Fast vs Slow Lenses on Mirrorless

[Wandalynn]

Since some of Canon's RF lenses are slower than most typical EF lenses and I know it is said that that's not an issue since the mirrorless camera sensors are better able to handle higher ISOs but I have a question about that. Am I misinformed in thinking that when any camera auto-focuses, for a split second, the lens aperture is opened to the max to let in as much light as possible? If so, then what's different with mirrorless in that regard?

I'm asking this because my new RF 100-400 seems to struggle a little with gaining focus so I have to spend a little more time with a subject than when I use my EF 100-400 L ii. Or maybe I'm just spoiled by the "on point" AF capability of the EF. It's not really fair to compare those two lenses. And, I am very happy with the new lens--when it does zero in on my usually small subject like a bee, the picture is sharp (not like the L of course)--and it's just more work getting there. But due to its super light weight, I can carry it on long walks and not miss shots I normally would without it. I'm just curious about how the AF functions. I'm using an R5.

[Waddizzle]

Are using any type of filter? UV filters are not really needed in a digital camera. CPL filters can sometimes wreak havoc with a phase detect AF system. ND filters are becoming obsolete as the mirror less cameras have shutter speeds hitting 1/32,000 or even faster.

Use a clear filter or nothing, at all.

[Wandalynn]

I am using a B+W clear filter although probably don't need it since I have the hood--I just automatically put it on there. I should try shooting without it though--thanks for that suggestion. I thought there was a bit of a haze on the picture but I couldn't get totally perpendicular to the bug for even focusing so assumed that was the problem instead of the filter. Thanks.

[ebiggs1]

The reason for the “clear” filter is protection. Nothing else. If you are shooting in a safe place remove it. If you are outside I would use it most of time. The hood does not provide enough protection by itself.
Some lenses require a filter to complete their weather sealing.

[FloridaDrafter]

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@Wandalynn wrote:

Florida Drafter, Thanks for your input. I agree that the AF is snappy and the IS is amazing on the RF 1-4 but since most of my subjects are tiny, I have more trouble getting the camera to focus on that particular point with the RF 1-4 vs the EF 1-4 ii L and was wondering if it was that extra stop advantage made that much difference. It's a terrific lens and I'm definitely not disappointed. The below image is one I took with the RF 1-4 of a damselfly that's about 1.25" long and is a 100% crop (it doesn't look quite as sharp though after being uploaded). They are about like photographing a piece of dental floss. I just have to work a little harder with getting the camera to focus on it with the RF than with the EF.

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Wanda, FWIW, I had some time this evening and caught some low light so I could do a "down n dirty" test and try to duplicate your conditions, which were overcast with the sun low (couldn't see it) and although you can't tell from the shot, it was pretty dark. The subject was behind a chair on the porch, which made it even darker. This Orchard Spider is about 1/2" and I was as close as I could get, maybe 4 feet. Anyway, the R5 and RF 100-400 caught focus right away in this dim light. The R6 didn't, but after using MF override, it never lost focus again, even after moving my focus point off and focusing on something else. The next time I tried to aquire focus (with the R6), it went right to this tiny spider. The R6 aslo does that with my EF 100-400mm L II, but once MF is used, it seems to "learn" where you want AF. Not sure if you've tried it, but MF Overide is pretty nice. My wife uses it, MF Peaking, and MF Assist, but she likes to manually focus and is really fast at it. Blows my mind, but that is the background she came from... 35mm film.

EOS R5 and RF 100-400 f/5.6-8 IS USM lens. 1/500th, f/11, ISO 3200, Lightly edited in DPP - Unsharp mask Strength 4, Fineness 4, Threshold 2.

Newton

[Wandalynn]

Nice shot--I am familiar with that kind of spider--it is indeed tiny! Thank you for doing the test--I appreciate that! Yes, I do use MF override--essential--although I'm not all that fast with it. I'm still trying to get used to where the rings are on the new lens because I'm used to the EF 100-400. I also love that Canon mirrorless cameras let me enlarge the image within the VF in One Shot. Because of that and some other terrific features, I sold my 90D. I've also got an R. Again, thanks!

[FloridaDrafter]

You are welcome, and thanks for the post. I've been meaning to test the RF 100-400 on the R5 and your post gave me a push. It's good to know what stuff will do.

Newton