Bryan at TDP has test charts up for the 200-800. IQ is very similar to the 800 f/11 but 2/3 of a stop faster. You can pick at the charts and say maybe the center contrast is a bit lower and the peripheral acuity is a bit better, but given that we are looking at single samples, the differences are well within typical sample variation (and Roger is not going to test 800mm lenses ). The good news is that the lens is consistently sharp throughout the zoom range, only falling off a bit at 800mm.
Canon RF 800mm F11 IS STM Lens Image Quality
View the image quality delivered by the Canon RF 800mm F11 IS STM Lens using ISO 12233 Resolution Chart lab test results. Compare the image quality of this lens with other lenses.
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