For next year's solar eclipse, I'm aiming to use my 500 f/4 lens. I searched around for solar filters, and came across this one. I'm quite pleased with the whole setup so I thought I'd share. I bought mine in Canada, so you'll just need to search for "Baader solar filter" to find a distributor near you. Note that there are quite a few models, and I spent a fair bit of time going through them all before settling on the ASTF 120 for my lens. It is a perfect fit. It holds on by friction and is quite secure, but it's also easy to pull it off quickly for the total phase of the eclipse.