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Pinhole cameras and eclipses
Posted By Marcus Wilson On November 15, 2012 @ 11:54 am In Science | No Comments
Well, the eclipse yesterday was fun. There were enough patches of sky between the clouds to get some good views. I was pleased that the pinhole cameras I made out of miscellaneous cardboard tubes, tins, paper and tinfoil worked really well. Also, the trees around the front of the sciences building gave some nice natural pinholes as the sunlight worked it’s way through the gaps between the foliage – we could see lots of crescents projected onto the wall of the building. Not something you see everyday.
The trick with the pinhole camera  is to get the combination of length between pinhole and screen and size of pinhole correct. (Basically – the f-number in photography-speak) A long length means a larger image – but also a fainter one. To increase the brightness, we need to let more light through (a bigger pinhole) but the drawback of this is that it blurs the image. It takes a bit of experimenting – best done well before the eclipse that you want to see.
On the subject of which…if you live in New Zealand…you don’t have a lot of opportunity for a while. We northerners get an iddy-biddy eclipse next May (10th) – sorry Mainlanders – you miss out – and then it’s nothing for ages before we get a few more feeble partials in the 2020s. BUT, as I said earlier, it’s then non-stop eclipse mayhem from 2028, with THREE total and THREE annular eclipses before 2045, for those of us who are still alive to see them. Details are all here courtesy of RASNZ .
There are a few videos up already from the Cairns region – here’s one. However, video does not do an eclipse justice, partly because of the difficulty in video capturing parts of the corona at different luminances simultaneously. If you want to see the fainter, whispy stuff at the far edge of the corona, you end up well overexposing the brighter area nearer the moon. The naked eye does a far better job of capturing the totality phase than a camera.
I note a fair amount of pink on the video – this is the chromosphere – a thin, cooler area of the sun, between the photosphere (the bright yellow bit that we normally see) and the corona.
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 pinhole camera: http://www.exploratorium.edu/science_explorer/pringles_pinhole.html
 Details are all here courtesy of RASNZ: http://rasnz.org.nz/Eclipses/solar.htm
 http://www.youtube.com/watch?v=CTbIufApsSk: http://www.youtube.com/watch?v=CTbIufApsSk
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