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Pożyczyłem Rkę, fajny aparat, leży mi w dłoni, wg specyfikacji też ok. Z moimi krótkimi szkłami rewelka pracy. Ale jak zwykle ze wszystkim sprzętem powyżej 300 mmm zaczyna się wyższa szkoła jazdy. Prawdziwy test AF. Dwa tygodnie temu męczyłem poprzez adapter MC,Sony A7 III, ciężko było, ale jak już trafił to klękajcie canony, obraz jak w akwarium. To zobaczcie co poszło nie tak? 32 klatki sarny spaprane, ONE SHOT, najmniejsza ramka AFu, ale i tak większa od głowy, szyi sarny. Wszystkie zdjęcia z BF. R-ka nie dla przyrodników? Lustrzanka mi takich numerów nie robi, trochę wte, trochę tam, 1/3 ok. Szkło zacny Canon 400/5,6L.
Kto nie miał jeszcze problemów z R-ką ten prędzej czy później będzie je miał.

Temat tego problemu z ostrzeniem wałkowany jest już od zeszłego roku.

https://www.dpreview.com/forums/thread/4332052

Potencjalna przyczyna występowania tego problemu i sposoby na radzenie sobie z nim. Wyciągnę kilka postów z tego tematu, nie będę ich tłumaczył bo nie mam na to czasu.

Potencjalna przyczyna?

I am thinking some of these problems may be related to the subject and contrast when zoomed in. The EOS R AF points are not cross type so if your subject does not have a vertical line with enough contrast then the camera cannot focus. What types of subjects are you zoomed in on?
Źródło: https://www.dpreview.com/forums/post/62247637

Sprawdź czy masz włączoną opcję "Szukanie ostrości po utrac.AF".

Try changing "drive lens when focus impossible" from OFF to ON. It should solve the problem.

I have tested in the shop the following and they all worked well

70-200 f2.8 (mk 2 and 3)
100-400
100 L macro
85 f1.4
50 stm
40 stm
35 L f2.8 (mk2)
But... when I first got the 50 stm I had this issue from time to time until I turned that setting on. When I tested those lenses stated above this setting was already on.
Źródło: https://www.dpreview.com/forums/post/61974483

Wyłącz przycisk AF ON.

I was the guy who posted about this problem 4 months ago. Anyways, my problem was the AF-On button. For some reason the way I hold the camera when zooming in my thumb would accidentally hit the AF-On button. This was never an issue on a DSLR. The AF-On button is on a different area and the body is smaller. I disabled the AF-On on my EOS R.
Źródło: https://www.dpreview.com/forums/post/62274233

Użyj trybu "SERVO" zamiast "ONE SHOT".

I have the same setup; R + adapter + EF 70-300 IS II. Same problem.

Solution: Use AI-Servo.

Problem only occurs in Single shot (or potentially BBF shooters). However, with the EOS R's knack of nailing things, even in AI-Servo, and especially with this lens, peak sharpness is not an issue with AI-Servo.

This has been an issue with this lens since the 80D. When operating this lens in DPAF on either an EOS M, or now EOS R, there is something finicky about nano-USM lenses which causes them to erroneously report a shooting distance not possible (IE false positive that you're beyond macro distance). This occurs on both the 70-300 IS II and EF-S 18-135 IS USM. I've witnessed the latter on an 80D in live view.

It doesn't happen all the time, but plenty in my observation. Enough to be notable.

It never happens in AI-Servo as the lens will continue to drive searching for a phase shift instead of "giving up". Always nails it without issue when in AI-Servo.

It did not occur on my former EF 70-300 DO adapter nor on any other lenses.

Hope that helps explain the phenomena, confirm it's there, how it behaves and what you can do about it.

Canon should firmware fix that though. Probably a lens firmware if I had to guess as those lenses have CPU logic in them. It doesn't happen on other lenses, hence that conclusion.
Źródło: https://www.dpreview.com/forums/post/62275543

Wyjmij i włóż z powrotem akumulator.

Try removing and reinserting the battery. Sometimes the R needs a soft reset to fully recognize older lenses. This assumes the pins in lens mount of your 70-300mm are clean btw.

In some instances I would remove and re-attach the lens from the adapter to body, as opposed to just re-mounting the lens on the adapter.
Źródło: https://www.dpreview.com/forums/post/62282617