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04-26-2014, 05:56 PM   #1
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Help with off center manual focusing.

I recently received my first manual focus-only lens (24mm sigma super wide)

I wanted to take an off center focused picture of my girlfriend.

The problem is that I would try the focus and recompose method (I use a katz-eye focusing aid with the splitprism in the middle) but it seems that due to the wide aperture setting once I adjust my composition my subject is already out of focus.

I assume this is due to the difference in distance between where my subject is when focused at the middle of the focusing screen versus when off centered.

Any ideas how to work around this?

04-26-2014, 06:02 PM   #2
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Instead of tilting the camera for the composition, move parallell with the focus plane. Still that's hard to do accuratelly but you won't shift the plane of focus.
04-26-2014, 06:33 PM   #3
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You might want to try the matte field. That is the area between the scribed circle and the microprism. You won't have the benefit of the split image, but my experience has been that things "snap" into focus very nicely using that part of the screen. The distance to recompose should be somewhat less. Still though, the DOF of your Sigma, even wide open, should be pretty generous. Are you sure the issue is missed focus?

Steve
04-26-2014, 07:09 PM   #4
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I wish there is a simpler way to do it too... I do that now with AF.C (release priority) so I can still trip the shutter even if it is not in focus according to the camera. I know I only move it slightly knowing that the DOF is not so thin.

04-26-2014, 07:13 PM   #5
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QuoteOriginally posted by stevebrot Quote
You might want to try the matte field. That is the area between the scribed circle and the microprism. You won't have the benefit of the split image, but my experience has been that things "snap" into focus very nicely using that part of the screen. The distance to recompose should be somewhat less. Still though, the DOF of your Sigma, even wide open, should be pretty generous. Are you sure the issue is missed focus?

Steve
Hmmm I'll try to post a picture when I get home.

I do know that my subject is relatively small, so maybe there is a chance that when I thought I was in focus with the split prism it actually wasn't?

I tried the matte area but what ended happening was that it wouldn't 'focus' anymore (if that makes sense) basically I twisted the throw all the way but it was just 'almost' in focus but never truly there
04-26-2014, 07:40 PM   #6
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Hey, welcome!
A couple of things to keep in mind. The in-focus area, the Depth of Field, is affected by aperture and distance from subject and the lens focal length. It is roughly parallel to the sensor. So focus and recompose means you need to move the camera parallel. If you have it on a tripod and you only rotate it, the focus area will shift dramatically. You need to "shift" or slide the camera. So you focus, and when you recompose you merely make a step to the left or to the right. If you turn your shoulders you will need to re-focus.
Secondly, the in-focus area is not perfectly flat and parallel. Usually it is different in the centre than it is on the edges (i think this is named Field curvature). This means that recomposing might not work when you are shifting between centre and extreme edge. An exception to this might be macro lenses, they tend to have a very flat field.
Anyway, to fix this, you can use the DoF preview feature or even the Digital preview. Check the manual, you might have to reprogram the green button to do this (Button Customization in Menu). This can help you see what the final photo will look like. Another thing you can try is live view with Focus peaking and Digital zoom. Once you have the digital zoom, just zoom in to 6x and move the little "preview box" to the side where the subject is. In Live view, you can even use AF in places where you don't have any AF points.

Oh, and finally, some lenses have better border/edge performance than others. My Industar 50-2 will never be sharp in the corner, no matter what aperture and focus I select! Macro lenses are again among the best performers in this regard. Not sure about your 24mm, never had it.

Last edited by Na Horuk; 04-26-2014 at 07:46 PM.
04-26-2014, 08:45 PM   #7
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What I like to do is focus a little short, put your camera in high speed drive, and fire away while moving the focus. One show out of 10 will be in focus, which is enough for a keeper. Electrons are almost free, so the wasted shots are not a problem.
04-26-2014, 09:35 PM   #8
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QuoteOriginally posted by ravenorxs Quote
Hmmm I'll try to post a picture when I get home.

I do know that my subject is relatively small, so maybe there is a chance that when I thought I was in focus with the split prism it actually wasn't?
You should make sure your diopter is perfectly adjusted. The numbers in the viewfinder should be as sharp as possible.

Then, your focus screen may need to be shimmed. If the focusing screen surface is not exactly the right distance from the viewfinder or the lens, what you see is not what you get in the photo. I like to set the camera up so it's at an angle to text on a page, manually focus on a line in the middle, remember that line and take a photo. Then see if the image shows the same line in focus. I use a tripod and 2 second delay, lens wide open. With the 24mm lens, the text will be pretty small and the depth of field large. It works a lot better with a fast 50mm or longer. My camera needed a shim about half as thick as the installed one.

QuoteQuote:
I tried the matte area but what ended happening was that it wouldn't 'focus' anymore (if that makes sense) basically I twisted the throw all the way but it was just 'almost' in focus but never truly there
Maybe you were trying to focus closer than the minimum distance, 0.18m? I just put my Superwide II on my Katz-Eye equipped K-7 and the matte field works fine for me. That lens should be reasonably sharp across the field. I don't know how curved the field is, I'd expect some.

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