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Old Oct 4, 2005, 12:54 PM   #11
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When you see someone mention backfocus, it's when what you're focusing on (selected focus point) is out of focus, and what's in back of it is in focus, hence the term backfocus.

In other words, the camera is focusing behind your intended subject.

This is more noticeable when you're "filling the frame" with a smaller subject (by using a closer focus distance or longer focal length),using larger apertures (smaller f/stop numbers), where Depth of Field is shallower.


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Old Oct 4, 2005, 7:34 PM   #12
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I also noticed that the 7D photos were not as sharp as the Rebel. However, when I tweaked the sharpness settings on the 7D, I was able to get photos as good or better than the Rebel.
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Old Oct 4, 2005, 8:04 PM   #13
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Thanks for the reply Jim C. If that's the case, my 7D "back-focuses" alot!! But I never thought anything of it. I usually press the "central focus" button on the 4-way, and recompose the shot. If the image I want to focus on is really small, I have to use manual focus for best results. Can't say if my Canon Digital Rebel is this way, because I use the Minolta far greater.:-)

It sounds like one of those things that's not so noticeable until someone points it out, and then you start to notice it all the time. :sad:



I can see where it would be a problem when shooting quickly is a need. I will pay more attention to see if mine is constantly back focusing or not.



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Old Oct 4, 2005, 8:31 PM   #14
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1958fury wrote:
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Thanks for the reply Jim C. If that's the case, my 7D "back-focuses" alot!!
Not necessarily. It could be that you're missing your subject, or you think it's backfocusing because the lens is sharper in one area compared to another.

But, if you notice some backfocusing in a consistent way, it's a good idea to check it out using a tripod and test targets (so you can see if it's focusing on your subject, or in front or behind it). I'd probably make sure to try more than one lens on it, too.

It's my understanding based on user reports of phone correspondencewith KM, that theyuse a 50mm f/1.7 to calibrate them, using some pretty sophisticated techniques (patterns generated that each AF sensor picks up, with software "talking" to the camera showing a numerical indication of where the adjustments are correct for each screw,so that they know when they've got it "just right").

You mayjust want to send it in to KM with a note that you think it's backfocusing, and let them calibrate it. Even though I'm mentioning a way that some users have found to do it themselves, the better way to approach it would be to let KM do it. For one thing, they're probably very good at it by now, and theyhave the expertise and equpment to do it very accurately.

Also, you wouldn't need to worry about any potential warranty problems, should they decide that you're abusing your equipment in some manner by doing it yourself (and there is always a possibility that you'd damage it in some manner, too).

Personally, I'd probably do it myself. But, then again, I do the same thing with a little Konica pocket camera I've got. I've used hidden service menus to change things, including AF calibration with it. ;-)


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