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David Camera focus and sine waves setting

The place for questions, problems, comments and tips regarding the camera calibration.

David Camera focus and sine waves setting

Postby KNSCI » Wed Mar 19, 2014 12:52 pm

Hi Forum, newb here, didn't yet find a thread on this topic, there are many advanced users with alternative cameras it appears. I'm just using the stock camera.
2 questions:
1) when turning the focus ring and viewing the live view, there doesn't seem to be much difference in focus throughout the full range of rotation. Is that normal? is there a distance range?
2) When adjusting the aperture and observing the red histogram sine waves, the manual and wiki seem to say there should be no cutoff. So we are adjusting aperture for the highlights and letting shadowy areas go dark, is that right? we want no cutoff anywhere in any of the scanned area or some highlights can be cutoff to obtain shadow detail, or am I thinking too much in photographic terms?
Many Thanks and Alohas.
KNSCI
 
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Re: David Camera focus and sine waves setting

Postby Sven » Fri Mar 21, 2014 6:47 pm

Hi KNSCI,

1)
When the aperture is very small (=dark), the camera has a large depth of focus, that indeed means that the focus dial does not make much difference. Setting it is not critical. If you want a perfect focus setting:
1. Turn up the aperture so that you get a very bright image (maybe also turn down "Projector Brightness" in DAVID)
2. adjust focus
3. undo what you did in 1.

2)
You are right, setting the brightness is about compromise.
Regard the red curves only where there are sine waves. When some areas are too much cut-off, there will be waves in the scan. You can do that deliberately to see what happens and get a feeling for it.
There will always be some regions where the sine wave is low. That is not a problem, it can cause a little noise.
Only when it's VERY low, noise will become a problem.

Sven
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Sven
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Re: David Camera focus and sine waves setting

Postby KNSCI » Sat Mar 22, 2014 7:11 am

Hi Sven;
Thanks very much for the clarifications!
I've been a photographer for many decades and digital for quite a few years now so all that makes sense.
KNSCI
 
Posts: 52
Joined: Fri Feb 28, 2014 8:18 am


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