Thinking of getting the 100-500 to replace my Tamron 150-600 G2

Dan-Z wrote:

I've been using my Tamron mainly for bird photography. I have an R5, what do you guys think, is it worth upgrading? I mostly stick to f/8.0 as I find the focus a bit soft when using f6.3 and f7.1 on the Tamron. So I don't mind that the 100-500 starts at f7.1 as long as it's sharp at that aperture, is it?

I’ve only been able to shoot with my R5 for a week now, so take this with a grain of salt.

The only (birding) combination I’ve used thus far is the RF 100-500 + RF 1.4x (and only with backyard birds).  This combo is very sharp (I’ve only used it wide open).  The handling and light weight are very welcome.  The image stabilization lets me shoot at 1/200 - 1/500 no problem (except for subject motion blur of course).

The reason "I think" I want the 100-500 is that I'm hoping the AF will be faster and more precise.

The AF is indeed crazy accurate.  Much more consistent than my 7D2 was (7D2 was no slouch with 100-400ii +/- 1.4x iii).  I’ve been testing Eye AF, Spot, Single Point, Assist Points. and have been using various combinations with the BBAF buttons.  Also trying various Use Cases.  Not enough shooting yet to draw any firm conclusions.

I find that sometimes on the Tamron, when shooting BIF that I get a lot of OOF shots, the camera appears to tell me that I'm locked onto the bird, but when I review my bursts, half the shots are often out of focus, and the focus point is not even close to the bird at times. I'm thinking maybe the R5 is too quick for the Tamron. Also I don't get the advertised 12 fps when in mechanical with the Tamron.

The 12 fps mechanical and 20 fps electronic have been wonderful.  I take too many shots though!    I still have to do a comparison to see if the difference in bit depth has any impact.  I’m usually at ISO 1600 (f10 has its down-sides).

I was also looking at maybe picking up a prime lens instead of the 100-500, like a used 300mm f/2.8. With a 2X extender.

Keep in mind that a 2x extender will slow the AF considerably (enforced by Canon, not the aperture).

So what do you guys think would be best for bird photography?

LOL 600 f/4?  

I haven’t tried my 100-400ii yet, or my 400/5.6 “BIF Lens.”  It’ll be interesting to see if IBIS adds some utility to the old prime.

Should I stick with the Tamron or will the other lenses be better? I know I'm losing 100mm with the 100-500, so I suppose I could get a 1.4X extender, but I'll be at f/10.

Now for the bad news.  In my (limited) experience thus far, I find f/10 to be a bit slow on the R5 for good initial AF acquisition.  Sometimes the AF just balks and won’t get started if the subject is too OOF to begin with (I do have Focus Search enabled).  And distant BIFs often don’t even get a lock-on (7D2 no problem).

So my next step is to see how the naked 100-500 does.  Unfortunately it’ll still be only with backyard birds for a while yet.  Darn pandemic!  

And do you know of any reviews that compare the 100-500 to any of the 150-600 lenses? I haven't found any.

I haven’t looked at any.

It hasn’t been all doom and gloom with the R5 + 100-500 + 1.4x of course.  If I have Eye AF enabled the camera will often be locked on instantly, and Spot/Single AF is also super consistent (like a pitbull).  It’s just when the scene is too OOF initially that you get issues.  So I’ll be testing next without the TC.

Sorry about the (very) narrow usage report thus far.  I’m sure others will be chiming in soon.  Best of luck,

R2