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Old August 20th, 2009, 02:00 PM   #1
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Setting exposure with the LCD - Yeah, right!

Over the past months, I've read a number of posts from people claiming that the LCD on the 5D Mark II is pretty good for setting exposure. My gut feel was that this was wishful thinking, but after our 48-hour shoot this past weekend, I've confirmed it. For best results, do not rely on the LCD screen.

This isn't to say that the display is bad. It's not. It's just that humans see things on a relative basis. Also, the LCD screen seems to crush the blacks.

On our 48-hour shoot, we used Magic Lantern's zebras with excellent results. We used 0xf000 for the highlights, and 0xb000 for light-toned skin. In the end, we touched the exposure of five clips in post for matching purposes. A simple luma curve adjustment took care of some accidentally, slightly underexposed shots. (In addition to the five clips that we matched, we did some grading for special effects. These don't count, as the topic is proper exposure.)

FWIW, we were shooting with the Faithful picture style, contrast and sharpness at minimum, and saturation one tick below mid scale.

By comparison, when we shot The Last Outpost in the snow, we had to do grading from shot to shot just to get exposure matching. Same thing with our Dirk Snowglobe short, which was all shot indoors under controlled lighting. Those were done with Nikon lenses, auto mode, AE lock, exposure compensation, and the original firmware.

Keep in mind that the 5D Mark II applies a curve when going from 14-bit RAW to 8-bit h.264. If you get the exposure wrong, not only do you clip the highs or lows, but you potentially push faces and other critical objects out of the linear range, risking contours when you compensate for a poorly exposed shot. So, don't expose to the right; expose to the faces or other important areas.

The other thing we discovered is that the LCD crushes the blacks. We did an outdoor shot, looking into a white van. We added a light (tungsten with blue gel) inside the van, but couldn't see a thing on the screen. We removed the gel, barely saw some light, and shot like that. We figured that it was helpful to get the background out of the noise. The final picture shows everything in the van clearly, though at a low level.

When we shot in a theater, the background was rarely seen on the LCD, but was almost always seen in when played back on a TV or PC monitor. On the other hand, we had one shot with a totally black background, when we would have liked some light back there. Having the blacks crushed on good scenes let us take our eye off the ball on a bad shot. We should have done some VERY low zebra tests to ensure that we didn't lose dark backgrounds.

Anyway, I highly recommend using ML zebras for setting up your lighting. You can disable it when shooting to eliminate distractions when framing. The LCD is good for framing, but won't guarantee that you've exposed consistently, shot to shot.
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Old August 20th, 2009, 02:13 PM   #2
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Histograms

How about using the histograms which are available in the exposure simulation mode?
I have compared the live display histogram to a recorded movie histogram and they appear to be the same . The only caveat is when shooting movies in this mode, 1/30 is the lowest appropriate shutter speed. I know when we do professional video and film shoots the LDs & DPs only trust metering and dont even consider zebras (as opposed to news or wedding shoots).
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Old August 20th, 2009, 02:40 PM   #3
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I wish we had a spot meter for the shoot. ...next time.

Actually, Magic Lantern includes a histogram display. We used it, and it helped, but still wouldn't have predicted that the difference between the LCD and the recording would be so large. It was like wearing two watches and not being quite sure exactly what time it was. Now we know not to trust the LCD for the dark areas!

A waveform monitor feature would have been more valuable than histogram for seeing how far we lifted the backgrounds off the noise floor. A full screen color temp display would be really cool too. It would be like seeing many zebra levels at once. I've requested those features for a future version of Magic Lantern.
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Old August 20th, 2009, 02:58 PM   #4
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I have already added the waveform and false color to magic lantern, but its not a simple port to the main branch because they modify a number of sections. There is just no really good way to add "modules" yet, but hopefully this will change soon.

I emailed Hudson about adding these features few weeks ago, still waiting for his comments concerning this.

Meanwhile, here are some (old & outdated) pictures of the 5D with the features:

Waveform Scope
http://dl.getdropbox.com/u/305574/waveform/1.JPG
http://dl.getdropbox.com/u/305574/waveform/3.jpg

False Color
http://dl.getdropbox.com/u/305574/falseColor/fc1.jpg
http://dl.getdropbox.com/u/305574/falseColor/fc2.jpg


You can also get exposure information without Magic Lantern. Take a still picture or shoot a sample video to access the already built in 3 channel histogram and highlight alert (zebra) by using the Preview button. This way you don't need to change the mode. Simple and accurate.

Finally, make sure that the auto screen brightness is disabled. The camera by default automatically adjusts the LCD brightness based on the environment.
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Old August 20th, 2009, 05:21 PM   #5
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Thanks Daniel,

I had forgotten about your additions. They'll really help us nail the exposure from top to bottom. Even a small waveform (size of the current histogram) would be nice. (A rotated waveform would be cool too, for instance, when looking at a horizon.)

I'm really looking forward to being able to script things. I'd like to have a standard sequence that I use, including a quick loop through my favorite exposure tools. Once I approve the exposure, I'd eliminate the tools from the display, with the possible exception of the zebras that show clipping, in case we get an unexpected hard reflection as things move.

I would like to start my standard sequence with a BIG DISPLAY of the shutter speed, then the aperture, then the ISO, so I don't take anything for granted from a previous shot. I think we had the shutter accidentally bumped to 1/100 for one shot. Given that we shoot most everything at 1/60, it's easy to get out of the habit of checking it.

With a quick, complete sequence, we can guarantee proper settings, no matter how rushed things are, or how long it's been since we slept...
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Old August 20th, 2009, 05:51 PM   #6
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Quote:
Originally Posted by Tom Daigon View Post
How about using the histograms which are available in the exposure simulation mode?
I have compared the live display histogram to a recorded movie histogram and they appear to be the same . The only caveat is when shooting movies in this mode, 1/30 is the lowest appropriate shutter speed. I know when we do professional video and film shoots the LDs & DPs only trust metering and dont even consider zebras (as opposed to news or wedding shoots).
This was one of the things that kind of sucked about the (canon) firmware upgrade. You can't use exposure simulation for movies when in manual mode -- cause if you do, you actually will be shooting in auto exposure mode regardless of being in M. Prior to the firmware release, I often shot video in exposure simulation mode just for the live histogram.
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Old August 23rd, 2009, 11:34 AM   #7
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Thanks for al this info.

I'll add that the histogram and zebra is derived from a small sample of the actual data and can be wrong. In critical situations it may be worth looking at a brief clip on a laptop. For example, small clipped highlight may not show on the histogram of zebra.

(I'm assuming zebra in ML is getting the same data as histogram. But it is "magic", so perhaps it's somehow looking at the full data stream)

RED is better for recovery of highlights as that one can actually work with the raw data in post.
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Old May 17th, 2010, 05:42 PM   #8
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Quote:
I wish we had a spot meter for the shoot. ...next time.
Jon, would you mind elaborating on how you would use a spot meter? I know how to use them, but I'm curious to hear specifically what you would be doing. Checking to keep highlights from blowing out? If so, how many stops above middle gray would you consider safe?
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Old May 18th, 2010, 09:13 PM   #9
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Originally Posted by Bill Binder View Post
Prior to the firmware release, I often shot video in exposure simulation mode just for the live histogram.
Is this different somehow than the histogram now available in movie mode?
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Old May 23rd, 2010, 12:55 PM   #10
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+1 on defining Exposure Simulation. I've seen it mentioned in the Canon manual but can't figure out how to use it.
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Old May 25th, 2010, 01:14 PM   #11
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Originally Posted by Jon Fairhurst View Post
I wish we had a spot meter for the shoot. ...next time.
Hi Jon - a simple but effective trick I use all the time -> I walk into the scene with the camera, and fill the frame with just the area I'm concerned about, highlight or shadow, and see what the histogram is just for that detail.

the problem with, for example, a master shot, is the 'critical' areas of information may be a very small percentage of the overall scene, and in the histogram of that master it's easy to interpret that incorrectly.

also, it's worth shooting a test still image, to see the RGB histogram - sometimes the brightness histogram 'hides' issues - eg a skintone that is pushing the red channel into over-exposure .

and yes, the LCD is pretty untrustworthy - whenever I'm doing a 2 camera setup, with the same settings on 2 cameras (and sometimes the same lens) the rendition on each camera's LCD is hugely different. I have to actively ignore the difference.

On a related note I've been talking to an engineer that's building a prototype HD monitor for the HD/DSLR cameras -one of his goals is to be able to add a monitor to each camera in a multi camera setup, and have all the monitors show the same image - ie a color managed display system. I'll post a link once it's been made public.

-cheers

andy
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Old May 25th, 2010, 05:14 PM   #12
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Quote:
also, it's worth shooting a test still image, to see the RGB histogram - sometimes the brightness histogram 'hides' issues - eg a skintone that is pushing the red channel into over-exposure .
If you set the histogram to RGB it applies to movie mode as well, I never use the brightness one for the very reason you mention.
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