Photographing the Eclipse: How Much Magnification?

How much magnification do you need to photograph the solar eclipse on August 21, 2017?

Sun KAC6341
This is the sun photographed at 10:21 in the morning, Canon 100-400mm lens with a 1.4x extender.  10-stop ND filter.  4000 shutter speed, f/4, ISO 100.

It’s going to take some magnification to photograph a big sun.

Solar eclipse, March 20, 2015, over Iceland.
This is the solar eclipse photographed in Iceland in 2015.  The lens is a 16-35mm on a full-frame camera.  I used the same 10-stop ND filter as above.  Notice how small the sun is in this frame.  (BTW, this is the same as using a 10-22mm lens on a cropped-sensor camera.)
Solar eclipse, March 20, 2015, over Iceland.
Solar eclipse in Iceland 2015 photographed with a 24-105mm lens on a full-frame camera.  I used the same 10-stop ND filter as above.  (This would be the same as using a 15-85mm lens on a cropped sensor camera.)
Solar Eclipse Sequence KAC1blog
This is a stack of images shot during the Iceland 2015 eclipse with the 24-105mm lens.  Then the entire image was cropped.  I used the 24-105mm because I wanted to build this stack later on in Photoshop.

Think about what lens you are going to use to photograph the solar eclipse on August 21, 2017.  The event will happen fast so the time to get prepared is now.