Apologies in advance for a long post, but I'm getting a little confused as to whom to believe when it comes to eclipse exposure calculations.
I had done my exposures based on one calculator, but after looking at some images posted recently on IIS that included exposure details, I decided to do some more research.
Rob posted a diamond ring shot at 1/2000, F9 at ISO400. I have a fixed aperture setup at F6.2, or 1 full stop faster, and would like to use ISO100 (2 stops slower) to maximise my sensor's dynamic range. Overall, the equivalent exposure for my setup would be 1/1000, F6.2 at ISO100 (1 stop slower).
The calculator I had been using gave suggested exposures of 1/80 second for the diamond ring - over 3 stops longer than what Rob used. It also recommends exposures that are one stop longer for partial phases through an ND5 filter, but 1.3 stops shorter for unfiltered exposures during totality, when compared to another calculator on the eclipse-chasers website (
www.eclipse-chasers.com).
Today I did some test imaging with my setup on the setting sun. Through a hazy sky at low altitude, the images that I selected as having an "ideal exposure" based on their histogram, matched closely with the exposures predicted by the eclipse-chasers calculator, when I asked it to compensate for altitude and "humid" conditions. (This is what I would have selected for the Cairns eclipse, given I'll be on the coast)
Given that I was shooting through a very hazy sky (ie greater atmospheric extinction) and my exposures matched eclipse-chasers more closely vs the other calculator (which was suggesting longer exposures again for the partial phases) - I'm tending towards the exposures predicted by eclipse-chasers. At the NACAA workshop, the comment was also made by those who had photographed successive eclipses with digital cameras that their images were brighter in the more recent eclipses with newer and newer cameras/sensors. Maybe this suggests the recommended exposures should be getting shorter???
So, according to the eclipse-chasers calculator (allowing 2 stops for atmospheric extinction), I should be shooting the diamond ring at 1/250, F6.2 at ISO100. (2 stops of extinction was mentioned at the NACAA eclipse photography workshop and matchers the eclipse-chasers calculator) I realise the brightness will vary greatly during the moments before and after totality, so no one exposure will be correct for the diamond ring. Obviously a longer shot will expose more of the corona, but if it's not taken just prior to the sun being completely eclipsed by the moon, it will be drastically overexposed.
I'm not terribly concerned about the varying exposure predictions during partial phases or the rest of totality - I'll got the time to bracket exposures to allow for that. For me, the diamond ring is the "money shot" of the eclipse, hence my pondering of the issue.
At this stage, my script will be written to shoot a 4fps burst of exposures at 1/250 just prior to C2 and 1/40 just after C3.
So, my question is, what exposures are you planning to shoot for the diamond ring shot?
DT
