So, here’s a plan that I had the idea for ages ago, but only managed to assemble the relevant ingredients (a slam-door intercity train, a first class ticket, a daytime journey, some decent weather…) for this weekend.
In all my slow-motion work so far, I’ve used a static camera to capture a high-speed event. But, I wondered, what would happen if the camera was the fast-moving object? Use a 210fps camera at 35mph, and on playback at 30fps it’ll seem to the observer that they’re moving at walking pace- but everything observed will be operating at 1/7th speed.
What I’d hoped to do was film the people on a railway platform from a train as it blasted past, but since the places they don’t stop at tend not to be listed in the timetables, this would be hard to co-ordinate. I figured that being at the very front of a fast train as it approached a stop would suffice; although the ‘frozen in time’ effect is less pronounced towards the end of the video, the platforms at non-stops tended to be mostly empty, so there’d be less to capture anyway. Helpfully, people don’t seem to move too much as their train arrives!
Here’s the most successful of my attempts, then- as it happens, the first stop, Bath Spa, had the best lighting. Youtube has, as usual, mangled things somewhat- it’s a lot smoother at the original quality, but vimeo does no better, so this’ll have to do.
Without a slow-motion camera you can achieve something similar by convincing a large group of people not to move! This improv-everywhere scene experimented with just that, which inspired a ‘big freeze’ flashmob in Edinburgh whilst I was living there. Portraying lack of motion in a photograph strikes me now as a fools errand, although like many others I did try, and the (annoyingly uncredited) photo in the BBC coverage is one of mine. The opposite problem, of compressing a block of time into a single frame, can give fantastic results, and is in some sense the inverse of what I’ve been trying here, which is to stretch a moment into an extended video. I find all this mucking around with time endlessly fascinating…
I’ve recently returned to the West Country to take up a postdoctoral research fellowship at the University of Bristol. As a result, I’ve expanded the maths subdomain to include content that used to be on my University of Edinburgh homepage, and to perform the same role for my time in Bristol. There are also summary pages for outreach activities and earlier content from my undergrad years, and I’m hoping (in some hypothetical future free time) to organise and expand the PhD-related content.
Similarly, I’ve refined my online photo sharing locations from four to two: travel-related content goes on Sosauce, everything else on Flickr. Now if only I could impose some order on the 15,000 files I keep offline…
This time last month I arrived in Malta for what turned out to be a very enjoyable holiday- my notes are now up on SoSauce, as well as an album of the better photos.
(Cross-posted to Modulo Errors)
Just a quick note to mention two talks from the Edinburgh International Science Festival, which my flatmate chaired and I took some photos at: Marcus du Sautoy’s The Num8er My5teries and Ian Stewart’s Cows in the Maze. Summaries, courtesy of Haggis the Sheep, can be found here and here respectively.
Spring is slowly taking hold in Edinburgh, so I felt it would be good to take advantage of the sunlight and try some high-speed shooting outdoors. With a friend, Jaclyn, as glamorous assistant, I had a go at an old standard: capturing water balloons just as they burst. Caught at the right moment, the water retains the shape of its now-absent container before collapsing.
It should be noted that sunny in Edinburgh needn’t mean warm… Next time I think it’d be a good idea to fill the balloons with hot water, as after a few soakings with cold water it’s hard to operate the camera! Still, at least the combination of 40fps and pre-record meant that we got the desired capture from each burst, although the shape and positioning wasn’t always ideal (I had hoped the balloons would be more spherical). The skin will end up on the opposite side to the puncture, so perhaps piercing at the bottom is best for a clear shot of the water- we discovered that simply dropping them onto a pin doesn’t work, however.
Last weekend Gravity Vomit held a juggling and circus skills convention at the University of Bath (where I spent my undergrad years), so I headed east to the west country with the high-speed camera. The flickr set contains some individual grabs from burst mode, as well as a few experiments with capturing multi-motion images.
However, slow-motion video quickly turned out to be the real crowd-pleaser, so I concentrated on that: as well as the highlights reel above, there’s also a playlist of longer clips available on youtube.
Whilst in Bath I also stumbled upon a chance to tour the Abbey tower, so there’s a few photos from that up on SoSauce, in my slowly-growing west country album.
A quick link-and-run as I’m just back from the Westcountry with 20Gb of video/photos to process, but whilst I was away a guest post I wrote for the SoSauce travel geek blog went live, which can be found here. It’s part of my ongoing ‘mathematical tourism’-themed contributions to the site, covering a couple of locations along the nearby Union Canal (a contour canal, and site of the discovery of solitons) as well as an earlier trip to Dublin.
My flatmate needed some dry ice for a vortex cannon demonstration which, even though we’re mathematicians, turns out to be surprisingly easy to get hold of through the university. In fact, she ended up with so much that I was able to use some of the excess for experiments of a photographic, rather than scientific, nature.
I quickly discovered that for seeing what’s going on, it’s better to add just a couple of pellets to plenty of water. That way you get to see individual bubbles of smoke before they burst – if you’re lucky, producing a smoke ring in the process. Carbon Dioxide is heavier than air, so it’s not a natural choice for smoke photography. But I did stumble on an approach that yielded an interesting set of abstract images. Placing a pellet in sufficiently shallow water prevents the gas forming large bubbles on the surface- instead, you get tiny streams of gas within the water, with the combined effect reminding me of magnetic field lines or iris patterns.
So what is actually going on here? I asked Dr Helen Maynard-Casely, the domestic scientist, for some insight:
These fantastic pictures are coming from the dry ice (solid carbon-dioxide) sublimating straight from its solid form to a vapour. This process of ‘cutting out the middle man’ (the liquid phase) happens when the atmospheric pressure surrounding it is insufficient to keep the solid together. When you expose molecules in dry ice to temperatures well above their melting point they vibrate: in the case of dry ice this is so vigorous that it is not contained by the air pushing in back. So instead of losing its crystal (solid) form and becoming a liquid the molecules fly off as a gas. The bigger the temperature difference the more vigorous the smoke will be (try putting dry ice in your tea….). Dry ice is only stable at -78°C so the large difference means you get more molecules flying off and a thicker ‘smoke effect’. Water ice often sublimates too, when sun shines directly on snow for instance. Also, this is how people who live in cold environments get their washing dry!
Sublimation may have also killed Napoleon Bonaparte. Arsenic also sublimates at the correct temperatures, and was used frequently as dye for wallpaper by British manufacturers in the 18th century. That was fine in Britain, where it was usually quite cold, but in a British-decorated house in St.Helena……
As well as photos, I captured a fair amount of slow-motion video too, which you can find in this playlist (the first few seconds of the first clip have unfortunately been mangled by youtube). For both stills and video, I was using a Casio Exilim FH20 camera, which is a bridge camera designed for high speed work. I’ve been playing around with this for several months, but was particularly pleased with this project: at high frame rates it suffers badly in low light conditions, rendering it all but useless indoors, so this time I borrowed a 500W floodlight which did wonders. So, not an expensive or sophisticated setup, nor all that complicated: camera stabilised on a tripod, either in super macro mode or manually focused, but otherwise making its own decisions about settings. Then it was just a case of sieving through 1300 photos and several GB of video for the best bits! Choosing between shots 1/30th of a second apart is near-impossible, but a set I’m happy with is up on flickr (and cycling through on the slideshow above).
I have now submitted my PhD thesis for examination; hopefully the viva will be in April. Until then, I finally have the time for various projects and trips I’ve been planning, so there should be a bit more activity here. Coming up:
The Bath Upchuck juggling and circus skills convention, where I’m hoping for plenty of high-speed photo opportunities;
A holiday in Malta, the furthest south I’ll have ever been;
I’ve slowly been collecting 210fps footage, and I’ve found shots of fire and water particularly compelling. I’ve still got a long way to go before I capture something truly spectacular (need to work on stability and focus, for starters) but some of the more promising results along the way are now up on Youtube. As well as the waterfall above there’s twoclips of fireworks, and this one of a fire.
