Calibrating a Light meter for Digital Video at FreshDV

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Calibrating a Light meter for Digital Video

Published by Kendal Miller July 25th, 2007 in Cameras, Featured Content, Tutorials

How To Calibrate a Light Meter For Digital Video [6:28m]: Download

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A light meter can prove to be an invaluable tool on any set, allowing you to quickly and efficiently set lights and know the correct exposure values of those lights. Light meters were initially designed for still photographers and cinematographers can easily calibrate them to a given film stock speed for shooting film. But what about today’s digital cinematographer? I’m glad you asked. In this tutorial I’ll show you how you can use a light meter to quickly and efficiently light a scene, and gain better control over your camcorder’s exposure.

To use a light meter in concert with today’s digital video camera, you must first obtain the native ISO rating, or “baseline” sensitivity of your camera. Since manufacturers assign a lux rating in place of an ISO rating it is up to you determine the ISO. In the video I will walk you through the steps of setting up a light meter and calibrating it to your camcorder. You will need the following gear to get started:

-Your video camera, make sure no filters of any type are in front of the lens, and ND’s are turned off.
-A flat, even light source. A softbox works well.
-A chip chart, or at minimum an 18% gray card.
-A light meter with cine functions, frames per second, and shutter angles. If you need to do shutter angle to shutter speed conversions, check out this post on the math to do those conversions.
-A waveform monitor of some sort if your camera does not have a built in spot meter. FYI, you can hook up your camera to a computer via firewire and use the waveform monitors in most NLEs.

So you have everything together and ready to go? Excellent! Lets jump on in, the water is fine.

UPDATE:
Just so people know this will setup your baseline camera to your light meter, changing settings like shutter speed, frame rates, or adding filters of any type including NDs built into the camera need to be adjusted and compensated for in the light meter.

56 Responses to “Calibrating a Light meter for Digital Video”

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1 Ajit Jul 25th, 2007 at 2:56 pm

Awesome tutorial.
2 peter Jul 26th, 2007 at 9:55 am

why would you use a light meter if you have a waveform monitor?
3 Kendal Miller Jul 26th, 2007 at 10:48 am

Okay well here are a few reasons for me personally, you’ll get different responses from different DPs on this topic though. Once you set up your light meter you won’t need a waveform monitor on set, so having a light meter handy is really nice and compact. The second is for setting lights in a smaller scene it is easy enough to just glance at a monitor or scope but its kind of hard to tell lighting ratios that way. In a large scene with lots of lights its super easy to simply take a reading and know with a mathematic absolute and set each additional light based off the values of your key lights, so you can easily set a lot of lights without running back and forth to a scope or monitor so it is super time saving in that regard. Advanced meters like the Sekonic 758 can accurately factor things like ND filters, and grads, as well as letting you set the dynamic range of your camera so you can instantly take a reading anywhere in your scene and see if the light will be over or underexposed.
4 peter Jul 26th, 2007 at 11:18 am

Different strokes I guess. After using a light meter almost daily for 15 years I haven’t pulled mine out of its case more than a dozen times in the past 5 years.
5 Kendal Miller Jul 26th, 2007 at 11:23 am

yeah I mean just another tool in the case, I like to have on handy and I find it can be time saving.
6 Iftakhar Ahmad Aug 29th, 2007 at 10:15 pm

Cool tool when you have difficult lighting or if you don’t have any field monitor/lcd screen.
7 James Sep 29th, 2007 at 10:38 pm

Excellent, if been looking for this for ages!

Few questions,

This was done with the 35mm lens adapter and 35mm lens on. Will it make a difference which lens I have on my 35mm adapter when taking the reading? Do I have to calibrate again when I take the adapter off? Is there an cheap easy way to see what the dynamic range off my video camera is?

Thanks
8 Kendal Miller Sep 30th, 2007 at 3:22 pm

Changing the 35mm lens will not change the ASA or ISO rating of the rig…changing the adapter will though. You need something like wedge chart or such…something to deliniate stops of exposure, then you basically count the chips from pure white to pure black using a waveform monitor
9 James Oct 1st, 2007 at 10:10 am

Thanks Kendal!!

FreshDV ROCKS!!
10 Adam Nov 20th, 2007 at 7:14 pm

Would the Sekonic 358 be Ok for this procedure as well?
11 Kendal Miller Nov 20th, 2007 at 7:40 pm

As l long as you have basic cine functions such as FPS and then you would just need to make sure you match your cameras shutter speed, to the light meter, most cheaper meters default to 180 degrees so you would just need to set the shutter speed on your camera to match that. For 60i footage you would want to use a FPS of 30.
12 Adam Nov 20th, 2007 at 7:49 pm

I’m not sure it has the functions yet. But this is the model I’m considering. But I will be shooting 24p though.
One thing I know for sure hough. The 358 is incident only. No spot.
13 Marco Marco Nov 21st, 2007 at 11:58 am

Excellent!!! One question…how do you get the scope to read on fcp whilst the camera is attached. I’ve tried no device control and just captured on the fly but the scope still does not read it. I would have to play back the footage on the timeline to get a reading. You seemed to be doing it as the camera was on.
14 Mark Gill Dec 9th, 2007 at 6:40 am

Hi Kendal

Great tutorial.

This is a similar question to one asked before but something I need to clarify.

I am using an FX1 with a Redrock Micro Adapator System and Nikon Primes.

Do i calibrate the FX1 to the Vectorscope or just open the FX1 iris to it’s widest point then use the relevant stops on the lenses to achieve the 50%?

Apologies if this seems a little repetative but i think it’s an important question.

I believe th FX1 has an ISO equivalent of 300-320 but with the adaptor there is significant light loss and it drops to around 100 ISO.

Hope you can help

Warm regards

Mark
15 Kendal Miller Dec 9th, 2007 at 10:09 am

Hey Mark,
Your question is a little unclear but let me take a stab at it. You need a waveform monitor or spot meter on the camera, you need to find out when an 18% grey card reads 50% IRE in the camera and then notate where that exposure falls. Easiest way is to point your camera at an 18% gray card and look at a wavefrom monitor, adjust the iris until the card reads 50% on the scope. Then its just setting up your meter per the tutorial until it matche the f-stop of the camera. Does that answer your question? As far as the scopes in FCP, you just open the log and capture window, and under the tab “clip settings” click “video scopes”.
16 Mark Gill Dec 9th, 2007 at 11:23 am

Hi Kendal

Thanks for your reply. I’ve followed the tutorial with no problem. However, I don’t think I was clear enough.

Watching your tutorial I notice you have a lens adaptor on the front. I use something similar on the front of my FX1.

Now the FX1 on it’s own can be calibrated to match the mid gray, via my spot meter or the vector scope. I have a signal coming into the vector scope which i can move up to 50% like you instruct by opening the aperture on the FX1. That is very clear and I have no problems doing this.

However if I then attach the Redrock adaptor, there is significant light loss into the FX1. To get enough light into the FX1 via the adaptor I have to open the FX1 aperture to it’s widest point.

Or put it another way, have you got your 35mm lenses wide open before you calibrate the video camera?

I am beginning to confuse myself.

Hope you can help.
17 Kendal Miller Dec 9th, 2007 at 12:11 pm

You have to recalibrate the camera with the adapter on obviously. And you have to have enough light to get the 18% card to read 50% IRE so the aperture you need to set on the lens is whatever it needs to be to resolve that exposure. I usually run the on camera aperture wide open and then dial down the aperture on the 35mm lens. But where it needs to be at is determined by the exposure of the Gray Card, you can always ad more light to the card as well, whatever you need to do to get it to read 50%. That help or only muddy the water?
18 Mark Gill Dec 9th, 2007 at 2:03 pm

Hi Kendal

No that sounds about right. I just wanted to make sure. I’ve shot three films prior to getting a light meter and they’ve come out with good exposure. So i just want to make doubley sure I’m going to make the step up with all the knowledge I can. I’ll be doing plenty of tests.

The ISO issues I’m continuing to look at.

Many thanks for the help.

Mark
19 toto Jan 11th, 2008 at 9:24 am

Thanks, but i can’t see any link to the Video!
20 Kendal Miller Jan 11th, 2008 at 10:01 am

Checking to see whats wrong….
21 Matthew Jeppsen Jan 11th, 2008 at 2:19 pm

It’s fixed now. There should be a download link at the top of the post.

-Matt Jeppsen
22 Marco Marco Jan 12th, 2008 at 9:41 am

Thanks for that Kendal,

If you’re ever in London, I’ll buy you a couple of pints!

:)
Cheers.

Marco
23 toto Jan 12th, 2008 at 11:30 am

Many thanks guys :)
24 Kendal Miller Jan 12th, 2008 at 4:52 pm

Good enough for me!!! You made it all worth while :)
25 Dennis Wood Jan 31st, 2008 at 11:11 pm

Guys, I reviewed this a few times to get set up for our own testing here with the DSC/Ambi charts. We picked up the Sekonic 358, but now that I’ve seen this, I’ve got meter envy. Great segment!
26 Karl Koelling Feb 24th, 2008 at 9:36 pm

I understand how to determine the ISO of your camera (great tutorial, thanks), but I’m still a little confused on how to actually use a light meter with a 35 adapter. With the adapter, you essentially have two sets of apertures (the camera’s and the adapter’s) allowing for many combinations of exposure. For example, if you take a reading with a meter of a subject’s face and it says to put your aperture at 5.6 for proper exposure, what does this say about where your slr f-stop should be? You could have your camera’s aperture at 5.6, but have the aperture on your slr lens at 2.0 giving you one exposure, and then move the slr aperture to f8.0, which would give you a completely different exposure. Can you please clarify?
27 Mark Gill Mar 5th, 2008 at 8:04 am

re: Karl

This is a good point and well put. I did ask Kendal something similar but I don’t think I got a definitive answer.
28 Kendal Miller Mar 5th, 2008 at 8:31 am

When working with adapters I baseline the cameras iris at 0 and then rate the ISO utilizing only the still lens then I use the still lens to control the aperture. Almost ignore the aperture controls on camera, and use the still lens to control that. Remember its best to use a light meter to light and rough in a scene with a lot of lights, and the finesse it bye eye once you get frame up.
29 pablo korona Mar 26th, 2008 at 9:42 pm

because of the site redesign, i now found this tutorial.
i’ve been looking for a tutorial like this, and little did i know it was my friends over at freshdv who are providing it.

thanks guys.
30 Matthew Jeppsen Mar 27th, 2008 at 9:32 am

Hey Pablo, great to see you here!

-MJ
31 Lonnie Apr 6th, 2008 at 3:04 pm

I have all the latest releases of FCP, QT, Leopard, you name it, but when I firewire my XHA1 to my MacPro Intel, I get no scopes in log and capture, not under clip setting, it is not to be found…

then in the FCP user manual it states: Note: Video levels can only be adjusted for analog video interfaces. But I watched you guys go firewire from HVX to FCP - help!

and thanks!

Lonnie
32 Matthew Jeppsen Apr 9th, 2008 at 5:40 pm

Lonnie,

You might try ensuring that your video signal is downconverted to DV as it comes out of the HDV camera. Most scope programs (and I think FCP) won’t work live with HDV signals.

-MJ
33 Lonnie Apr 9th, 2008 at 9:07 pm

Yes, I finally solved the problem. No HDV live scopes in FCP. Must capture as DV as you suggested…
thanks for getting back though!
Lonnie
34 Kurt Apr 11th, 2008 at 4:46 pm

The Video links are offline. Please fix them. Thank you :)
35 Matthew Jeppsen Apr 17th, 2008 at 12:12 pm

Links should be working now. Thanks for the heads up!

-MJ
36 Adam Apr 19th, 2008 at 5:23 pm

So is it possible to rate a camera with an incident meter or must it be a spot meter?

Thanks.
37 Javed Atique Sep 11th, 2008 at 7:32 pm

Dear Kendal Miller & Matthew Jeppsen thank you very much for such a nice piece of work. The video about calibrating video camera is very helpful. One request I want to make is that you please provide us another video about how to use a light meter for film and video work. It really will help us in our practical work. However, for the work you have done, I want to say hats off to ya…
38 Darrell McConduit Sep 12th, 2008 at 9:04 pm

Really great video!! I’ve been wondering how to do that for a very long time. Now I can go ahead and order my Sekonic Light meter (with cine functions). Thanks Kendal!!!
39 Kendal Miller Sep 12th, 2008 at 11:16 pm

Hey guys how about some feedback for a follow up segment what exactly would you like to see in regards to metering on set? Any specifics??
40 Javed Atique Sep 22nd, 2008 at 7:42 pm

Hey Kendal, how are you doin? I think that not every working professional knows about the basics of using a light meter. It would be helpful if you please clarify on what is contrast ratio and brightness ratio in lighting a scene. It would be particulary helpful if you clarify how to meter for your camera when all the lights i.e; Key, Fill and backlights are setup. Any suggestions would really be helpful. Thanks!
41 Javed Atique Sep 22nd, 2008 at 7:47 pm

Hey Kendal how are you doing? I think that not every working professional knows about using a lightmeter. It would be particularly helpful if you please clarify brightness and contrast ratios in lighting and using a light meter for your camera when key, fill and backlights are available in a scene. Thanks!
42 Javed Atique Sep 22nd, 2008 at 7:48 pm

Hey Kendal how are you doing? I think that not every working professional knows about using a lightmeter. It would be particularly helpful if you please clarify brightness and contrast ratios in lighting and using a lightmeter for your camera when key, fill and backlights are available in a scene. Thanks!
43 Javed Atique Sep 22nd, 2008 at 7:50 pm

Hey Kendal how are you doing? I think that not every working professional knows about using an exposure meter. It would be particularly helpful if you please clarify brightness and contrast ratios in lighting and using an exposure meter for your camera when key, fill and backlights are available in a scene. Thanks!
44 Javed Atique Sep 22nd, 2008 at 7:53 pm

Hey Kendal how are you doing? I think that not every working professional knows about metering. It would be particularly helpful if you please clarify brightness and contrast ratios in lighting and using a sekonic L758Cine for your camera when key, fill and backlights are available in a scene. Thanks!
45 Kendal Miller Sep 22nd, 2008 at 10:51 pm

Javed,
I think we can figure out a way to do a tutorial like you want at some point in the future.

-Kendal
46 AD Sep 26th, 2008 at 9:19 am

A tutorial about setting up camera exposure profiles would be very interesting (clipping points and dynamic ranges).
47 Kendal Miller Sep 27th, 2008 at 6:47 pm

AD,
please clarify what you would like to see…profiling is so unique to each camera.
48 AD Sep 28th, 2008 at 10:33 am

Sorry for not being clear. I am speaking about calculating the dynamic range of a certain camera with a light meter. like you are speaking of in one of the first posts:

“Advanced meters like the Sekonic 758 can accurately factor things like ND filters, and grads, as well as letting you set the dynamic range of your camera so you can instantly take a reading anywhere in your scene and see if the light will be over or underexposed.”

I have the option on the sekonic 758Cine to setup camera profiles and it goes beyong simply knowing the iso rating of the camera. You also have to know the clipping points in the white and in the blacks and the dynamic range of the camera.

I tried to test this with a HVX200, but I am not sure if my procedure and the results I had were accurate.

- I first check the iso rating of the camera with my 18% grey at 50% white on the camera.
- Then, I cut the light by one stop. The value is now 30% on the camera.
- Then, I cut the light by two more stops. The value is now 10% on the camera.
- Then, I do the opposite by adding one stop of light, then two stops, etc. until I overexpose.

Is it the proper way to check this ?

Moreover I wonder if this can fluctuate depending on other factors like the focal lenght and the aperture. When I am at F2 is my dynamic range the same as when I am at F11 ? When I am all zoomed in, is my dynamic range the same as when I am fully zoomed out ?

I am trying to be as clear as possible, but feel free to correct me if I am not.
Thank you again !
49 Kendal Miller Sep 28th, 2008 at 3:29 pm

Okay there are alot of ways to do this but here are some basic steps I’ll publish a more in depth tutorial on this later. Basically you could shoot say a stouffer wedge chart, and then extrapolate what your DNR is from that and manually enter that detail into the meter. (Say 8stops) then once you set your midtone the camera will figure from there where your clip points would be. Keep in mind that the cameras DNR is the same throughought the aperture range BUT changing gamma curves etc…will impact the sensitivity of a camera and therefore affect the DNR. Alternately you can use Skonics software and profiling target to setup your lightmeter. Follow the instructions located here just take frame grabs from your video source:

http://www.youtube.com/watch?v=_7SZ58CugpY
50 Philip Borgnes Dec 8th, 2008 at 10:53 pm

Hi Kendal,
I’m in the same situation as AD meaning I have the 758Cine and am wanting to setup profiling for my Sony EX1. How to do this? I have looked at the profile video that was also referenced, but am not able to understand how that works for the EX1. Looking forward to your update on this! Thanks!!
51 Kendal Miller Dec 11th, 2008 at 3:43 pm

Phillip the process is exactly the same but just use the spot meter on the EX1 to meter 50% on the gray card.
52 Víctor Aguinaco Dec 15th, 2008 at 7:35 am

Hi Kendall, nice tutorial… I can’t wait to see the depht tutorial…

To Philip Borgnes: Be careful with the EX1… If you change the picture profile maybe you’re changing the gamma curve or the sensitometry (not the cmos but the recorded)

I think you must do different calibrations for each “picture profile”…

I don’t know how do you understand my explanation. I’m not an english native speaker so I hope you just do…

Bye!
53 Alex Dec 15th, 2008 at 10:56 am

Hi:

I have a Sony DSR-PD170 camera, I’m an adobe premiere user, so I don’t see in my camera a light meter, however I tried to use adobe premiere to see the graphic you mentioned but not sure how to do that. How can I do to calibrate the right exposition?

Thanks.