Looks like I will get to see the eclipse next month. I intend to bring two cameras. A Canon with the 100-400 lens to shoot video and a Sony with the 200-800 lens to shoot stills.
I realize I need a 22 stop ND filter.
Here are the questions:
What should I look for in a filter? I see they range in price from $8 to $150.
Can I use a square filter and holder?
Can I stack ND filters to make 22 stops?
What is the recommended way to photo the sun?
These universal lens film filters are just fine.
I STRONGLY recommend shooting bracketed raw shots, at least +/- 2 stops in increments of one stop or less.
Single shot:
Bracketed shot (this is how it actually looked through binoculars).
Realize that at the moment of totality, you should remove the filter. The filter is for the portion before and after totality.
Most importantly, set up to do this mostly automatically during totality. I used a remote timer. This is so you can watch the eclipse with your eyes, ideally through a quality pair of binoculars (I used Canon 10x42L IS binoculars).