Digital Bolex D16: Preliminary Dynamic Range Tests

This weekend myself and Mike Gibson, whose camera we used, got to test the dynamic range of the D16. What you’ll find in the following is an analysis of the images recorded while testing. The findings in this test are meant to help shooters get acquainted with the D16’s abilities and limits.

BTS 10 BTS 2 BTS 5

Disclaimer: These tests were performed on a beta firmware. Therefore the results of this test should be considered as guides rather than concrete results. End user results are subject to change with firmware updates.

Equipment used in testing:

  • Sekonic Exposure Target II
  • Sekonic L-758DR Light Meter
  • Two 5500K balanced fluorescent light banks with softboxes
  • Digital Bolex D16
  • Zeiss ZF.2 25mm f/2 w/ F-mount to C-mount adapter

Procedure followed in testing for ISO:

  1. Turn off all lights and block out all windows where light is coming through, except the two used for exposing the chart.
  2. Expose middle gray for selected ISO, f/5.6 aperture, and 180° shutter by moving the two light banks
  3. Make sure that exposure across entire chart is even, keeping differences within 110 of a stop
  4. When done recording the exposure, we go up the exposure range to +4 EV, and down the exposure range to -6 EV. This is all done in increments of 2 EV using aperture and shutter, leaving the ISO and light position constant.
  5. Repeat the process for each ISO

Procedure followed in testing for Exposure Index (EI):

The process here was the same as for analog ISO, except we kept the ISO constant at 200, the unity gain ISO of the D16. Then all we did was light the chart for the intended EI. So for EI 100, we set the meter to ISO 100 while keeping the camera at 200, and the same was done with EI 400.

BTS 4
Mike metering the chart
BTS 6
Prepping our “slate”

BTS 9

The Data:

d16 Dynamic Range Charts
All footage was processed in DaVinci Resolve 11 with an exposure boost of 1.56 to scale the footage to scene linear values. Color space and gamma were set to BMD Film with Highlight Recovery enabled.

The charts here from top to bottom are ISO 100 to 400. Left to right is -4 to +4. Please note not all charts were included in this image. The first thing you likely noticed was the magenta in the ISO 100 highlights. This is a known problem with the D16 that many have encountered and has been acknowledged by Digital Bolex, who is working on a solution. I have found a band-aid method for this that involves messing with metadata, but that’s for another post. Now, take a look at the +4 EV exposures for ISO 200 and 400. We found it interesting that the image clipped at the exact same amount of light: 416 stops. Further analysis showed that they had the same total dynamic range, though ISO 200 had cleaner shadows as expected.

More Charts:

D16_DR_dist

After pixel peeping over every single file to make sure we got the exact numbers correct, these are the results for the dynamic range distribution we found.

You’ll see here that using the EI method of exposure, we got better dynamic for each of the corresponding sensitivities. EI 100 didn’t exhibit the ISO 100 magenta problem so it retained nearly a full stop more of detail in the highlights. And as for the shadows, the same number of chips on the chart were visible, but, some were slightly less usable because of the difference in noise caused by the analog gain. ISO 100 by far has the most detailed shadows because of the lesser gain applied during ADC.

You may notice that all of the exposures have pretty much the same dynamic range in the shadows. Well, this is only partially true. The noise in 200 and 400 start to cover the lower chips more heavily than in ISO/EI 100. This makes them less “usable” when lighting a scene. But, because they are clearly distinguishable from the black background and lining, we mark it down as part of the total dynamic range.

At the far right on the chart we find something very interesting and enlightening. Lighting for ISO 400 while shooting at ISO 200 gives us a boost in overall dynamic range by about 12 a stop, putting the D16 at 1213 stops of dynamic range. Because the shot is underexposed there’s more headroom before the highlights clip. In the shadows one chip got lost underneath the noise to where it was completely indistinguishable from the noise. Another finding was that shooting in EI style and compensating by boosting a stop in post yielded cleaner shots than shooting with analog ISO 400.

DR_vs_Exp

This graph shows how the total dynamic range changes across the different sensitivities. You’ll see one line marked as “Ext”, and the other as “Safe”. The “Safe DR” was based on personal preference accounting for things like the magenta highlights and increased noise in analog gain ISO; for explicit capacity look at “Ext DR”.

Results:

The D16 operating at its unity gain, ISO 200, has a total dynamic range of 1123 stops. You will see the total usable dynamic range decrease when changing the analog gain. When using the D16 at unity gain, but lighting for ISO 400, an increase of dynamic range was experienced, resulting in 1213 stops.

Opinion:

Based on the data we’ve collected, we’ve come to the following conclusions:

  • Shoot at unity and push or pull exposure in post because it results in cleaner footage and more dynamic range
  • Exposing for this camera is extremely similar to exposing for film. The only difference is where the dynamic range lies.
  • The Adams’ Zone System is actually perfect for this camera. Lighting using the ZS will allow for 2 stops of roll-off room giving a nice shoulder and toe to the images
  • This thing likes and needs light, like any camera. But this one forces you to light because there’s no in-camera noise reduction. We found this keeps our discipline up and yields far better results than trying to play the high-ISO game.
  • The footage from the D16 plays very nicely with Neat Video. I will likely make another post on this. Light Neat Video usage on D16 footage results in very clean shadows without turning the image to plastic (thank you, unaltered D16 pipeline).
  • The luminance noise at ISO 200 is very pleasant. If you really felt the need to do noise reduction, you could get away with just using it on the color channels and leaving luminance alone.
  • ISO 100 is kind of a wild card right now. If/when ISO 100 gets fixed it will be the cleanest ISO, and will very likely boast more dynamic range than ISO 200. 100 grain looks fan-freakin-tastic, especially on a 50″ at full res. Because there’s no extra tomfoolery during ADC, the noise isn’t smoothed out and doesn’t look plastic at all. This is the closest to film grain I’ve seen on a digital camera, period. If the fix does happen, which I really hope it does soon, shooting EI style will bring an even bigger gain to dynamic range than when using 200 as the base.
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