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Author Topic: H4D-40: Sample files  (Read 25789 times)

BJL

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H4D-40: Sample files
« Reply #140 on: April 08, 2010, 09:23:23 AM »

Quote from: John R Smith
All of this is completely true, and always was true with film as well. Depth of Field scales were worked out on the basis of an acceptable "circle of confusion" IIRC, which was fine in the 1930s when they were defined with the films of the day and relatively small-size standard prints.
Indeed, I believe that the standard criterion used for almost all DOF scales on lenses and traditional DOF chart is something like what will not be noticeably out of focus to reasonably sharp eyes when
- printed at 7"x5"
- viewed from 10", which is about the diagonal length of the print.

Since what counts most is the ratio between viewing distance and image size, or to get fancy the angular size of the image, I would summarize this as saying that:
traditional DOF guidelines try to ensure that everything within the stated range of distances will probably appear in focus to most viewers so long as they view from a distance at least as great as the diagonal length of the uncropped (or minimally cropped) image.

Problems arise when images are viewing more closely that that, whether it be close scrutiny of large prints, or by viewing only a crop from the full image size for which the DOF guidelines are computed. The latter happens big time when a small fraction of the image is enlarged to fill a computer's display, or the camera's rear screen. It also happens to a smaller degree with the "sensor crop" of DMF sensors smaller than the film format on which the DOF scale is based, and the related higher enlargement factor needed to get a given size of print.
« Last Edit: April 08, 2010, 09:25:37 AM by BJL »
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Dick Roadnight

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H4D-40: Sample files
« Reply #141 on: April 08, 2010, 02:10:33 PM »

Quote from: John R Smith
* The thickness of the emulsion and the backing layer produces a degree of halation which means that film is never as sharp as a digital sensor (comparing like for like, same lens and sensor/film area).

However, saying as above that there is only one point in the frame which is actually going to be truly in focus,

John
They used to like to imagine that the three colours got focused on the three colour layers in the emulsion.

There is one plane of sharpest focus, so, with a co-planar subject, you can have it all in focus, and, with a view camera, it is supposedly possible to get three points in perfect focus.
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Hasselblad H4, Sinar P3 monorail view camera, Schneider Apo-digitar lenses
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