Focusing Issues

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Gene
Posts: 1508
Joined: Fri Mar 14, 2008 11:58 am
Location: Buda, TX

Focusing Issues

Post by Gene »

I started taking a very critical look at my recent work from my Nikon D90. I noticed that in some conditions my shots were a bit "soft", and in a couple of lower light cases they were just plain out of focus.

I reset my cameras focus setting - changing the focus point to locked in the center - reasoning that if that was my main subject (as it would be most of the time) then I would force the sensor to concentrate its focusing powers there.

But - in situations where there was not a lot of depth-of-field support (cloudy, indoor, etc.) the focus was still off a bit. Oh - I don't mean when I reviewed them on the camera screen - those appear to be optimized for showing your work in its best possible way. I mean when viewed on a monitor while post processing.

So - I started researching back focus complaints about my camera. There were a few for sure. many of the later Nikon's allow for micro adjustment of the focus system in camera firmware. Pretty nice, and you can get dead on with each lens you use. The D90 is a bit older, so no firmware adjustments are available, but there is a manual adjustment - but I don't want to stick a tiny Allen wrench anywhere near my sensor or mirror - I'll gladly let an expert do it.

So - I checked my local Big Box camera store - in Austin that's Precision Camera. They charge $29.00 to micro adjust your camera - what a bargain. They took a couple of shots that look fantastic on the camera screen - until you blow them up. Then the back focus issue comes into clear view (bad pun). Here is a shot of their focus board:

Focus 1.jpg
Focus 1.jpg (195.53 KiB) Viewed 1243 times
This is a crop of the original - centered on the focusing jig. The main focus point for the shot is the zero mark - and focus, I guess, should be crisp at zero and equidistant up and down the line.

When I re-crop to enlarge just the scale we see this:

Focus 2.JPG
Focus 2.JPG (234.94 KiB) Viewed 1243 times
Clearly this shot shows the image as favored more to the back - the reference point marked 8 is in focus behind the zero mark, but not in the front. In fact - the small 16 at the rear is still sharp and clearly not focused in front.

Apparently front/back focusing issues can be found in many cameras. If you think your shots look too soft you might want to check it out.

BTW - I get the camera back tomorrow, just in time to fly to Portland, OR, to watch my daughter graduate Chiropractic School. I get to ask her "What's up Doc?" with a straight face, now!
Gene

"It could probably be shown by facts and figures that there is no distinctly American criminal class except Congress."
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"People shouldn't be afraid of their government. Governments should be afraid of their people."
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drmoss_ca
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Re: Focusing Issues

Post by drmoss_ca »

There's also an issue with focus-shift with some lenses - they focus correctly wide open then shift the plane of focus when you stop down. The last generation of Leica Summilux 35mm ASPH was affected, not enough to show on a film camera, but would show up on a digital Leica with a thinner sensor layer than the emulsion of a film. That was the reason for the current floating element version of the Lux 35.

Chris
PS Congratulations on your daughter!
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jww
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Joined: Sat Mar 11, 2006 10:49 am
Location: Ottawa, Canada

Re: Focusing Issues

Post by jww »

This thread reminds me that I am way overdue in getting out locally to take some snaps of winter in Ottawa .... cruddy lighting today, so there is no way that's happening. We have our oldest granddaughter this weekend for the season's first sledding runs, so I expect my wife with be Instagram-ming like mad throughout the day ..... :wink:
Wendell

Resident Wool Fat Evangelist & anglophile. Have you hugged a sheep today?
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