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Canon 800mm F11 lens


I am new to the forum and have what I believe to be a odd question.  This might have belong in lenses.


I purchased a Canon R6 and 800mm f11 lens in Jan and for my purposes it was doing great.  I recently added the 15-35mm RF and 100-500 Rf lens.  I shoot mostly wildlife and landscape though now getting into astro.  This is not my first canon cameras or lenses.


But after getting the new lenses, I noticed something odd when using my 800 lens.  There is a big white box in the middle of the screen that my focus point can not go out of.  My other two RF lenses do not have this.  Is this normal and I'm just now noticing this.


Anyone with a 800mm f11 see this?


I use back button focusing with animal eye detection.





The auto focus area is limited because the RF 800 f11 aperture.  "Faster" (wider aperture) lenses have a greater area where auto focus is functional.


The RF 800 puts a lot of focal length into a compact and fairly inexpensive package but the tradeoff is a narrower maximum aperture. 


I often shoot wildlife with an EF 800 f5.6 which is comfortably hand holdable for only very short periods of time. Besides purchase price, cost of the wider maximum aperture 800mm is a lens that is 2 feet long and weighs just over 10 pounds with its carbon fiber lens hood mounted. 



EOS 1DX M3, 1DX M2, 1DX, 5DS R, 1D M2, EOS 650 (film), many lenses, XF400 video


The f/11 maximum aperture means only about the center 3/4"sq. section of the lens will have autofocus. You do lose two stops over the big brother ef 800mm f5.6L. Plus, as I understand it, you only have f11.  It doesn't have the ability to stop down any further. It also lost about 9 pounds, too!  Big plus it is over ten grand cheaper! And, it takes comparable photos for that price.

So, you have pluses and minuses.


I am not interested in mirrorless currently but I must say there are some fairly interesting lenses for them.

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