Focusing on Red subjects

Started 1 month ago | Questions thread
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John Mason
John Mason Veteran Member • Posts: 6,114
Focusing on Red subjects

I have an A7r4.  I'm not able to focus with the 200-600 or 100-400gm on red subjects like a red flower or a red cardinal.  I can go grab my Em1x and 300mm F4 and it'll snap right into focus on the same subject.

Anyone notice this themselves?  Does the A1 have the same issue?

Here's the flower in question. I could move the Sony to point to a similarly distanced blue or white flower and it'd snap into focus.  Also, the pinkish flower snaps into focus too.  
In bird shooting the duller female cardinals are not problem while the bright red male ones won't focus at all.

I'm using tracking starting with the center.
Here are some context shots:

Here's the flower bed I was shooting

Note, that this redish but with white flower snapped into focus just fine as well as the other colors.

But this one would not, just like the problems I have with shooting the bright red male cardinals - females are fine.  I grabbed my Olympus kit to get this picture.

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John Mason - Battle Ground, Indiana USA

 John Mason's gear list:John Mason's gear list
Olympus PEN-F Olympus E-M1 II Olympus OM-D E-M1X Sony a7R IV Olympus Zuiko Digital 1.4x Teleconverter EC-14 +14 more
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Sony a1
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