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05-28-2016, 08:23 AM   #1
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is part of the reason?

I don't want to take up a subject that is already debated but here is a dumb question..
is part of the reason FF has a shallower depth of field is that you need to move closer to the subject as compared to crop sensor for the same field of view?

thanks

Randy

05-28-2016, 08:37 AM   #2
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The mechanics of DOF are a little complex. Basically, same lens, same distance same f-stop = same DOF. BUT, a "normal" lens in APS-C has a shorter FL than for FF. So from the same tripod position, exactly the same framing of an image, exactly the same f-stop, the APS-C image will have more DOF because it will be taken with a shorter FL, about 2/3 that of the FF. If you were using 50mm on the FF, the APS-C would be using about 33~34mm to achieve the same framing from the same tripod position, so you'd be getting DOF with the smaller sensor equivalent to using a WA at the same aperture with FF.
05-28-2016, 08:39 AM   #3
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Yes, because you are focussing closer your DOF narrows. When you keep the same distance your DOF will be the same, but your FOV bigger. So relative to the frame it will be narrower, but in cm/inches it will be the same.
05-28-2016, 11:50 AM   #4
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"For the same perspective, framing, f-ratio, and display size, larger sensor systems will yield a more shallow DOF than smaller sensors in proportion to the ratio of the sensor sizes.

For the same perspective, framing, aperture diameter, and display size, all systems have the same DOF.

If both formats use the same focal length and f-ratio (and thus also the same aperture diameter), but the larger sensor system gets closer so that the subject occupies the same area of the frame, and the photos are displayed at the same dimensions, then the larger sensor system will have a more shallow DOF in proportion to ratio of the sensor sizes.

For the same perspective and focal length, larger sensor systems will have a wider framing. If the same f-ratio is used, then both systems will also have the same aperture diameter. As a result, if the photo from the larger sensor system is displayed at a larger size in proportion to ratio of the sensor sizes, or the photo from the larger sensor system is cropped to the same framing as the image from the smaller sensor system and displayed at the same size, then the two photos will have the same DOF." Equivalence

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