Just read your updated page and was curious about one of the parameters in your Exposure Sequence, specifically ISO. Why ISO 200, not 100 during partial phases?
I get why you’d want a higher ISO to shorten shutter speeds during totality—more images. But during partial phases, I'm curious about the need for speed?
Thanks for the helpful info & insight.
I'm not using 200 during totality just to get higher shutter speeds. The difference between exposures, most of them over 1/2 seconds, are going to give you a trivial amount of extra time to shoot extra frames. For all practical purposes you are not going to shoot any more frames because all of the overhead is in sending the control info like shutter speed changes over the USB. That takes 3 seconds. Using a higher ISO for shorter shutter speeds actually takes longer because in terms of signal-to-noise ratio, you need 2 frames at the higher ISO and that increases your USB overhead. So for the same signal to noise ratio as a lower ISO you would need twice as many frames and that would kill your framing rate.
For me, for my camera, it was a complicated technical set of considerations balancing readout noise, quantization effects and dynamic range. There's no one perfect ISO, I just though 200 was the best compromise for my camera for this particular subject with a huge dynamic range, and seemingly plenty of light in the bright inner corona, but faint outer corona fading into the sky background.
I also have a holdover feeling, maybe you could call it a superstition now days, but there were weird things, like banding noise, that used to happen at ISO 100.
The partial phases are, let me see how I can say this without offending any of the lunar population... kind of a joke at a total solar eclipse. Something to pass the time until the real show begins.. No one cares about the partial phases. I'm really just shooting them for a time-lapse and maybe a multiple-image composite. But with a filter, there isn't really much dynamic range you have to deal with so using the lowest ISO doesn't really gain you anything much here at all. I'm not really going to be resolving any sunspots at 420mm, so I'd rather go a little high to get an over one-thousandth of a second exposure just in case of wind or vibrations. There ain't going to be much to see at 420mm with a filter during partial phases, so the ISO doesn't really matter much to me here.
The show is totality, that's what I really care about.