Virus Illusion Confusion

Thanks to the very good offices of Matt Brown, who knows everything about everything happening in London, I found myself at the Smithfield Gallery last night. Jenny, Richard and myself joined Matt there to gaze at Luke Jerram’s artful glassy virus sculptures.

Matt has already blogged about the evening so I will leave it to him to tell you more about the exhibition (which may also get a mention on Lablit before too long). I want to go in a slightly different direction.

You will also see some beautiful photos on Matt’s post, but when I dug out my iPhone to snap a picture of one of the sculptures displayed on a light table, this is what I got:

Virus on a light box
Strip-lit sculpture?

Jenny asked me why the background was ribbed in the photo since no stripes were evident to our eyes – or in Matt’s or Richard’s pictures, taken on ‘real’ cameras. I had to confess that, despite being in possession of a degree in physics, I was stumped.

However, I guess the question must have been gnawing away at me in the background because this afternoon, whilst traipsing back-and-forth between my office and the laser printer, I stumbled across a solution. Or, at least, I think I did.

But before we get to that – would anyone else care to puzzle it out?

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28 Responses to Virus Illusion Confusion

  1. Cath Ennis says:

    Is the answer that the iPhone camera sucks?

  2. Stephen Curry says:

    You’re on the right lines, Cath, though I’m looking for a little more detail on the particular nature of its limitations.

  3. Alan Henness says:

    Beating of the camera refresh rate with the mains lighting? What was the lighting? Incandescent? Low energy fluorescent?

  4. Sean Seaver says:

    The iphone camera shutter speed is different (think slower) than the rate at which the sculpture is projected on the light table?

  5. Stephen Curry says:

    Getting warmer – I think the illumination (from beneath the glass tabletop) was fluorescent.
    And a very warm welcome to NN Alan!

  6. Cath Ennis says:

    Are there any “normal” photos of the same thing, so we can get a better look at the set-up and the form of the sculpture itself? If it was on a light table, I’m guessing it may have been some kind of etched sheet of glass?

  7. Stephen Curry says:

    Cath – you can see the same light table in a decent picture on Matt’s blogpost (the one with the artist standing and clutching his creation.
    Sean – it’s not exactly shutter speed, but the speed of something else that is crucial here…

  8. Jennifer Rohn says:

    The speed of light?
    Thanks for not telling them that I asked you whether people might be able see colors on proteins if only they (the people) were small enough.

  9. Stephen Curry says:

    Afraid not Jenny – the speed of light isn’t involved. The answer β€” I think β€” is a bit geekier than that and is to do with the behaviour of the sensor in the iPhone…
    Unphysical it may have been but the notion that tiny, tiny people might be able to see colours in viruses was an utterly charming notion! (Wanna sign up for my crystallography lectures in October? I’ll deal with with the colour problem there.)

  10. Jennifer Rohn says:

    Chivalrous to the end.

  11. Alyssa Gilbert says:

    Well, I know CCD cameras use red/green/blue filters that make the photos into color images. Some of them use filters that cycle in front of the image, others use beam splitters. Is it something to do with the efficiency of that process?

  12. Cath Ennis says:

    See, it’s not rocket science.

  13. Bob O'Hara says:

    I guess Alyssa oort to know.
    The one thing I can think of that would cycle like a sine wave is the AC, which would make the light pulse. If the camera were scanning across the picture, taking thin slices, I guess you might get this pattern. I’m sure a real physicist would set this as a problem for students to work out how fast the camera was scanning.
    All in all, it is very pretty.

  14. Cameron Neylon says:

    We get exactly the same effect on our UV transilluminator if you don’t use the correct colour filter. The diffusion on the top of the light table isn’t effective into the UV so that although the glass is cloudy in the visible range as you go beyond the human/decent-camera range it becomes clear. This means you can actually see the bulbs – which have a significant UV emission.
    My guess would be that the colour balance on the iPhone camera or the sensitivity of the CCD is such that it is sensitive at those near UV wavelengths. You wouldn’t notice this usually because a picture of a fluorescent bulb just looks “whiter” than it should. I would guess it means in turn that the colour balance of iPhone photos should look “colder” than a more expensive camera.

  15. Stephen Curry says:

    Ha, ha Cath, you’re on fire! I hope Alyssa appreciates your wit!
    @Cameron – nice try (if I have understood correctly) but I think Bob is on the money. Someone give that man a banana!
    The sensor in the iPhone camera is rather cheap and therefore relatively slow to read out. It contains a grid of pixels that are read out line by line, so the image is made up effectively by scanning across the surface of the chip. Since the lights are powered by 50 Hz AC, the intensity is oscillating (actually by 100 Hz – 100 times per second) and the time taken to do the readout of the chip is long enough for several cycles to pass. I counted 11 cycles in my photo which suggests the readout time is about 110 milliseconds – rather slow for a camera.
    This readout ‘problem’ has given rise to other interesting photos. Digging around a little I found this picture of a spinning propellor at the Scalar Motion site:

    It’s quite a striking effect. The strange appearance of the propellor is explained on the site with a clever video:
    Cool, huh?

  16. Cameron Neylon says:

    I’m unconvinced. If the read time is so slow then taking pictures of moving objects wouldn’t work at all? e.g. a person walking at 1m/s would appear a complete blur at a few metres distance from the lens. The propellor example is very cool but its presumably going quite a lot faster? Apparently that picture was taken with an iPhone so if the propellor rate was around 50 Hz then I will stand corrected but I would have though it would be in the high hundreds/low thousands of Hz.
    Though looking at the picture now on a computer screen rather than a phone the light box would have to have an awful lot of tubes as opposed to three or four that are usual and the would be very close packed.

  17. Stephen Curry says:

    Cameron – I know what you mean about 1/10th sec being too slow for a camera – but it’s true that the iPhone’s performance with moving objects isn’t great.
    I think the explanation is certainly along the right lines (and would work for a prop going at much higher than 50 Hz).
    I feel an experiment coming on…

  18. Cameron Neylon says:

    Some other pretty striking examples out there on teh interwebs.

    This one more or less convinces me that the timeframes are about right for Bob’s explanation to be the right one. That’s a US intercity train going past in the background.

  19. Alyssa Gilbert says:

    Very cool stuff – and I always appreciate the wit of the NN bloggers!

  20. Stephen Curry says:

    Ha – nice one Cameron. I guess the inclined angle of the train window is the artefact of the scanning. Normally the right hand edge would be perpendicular.
    This reminded me of a photo I took in the metro in Budapest, which is weird looking but not due to any camera artefact:

    So how come it’s so easy to lean back?

  21. Richard P. Grant says:

    Oh that’s brilliant Steven, I’ve been playing with similar on the Tube. It’s great with a 1/4-1/2 second exposure so you get a blurred background.

  22. Cath Ennis says:

    Wow, I love the propellor and metro shots!
    I did a lot of (real) leaning forwards on the Rome metro1 – the hand rests move quite a bit faster than the escalator itself, so if you’re not paying attention, your hand starts moving further and further away from you.
    1 I typed “Roman metro” first, but that just felt wrong.

  23. amy charles says:

    “So how come it’s so easy to lean back?”
    I used to ask myself this all the time in my 20s 30s nevermind.
    I am so extremely jealous of you guys’ being able to be there and see these sculptures. Will he please send some here? And can we use them or images of them in nightclubs?

  24. Clare Dudman says:

    Just been reading this string of comments – highly entertaining – and interestingly Cath’s initial comment seems to be a pretty decent summary. πŸ™‚

  25. Stephen Curry says:

    Back from the dead synchrotron…
    @Richard – who the hell is Steven?
    @Cath – not even the Romans were that clever, I suppose. Though what an archaeological find that would be!
    @Amy – I was a nice show and the sculptures are beautiful though there weren’t that many different viruses on display (influenza, smallpox, HIV, SARS – and a rogue E. coli). They go for up to Β£5000 (!) but there were prints on sale for considerably less, if you’re in the market.
    @Clare – thanks! And kind of spot on, though I quite like working with the limitations of the camera. Plus it’s great to have one on you by default the whole time. Here’s one I took on the way home the night of the viewing. Blurred and grainy from the low light, but captures a moment…

    Walking by the Thames near Temple tube station

  26. Richard P. Grant says:

    You lot should sort your nomenclature out. We have a ‘Steven’ at work who’s called ‘Steven’ and a ‘Stephen’ who’s called ‘Steve’ so it’s your own fault.

  27. Stephen Curry says:

    Sorry Dickie. I should have known I was to blame…

  28. Richard P. Grant says:

    Damn right, Steptoe.

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