Sunday, May 22, 2011

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X100: Low-light focus and a film set...

Actresses Bernadeta Wrobel and Julia Dordel in the lab. (f/2.8 - ISO 1600)

Note: Before I get started, some of you might be wondering where the heck my X100 review is, the one I said I was working on quite some time back already? Well I've been super busy, one of the things taking my time recently being the work on this film set for example. I have decided to write about the X100 piecemeal, with today's instalment covering low-light focusing. So no big review, rather a bunch of relevant observations, praises and even some criticisms and suggestions spread out over numerous blog entries. Starting here...

Recently I worked on set with my Fujifilm X100, shooting stills during the filming of several episodes of a production called Libelle The Series, the brainchild of my friend Julia Dordel, producer, actress and PhD holder. If you're interested, see page 8 of UBC's Branchlines publication for an article on this project. Note that this production started out being called "Dragonfly The Series", but due to a naming conflict it was changed to Libelle, the German word for dragonfly.

The X100 was ideal for this shoot since it is super quiet, especially when a filter is mounted as it deadens the already quiet camera even more. It also performs extremely well in low light and high ISO settings with outstanding image quality and amazingly effective auto white-balance. The X100 is even quieter than a standard DSLR in a sound-proofing enclosure (a camera blimp), so I had way more freedom to shoot close in and intimate with the action, without having to worry about camera sounds being picked up by the microphones while filming.

Julia in her lab coat. (f/2.8 - ISO 1600)

The X100 handled the multiple mixed white-balance of the many gelled lights with aplomb and the raw files were very malleable with superb shadow detail even at higher ISO settings. The lens quality is good enough that even images shot wide-open at f/2, or just slightly stopped down to f/2.8, proved to be razor sharp. This allowed me the best possible shutter speeds in low light and under very challenging situations. But what about focus accuracy...?

A sample being placed for analysis. (f/2.8 - ISO 1600)

There seems to be some talk on 'Net about the low-light focus not being very accurate on the X100, or even at times performing poorly in good light. This is most definitely not the case with my X100! It has proven itself to be extremely accurate and I would say that 95% plus of the shots I took on set with the X100 were perfect... the focus was exactly where I wanted it. There was minimal hunting and it locked accurately time and time again. In fact, I ended up with a considerably higher percentage of shots slightly out of focus on my EOS-7D in those same conditions, shooting with it during rehearsal takes or just behind the scenes when I did not need a quiet camera. So what gives... are there a bunch of defective X100 cameras out there or is it user error?

What the heck is this blue stuff? (f/2.8 - ISO 1600)

Well my theory is that it is not defective cameras... although who knows, there might actually be some of those too? Rather, I believe it is one of two things. Firstly, as wonderful as the OVF is, it is simply not suitable for those situations when you need to pick a precise focus point of a close-by subject. Take a shot at f/2 of a person standing 6 feet away and the camera is just as likely to pick the background to focus on as it is to pick the person. Secondly, in low light levels when the majority of the light is coming from flickering light sources, such as fluorescent lights with a 60 Hz frequency, the camera does indeed seem to hunt around sometimes and have difficulty locking focus. First to address the OVF issue...

No more funding for your research: you're cut off! (f/4 - ISO 200)

Since the optical viewfinder is offset up and to the left of the lens slightly (when viewed from behind), the traditional position for a "rangefinder" style camera, the closer the subject, the more parallax error you will get. While the electronic framing lines will shift when you half press the shutter and lock focus, by default they are lit up in their infinity alignment and the focus rectangle is centred within that frame. The upshot of this is that if your subject is close in and you center the focus rectangle on them, then half-press the shutter to focus, in reality the focus rectangle might indeed be missing the position you intend entirely and so the camera may lock on something closer in or further away, resulting in a drastic focus error. I would suggest activating the built-in focusing scale and glancing at the focus position indicator after achieving focus lock, just as a quick sanity check to ensure the camera is focused at the distance you more or less expect.

Ah... not for real, just in the film. Whew! (f/4 - ISO 400)

However a better method of focusing on closer subjects is simply to get used to using the excellent electronic viewfinder instead of the OVF. Yes I know, the OVF is so much nicer to use than the EVF, but really the EVF is not all that bad! Plus it is very quick and easy to switch between the two when the camera is up to your eye since Fuji placed the lever perfectly for quick operation with your shooting index finger.

What I got used to doing while on set at times, is flick the lever to activate the EVF, place my focus point and then lock focus (I custom set the rear AEL/AFL to only lock focus in push-to-lock/push-to-unlock mode), switch back to EVF and then squeeze off a bunch of shots in rapid succession during a take. The whole switch-to-EVF / lock-focus / switch-to-OVF / shoot sequence became somewhat second nature and I frequently used this when shooting wide open with closer subjects. The camera seems slightly more responsive in OVF mode too, but if the action was more slowly paced, I would just leave the camera in EVF mode in those same circumstances. For subjects that are further away and thus don't have major parallax issues I find that generally leaving the camera in OVF mode works perfectly fine.

Actor Douglas Roy Dack preparing for an emotional scene. (f/2 - ISO 200)

As far as the second point, where the camera has difficulty under flickering light sources in low light, well that is something you cannot really do anything about. My theory is that the camera is sampling the data coming off the sensor at a close-to-60 Hz rate that "beats" with the lighting flicker, thereby causing some of the captured frames that the camera is analyzing to be much darker, thereby making it much harder for the X100 to do its contrast-detect AF calculations. I certainly might be wrong about that, but since the camera seems to have a much easier time if a low-light scene is illuminated by a continuous light source, like a regular tungsten bulb which does not flicker or by a high-frequency HMI light, this is the only thing I can think of that might cause what I'm seeing.

So if you are experiencing that dreaded hunting and subsequent red focus rectangle (meaning focus lock failed) then try aiming the camera at a different point, locking focus where it is brighter, where the scene has more contrast, or maybe where the light source is of a different non-flickering type, then recompose and shoot your frame. Unless Fuji can reprogram the firmware to sample the data off the sensor at a different rate (doubtful as it may well be tied in with the sensor-readout circuitry at a very low level), this is something that might not be readily solvable... again presuming of course my theory is right, which it well might not be of course.

Actress Anita Reimer contemplating her situation... (f/2 - ISO 800)

In any case, once you get to know the camera, I'd say the X100 is wonderful to work with, despite its quirks, and the image quality is absolutely superb. During this recent movie still shoot I did, the camera proved again and again to be more than capable of nearly everything I threw at it. I got thousands of sharp images that often times were better than what I could get with my Canon EOS-7D, from a sharpness, colour-balance, dynamic range and even noise level standpoint. Yes my EOS-7D generally worked very well too, especially when I needed a longer lens more suitable to a given situation, but I was very happy to have the competent little X100 for much of the close-in shooting, and indeed for all the shooting I did while the filming (and sound-recording) was happening. I do wish its continuous mode was better (bigger raw buffer) and more responsive sometimes (not locking the camera up after each burst, even if it was a short one) but that is something for another blog entry.

... just before being drugged and passing out. (f/2 - ISO 800)

The one way in which I feel Fujifilm could improve the OVF parallax focusing situation is to optionally have the framing lines, and most importantly also the focus rectangle, always show in their parallax corrected position based on the lens' current point of focus. That way once you get a closer subject focused properly, if there is any slight movement closer or further from the camera, you could accurately position that focus point to refocus and know that its position is parallax corrected and thus right on target. Some people might be bothered by such a perpetual parallax offset (although I don't really know why) so this could be made a user definable preference. Heck even if the current behaviour remained, but at least the focus rectangle tracked with the framing lines to show its parallax corrected position after a half-press of the shutter, then one could either quickly reposition and refocus or if the mark still seemed close enough on target, you could shoot with far more confidence.

In closing, I'll leave you with a few more X100 shots I took during this production...

Actor Eric Breker: Libelle agents outside? (f/2 - ISO 1600)

What have I gotten myself into this time...? (f/2 - ISO 1600)

Partners pondering their future with the mysterious Libelle organization... (f/2 - ISO 1600)

A gun and the Libelle iPad... (f/2 - ISO 1600)


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