03-05-2013, 07:59 AM
Quote:however i don't see why Canon can't put in compensation no matter which mode (Tv, Av) the camera is in, if the camera and therefore lens knows what the correct exposure is, it can then put the comp in for the aperture, no? ... but to do this the manufacturer would have to admit that my lens has a problem...Wow, the overhauled forum software is not without its bugs... Took me 6 tries to get this part quote correctly (well, I have not posted it yet, so it might still be wrong.. and then I can't edit the post anymore...).
soLong, in theory you can only compensate for a focus shift when the aperture is known,/"set" at the same time the AF takes place. When you separate the AF and metering in Tv or M it will not work.
There are many situations where that occurs. When you have it in Tv, and focus on the subject, then recompose, and do not hold the metering, the f-value used can change. When you separate the AF from the metering (not both with the shutter button) the f-value used for the final image will always be unknown at AF time.
Also, it is unknown which (the lens, or the camera body?) has to take care of the focus shift compensation. If it is the body, only the newer bodies will know what a new lens needs.
How bad is the focus shift in "normal" use? And how bad is the focus shift in macro use? And does it occur over the entire focal range?