RF800mm/f11 and size of AF-area on EOS R3/R5/R6/R7/R10

RDM5546 wrote:

Stig Nygaard wrote:

drsnoopy wrote:

Several of the YouTube reviews of the R7 have shown that the AF area is proportionately bigger on the crop sensor when using the RF 600 & 800 f11 lenses.

Isn't that also what I'm writing for the R7/R10 vs. R5/R6? (You might be answering an earlier version of my post before I edited it)

But how does one explain the 80% x 80% coverage on the EOS R3. Some other factor than sensor size must be involved too (in general)?

It is not the sensor size per se but the individual sensor design that matter. The R3 uses a stacked CMOS image sensor design using a radically different technology than the R5 or R6.

I think it's a geometric thing, a combined effect of the angles of the light from the opposite side of the lens, the relative sizes of the microlenses and the photocells and the distance of the microlenses in front of the cells. I'd expect the patches over which the DPAF works properly would be very roughly similar absolute sizes for the front illuminated sensors (which makes it a bigger proportion of the cropped sensors) and noticeably larger for the back illuminated stacked sensor in the Eos R3.

Stig Nygaard wrote:

The 600mm/11 and 800mm/11 both has an restricted AF area on the cameras we know.

Using these lenses on the R5 and R6 gives you an AF area covering 40% x 60% (width x height). I have always guessed that was caused by a combination of lens aperture (f11) and sensor size, and would expect that area to be scaled proportionally in both directions when used on a smaller APS-C sensor. I haven't done the exact math (and I think the Canon number are approximately anyway), but it seems to be somehow in line with that, when looking at AF area for EOS R7/R10 on https://cam.start.canon/en/H001/supplement_0110.html :

R5/R6: 40% x 60%
R7/R10: 60% x 80%

But to my surprise, the same table also show for EOS R3:

R3 : 80% x 80%

I'm confused. Apparently the size of AF area are not related to the size of sensor after all (or more factors than I thought are involved here) ?

PS. Notice that I have swapped width and height compared to the way Canon is showing it. Canon's way was confusing me (even more).

There is clearly no consistent correlation, better than body price. It can't be pixel density, because the R5 and R6 are the same. It can't be millimeters from the center of the frame, because the R3 goes way farther from the center than R7 and R10.

Therefore, and considering other decisions, I would guess that this is just a cripple to protect the sales of other lenses which have a higher markup.

drsnoopy wrote:

Several of the YouTube reviews of the R7 have shown that the AF area is proportionately bigger on the crop sensor when using the RF 600 & 800 f11 lenses. I suggest you search the video reviews for a demonstration of the difference.

If you set crop mode on an R5/6 you get the same effect.

While that is true in the viewfinder and regarding the output frame, the actual area in mm x mm on the sensor is still smaller, and therefore the angle of view with active AF can still be smaller with the smaller sensors and crop mode, if they do not make the box 1.6x as wide and tall inside the viewfinder.

Stig Nygaard wrote:

drsnoopy wrote:

Several of the YouTube reviews of the R7 have shown that the AF area is proportionately bigger on the crop sensor when using the RF 600 & 800 f11 lenses.

Isn't that also what I'm writing for the R7/R10 vs. R5/R6? (You might be answering an earlier version of my post before I edited it)

But how does one explain the 80% x 80% coverage on the EOS R3. Some other factor than sensor size must be involved too (in general)?

The highest-price body buys you less lens cripple, perhaps?

RDM5546 wrote:

Stig Nygaard wrote:

drsnoopy wrote:

Several of the YouTube reviews of the R7 have shown that the AF area is proportionately bigger on the crop sensor when using the RF 600 & 800 f11 lenses.

Isn't that also what I'm writing for the R7/R10 vs. R5/R6? (You might be answering an earlier version of my post before I edited it)

But how does one explain the 80% x 80% coverage on the EOS R3. Some other factor than sensor size must be involved too (in general)?

It is not the sensor size per se but the individual sensor design that matter. The R3 uses a stacked CMOS image sensor design using a radically different technology than the R5 or R6.

Maybe, but don't forget, if you take a lens that allows full sensor AF and put lots of non-reporting TC magnification behind it, it still focuses well in the corners, so I lean towards "less cripple for the R3".