You make a compelling case for the RF100-500.

Money isn’t a problem per se, but I just set a limit for myself not to spend over $2,000 (additional out of pocket). Your assumption is correct that this will be mainly for birds and to a lesser extent general wild life. As I mentioned in another reply, the Sigma is good but I’m sure the keeper rate would be better with one of the RF mounts.
My current gear (for birds) is the R5 with the Sigma 150-600.

Well, probably the main thing is, while it does take sharp pictures, I find that the keeper rate isn’t what you would call super high. I have heard that the RF lenses are much better at auto focus and tracking. So I don’t know if I would call that a shortfall, but it would be nice to have a better keeper rate when I’m shooting for example, birds in flight.

Weight is another factor, though less important. The sigma lens is not super heavy but it’s also not super light. I can handhold it but it does get tiring after a while. Of course, the 200–800 would be even worse in this regard.

Thanks for the links. I actually had already watched the Jan Wegener comparison of the 100-500 vs 200-800.

When you say if you were to make the choice today, do you mean you'd get the RF200-800 instead of the RF100-500? My biggest hesitation with the RF200-800 is the small aperture. If I sold the Sigma for the RF100-500, I'd only be giving up a 1/3 stop but also be giving up 100mm of reach. If f/7.1 is a handicap, I can only imagine f/9 is a much bigger handicap. I like to shoot birds at the Bosque Del Apache and some of the best shots occur in sunrise or sunset conditions. I'm wondering how high I'd have to crank the ISO to compensate.

If I were to get the RF200-800, I would not need to sell the Sigma.

Thanks! That's a valuable data point.

That's likely true. My Sigma does pretty well on the R5, but I'm sure there would be a higher keeper rate with a native RF lens.

So, if you were in m y shoes, given you have a "similar" Tamron, and you have the RF100-500L, if you were in my shoes, which of the three options would you choose? (Assuming you had to give up the Tamron to get the RF100-500)

I wasn't as clear as I could have been. I'm talking about under $2k "additional" out of pocket. So, if I sold the Sigma for, say $700, then my "additional out of pocket" would be around $1900 (or maybe less if I went with a Canon refurbished).

Without listing all the specs of each (most Canon shooters probably already know the specs), if you have or had the Sigma 150-600 with an R5 or R6, which of these three options would you choose, if you wanted to keep expenditures under $2k) and why?

1. Keep the Sigma and use the money to buy a R7 as a second body
2. Sell the Sigma and put the money towards the RF100-500
3. Keep the Sigma, don't buy a second body, but instead buy the RF 200-800

Which would you choose and why? Curious.

The one I used is this;

https://formatt-hitechusa.com/products/firecrest-ultra-neutral-density-irnd-solar-eclipse-filter?variant=43967732089081

Note this filter will not add any additional tint to the image. The sun is actually white and this lens will yield a white disk

I’ve had good luck with these folks:

https://bluemooncamera.com/

Yes, it does make a difference. You said, "I need something I can look at the sun thru the camera viewfinder with." You were specifically asking about a filter that would allow you to "look through the viewfinder." The reason I asked whether you have a EVF (electronic viewfinder) or a rear LCD screen was NOT to suggest in any way that you should point your camera at the sun without a filter. I didn't say that at all and sorry if you inferred that.

The reason I asked about whether you have an EVF or a rear LCD view finder is because, with the filter I use (Firecrest 16-stop Eclipse filter) you can safely point the camera at the sun AND can view the sun on a rear LCD screen OR an EVF. BUT, if you have an optical viewfinder, you should NOT look through that with this filter nor should you use this filter (Firecrest) to look through it directly at the sun. I hope that makes sense.

By the way I shot the 2017 eclipse with this filter but I ONLY looked at the sun on the back of my LCD screen (WITH the filter attached until totality, at which time I removed the filter). Because my camera at the time (5D Mark IV) had an optical view finder, I did NOT look at the sun via the viewfinder, only via the rear LCD screen. My current camera is the R5 which has an EVF (but I'll still probably only view the sun via the rear screen as it's a lot easier).

Me shooting the 2017 Eclipse from a ranch near Glenrock, WY


My composite total eclipse image from the 2017 eclipse.

Does your camera have an EVF or rear LCD screen?