28 August 2012

Discs, media and encoding

Recently I've seen more folk try burning AVCHD discs as they've started using high definition camcorders and have balked at the cost of Blu-ray burners and blank BD-R discs. Unfortunately there's a bit of confusion about what an AVCHD disc is, which is not surprising since it is a strange hybrid of things, and (for most of us) arrived quite unexpectedly.

The key to it all is understanding the difference between what is disc media, and what is encoding ("encoding" is often informally referred to as the format of the disc).

26 August 2012

New film: Burpee Mile

Recently I helped edit a film for a friend. Caroline Birkinshaw, a personal trainer from Leeds, decided to do the Burpee Mile, a full mile of one of the most gruelling exercises ever imagined. Dave Hackney was on hand to shoot the event, getting some great shots of the hard work and the struggle Carrie went through to complete her task. After a bit of a delay Dave and I sat down to review the footage and I put together an edit.

Going through the raw clips I could see there was plenty of great material to use, and seeing them chronologically there was a plot arc of sorts emerging. Caroline begins alone on the running track but is soon joined by her parents, more family and friends and by the end she had a small crowd cheering her on, jumping burpees alongside and celebrating when she made it over the one-mile mark. This slow build up of momentum was a key feature I wanted to preserve in the edited film. The latter shots of Caroline feeling the strain contributed to the film reaching the peak of tension before the relief at her achievement.

Originally it was discussed this film would be set to rousing music, but when I saw those raw clips I was certain that a documentary style would suit it better, lending more gravitas to Caroline's achievement. A little comedic relief is provided by interviews with Caroline's dad and some spectators who were impressed by her determination.

25 August 2012

Fun with a variable ND filter

A little while ago I set out to do a bit of casual filming using my stabilised 18-55mm lens. I wanted to shoot wide open for narrow depth-of-field so I screwed on a ND8 filter (which blocks 8 stops of light), but at the maximum aperture of f/3.5 the picture was underexposed. The weather was a little overcast but mostly bright. So I swapped the lens for my 50mm f/1.8 and the picture was exposed enough, but I was shooting hand-held so the unstabilised 50mm wouldn't do.

Back on the computer, I ordered a variable ND filter. Comprising two polarisers that darken considerably when their orientations are crossed (see video at the bottom), these filters are great when you want fine control over exposure in bright environments. As soon as it arrived I tried some experiments in my back yard.

Shot at f/3.5 with variable ND filter
f/3.5 with variable ND filter

Shot at f/18 without ND filter
f/18 without filter

These two stills are grabs from video clips I shot with 1/50th shutter. In the first picture I set the aperture first, at the maximum of f/3.5, and then adjusted the filter so that the highlights were just below clipping. In the second picture the filter was removed, and then I adjusted the aperture to retain the highlights, which turned out to be at f/18. Quite a difference, which is demonstrated in the noticeably narrower depth-of-field in the first picture.

One other noticable difference is the colour tone. With the filter, the picture looks cooler with a blue tint, and possibly desaturated. I have found with cheap ND filters that the optical quality is not perfect and colour shifts can occur, usually pushing towards blue. The effect varies with the severity of the light loss, and the quality of materials used -- one time I tried a plastic filter and the effect was something akin to picture taken with a Lomo/Diana toy camera, or something tweaked with Instagram. In the case of this variable ND filter, the colour shift is not so bad that it can't be corrected during editing.

A short video to demonstrate:

20 August 2012

After Effects CS3 performance comparison

A while back I had an After Effects project with 640 layers of footage. I've had to learn patience with my ancient Power Mac which struggles to render anything in real time, even simple comps, but I shouldn't have been surprised to find that 640 layers took about 40 seconds per frame. The entire 90-second animation took 23 hours.