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using an 18% grey card


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#1 Lukeo

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Posted 04 June 2006 - 08:10 PM

Hey all,

I've been doing some videography with the panasonic gs400 to make small "films". I'm wondering how to use an 18% grey card to expose. How exactly do you set one up to use it, or if it is even worthwhile using one. With my camcorder i have control over exposure, zebra striping, and colour bars. I've been just using the zebra stripes to prevent over exposure. Is it just better to use auto exposure for a wide shot of the scene and then locking it off with AE lock? I don't know how to use colour bars at all. What is the typical set up for exposing video with the greay card?

Luke
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#2 Michael Nash

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Posted 04 June 2006 - 08:21 PM

These books are a good place to start:

http://books.elsevie...0R8UG2SGGPJFP99

http://books.elsevie...0R8UG2SGGPJFP99
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#3 Laurent Andrieux

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Posted 05 June 2006 - 07:29 AM

The color bars are to used to determine exposure. They are used as a reference for editing. You shoot 30 seconds of them at the beginning of each tape. Also they help you to properly set your viewfinder (contrast and brightness).

You don't need to use a grey card as to determine exposure. Use the auto exposure and zebras instead.

From what the auto exposure gives you (giving you a strating point), adjust the exposure manually, using zebras and the viewfinder, since you have correctly set it with the bars.
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#4 Bob Hayes

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Posted 05 June 2006 - 12:15 PM

I continue to stumble along through digital world. Currently I use the Kodak Grey card plus. It has a large 18% grey card with Black and white square on opposite corners. It gives me three clean references so it easy to ID on a waveform. I don?t use it to set exposure because I find that in a properly exposed shot the grey card or chip chart is rarely properly exposed. When people talk about a properly exposed grey card they are talking exposing the grey card as a color and exposure reference not as a tool to expose the scene. Currently I am shooting HD with a waveform. I set the exposure by monitor. I check the wave form to make sure my exposure gives the right amount of information to the post guys. Then I insert a grey card and check it on the waveform. I often run it at 35 IRE. A ?properly? exposed grey card should read 50%. Then when I get my dailies back or look at the footage later I can get a second opinion on how I am running my exposures. That said because I seem to run my 18% grey card at 35 IRE I can throw it into a shot and get a quick idea how close my exposure is.
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#5 John Pytlak RIP

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Posted 05 June 2006 - 12:19 PM

I continue to stumble along through digital world. Currently I use the Kodak Grey card plus. It has a large 18% grey card with Black and white square on opposite corners. It gives me three clean references so it easy to ID on a waveform. I don?t use it to set exposure because I find that in a properly exposed shot the grey card or chip chart is rarely properly exposed. When people talk about a properly exposed grey card they are talking exposing the grey card as a color and exposure reference not as a tool to expose the scene. Currently I am shooting HD with a waveform. I set the exposure by monitor. I check the wave form to make sure my exposure gives the right amount of information to the post guys. Then I insert a grey card and check it on the waveform. I often run it at 35 IRE. A ?properly? exposed grey card should read 50%. Then when I get my dailies back or look at the footage later I can get a second opinion on how I am running my exposures. That said because I seem to run my 18% grey card at 35 IRE I can throw it into a shot and get a quick idea how close my exposure is.


Instructions for using a Gray Card:

http://www.kodak.com....4.10.8.4&lc=en

http://www.kodak.com....10.8.4.4&lc=en

http://www.kodak.com....10.8.4.6&lc=en

http://www.kodak.com....10.8.4.8&lc=en
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#6 Michael Collier

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Posted 05 June 2006 - 01:15 PM

Bobs advice is spot on. A waveform monitor is a much better exposure tool for exposure than a grey card (grey cards are also pointless if you dont have a waveform)

As for auto exposure, I would leave that off all the time. You should expose to the iris setting your going for. If you dont you will find your exposure drifting throughout the shoot. Say you shoot one shot of a dialouge scene and then turn around for the reverse shot. You find that a key is too dim, so you iris up. Now your background lights are too hot and you have more depth of field. You have changed the entire look of the reverse shot (which wont match the first shot) all to correct what should be taken care of by moving a light.

Ultamatley you want to watch your monitor and waveform. As long as you provide a wide band of information, you can color correct just about anything. But if your white wall clips and becomes a white mass, you wont be able to tone that down at all. Learn how to use a waveform properly. You may find the grey card useless after that.

(I have also heard of people turning on the auto exposure and then adjusting from there. It works, but I dont make it a practice because your using your best judgement anyway. The auto can get you within +/-1-2 stops from proper exposure, which is too far off anyway. best to use a waveform and watch very carefully what those bits are doing.)
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#7 Laurent Andrieux

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Posted 05 June 2006 - 01:25 PM

I think this mate is more into some easy to do method, more like eng than studio work... Using a waveform monitor in a standard low cost sd shooting is certainly complicated on this point of view, I guess...
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#8 Bob Hayes

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Posted 05 June 2006 - 04:28 PM

I think this mate is more into some easy to do method, more like eng than studio work... Using a waveform monitor in a standard low cost sd shooting is certainly complicated on this point of view, I guess...

On lower end cameras you can use the zebras as a low budget wave form. Often they are adjustable usually 100% and 70%. By using Kodak Grey Card Plus, setting exposure so the zebras are on the white square and then stopping down till they disappear your whites are probably at 95 IRE. Now the card is probably at least 10 IRE overexposed. If you set your zebras at 70% and put Zebras on the 18% your card is 25 IRE over a properly exposed grey card. You can sort of create your own waveform monitor. A professional video grey scale will give you more accurate steps. But again just because you have a properly exposed grey scale doesn?t mean your shot is properly exposed. In video these charts are used primarily to calibrate and match cameras and their proper exposure is designed to tech cameras.
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#9 Lukeo

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Posted 05 June 2006 - 05:07 PM

Hey all,

Thanks for the replies guys. For what I'm doing the grey card is probably not needed, the auto exposure, then manually setting the iris while observing zebra stripes is probably best for me. I just thought I'd ask to see if a grey card is really a necessity.

About the colour bars, I understand to record them at the beginning of the tape, and to adjust the colours and contrast for my post production monitor (will be my old small sony tv) hooked through my camcorder to the computer for during editing. Not sure exactly how to do it tho. How do you set up your viewfinder with colour bars? when I go to colour bars in my cam it just shows them on the lcd and doesn't let me change any settings that i know of.

What Michael Collier was saying about determining an exposure for the scene. I have the following f stop and gain levels on my camcorder goes from F 16, 14, 11, 9.6, 8.0, 6.8, 5.6, 4.8, 4.0, 3.4, 2.8, 2.4, 2.0, 1.7, OPEN, Gain 3, 6, 9, 12, 15, 18 dB (just out of curiosity what would be the best f stop to record at, don't most lens have a sweet spot?)

I find that the auto exposure is usually off a couple stops according to the zebra stripes, I then usually adjust accordingly. but I do find my shots are not consistent looking. Is it better than to adjust the exposure for my master shot at whatever f stop,for example f 1.6 and then just keep using that f stop # for the rest of the scene, close ups, cut aways, over the shoulders etc? I do find that my cam is not the greatest in low light, so i'll probably have to invest in some more lighting, I just have some hardware lights reflectors , foam core boards, some gels and aluminum foil. I'm guessing my shots will look a lot better when using an actual fstop instead of gain! I will be doing the lighting myself as well, do you think it's best to light every shot individually and then adjust exposure for each shot accordingly, or again just keep the same f stop throughout the scene? What is my best way to keep a consistent look to each shot with minimal lighting set ups as well.


I'm a bit of a crazy man and doing the camera work, lighting and directing myself, it's is not a professional shoot, just doing a 15 min short for a festival. Forgive me, I understand the importance of individuals assigned to each job like lighting, and camera work but right now i have no choice haha. Sorry for the amount of questions. i appreciate your feedback.

Luke
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#10 Laurent Andrieux

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Posted 05 June 2006 - 06:25 PM

First, you have to know if your zebras are set for 100 % or 70 %.

I huess you should find this in your user's manual. (On Sony cameras it's easy because they superimpose on the color bars. If they appear on the whit bar, it's 100 %, if on the yellow one, 70 %) %May be you can set this up in your menus.

If it's 100 % it means the zebras should appear in a white area. No need for a whit chart. Just find something you judge white by eye in your frame. It may also be the clouds in the sky. Open or close your iris so to have the zebras on those white things. Also since your viewfinder is properly set (I'll come back on this point), judge the whole image...

If it's set on 70 %, it should only be on the lightest parts of a caucasian skin. Ideally exterior day. Remember it's designed for ENG. Imagine an interview outside by day in. So the zebras should take place on the front, the chick where it's really bright...

Now how to set both your viewfinder (I guess you have a bright and contrast knob on your camera's viewfinder, don't you ?) and your control and postprod monitor :

- Bright is for the black level. Contrast is for the white level.

Put the chroma off by turning the color/chroma knob to zero

Put the contrast knob in its middle position , turn down the bright knob so the image gets dark and turn it up again so that the black bar is black but a bit less than the black mask of the monitor surrounding the bars.

Then contrast : turn it up until the white looks white and so that you see all bars as a grey scale.

Then turn on the chroma again so that the colors look well saturated but not too much. You'd need a blue only switch to set it more properly but I guess you don't have any do you ?

About iris stop values and gain :

It depends if you like a shallow or deep depth of field, but the values beetween 4 and 8 I'd say is the sweet spot.

Sometimes you have not much choice, but don't forget to use the built in filters when it's much too bright by day outside so you don't get too closed (around 11 or 16). Also try to avoid opening up to much. That means tha some light will be needed if you fall under 3.4.

Gain is an electronic amplifier that add noise. The value +3 giving you the equivalent of a half stop should not be noticed, though and even +6 (equivalent 1 stop) not too much noticable.

By night in the street, you should not have any choice but using +9 for instance, that giving a crappy look but sometimes it helsp (think of a ENG situation, crappy would be better than nothing...)

If you light for a wide shot let's say around 4 / 5.6, you should not have any problems for CUs. JUst lit them up a bit with a foam reflection, open up a half stop if necesary, it should be fine.

Remember you may have been unhappy with your exposure settings till now if you didn't set your viewfinder properly or/and didn't know what value was the zebras supposed to show on.

Test, test and test again.

Good tests.

Regards.
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#11 Michael Collier

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Posted 05 June 2006 - 10:47 PM

As for the best F-stop for a lens (especially since I gather you are probably on a prosumer mini-DV camera, sounds sorta like the GL-1 or 2?) you have several things to consider. First the lens' aren't that good. Also you will probably not be able to find tests for sharpeness at a given F-stop and camera (you can get a sharpness scale and take some time to do one yourself) so you just gotta follow some basics guidlines that apply to most lenses.

First the wide open is a killer. Any time you open a lens to its widest appeture the lens will soften slightly. It wont be noticable on the screen but when you play the video through a bigscreen, you will notice it. Also try not to shoot at too high of an appeture. If you stay within 2.8-8 that is usually good. I find on most video cameras f4 is a good place to be.

Since you probably have a 1/3" sensor you will probably have too much Depth of Feild. The only way to reduce this (and thereby provide speration to your subject by haveing a slightly out of focus forground and background) is to reduce your f-stop. (also why its important to expose to a given iris setting, when your not in run-and-gun mode)

Lighting is a bit trickier. You have to think about how you want the scene to ultamatley look. You will change lighting as you move from wides to close ups. This makes sense of course, you can see more detail in the close-ups, so your lighting too should be more defined. Generally I plan out the close up lighting first, then I use that plan to light the wide shot. That way when I finally get to the CU not only do I have the look I am going for from the plan, I also have the experience from lighting the wide to apply to the CU.
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#12 Lukeo

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Posted 06 June 2006 - 12:05 AM

Hey thanks

The Camcorder I have is a Panasonic GS400, it's a decent little cam for the price. you were talking about the sharpness, there is the ability to control sharpness in the camcorder. People have recommended that i bring it down a few notches because it contributes to more of a film like look. Since my camcorder doesn't perform the best in low light at apertures 2.8- 8 I'm going to have to blast my scene with much light, but if you say it's worth it for the sweet spot on the lens, I trust your judgement 100%. the actors will have to suffer slightly. So say I light a scene (I'm using worklights with parchment paper as diffusion, and some foamcore and cardboard as flags and cookies) So I blast the scene with all my light set up my wide shot, get my lighting source from a window for example and then set my cam to hopefully within that 2.8 - 8 range so says it's F 4. then when I move my lights for the close ups do I remain at that f stop or change it at all?

I understand I will also run into some lighting continnuity issues, because I'm not using a light meter. I was planning on just drawing up lighting diagrams and measuring the distance of lights to the actors. Would this work decently for achieving relatively similar look from shot to shot?

Sorry if these questions are juevenile. i have read through kris mallikewz book on film and video lighting, and read lots on the internet and in videomaking books, but nothing has given me the practical information that people like you know. I care about lighting very much, i think it's soo important, but i just need a way of doing a relatively easy set up to maintain my lighting continuity and correct exposure shot to shot.

thank you very much

Luke
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#13 Laurent Andrieux

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Posted 06 June 2006 - 04:46 AM

This is the beast : http://www.digitalca...00-reviews.html

Not the kind of camera you'd control with a waveform monitor ! B)

then when I move my lights for the close ups do I remain at that f stop or change it at all?


You're not supposed to "move" them that easily. It's just that when you see the close up, you may feel like you 'd need to make it a bit better than what it looks like from the wide shot light... It that case, it may be enough to just move 1 light or add a foam or something so. But you are not supposed to change it too much because it won't match the wide shot if you do so... Then after you've touched the light, well, yes, you are supposed to change the iris setting if needed. It may be about 1/2 stop or so so don't worry. But it's got to be correctly exposed ! forget about keeping the exact same f-stop since it's going to be maximum at +/- 1 stop anyway !
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