I'm planning to shoot the solar eclipse coming up in August, and intend to use an astrophotography rotating mount to allow me to keep the camera aimed at the sun for the whole duration.
Needless to say, I will not be able to align it with Polaris optically, since this will be during the day. So I intend to do so by using a compass to align my "local right ascension" to due south, and then use a plumb line and a mark on the tripod head to set my "declination" equal to 90 degrees minus my current latitude. And on the first of these two steps, I am aware of the 15 degrees magnetic declination present where I'm shooting: Salem, Oregon.
I'm expecting that I'll probably have an error of several degrees in each of these adjustments. Assuming that I'm aligned on a axis that is 5 degrees "off true" that will lead to the sun having some rotation.
Without any sort of rotating mount, the sun moves at 15 degrees per hour, i.e. 15 minutes of arc per minute. With the setup I'm describing, including the error, what rate of angle per minute would I see?
More to the point, will it be significant if my longest exposure is an anticipated 8 seconds for the corona, during totality? I don't mind too much if the sun drifts a little between shots during the partial phase, it's the ten minute time period that surrounds the total phase that I'm concerned about.
I'll be shooting with a 1000mm focal length on a full frame Nikon, which according to this web site: Field of View Calculator gives me 2.06 degrees horizontal by 1.38 degrees vertical.
For what it's worth, this gives me an image of the size I want, I've tested the lens / camera combination aimed at the moon, which is pretty much the same size as the sun when viewed from the surface of the earth. It doesn't completely fill the viewfinder, but then I don't want that, since I'm expecting to catch a solar radius or two of the corona during the period of totality.