflector for fill.

But in order to even get some readings on your light meter it might be necessary to put the ISO of your meter to something like 250 or 500. Then once you start taking meter reads, depending on your lighting you will start getting reads between f1.4 and f11. If your camera does not have fps (frame rate) settings just use 1/48th or 1/60th - again it really doesn't matter what you set this too because you're lighting by ratios not actual settings - the point is you want to be able to get some readings in fstops on your meter.

[John Astad]

Dennis, I'm trying to figure how manually setting my shutter speed in regard to your post. You listed several options and my scenario is not listed for the Canon Gl-2 "1/60th for 60i, 1/48th for 24p or 1/50th for 50i (PAL) shutter speeds" I beleive the GL-2 is close to 30 fps, but not sure.

Okay, so have the f/stop as open as it will go and keep the gain at 0db

Thanks for the tip in locking the Zebra strips near 75

In regards to contrast ratios, I'm still on a learning curve regarding that point. How do I measure contast ratio to know tha I'm at 2:1 for DV?

Overall, I see that the point of your post is that the we are operating by contrast ratios and not settings. Again, how do I obtain a definitive measure of contrast ratios?

I learned quite bit from your post and it gave me more questions than answers, which brings me on the quest for additional knowledge on the subject of photon management. Thanks

John
Santa Fe, Texas

[Dennis Hingsberg]

I don't know the GL2 very well, but the default will likely be 1/60th for you. There might be an option to increase it or decrease but definitely stick with 1/60th.

Some light meters have an "ave" button which will do the work for you and show you the constrast ratio. (Check your light meter manual.) If not then you have to do the math yourself using the f-stop ranges ie. f1.4, f2.8, f5.6, f8, f11, f16.

[Josh Bass]

Aren't the ratios kind of subjective? 2:1 is like a sitcom. What if it's supposed to be night? What if things are supposed to almost fall into black? Can't the DV cameras, for the most part, handle about 5 stops?

[Dennis Hingsberg]

Sorry I originally confused the AVE value of 2.0 on your meter which really is a 4:1 contrast ratio. My bad - I will edit my original post.

Whether your scene is night or day, for good lighting and capturing the contrast range of the scene on DV you should always ensure your range of contrast is 4:1. Even night scenes should have lighting on the background where the foreground (or subject) is lit "more" than the rest of the scene.

If you want black areas within a scene they should still be lit, relative to your key subject then brought down overall in post. If you shoot your background in the dark because you want it to look black you will have NO detail in the shadows and if anything grain and noise from your camera.

[Benjamin Kantor]

Question is, what do you set the ASA at on the light meter dial? Anyone have any ideas?

But in order to even get some readings on your light meter it might be necessary to put the ISO of your meter to something like 250 or 500.

Using a light meter while shooting digitally is a very good idea, but there's no need to guess or fudge the ASA. The following is the method that I use before every shoot:



1. Setup a chip chart with even lighting, and with the color temperature of the light appropriate to any filter you have on the camera. (85, etc).

2. Monitor to a waveform monitor.

3. Set the desired gain, gamma, and filter settings.

4. While balance with auto iris on, then turn auto iris off.

5. Set your incident meter to 24 fps, 180 degree shutter angle (this is just a reference to film).

6. Adjust T-stop so that the brightest chip is at 100 IRE.

7. Measure the light on the chart with your meter.

8. Change the ASA on the meter until the T-stop reads the same as the T-stop on your lens.

9. This is your ASA for this camera setup. Additional evaluations need to be made for different gain, filter, gamma, etc settings.


If the camera I'm using supports scene files, I typically evaluate and record the ASA for each of those files, and then only use those scene files for the rest of the shoot.

I really like using a meter while shooting digitally because it allows me to use the same methodology across both film and video mediums. Lighting to a monitor (or a viewfinder) as an inhibiting factor that prevents you from knowing what's really going on in terms of exposure.


Hope that helps.

[Dennis Hingsberg]

John - I'm sorry if I understood your original question incorrectly. I assumed since you wanted to use a light meter for digital video that your intention was for digital filmmaking and thus I wrote completely from that aspect.

If you are in fact shooting DV for filmmaking I don't see any point in taking a meter read in order to know what f-stop to set your lens to on your digital camera. Why? Because if you are shooting on DV with 1/3" CCD's your depth of field is small enough as it is and the only way to open it up and make it as large as possible is to shoot with your lens completely open. Open to the point that if you are outdoor you stack on Neutral Density filters until you're camera says you are near open (ie. f1.4 for f0). Opening up wide indoors can be tough so you need to light your backgrounds with EXTRA fill light, measure it on your light meter... then remember the contrast ratio I mentioned earlier of 4:1 and double that light on your subject! Your indoor scene will look like the sun has parked itself your house, but in camera your darker areas will have detail and your subjects will stand out nicely and properly. Once you put your footage through software like Magic Bullet you will be giving your footage a lot of flexibility to work with and it will be flexible to manipulate properly and get really beautiful and cinematic results. (assuming that's what you're after)

Many great lighting techniques can be learned by reading online what others have done with their projects and also by just trying it out yourself! Study the films you watch, try and guess where the lighting has been placed, look at the shadows on faces or hair lights on people - guess where all these lights have been placed...

Below are some links you can read on lighting, also there is an indie film called "BROKEN" in the DV for the Masses section with 2.5 hours of bonus footage that can be ordered that is helpful to see and learn how some of the lighting and overall look of the film was accomplished - check that out!

http://www.mvwire.com/dynamic/articl....asp?AID=10564
http://zimmer.csufresno.edu/~candace/design1.htm
http://www.film-and-video.com/broadc...les3point.html

[Charles Papert]

Well, a lot of this is indeed subjective. I would hate to tell anyone what a "proper" contrast range is within a scene--generally having a decent highlight somewhere in a low-key, dark scene will make it look less murky but overall ratios should be set for the individual scene, not to a specific formula.

I don't like using light meters for video any more because the cameras don't have a predictable ISO--they tend to be more sensitive at the low end than in the mid-range than film.

I'm not even sure I like universally recommending that people shoot wide open on DV, because the relatively inexpensive lenses are not optimized for that type of shooting and will be sharper a few stops down. Realistically, there's such a great depth of field on a 1/3" camera that at a wide angle lens setting you won't see much of a difference between f2 and f5.6, which is not the case with larger formats. When shooting telephoto, there's always the option of laying in some ND to open up further, which works out because the lenses are less challenged at telephoto settings than full wide anyway.

Finally, it is true that 1/48th is a standard 24 fps film-style shutter speed, but of course a "skinny shutter" look may be desired which would mean a shorter shutter (i.e. the Saving Private Ryan/Gladiator aka now-overused fight scene look) or a long exposure (Requiem for a Dream).

I present all this not to be specifically contrary, but perhaps to point out that there are many philosophies and approaches to achieve similar ends--it all has to do with what one is comfortable with. I could never get through a film shoot without my spot and incident meters but after countless video shoots where I just don't use them, I've finally learned to keep them in the case.

[John Astad]

What is a chip chart,? I googled it and couldn't find it.

[Graham Bernard]

Great thread! - And so timely for my development.

Charles thanks for the "permissions" too!

Grazie

[Benjamin Kantor]

John-

A chip chart is a precise chart that includes 18% grey as well as a stepped greyscale and some color chips. Besides the obvious colors, some charts include flesh tones. DSC Labs makes some really good (and expensive) charts. Less expensive charts are available from TecNec and Fotokem.

[Seth Bloombaum]

Originally Posted by Benjamin Kantor

...Less expensive charts are available from TecNec and Fotokem.

And markertek.com.

[Larry Vaughn]

I was wondering the same thing. I have a Minolta autometer 4F and want to use that to get a base reading to set up my lights.

Light meters used to respond to tungsten light differently than daylight, I assume because there is less blue light in the tungsten light. I read somewhere that the film sensitivity is about 1/2, or 1/2 the iso when dealing with tungsten light. The paper charts that used to come with film verify that.

However, with digital still cameras a more accurate reading would be from the histogram in the camera after the photo is taken. You still need to know where to point the camera, but a light meter will get you in the ballpark and the histogram will get you home.

So, it occured to me that in my XH-A1 every time I snap a photo, a histogram appears.

As long as I use the same shutter speed and f-stop settings with the still photos as I do with video, I'm assuming (bad thing to do) that I could use this histogram to measure the exposure for my video settings. The histogram measures the light that actually gets through the lens onto the sensor, so that would be the most accurate way to measure it.

Yes, I could use Zebras, but I shot a bike race outside last weekend and no matter what I did I couldn't make the zebras go away when someone with a white t-shirt was in the photo. It was an overcast day and the images didn't look overexposed in the lcd or through the viewfinder on playback. The zebra setting was default so maybe it never will go away at the lower numerical setting.

So, my next question is what software to use as a vectorscope? I don't want to pay $600 for the Canon software at this point, anyways.

[Larry Vaughn]

Sorry..........double post.