topic Re: Fast vs Slow Lenses on Mirrorless in EF & RF Lenses

Fast vs Slow Lenses on Mirrorless

Wandalynn — Thu, 04 Nov 2021 14:26:38 GMT

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.

Re: Fast vs Slow Lenses on Mirrorless

FloridaDrafter — Thu, 04 Nov 2021 03:33:19 GMT

I haven't studied it intensively, but I don't think cameras, in general, open up the aperture to get focus. My thinking is, at wide open, DOF is razor thin, at times, so it would be hard to get focus that way. The R's use "Dual Pixel AF II" and is 100% phase-detection coverage across the sensor and is a "new animal" for the most part [edit] The way I understand it is each pixel has a twin so it gets a "stereo view" to aquire focus [/edit]. I think the only other Canon camera to do this is the 1DX mark III, but only in "live view".

What I can say for sure, is we have had the RF 100-400mm for a couple of weeks now and my wife has been using it on her R6, for the same reasons as you... It's light and produces great photos! She is disabled and just can't lug L glass around. I haven't used it yet on my R5, so I can't comment on that, but she reports (I just asked her) that AF is snappy in low light situations with no lag. Now, I have read that the R6 is better with low light, so I won't know how the RF 100-400 behaves on my R5 until I can give it a go. I plan on doing comparisons with my EF 100-400 L II, I know, apples to oranges, but dang, that will be a good test. So far, they look comparable as I have shot the same birds, same location, same distance, that she has, and TBH, I'm impressed with this budget RF 100-400 lens.

We shoot in low light, usually under tree canopies and thick brush to get birds, flowers, and insects.

Newton

Re: Fast vs Slow Lenses on Mirrorless

MikeSowsun — Thu, 04 Nov 2021 12:02:38 GMT

All modern DSLR cameras focus with the aperture wide open. The aperture is always held wide open regardless of what is set on the camera. The aperture only stops down as the photo is taken.

If you want to see the effect of the selected aperture value, you can press the Depth of Field Preview button. The aperture will stop down to the selected value, the viewfinder darken, and there will be a change in the depth of field.

All DSLRs work this way, and I assume it is the same for those newfangled Mirrorless cameras. 🙂

Re: Fast vs Slow Lenses on Mirrorless

FloridaDrafter — Thu, 04 Nov 2021 05:30:45 GMT

Thanks, Mike. That makes sense. I should have known that since I use the DOF preview quite a bit for macro 🙂

Newton

Re: Fast vs Slow Lenses on Mirrorless

jrhoffman75 — Thu, 04 Nov 2021 10:13:09 GMT

Many of the RF lenses have smaller max apertures than DSLR lenses because of the ability of the sensor AF system to focus better than the DSLR systems at lower light levels. The majority of DSLRs are limted to f/5.6 for AF. The higher spec models, like the 1D series, can AF at f/8. Canon has releasesd RF lense with f/11 max aperture. But it is still going to be harder for the camera to focus at lower light levels compared to brighter levels.

The RF 100-400 is an f/5.6 max, whereas the EF 100-400 is f/4.5 max.

Re: Fast vs Slow Lenses on Mirrorless

ebiggs1 — Thu, 04 Nov 2021 14:03:48 GMT

If it is possible to use and the fact slower, higher f-number, lenses are easier and cheaper to make, why not. Slower lenses are also smaller and usually much lighter. Canon feels that is the way to go. They can be good but have certain other issues beside AF functions like lens diffraction because of the tiny apertures. I personally would not be interested in a lens that only had a f11 max aperture.

Re: Fast vs Slow Lenses on Mirrorless

wq9nsc — Thu, 04 Nov 2021 14:15:03 GMT

The camera initial focus is going to occur with the lens wide open. Even when a camera can still AF with a "slow" lens, the AF is going to be slower but this is somewhat offset by the less critical focusing with the smaller aperture glass due to the greater depth of field around the critical focus point.

From a cost and weight standpoint, there is a rationale for making these narrow aperture lenses and a big driver for mirrorless cameras is the reduced complexity and thus cost of manufacture so the two somewhat fit together.

Like Ernie stated, there are a lot of things a wide aperture lens can do that a narrow aperture cannot so it isn't just about focusing. The slowest lens I own are 400 and 800 f5.6 primes. I use the 400 f5.6 when hiking but it is a big step down in speed AND quality from the EF 400 f2.8 I use for sports. Outside of macro glass, I rarely have a lens stepped down to the f11 range and I would feel very limited with a telephoto of that type. I might change my mind when the fast glass starts feeling too heavy 🙂

Rodger

Re: Fast vs Slow Lenses on Mirrorless

Wandalynn — Thu, 04 Nov 2021 14:30:33 GMT

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.

Re: Fast vs Slow Lenses on Mirrorless

ebiggs1 — Thu, 04 Nov 2021 14:36:26 GMT

" I might change my mind when the fast glass starts feeling too heavy"

I use to carry two 1 Series camera bodies with big lenses all the time and not really think about it. Now I think I about it.

I am still not interested on a f11 or even a f8 lens. Had them in the past!

Re: Fast vs Slow Lenses on Mirrorless

jrhoffman75 — Thu, 04 Nov 2021 14:56:43 GMT

Despite what Canon has in its marketing material, I wouldn't consider the RF lens for sports/action or birds in flight. but I suspect that the difference in cost between $13K for the 800mm EF lens and $900 for the 800mm RF lens, coupled with the apparently very good IBIS for the mirrorless bodies would make that lens attractive to wildlife photographers. Many wildlife shots are basically still shots so fast shutter speed isn't essential.

Re: Fast vs Slow Lenses on Mirrorless

Waddizzle — Thu, 04 Nov 2021 16:34:04 GMT

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.

Re: Fast vs Slow Lenses on Mirrorless

Wandalynn — Thu, 04 Nov 2021 17:20:35 GMT

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.

Re: Fast vs Slow Lenses on Mirrorless

ebiggs1 — Thu, 04 Nov 2021 18:30:08 GMT

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.

Re: Fast vs Slow Lenses on Mirrorless

FloridaDrafter — Fri, 05 Nov 2021 04:05:54 GMT

@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.

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

Re: Fast vs Slow Lenses on Mirrorless

Wandalynn — Fri, 05 Nov 2021 14:54:25 GMT

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!

Re: Fast vs Slow Lenses on Mirrorless

FloridaDrafter — Fri, 05 Nov 2021 23:15:54 GMT

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