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12-17-2011, 01:35 PM   #1
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Tweaking the screen

Hey all.

After noticing some of my shots were out of focus, I checked the calibration on my KatzEye screen in my K-x & found it was front-focusing. No problem, as I have a set of shims, so I went to work calibrating it.

There's a shim in there now that I thickened up with a layer of scotch tape around the perimeter on one side. Before I added the tape, it was backfocusing 1/4 to 1/2 inch. Now it's anywhere from dead on to 1/8" backfocusing, and even a couple that were front focused 1/16" an inch. After taking a variety of shots with every lens I own wide open at all focal lengths and a variety of distances from macro to infinity, there still seems to be a very slight preference toward back-focusing. (9 out of 45 shots were about 1/8" backfocused)

When all of the shots were taken, the focus confirmation beep sounded at the point the image showed in focus in the viewfinder.

Is it reasonable to expect every single shot to be absolutely dead-on focus, or is there normally a small margin of error?

One thing I've noticed with the KatzEye screen, it doesn't "snap" into focus the way my Chinese screen does on my K100D. It's more of a PITA to focus the Chinese screen with a slow lens (like my f8 mirror lens) but once it's lined up, the shots are pretty much on the button. With the KatzEye it's a little tougher to tell when you have it absolutely nailed, IMO.

What do you guys think?

Cheers,
Bobbo :-)

12-17-2011, 03:05 PM   #2
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QuoteOriginally posted by GibbyTheMole Quote
When all of the shots were taken, the focus confirmation beep sounded at the point the image showed in focus in the viewfinder.

Is it reasonable to expect every single shot to be absolutely dead-on focus, or is there normally a small margin of error?
There is and will always be a margin of error when relying on the AF mechanism to tell you when you have focus. That's independent of any screen you use, or any calibrating you do with it.

There will always be a margin of error when using our eyes and judgment, as well. Even with a great screen, there will be times where we think we've nailed it, and it just isn't so.

It sounds to me like you've done a good job minimizing those times with your screen choices and shimming work. That and practice are all anyone can do. From my own limited experience, all I can say is, it's a damn good thing I'm not using film.
12-17-2011, 03:56 PM   #3
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Yeah, I think I will call it a day. After I posted, Just couldn't leave well enough alone, and I thought if I just added one more layer of tape to the other side, maybe it would be dead on most all the time. That added layer of tape made 2/3rds of the photos front focused, so I removed it & I'm back to having 70 percent in dead-on focus at f1.4, with the remainder up to 1/8" off either way.

I took a handheld shot of our electric meter outside with my mirror lens at a distance of 100 feet & the smallest text on the meter face is nice & crisp.

In another shot, I can read the fine print nutritional information on a cereal box taken at 300mm at f3.8 ISO 3600 at 30 feet.

I've worked on it for about 9 hours total. I think I'm done. I need a beer or 9.

Cheers,
Bobbo :-)
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