Barry Green på dvxuser.com skrev:DOF (depth of field) myths
Myth 1: "imaging size affects DOF, larger imagers = shallower DOF". *False.*
The imaging size has nothing to do with the depth of field. *The imager size (whether larger like 35mm film, 16mm film or 2/3" CCD's, or small like 1/6" CCD's) affects the FIELD OF VIEW, but not the DEPTH OF FIELD. *And larger imagers require longer lenses to deliver usable fields of view. *Smaller imagers require shorter lenses. *A 35mm camera uses 25-250mm for a zoom, a 1/6" CCD camera might use 2.5-25mm. *So the 35mm camera gets its shallower DOF from its longer lenses, not from its imager size.
Myth 2: "focal length is irrelevant in DOF.
*To use telephoto, you have to back up (which increases DOF). *To get close, you have to use wide-angle (which increases DOF). *They cancel each other out." *No they don't. *I mean, yes, technically they do, but just try it, look at your shots and you'll see, the telephoto shot clearly, clearly looks like the background is more out of focus. *Whether it's technically as "in-focus" or not is irrelevant, the telephoto lens delivers the optical illusion that the background is more out of focus, and that's what we want: the APPEARANCE that the background is out of focus. For comparison, reference these shots:
http://www.icexpo.com/dvx100/DOF-Test2Wide.jpg
http://www.icexpo.com/dvx100/DOF-Test2Tele.jpg
Both were shot at identical aperture (f/2.8 ) and in the wide shot, I moved as close as possible and focused as close as possible to minimize DOF. On the Tele shot I zoomed in as far as possible, then got as close as I could (while maintaining the same image size). I think most viewers will agree that the tele shot, while maintaining the same aperture and the same image size, looks like it has much shallower DOF.
Barry Green skrev:The imaging size has nothing to do with the depth of field. *The imager size (whether larger like 35mm film, 16mm film or 2/3" CCD's, or small like 1/6" CCD's) affects the FIELD OF VIEW, but not the DEPTH OF FIELD. *And larger imagers require longer lenses to deliver usable fields of view. *Smaller imagers require shorter lenses. *A 35mm camera uses 25-250mm for a zoom, a 1/6" CCD camera might use 2.5-25mm. *So the 35mm camera gets its shallower DOF from its longer lenses, not from its imager size.
Gisle Hannemyr skrev:The measure for DOF most people are interested in when moving between equipment with different sensor sizes, is the shift in DOF that happens at identical FOV. As explained in the FOV-section, to maintain FOV we need to change the focal length by the amout indicated by the crop factor.
[...]
The reason digital compacts has large DOFs is not because a smaller sensor gives a larger DOF, but because the very short focal lengths of the lenses these compact cameras are equipped with, gives you a large DOF.
carlk på dpreview.com skrev:All theory this and theory that just make people more confused. Here is a very simple and straightforward way to understand it:
The ONLY difference between full frame and crop is the FOV (field of view). Essentially you got the center 60% of image on the crop sensor and that is it. Everything else, aperture, FL, DOF... are exactly the same when using either systems.
However to make up for the lost FOV you need to move 1.6X away from the object or use an 1.6x wider lens on a crop camera thus resulted in an increased DOF.
Nikon skrev:The rectangular geometry and common dimensions of CCDs result from their early competition with vidicon tube cameras, which required the solid-state sensors to produce an electronic signal output that conformed to the prevailing video standards at the time. Note that the "inch" designations do not correspond directly to any of the CCD dimensions, but represent the size of the rectangular area scanned in the corresponding round vidicon tube. A designated "1-inch" CCD has a diagonal of 16 millimeters and sensor dimensions of 9.6 x 12.8 millimeters, derived from the scanned area of a 1-inch vidicon tube with a 25.4-millimeter outside diameter and an input window approximately 18 millimeters in diameter. Unfortunately, this confusing nomenclature has persisted, often used in reference to CCD "type" rather than size, and even includes sensors classified by a combination of fractional and decimal terms, such as the widely used 1/1.8-inch CCD that is intermediate in size between 1/2-inch and 2/3-inch devices.
It doesn't matter that the digital device is CMOS or CCD and that it does not have any glass tube around it, the makers still insist on using the archaic and misleading glass tube diameter measurement of that old Vidicon tube. Bizarre.
Registrerte brukere: Google [Bot]