Finding the 'right' exposure levels...

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JustJazz
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Joined: Jul 9 2008

I recently filmed a studio discussion driving 2nd camera for a friend, and we ended up with very different looking footage as we'd each gone for 2 different exposure styles. He'd racked every shot to hover near 100% - I'd exposed for the brightest shot (a wide) - kept that iris setting and allowed some of the CU's of faces to be 1/2 to almost a full stop down at times. My friend considers my rushes are underexposed and is adding gain in the edit so they match his.

By chance, I had to edit some BBC drama archive recently, and I was struck by how dark the picture was at times - sometimes nothing was above about 40-50%. Even so, it looked really atmospheric. In contrast (no pun intended!) a while back, I was on a course with a BBC (News) cameraman who confessed his exposure method was to set the zebras at 75% and expose for faces to just trigger the zebras. He wasn't worried about anything else.

My feeling is that racking for 100% or setting faces to 75% is a bit like compressing music to a fixed level. It's good for signal to noise - but not very good musically! On the other hand - if you let the light levels fall into the shadows too much, you can end up with muddy/noisy pictures.

My question is - how do other people select exposure levels? I know it's partly an artistic question and depends on other things like how your camera handles highlights and how noisy the bottom end of your gamma curve is - but does anyone have any good rules of thumb that help get a consistent look? I shoot on a PMW-350 and I also have a Panny AF-101 which at least gives you a useful luminance waveform display - though that's only part of the story. I'm coming to the conclusion that the only 'safe' way to get the right picture is to spend as much as you can afford on a really good field monitor, calibrate it and trust your eyes. Not easy when you're on the hoof though! I'd be interested to hear other people's views on all this. Thanks!

SimonMW
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Joined: Nov 16 2004

It depends. For creative cinematography where lights are being used, ie drama, I will select what f-stop I want to use and then light for that. For on the fly camerawork I will try to balance the exposure, sometimes you have no choice but to make a compromise.

infocus
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Joined: Jul 18 2003

There are two sides to this - what is the right exposure, and how to consistently achieve whatever you think it to be.

As far as the first part goes, then I'd say it depends on what you're filming. A straightforward i/v for news is a different kettle of fish to a nighttime drama sequence. Generally, yes, get the flesh tones to the right level, but I'm reminded of some truly awful rushes that a director friend wished my opinion of recently. His "cameraman" had purely gone for technically correct flesh tones of about 70% - seemingly unaware that because the face was shaded by a hat large areas of the image were overexposed and burnt out.

My own opinion is that waveform monitors and histograms are of very limited use in a camera viewfinder because they obscure too much of the image to be used in other than a setting up mode. Far better is to have a good zebra facility, which in my book means two zebras which can both be displayed together, with different patterns. (Beware - I've just become aware that some cameras state they offer "dual zebras", but only one at a time can be on! Doh!)

My own preference then is for one to come on at peak white, the other in a fairly narrow band, and I've got used to about 86-90%. You then need to get used to how it all works, but when familiar with it, it's possible to be remarkably consistent.

As far as face exposure goes, it's normally accurate if just the highlights of the face show zebraing in the 86-90% zone, and having the 100%+ pattern would have stopped the blowing out that has caused my friend so much grief.

As far as the idea of setting them to 70-75%, then my objection to that would be that for correct exposure it normally means having the whole face a mass of stripes, rather than just the highlights, so making assessing of the overall picture more difficult. There's also a specific side in that I grew most used to a DSR500, where the onset is adjustable, but they go away at 90%. So 86-90% = not too many zebras, 70-90% = too many to see the picture clearly, more like the situation with the waveform monitor in the viewfinder.

JustJazz
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Joined: Jul 9 2008

Thanks for the thoughts on that. I forgot to mention that I've found the "false colour" on Marshal monitors (and others) very helpful. Whereas zebras just show you up to 2 peak points, the false colour display shows the continuous levels of light across the picture. Maybe something that Sony could incorporate into its viewfinder displays as well as Zebras!

I guess the answer is to use whatever tools are on offer - but that in the end exposure is an artistic judgement. Sometimes you can get away with burnt out highlights - other times even small hot spots can look horrible.

SimonMW
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Joined: Nov 16 2004

The right exposure is the one that makes the picture look nice.

As Infocus mentions, rigidly exposing the 'technically correct' zebra for skin tone around 70% can cause all sorts of problems elsewhere in the image.

Zebras are just a guide. I noticed a nice feature of the Magic Lantern firmware for the Canon DSLRs. It doesn't just give the option of the usual zebras, but also allows low level zebras showing where shadows areas are being crushed as well.

When all is said and done though, if you shoot for the light as much as possible, exposure balancing issues can be minimised to a good degree. I am finding this with the kayak based videos I have been making. Kayaking really tests your exposure abilities because a canyon or gorge may be in deep shadow on one side, and in bright sun on the other. Or it maybe dull overall, but the white water might be clipping all over the place. It is an absolute nightmare.

So often shooting in grey overcast conditions, rain and all, is often the easiest time to shoot such things. In sunshine though you really have to place yourself for the light first and foremost rather than for the angle.

So I think that the question of "what is the right light?" should arise before "what is the best angle?" and should then be followed by "what is the best or right exposure?"

JustJazz
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Joined: Jul 9 2008

Simon - def agree with "making the picture look nice" - but it takes me back to my thoughts about monitoring on location. I filmed someone doing a piece to camera in front of a window last week and on my (not cheap) field monitor it all looked nicely balanced with the aid of a Divalight and a couple of Dedos. When I looked at the rushes on my edit monitor at home - I'd overcooked the light on his face - not hugely, but enough to stop it looking natural. There was a BBC HD shooting guide not long ago which carried the advice to "take the biggest monitor available on location". Probably not very practical if you're shooting Kayaks (!) - but maybe not a bad idea in principal. Maybe in 20 years all cameras will have a computer chip to analyse the picture and make 'helpful' suggestions about composition and exposure. All we camera ops will have to do is carry the gear and point the camera in the right direction whilst it tell us where to stick the ND!

noddydog
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Joined: Feb 28 2004

I often have to shoot in bright outdoor conditions (where the LCD, zebras, histogram is next to useless) and on the fly where things change quickly or you have a window of opportunity that passes in seconds. So there is no time to play with the iris ring even if the LCD was providing a viewable image. In such conditions I'm regularly forced to put the camera in auto exposure. However I was taught that it's always better to underexpose and pull things up in Post than run with the camera's default AE. So I tend to dial in anywhere between -1 to -4 AE shift depending on the severity of the lighting conditions. This has so far worked well for these type of doco rushes, giving me about 95% of usable material back in Post. Obviously it looks naff if you show it to the client before any grading, but the people I now work with have come to trust that what they see is not what they get.

infocus
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Joined: Jul 18 2003
JustJazz wrote:
There was a BBC HD shooting guide not long ago which carried the advice to "take the biggest monitor available on location". Probably not very practical if you're shooting Kayaks (!) - but maybe not a bad idea in principal.

The trouble with monitors on location (apart from being impractical in a kayak! :) ) is that if the shot doesn't look quite right, is it because the camera needs adjustment - or the monitor?

Sounds silly, but a correct setting for the monitor at nighttime will be very different to what it should be in daylight, and there's also the problem that the eye can adapt and "correct" for such as a monitor colour cast. In studio or OB control rooms a lot of effort goes into monitor setup, controlled ambient lighting, and making a reference available.

If you're not able to have that, making exposure etc judgements on a location monitor can be very risky. The picture looks dark - but is it because the camera iris should be opened up, or the monitor contrast turned up?

That's why I'd say the best option is to learn to use zebras accurately - because the viewfinder can be badly misadjusted for contrast/brightness but it shouldn't affect the accuracy of exposure. A histogram or waveform display will also be OK in that respect - but as said before, they tend to obscure much of the image, so not much use other than for setting up before starting to film.

Alan Roberts
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Joined: May 3 1999

Those tools are all there to help you, but you don't need them on all the time. A quick check with any one of them will get you in the right ball park.

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