[Leica] Longest known time exposure!

[Howard Ritter]

The exposure was on photo paper, so ISO maybe 0.1? The diameter of a beer can is, say, 65 mm. The pinhole, I’m guessing, was ~0.1mm so, f/650 @ ISO 0.1. Rule of thumb is daylit scenes take 1/ISO @ f/16. That would be 10s @ f/16. 650/16 = ~40 and 40^2 = 1600. So daylight exposure would be 10s x 1600, or about 5 hours. 

Then you gotta figure how many equivalent hours of full sunlight there are in an average Hertfordshire day over the course of a year, figuring in clouds, low sun angles, etc. Three, maybe? So 8000-9000 h of exposure. Just a trifle overexposed.

Of course, even the direct imaging of the Sun on the paper didn’t blast it out, so maybe the pinhole was more like 0.01 mm, making the proper exposure 500h. And then there’s monumental reciprocity failure…


—howard

> On Dec18, 2020, at 1653, Douglas Barry <imra at iol.ie> wrote:
> 
> Incredible. We know the shutter speed, and should be told the film type and aperture...
> 
> Douglas
> 
> On 18/12/2020 14:19, Howard Ritter via LUG wrote:
>> Some seek world records. Others have world records thrust upon them…
>> 
>> https://www.herts.ac.uk/about-us/media-centre/news/2020/longest-known-exposure-photograph-ever-captured-using-a-beer-can <https://www.herts.ac.uk/about-us/media-centre/news/2020/longest-known-exposure-photograph-ever-captured-using-a-beer-can>
>> 
>> 
>> —howard
>> 
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