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Old September 4th, 2004, 08:34 AM   #1
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maintaining exposure

Just have a question re exposure in manual mode. In automatic the camera has its own algorithm for exposure. If you are shooting with full manual what guidelines do you use to keep the camera to maintain the same exposure throughout the day? With film they have light meters and tables to use . If you shoot under different environments you adjust the f-stop until it looks "right" for you by using your monitor . But what would be the "correct" exposure is, or is it just a matter of choice? I ask this because as you shoot throughout the day the lighting changes but if you dont take this into account you may underexpose or overexpose and make midday shots look like early morning shots and vice versa.
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Old September 4th, 2004, 08:52 PM   #2
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I always readjust the F-stop to my liking as the light around me changes, so I usually don't worry about under or overexposing.

I emailed Panasonic about two different CCDs (a 1/6" and a 1/4"), asked and what their equivalent ASA ratings were, and both times I got a response that all Pana CCDs are ASA 100 (which doesn't make any sense). If you got the real ASA rating of a cam's chip you should be able use a light meter to get the optimal exposure. Otherwise, the best exposure to me seems to be as wide open an iris as possible, while not clipping with about a 75-80 IRE zebra stripe on.
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Old September 5th, 2004, 01:21 PM   #3
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And if the day has small overhead clouds, you can be in for a really interesting time. Especially with cameras that don't have stepless aperature control.
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Old September 5th, 2004, 02:32 PM   #4
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Tung:

That's a really good question: what is "correct" exposure?

I personally think that it is, as you were wondering, a matter of choice. Most people (and the automatic settings of every camera I know) overexpose video, in my opinion. The well-known 70 IRE setting for skin tones is to me too hot. With exteriors, since bright sun will tend to wash out video, I often underexpose a radical amount compared to what the camera "thinks" is correct, in order to capture the widest range of tones on tape.

One example of this was a daylight exterior spot I shot with the XL1s last year (it can be seen on my DP reel on this page ; about 6 minutes in, the first few shots after the "digital--mini-DV" slate). In order to keep backgrounds from blowing out, I was dialing down the exposure extensively. In particular, the wide shot that dollies past the tree with the kids across the street was maybe three stops down from what the camera "suggested", but this allowed me to not have that ugly blown-out backlit look.

My suggestion: get a good calibrated monitor, and play with the exposure until you are happy with what you see. Also experiment with what you can do with images in the color corrector of your NLE (easier to bring them up than bring them down). Some find light meters helpful--I tend to keep mine in the case for video work, as video does not handle exposure as linearly as film.
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Old September 5th, 2004, 02:40 PM   #5
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Charles,
I couldn't agree with you more.
I will always take the exposure down from the norm.
It may be subjective, but I also perceive that I get a sharper image as well - and with DV , that's everything!

Robin.
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Old September 13th, 2004, 07:12 AM   #6
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Guys,
I definitely agree with underexposing. It brings out a 3 dimensionality to the picture which isnt there when your pictures are bright and washed out. There's a setting on my sony tv that radically reduces picture brightness which does a similar thing.

However what I was asking was how do you maintain the exposure across time. Changing the exposure radically alters the mood of a shot. If we always underexpose by say 2 stops then we should do it consistently throughout the day assuming we want a sense of time of day in our film. Or we should alter the exposure throughout the day to compensate for the changing light so that all our shots have the same exposure and hence look like they were all taken at the same time of the day. The question is how do you objectively measure this.

Short of using the light meter and asa rating am I correct in saying that you really have to play around in post to alter the shots exposure to make them match or mismatch as desired? I saw a film student shot where they stuffed up the exposure between two shots, one shot was brighter than another, leading to a continuity error. Unless you have to shots side by side to compare in the field , our eyes can deceive us and our memories are terrible at remembering exposure.
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Old September 13th, 2004, 09:36 AM   #7
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If you want to effectively make shots match or mismatch in expsoure, always underexpose, and then match things while color correcting. That's the only way to get exactly what you want. You won't find a quick and easy way in the field to make everything match. I think that's part of what a color corrector's for...Am I wrong?
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Old September 13th, 2004, 09:52 AM   #8
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Always under exposing increases the noise and can produce banding when "fixed" in post.
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Old September 13th, 2004, 02:55 PM   #9
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"Underexposing" is a multi-faceted term, Jeff. I use it more in reference to what the camera "thinks" is correct exposure. I suppose a more accurate term might be that I rate the camera for a higher exposure index. With exteriors, by stopping down a bit we are not truly underexposing the image, just placing the tones at a different point on the scale. For instance, if I were to expose flesh tones at 50 IRE rather than 70 IRE, I won't necessarily need to bring them back up to 70 in color correction, as I rather prefer how the look at 50 all the way through.

Even when there is a situation where I need to crush down the exposure and then bring the midtones back up in post, which may indeed create some video artifacting, I find that the results are ultimately preferable to allowing the image to expose as "normal" i.e. blown out highlights.
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Old September 13th, 2004, 03:09 PM   #10
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Highlights should never be allowed to over expose or get blown out. Unless, of course, it is the desired effect. However, in your example, if the flesh tones could be exposed at 70 IRE without blowing out the highlights, then in post reduce the exposure to 50 IRE, you would have less noise in the shadows and less chance of banding or artifacts. This method requires more rendering, but will give better results in almost all cases.
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Old September 13th, 2004, 03:57 PM   #11
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That's true, Jeff. I have done this on the occasion and liked the results (although I notice I usually have to decrease the saturation as well).

In the case of exteriors, unless it is an overcast day, inevitably there will be hot sun somewhere that needs attending to.

As far as Tung's question about matching, I find that directionality and color tend to have more to do with a changing light feel than anything else. Unless one is going for a harsh look, the midday overhead sun is to be avoided as much as possible. Traditionally, wide shots are done in the morning or late afternoon when the sun has some directionality while closeups are done in the middle of the day when they can be controlled (overhead silks, etc.). Very often the budget or schedule doesn't allow for this when it comes to DV filmmaking though. For the viewer, a daylight scene is usually hard to identify by time of day unless it is early morning or late afternoon, when the sun is low (or we create that feel artificially).

I would say that the formula I would follow for a full day would be as follows:

Dawn (very blue ambient daylight, sky visibly dark, faces underexposed several stops)
Sunup (ambient still blue, warm low angle sun, faces at stop or slightly hotter to accent brightness of sun)
Morning (neutral ambience, sun still a bit warm, frontlit faces at stop, backlight faces 1-2 stops under with backlight 1-2 stops hotter
Noon (neutral sun, "ugly" light (toplight), best to cut down overhead and relight a bit lower to emulate morning or afternoon light)
Afternoon (same as morning)
Late afternoon (blue ambient light, sun becoming warmer and warmer until sundown. Frontlit faces at stop, dropping down to 1-2 stops under as light dies.)
Sundown (very blue ambient, faces 2 stops under).

Which is all to say that there isn't really a formula at all, mostly it's a taste thing. And as far "memories being terrible at remembering exposure", that's something that can be improved with experience.

I shot a feature years ago that took place all in one day. I had noted in the script approximate times of day, and once we got to the late afternoon I started to introduce hints of the dropping sun, which was almost always artificial (HMI's). However, the film itself was shot in burst over the course of two months, so consecutive scenes were often shot weeks apart. Somehow it all seemed to work (I was amazed that my efforts were even noticed by this otherwise pretty negative reviewer!), and that was without supervised color timing. I've worked for some amazing cinematographers who can do this sort of thing effortlessly.
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Old September 22nd, 2004, 12:20 PM   #12
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Your notes are incredibly thorough and chock full of great information. Someday I hope to be able to understand it!

In the meantime, I have a basic question. I shoot a lot of outdoor sporting events. I move the camera a lot, and obviously the lighting changes all the time too. My camera (Sony TRV 950)doesn't tell me what the exposure settings are, it just displays a little bar graph that is pretty useless. So I rely on just my eyes and use zebra stripes to help. My question is, how do I know when I'm underexposing just slightly, as you recommend? Should I dial it down until the zebra stripes just disappear? I have been setting my cam at 100 IRE and allowing just a touch of stripes in the very hottest part of the shot. Thanks in advance.
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Old September 22nd, 2004, 03:18 PM   #13
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Here's an alternate idea: if you use DV Rack in the field, you can reference back to your clips and exactly match exposure. Record the clips using DV Rack, then when it's time to shoot another clip and you want to match exposure, you can A/B back and forth between the other clip and the new shot. And you can judge not only by the monitor, but also by the waveform monitor. That way you could exactly match exposure.
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Old September 22nd, 2004, 03:39 PM   #14
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Rob, adjust exposure as you have been with the zebra stripes, but set the max IRE lower than 100, maybe 75?

If you are unable to use DVRack you can try to match clips (A/B) later in most NLE's with the waveform monitor also.
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Old September 22nd, 2004, 04:01 PM   #15
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I have been using my NLE to adjust shots to match, and for the most part I'm able to. I think a separate issue is the color tone (maybe temperature is the right word?) that is difficult to match when shooting in the evening as the sun goes down. I've been struggling with that a bit.

Sorry, I don't know what DV Rack is.
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