RF 100-500mm F4.5-7.1 L IS USM, Auto Focus focuses too close

[carl_schnurr]

I just returned from a great week in the rainforests of the OSA peninsula in Costa Rica.
I took a lot of photos of birds and monkeys high up in the trees.
I had difficulty as the the AF seemed focus very close.  I had to manually focus farther out before I could get the AF to zero in on my subject.  Alternatively I could find something close to focus on and gradually raise the camera so the subject gets progressively farther away, until I was pointing at the subject.
This issue eliminated any Bird in Flight photos for the entire trip.

Here is my set up.

• R6 Mark ii
• Manual Mode, Auto ISO, with max set to 6400, typically wide open aperture.
• AF set to Animal Eye detect, Case1.
• RF 100-500L lens, with buttons set to 3m to infinity, AF ON, Stabilizer ON, Stabilizer Mode 1.

I tried varying the following camera settings but didn't notice any difference

• ONE SHOT and SERVO AF
• Different AF area shapes
• Whole Area tracking Servo AF ON/OFF
• Back Button Focus ON/OFF

Here a couple things that were different.

• Before leaving I thoroughly cleaned the front and back lens elements, both sides of my UV filter and the electrical contacts on the lens and camera
• The heat and humidity were fairly high, the first time shooting there was a build up of condensation on the back lens surface which evaporated immediately when I removed the lens for a minute.
• This is my first time using a USB charger for the camera batteries, and they appeared to fully charge as desired.

I also took a RF24-70 f2.8 lens which did not show any of these problems.

Since returning I have been trying to trouble shoot this issue.
I set lens to 500mm, f7.1, with camera touchscreen closed to avoid any errant touch screen focusing.
I tried several ISO/Av combinations with the same results.

With camera set to ONE SHOT, I am able to turn the focus guides ON; and they become visible when I manually adjust the focus ring.  When I have the lens focused on an object far away and then aim the AF point an object 7m away from the camera, it cannot achieve auto focus, and the focus guides are grey until I manually focus to get close to the subject being in focus.  Similarly when focused on object 7m away, and then aim the AF point at an object 4m away, it cannot achieve autofocus; and the focus guides are grey until I manually focus to get close to the subject being in focus.

Camera set to SERVO AF, focus guides are not visible, (should they be?)
Essentially the same result, except instead of focus guides being grey, the focus point is coloured Red, until I manually focus to get close to the subject being in focus and it turns Blue.

The lens needs to be fairly accurately dialed into the correct focus distance for the AF to kick in.  Do you recommend getting it repaired, or is there something else I can try?

[Waddizzle]

When I purchased the EF 70-200mm f/2.8L II USM, the images were a little soft. I didn’t have a Clear filter on hand. So I used the UV filter I had laying around.  Once I swapped out the UV for a Clear filter, the images were tack sharp.

I repeated the same mistake with the EF 100-400mm f/4.5-5.6L II USM.  I had forgotten to order a filter. Same result.

I have no experience with the RF telephoto zooms and filters, yet.  But the EF lenses didn’t like the filters.  I suspect the filters and some of the internal elements didn’t work well together. No lens damage.  Just photos that weren’t tack sharp.