Ryan E. Walters's Blogs - RED - Profiling The Sekonic L-758c

Since the advent of digital acquisition many people are of the opinion that light meters are no longer needed. After all, just fire up the camera and see what you are going to get. However, I think that now more then ever meters are needed in digital cinema, specifically with cameras like the Red One. Film has amazing latitude, and its roll off into the highlights can be very forgiving. In the digital world, once you clip your highlights they are gone, no software can recover information that doesn’t exist. Further more, having a properly calibrated meter opens up a whole new world of learning, communication, and flexibility that you just cannot get any other way. For example it is not always feasible or advisable to bring your camera along and set it up when you are scouting locations. Having a properly calibrated meter will allow you to take quick and accurate readings allowing you to figure out what the light levels are and what you need to supplement them. The meter will also allow you to quickly read and evaluate ratios and levels within a given scene- so you do not have to guess where a specific value falls, or do calculations in your head. The meter can take the readings and do the calculations for you. And finally, the meter will allow you to communicate specific measurements that can be told to the rest of you lighting crew, and notated for future reference should you ever have to come back and relight a given scene. At a bear minimum I would recommend getting an incident meter. And I would strongly recommend that you get a meter that offers both incident and spot metering, like the Sekonic L-758c. If you are good at snatching items on ebay, you can get one of these meters for in-between $400 - $600. Be sure to get the “c” model as it offers additional features that are important to the cinematographer that are not available with the “dr” model which is geared for stills. The last time I would recommend getting is a properly calibrated test chart. In this case it would be the Sekonic Profile Target II (Cat. #401-757). If you get version 2 of the chart you will only have to shoot 3 test images as apposed to the 11 images if you use version 1. (Which is a considerable time saver.)

With meter, chart, and camera in hand it is now time to shoot a series of test images to calibrate the meter to the camera. For a step by step guide on how to shoot the test images I recommend checking out the tutorial video on Sekonic’s Site. Following the method as outlined by Phil Bradon, I shot a series of test in Tungsten, HMI, and Daylight. Phil Bradon was very helpful with providing input and guidance to me in the process of completing these tests. As of this writing (11/10/02008) the Sekonic software version 2 for processing the images does not support a shutter of 180 degrees at 24 fps (or 1/48). The only options are for 1/60 or 1/30, both of which are slightly off of ideal. To compensate for that difference Phil helped me to figure out other frame rates and their corresponding shutter speed in the software. After spending a full day shooting tests, another full day processing the images and creating the profiles, and then some additional time evaluating the results I have created. If you want to download the profiles, test notes, and sample charts you can do so here (6MB): Sekonic Profile for the Red One. The profiles that i have provided contain no additional processing to them. Because the images from the Red One can be manipulated in any fashion, I would recommend that you use the original Red RAW files to create your own profile if you find that you are adding your own curves to the images. This will ensure that the Sekonic profiles match your own workflow. Ordering information for the $7 DVD containing all of the needed files can be found in the test log pdf of the Sekonic Profile download.

Going into this test I was under the assumption that shooting with the Red One under the different light sources (tungsten, HMI, and daylight) was going to yield drastically different results in the profiles. However, the results show this to not be the case. The camera has a remarkably similar response curve regardless of the light source. This is contrary to my own experience in that when shooting under tungsten light the underexposed areas become much more noisy, more quickly, then when shooting in daylight balanced light. The Red One does have a 5000k balanced sensor which is why it is more favorable to daylight sources. But when the images are processed purely by the numbers, which is what the software is doing, the response curves are the same. What this means is that you may or may not agree with the acceptability of the noise floor as determined by the software. To know for sure, you will have to conduct your own tests and adjust accordingly. Additionally I found that white balance and frame rate had a negligible effect on the results. Using the camera white balance or a default white balance yielded in a 0.1 EV difference between the results. While using the incorrect 24p @ 180 degrees (1/48) yielded results that were 0.2EV lower then the correct 32p @ 180 degrees (1/60).

What I did find from the test results was that the color space and output gamma has a bigger effect on the dynamic range and response curve of the camera then the light source. Further more, while I find RedSpace to be more pleasing visually then REC709, it actually offers less range then REC709. The final results of the dynamic range stack up in the following order: RAW = 9.1 stops / REC709 = 7.9 stops / RedSpace = 6.7 stops. While these numbers are important when you are exposing the image, I think it goes to show that the final image cannot be judged on numbers alone, for aesthetics are not quantifiable by a software program.

RED - Profiling The Sekonic L-758c

Comments

Waveform monitor instead?

Waveform VS Meter-

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