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Forum: Pentax K-1 & K-1 II
08-18-2016, 04:21 PM
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No need. I (and one other commentator) answered the OP's question early on. The DOF is the same in crop mode as with a crop sensor camera.
As for your photos, you made my point nicely. Thanks!
Steve
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Forum: Pentax K-1 & K-1 II
08-18-2016, 04:15 PM
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I hate to beat this dead horse any longer, but it may help to consider that the concept of DOF is defined in terms of the subject space in front of the camera lens and the final image as perceived by the person viewing. In the subject space we have the point/plane of focus as well as an infinite number of planes both near and far from that point. There is a corresponding range of focus points/planes at the nominal focal plane, but only one of those becomes part of the capture (important). What is perceived in the final image is a more sharp image of things at the plane of focus and progressively less sharp images of those in the planes to front and rear. The ability to differentiate more from less sharp is related to the distance from the viewer such that as distance from viewer to image increases average sharpness approaches infinity.
Steve
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Forum: Pentax K-1 & K-1 II
08-18-2016, 03:43 PM
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A link would be helpful.
Edit: it is my understanding that Northrup asserts (quite properly) that images must be normalized for crop when calculating DOF.
Steve
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Forum: Pentax K-1 & K-1 II
08-18-2016, 03:27 PM
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Only if there is the same discrepancy in the final image size or if you crop the FF image in PP to the APS-C pixel dimensions. The images are fully equivalent at this point. The converse is easy enough to demonstrate by down sampling the FF image to the same pixel dimensions. FOV is not a factor nor is "framing", but magnification is. Or coming from the other direction, both my avatar image and the photo below were from the same APS-C capture. Which has the greater DOF? (Hint: The only difference is the magnification.)
Steve
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Forum: Pentax K-1 & K-1 II
08-18-2016, 09:23 AM
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I will not comment regarding other comments on this thread except to say that statements on this topic are generally correct, but also sometimes misleading or incomplete. I answered your question in as direct and accurate manner possible. Crop mode is a simple crop of the 24x36 format and equivalent to the same capture using the same lens, subject, and camera position as if it were taken with an APS-C body. Ditto for a crop in post-processing. As for DOF, I will elaborate below.
By definition DOF is the range of planes of focus where an observer will perceive acceptable sharpness in an image. The long answer regarding factors for calculation and "equivalence" goes something like this: DOF depends on the visual acuity of the observer, the final magnification of the displayed image (by convention to an 8x10 print), the absolute aperture (not f-number)*, and the viewing distance.** Because of the difference in magnification to attain the final image size, DOF varies by format/crop, all other variables being controlled.
Steve
* Absolute aperture is the diameter of the lens entry pupil. Relative aperture (written as f/n) is the ratio of the lens focal length to the absolute aperture expressed as a fraction (e.g. f-stop, f-number, f-ratio).
** This is all related to the ability of the eye to perceive detail. The nominal resolution of human vision at the fovea is about 1 minute of arc (1/60th of a degree).
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Forum: Pentax K-1 & K-1 II
08-18-2016, 07:04 AM
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In crop mode the K-1 IS a crop sensor camera and all "rules" and conventions associated with the APS-C format apply, including DOF. There are implications in regards to the perception of DOF in the viewfinder as compared to that of say, the K-3II, but those do not affect the DOF in the final image.
So the answer to your question is, "For a given aperture you will get the DOF for a crop sensor".
Steve
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Forum: Pentax K-1 & K-1 II
08-17-2016, 04:06 PM
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The word crop is used twice in this question. I believe it answers itself.
Steve
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