When do you see the difference between RF lenses that are 2.8L vs 4.0L

I’m thinking through what lenses to purchase for my R series Canon. While the 2.8L lenses are optically superior, the 4.0L lenses are still very good and less expansive and heavy.

Under what shooting conditions will I see the difference in quality between one line of lenses against the other line of lenses?

The main differences I can think of are light gathering capabilities, bokeh, and depth of field/blurred backgrounds. None of these usually matter to me so I never saw a need for an f2.8 zoom.

jclin10 wrote:

I’m thinking through what lenses to purchase for my R series Canon. While the 2.8L lenses are optically superior, the 4.0L lenses are still very good and less expansive and heavy.

Under what shooting conditions will I see the difference in quality between one line of lenses against the other line of lenses?

The 2.8 lenses gives you better background separation and low light capabilities. AF system receives twice the amount of light as well. I would go with the excellent f/4 lenses if you are in doubt and don’t need f/2.8.

I use the 70-200L f2.8 for in door horse shows where I need borh the backgroind separation and fast shutter soeeds. I often need to use ISO 10000 to freeze the motion. I some times also ise the 200L f/2.0 to achieve what I want.

That's super helpful. Some of it is also a practical consideration, namely, how much I want to carry on these aging shoulders and back!

jclin10 wrote:

I’m thinking through what lenses to purchase for my R series Canon. While the 2.8L lenses are optically superior, the 4.0L lenses are still very good and less expansive and heavy.

Under what shooting conditions will I see the difference in quality between one line of lenses against the other line of lenses?

You will feel the lightness of the F/4.0 over the F/2.8 every friggen time you pick up the camera.

You will use the F/2.8 every once in a while--when you want to blur foreground/background parts of the image; or when you need the speed to get the shot (low light) where you are pushed up to the limit with ISO.

Only the blur part is impossible with the F/4.0 lenses.

Used between F/4.5 and F/8.0 there are no realistic differences, and between F/8.0 and F/16 there are realistically no useful differences. Used at F/4.0 the F/4.0 lens may (M A Y) underperform the F/2.8 lens at F/4.0 by a little.

You'll see the differences at f/3.5 and f/2.8, which the f/4 lenses obviously can't do. The pro f/4 lenses, especially the newer L versions, are great optically, and will usually do as good as the faster lenses. But if you want more background blur, better focusing in low light, and the fastest shutter speeds possible with a given amount of light, then f/2.8 has definite advantages. But if you keep both lenses at f/4 or smaller, you shouldn't notice much difference. (Except perhaps focusing speed, which uses the widest aperture.)

you‘ll see the difference when you’ need that extra f stop.

most won’t even register the difference in blurred background if they don’t know that the compared images are made with different f stops

jclin10 wrote:

I’m thinking through what lenses to purchase for my R series Canon. While the 2.8L lenses are optically superior, the 4.0L lenses are still very good and less expansive and heavy.

Under what shooting conditions will I see the difference in quality between one line of lenses against the other line of lenses?

in my experience, i owned 70-200 f2.8 non-IS and 70-200 f4.0 IS, and to be frank, i much preferred the f4.0 IS quality, no doubt about it. the fluorite element in f4.0 IS is doing magic. But, the f2.8 mk3 has 4 fluorite elements so i can imagine the IQ of this lens.

Besides the obvious fact of f2.8 and the ability to more background blurr, there also are other differences.

You can google 2470 vs 24105 comparisons and you can see that the 24-105 has more distorsion (which needs to be corrected in software and which can influence IQ in the corners). Also there can be differences in sharpness.

I compared the 70200 rf 4.0 vs rf2.8 and you can search such threads.

In this case both are equally sharp, but you can see the difference in subject isolation f2.8 vs f4.0. Also the 7022/4.0 at 4.0 vignettes more at this f-stop than the 70200/2.8 at 4.0. For indoor sports the f2.8 helps me also to keep iso in an acceptable range even when shooting at 1/1000.

For portrait I feel f2.8 does make a difference.

Maybe its also a question, if a lens should replace primes or if it should be combined with faster primes.

Very helpful. I'm mostly deciding how much of a trade off there is if I opt for weight savings over size of aperture.