Autofocus problems are referred to as "front focus" or "back focus". It
simply means that, when the camera thinks it has achieved proper focus,
it's actually focused either in front of or behind the intended focus
point. For example, in making a portrait, you will focus on the eyes
but might discover that the best focus is actually on the ears. It may
focus that way consistently or it may vary with the lens. Sometimes,
correcting the problem may require calibration of camera and lens together.
I don't understand why it can vary with the lens but I have often
wondered whether "coasting time" is a problem. That is, when the focus
motor is commanded to stop moving it doesn't stop instantly but instead
maybe continues turning for another millisecond or two or three. That
would mean the camera has to anticipate the approach of best focus and
shut off the motor before best focus is actually achieved. This is
purely uninformed speculation on my part. I have no idea what really
causes focusing errors.
Chuck Norcutt
bj@xxxxxxxxxxxxxxx wrote:
> C.H.Ling wrote
>> Don't know about E-420 but the E-520 I just purchased is solid built,
>> image quality is on par with E-3 and focus is very fast. Unfortunately it
>> has front focus problem, quite consistent and serious especially at the
>> wide end. I backed to the shop and tried for another three, all have the
>> same problem. I'm planning to send the camera to Olympus for repair after
>> new year.
>
> CH, can you explain please what you mean by "front focus problem"? I
> don't really understand what you are saying (since all focus has to be in the
> front).
>
> Thanks, Brian Swale
>
> Brian Swale. Daytime phone 03 326 7447
> http://homepages.caverock.net.nz/~bj/
> Mobile 021 143 4249
> 3/7 Menzies Street, Sumner, Christchurch 8081
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