Tom Reichner wrote in post #18729455..
Yes, Mike, the focus-related effects of those faults do
simply disappear when the lens is put on a mirrorless body, because the focusing is done on the sensor itself, thereby automatically accounting for and correcting all of the focus-related "faults" that may lie between the subject and the sensor.
People in this thread keep explaining this to you over and over again, yet you seem to be impervious to understanding it. .
It's like, somehow, your brain just isn't grabbing ahold of the concept of focusing being done on the sensor, and all of the implications that go along with that..
I apologize if you find my questions to be frustrating, Tom. Feel free to pull up my profile and hit the "Ignore" link at any time.
I get that in a DSLR, the AF sensor and the image sensor are physically different components in different places. The camera manufacturers do their best to equalize the optical path distances to both of these, but tolerances are extremely tight to achieve critical focus. AFMA is provided to allow that difference to be fine-tuned by the end user in order to account for mechanical tolerances and other factors.
That much I get, and I believe I have now stated that at least three times in the past 24 hours.
The "concept" which my brain "just isn't grabbing ahold of" is that this explanation involves elements which are entirely within the camera body, so I don't understand how the lens affects this. If the two optical paths in the camera body are mismatched, wouldn't they have the same mismatch regardless of which lens was on the camera? So why do I have to set different AFMA values for each lens?
Obviously, the lens does affect the optical path length difference between the two sensors, otherwise Canon wouldn't provide AFMA settings for different lenses or different focal lengths. (or maybe it's a marketing gimmick that we've all swallowed hook, line, and sinker).
A mirrorless camera only has one optical path, and the image sensor is the AF sensor, so when it sees focus, it's in focus. I get that. My real question is how does the lens affect the differential optical path length difference within the body of a DSLR, making it require different AFMA settings for different lenses?
I admit that I may not have asked the question clearly. It's less about why mirrorless cameras don't need AFMA (which I understand), and more about why DSLRs need AFMA values for every lens and even for the wide/long ends of the same lens. And please don't answer by saying that the AF and image sensors are in different places. I understand that (that's four, BTW). Explain how the lens construction and focal length affects the path length difference within the camera body.