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04-02-2012, 10:24 AM   #1
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Manual focus difficulty

So I'm out yesterday evening about 45 minutes before sunset to take a coupleof shots with my K20 to stitch together for a panorama. I'm on a hillside looking over a lake with the opposite side of the valley probably 3 miles away. The setting sun is out of the frame, but very bright, so I have the aperture at f22.

On the lens I turn the focusing ring to 10 feet, thinking that the DOF will take me to infinity, and put the opposite side of the valley in focus. I press the shutter half way thinking that the camera will focus, allowing me to take the shot. Of course this didn't happen and I had to resort to catch in focus for the shutter to finally shoot. Needless to say, the results weren't great.

Being that I was on a hillside, there was nothing in the frame that was within 100 yards of the focusing point in the viewfinder. Was this why I had so much trouble focusing or is there something else at work?

04-02-2012, 10:26 AM - 1 Like   #2
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I'm not sure about the K20D, but my k-x will let me shoot regardless whether my shot is in focus or not, as long as I have the AF switch to manual.
04-02-2012, 10:37 AM   #3
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As posted above you need to switch focusing mode to manual
04-02-2012, 10:41 AM   #4
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Where's the face palm emoticon? Given that I removed the kit lens before heading out, that's got to be it. Thanks for the quick response.

04-02-2012, 10:56 AM   #5
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In the menu (the K20 will be slightly different to the K7/K5s I use) there is a shutter priority or focus priority switch. If your camera is set to FP then the shutter won't fire unless it is in focus. You don't need to change that for your landscape but I fail to see the issue based on the assumption below.

Assuming you are using a 28mm MF lens (for this example there is virtually no important difference no matter if the lens is 16mm or 50mm) and you are set at f22 then Hyperfocal distance is under 2m ... so if you are focused at 2m or over then everything into infinity should be in focus too.
04-02-2012, 11:44 AM - 1 Like   #6
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Hyperfocus is a subset of zone-focus. If a focus zone extends to infinity, it's hyperfocus. Zone focus is tricky with modern lenses lacking aperture rings and DOF scales -- computation or a data table are needed to get the focus zone right. It's much easier with older FF lenses, but a tweak is needed; DOF is off by about 1 f-stop.

So if I want DOF within a non-infinity zone, I'll do this: set the lens to maybe f/11, put the far end of the zone at the f/8 mark (that's the 1-f-stop adjustment) and read the near distance from the other f/8 mark. I'll expect that the actual acceptably-sharp DOF zone is just inside those distances.

And if I want hyperfocus, I'll adjust by about 1.3 f-stops, because I want to ensure that infinity is indeed in focus. So with the lens at f/11 I'd set the infinity mark slightly inside the f/8 mark, like to around f/7 or so. And I'd read the near distance as about 1/3 f-stop above the other f/8 mark.
_________________________

Autofocus and focus confirmation / CIF with 'scapes is even trickier, needing a target sufficiently lit and contrasty in order to work. AF-CF-CIF just can't zero-in on clear skies, bland clouds, other blank targets. A bland infinity ensures focus-seeking and frustration. I have enough of that in my life.

But manually setting focus to infinity with the aperture wide-open is problematic too -- some lenses don't stop at infinity! If infinity is important for a shot, stop-down a bit and focus like a paranoiac. Allow some leeway. If using DOF scales, adjust by two f-stops, just to be safe. This works for me.
04-02-2012, 12:16 PM   #7
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More like a tip.
You can remove the AF from the half shutter button press, that way you can always press the shutter button fully to make a shot.
You need to use the AF button on the back side to autofocus.
04-02-2012, 01:38 PM   #8
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Note that if you are in AF-S the shutter will not trip unless there is focus confrimation

use either MF (Best) or If using MF lens, USE AF-C as these modes let the shutter trip regardless of focus confirmation

04-02-2012, 07:37 PM   #9
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AF-C mode also wait for shutter confirmation.
04-02-2012, 08:11 PM   #10
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QuoteOriginally posted by Anvh Quote
AF-C mode also wait for shutter confirmation.
Not quite. My K20D manual says:

QuoteQuote:
AF.C -- Continuous mode -- The subject is kept in focus by continuous adjustment while the shutter release button is pressed halfway. Even if the subject is not in focus, the shutter can be released when the shutter button is pressed fully.
04-03-2012, 09:18 AM   #11
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I had the K5 in mind, that one has two kind of AF-C modes... ^^;
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