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Old September 29th, 2009, 10:30 PM   #1
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over exposure vs under exposure in HD video

Hello,

Since I don't have any formal training I'd like to bring this question to the experts in the DV field on the board for some clarification.

I own a Sony FX-1, that has an adjustable Iris. When I'm filming it seems that the most important thing is that the exposure (f stops) is correct.

My question to everyone is: is there such thing as correct exposure?

I filmed one shoot and if the iris was open too much certain elements were clearly over exposed @ the expense of others being brought out of the "too dark" region.

On other shots It seems like underexposure (iris closed too much) is the only way to get correct contrast (I'm thinking nevermind the subject being filmed as long as there is a nice seperation between the sky and the clouds in the background).

I look at this one clip here shot with a Canon 5D and it looks like what I'm thinking, the sky and the clouds are in perfect contrast and the expense of the actors face (cleary if the iris was open more the details in the face would have been more visible).


YouTube - Canon EOS 5D Mark II and Glidecam 4000 Pro

to contrast, this video was filmed in the early hours of the morning and the suns glare made anything (including the actors) in the shadow too dark. You can see me adjusting the iris and the cameras ND filters on and off to find the ideal setting.

Is there such thing as an ideal setting in exposure?

YouTube - CCLEC

any info/help always welcome
Martin Wiosna is offline   Reply With Quote
Old September 30th, 2009, 12:46 AM   #2
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Correct exposure isn't always the same as creative exposure, but in most situations (at least where faces are concerned), you'll want to expose for skin tones. Learn to use the zebra function on your camera. I set mine for 70. When I see the lines on hot-spots of the faces, I know I'm getting a 'proper' exposure for that part of the image. All situations are different, and cameras can only handle a limited dynamic range. So even if you are 'properly' exposed for the faces, you can still blow-out the background (especially if the subject is backlit). The creative part of exposure comes to play when you want to direct the viewers attention to an element of the image. If you're going for a silhouette, then the faces will not be 'correctly' exposed as per the illustration above.
If you're not dealing with faces, then you can choose to expose for the sky, the ground, somewhere in-between....or (and this is where your skill comes to play), add/subtract light from a scene to control contrast or use gradient filters to balance them out. I suggest you read up a bit on exposure for photography, as the principles are the same.
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Old September 30th, 2009, 12:56 AM   #3
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Quote:
Originally Posted by Martin Wiosna View Post
Hello,

Since I don't have any formal training I'd like to bring this question to the experts in the DV field on the board for some clarification.

I own a Sony FX-1, that has an adjustable Iris. When I'm filming it seems that the most important thing is that the exposure (f stops) is correct.

My question to everyone is: is there such thing as correct exposure?

I filmed one shoot and if the iris was open too much certain elements were clearly over exposed @ the expense of others being brought out of the "too dark" region.

On other shots It seems like underexposure (iris closed too much) is the only way to get correct contrast (I'm thinking nevermind the subject being filmed as long as there is a nice seperation between the sky and the clouds in the background).

I look at this one clip here shot with a Canon 5D and it looks like what I'm thinking, the sky and the clouds are in perfect contrast and the expense of the actors face (cleary if the iris was open more the details in the face would have been more visible).


YouTube - Canon EOS 5D Mark II and Glidecam 4000 Pro

to contrast, this video was filmed in the early hours of the morning and the suns glare made anything (including the actors) in the shadow too dark. You can see me adjusting the iris and the cameras ND filters on and off to find the ideal setting.

Is there such thing as an ideal setting in exposure?

YouTube - CCLEC

any info/help always welcome


Congratulations Martin - you've naturally come to one of the central questions of Cinematography.

The human eye/human brain combination is able to nearly instantly and nearly perfectly handle a huge range of contrast and "expose" what we are looking at properly.

But no camera can do this. So we have to manipulate exposure and lighting in order to achieve on film or tape what our human senses do for us automatically.

This is why you see so much discussion of lighting on these boards. Outdoors, the sun is many times brighter than any but the strongest man-made add-on lights. So we reflect sunlight where we DO want it and use light control devices like scrims, filters and flags to remove light from where we don't want it.

The goal is to REDUCE the range of contrast (the brightest verses the darkest parts of a scene) so that we can use an exposure that balances foreground and background properly.

This involves choosing the angle of the shot verses the sun. The angle the subjects face relative to the light. And the position of any sun modifying tools we use.

The time of day - the time of year - and the current weather may also play a part.

To soften shadows you might need an overhead scrim on a bright day - but none on a cloudy day.

Or you can expose once for the sky, and once for the subject and combine the shots in post.

But you're correct in noting that it's no small challenge to get an outdoor shot where background and foreground shots are both properly exposed.

Particularly if you're working without a full crew and without all the equipment you might want.

Here's a still frame from an outdoor interview I shot in San Diego this past weekend for a project we're doing in both English and Spanish

I faced the subject, Myriam S. at an angle into the late afternoon sun - then filled with a large (5') silver/gold flexfill on a stand from 3/4 behind her right side. That was enough to pop her out of the late afternoon background. Two hours earlier, I would have needed an overhead scrim, plus front fill. Two hours later the sun angle would have been very low and I would have needed to lose the lake in the background in order not to make her look like she was halloween uplit.

As it was I could have used some diffusion like a silk front of her to soften those cheek highlights, but since we had to shoot everything twice (once for the English Version and once for the Spanish Version) the time in the interview schedule just wasn't there to do more.

The point is that every setup requires you to THINK about what you have in environment and sun and shadows - what you need to make the talent look their best - and you need to have the tools necessary to change what you can.

Keep learning. You'll never stop and that's what makes this adventure so constantly interesting.

Good luck.
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Bill Davis is offline   Reply With Quote
Old September 30th, 2009, 03:53 AM   #4
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For what I do (run and gun) the cardinal rule is never burn out the highlights.

The second rule is that the first rule isn't hard and fast. There are times when those highlights need to be sacrificed to make sure the prime area of interest is usable.

By knowing how your camera records tonal scale, you can make good judgements on the fly. I had to do that as a news photographer shooting black-and-white Tri-X, then color neg film, and then digital. And I still do that today with a Sony EX1. I make use of all the tools available including zebras, histogram and whatever I see in the viewfinder. Everything helps.

... and then there's audio....
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Old October 1st, 2009, 01:30 PM   #5
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Your zebras will guide you as far as exposure and you'll find if shooting a lot of reality/documentary with no second takes, leaving it in preset is best. Yu can always color correct/create in post but you can't create information lost due to inproper exposure.
I like the 30 shutter and I simply set some saved PP settings for various exposures and settings per location. I can then quickly fine tune from there on the fly.
In post, go by your scopes. That's the bottom line.
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