# Exposing for the sun (transit of Venus)

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• 06-05-2012, 08:54 PM
Newt_on_Swings
I totally missed it, forgot to look out as I was in darkroom at 6:40 for sunset. Didnt get out of work til now. Oh well maybe I'll live to see it again with the advances in medical tech. On the upside the students made excellent still life prints while we were in there.
• 06-06-2012, 12:05 AM
polyglot
You ain't missed it yet, there's still about 45 minutes left (assuming you're not on the dark side). We finally got some breaks in the clouds in Adelaide (about 50% coverage now), and I got my (digital photo) of a projection out of a telescope, complete with a bunch of hairs in the picture because someone's eyepiece ain't real clean...
• 06-06-2012, 09:38 AM
couldabin
OK, as usual I'm confused. I thought EV was bound to f-stop/shutter combinations. The exposure that results in will depend on the light energy and the film speed. So my question was (before the transit) what density one would expect for the sun's disk with ISO 100 film and EV 33 (or 11 stops less than 1/1000 and f-64)? And, FWIW, do you know if the welder's glass rating is on an EV scale? That is, #12 reduces brightness by 2^12 times?
• 06-06-2012, 08:03 PM
polyglot
EV is "exposure value", which means a quantity of light coming from a source in the scene. You can think of it as being source brightness, or you can think of it as the camera settings to capture that particular source brightness as a midtone on your film. It's also the value returned by a reflected-light meter.

So EV15 is 4096 cd/m^2 or it's ISO100 f/16 1/100s. Likewise, the sun (according to andrew.roos) is 1.6e9 cd/m^2 = EV33.6, which would be ISO100 f/16 1/39,000,000 (a 25.6 nanosecond exposure) to hit Zone V.

I think you're right about the numbering of welding glasses being stops but I don't know. They also have some odd spectral effects (kind of green, lots of UV-blocking) so it's not a simple ND and therefore you can't state a simple filter-factor without knowing the spectrum.
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