On Sun, 14 May 2017 12:22:33 -0400, Davoud wrote:

...for eclipse photography purposes. I will be photographing the
eclipse with a "full-frame" DSLR. I have several 'scopes of varying
focal length and photographic fields of view and I want to ensure that
I do not crop the corona during totality.

I've seen images where the diameter of the corona exceeds 3°. It
depends on how tricky you're planning on getting with your processing.
Conventional single shot images tend to yield coronas that extend
perhaps a solar radius from the limb. But HDR imagery pushes this way
out. If you're planning the latter, I'd probably go with no more than
a 400-500 mm focal length. While that costs you some theoretical
resolution, most likely the seeing conditions will be what determines
resolution, and your pixel scale will be finer than the actual
resolution you can reach.

I'm planning on using a 400 mm FL refractor with a full frame camera
for my primary imaging instrument. I'll be running the camera from a
computer to shoot a rapid sequence of different exposures to try and
capture as much dynamic range as possible.