What circle of confusion and depth of field values should I use for a full-frame portrait intended for 8x10 prints?
Asked 1/21/2019
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I’m shooting a portrait on full frame and want a practical way to choose aperture. Assume a 100mm lens, subject distance around 1.5m, and the goal that the face looks sharp while the background is noticeably blurred in an 8x10 print. In practice, what circle of confusion value should I use for this viewing/print size, and what kind of depth of field is typically appropriate for portraits?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
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With full frame, use f/8 with appropriate lens (maybe 100 to 120 mm) to allow 8 or 10 foot subject distance, and focus on the near eye, and you'd do fine (with the subject sharpness). That is perhaps 7+ inches of total DOF span, with subject in the middle.
Lenses are "sharp" at only the one focused distance, and become progressively less sharp with distance away from focus.
Full Frame CoC is typically used as 0.03 mm, which in practice has seemed mostly reasonable. CoC only provides a limiting guide for calculating DOF numbers for an 8x10 inch print (meaning, at the DOF extreme near or far range, CoC WILL BE 0.03mm diameter blur there of a point source. The 0.03 mm on the full frame sensor is historically judged to Not be very detectable by the human eye on an 8x10 inch print (viewed at about 10 inches). When CoC grows to 0.03 mm with distance, DOF calculations announce that is the DOF limit distance). Whether that result pleases you or not is your own decision. If it does, then DOF calculations can tell you if your focal length, distance and aperture will provide that range. Deciding a different CoC does not affect the image sharpness in any way. It simply produces different DOF numbers which you may find more appropriate (or not), but it does not change the image in any way. The lens does what it does. DOF tries to compute what it does, based entirely on the decided CoC guideline that you find acceptable.
Originally by user38978. Source · Licensed CC BY-SA 4.0
user38978
7y ago
0
Generated from our catalog & community — verify before relying on it.
For the usual depth-of-field assumptions behind 8x10 prints viewed at about 10–12 inches, a standard full-frame circle of confusion is 0.03 mm. That’s the common value many DOF calculators use.
If you print larger and view at the same distance, use a smaller CoC; if you print smaller, a larger CoC is acceptable.
For portraits, there isn’t one universal “correct” DOF value because it depends on pose and what features must be sharp. A practical approach from the answers: with full frame and about a 100–120mm lens, f/8 at roughly 8–10 feet can give around 7 inches of total DOF, which is often enough to keep the subject’s face sharp if you focus on the near eye.
Key point: “acceptable sharpness” is a viewing standard, not a hard optical cutoff. The plane of exact focus is only at one distance, and sharpness falls off gradually. So use 0.03 mm CoC as your starting point for 8x10 prints, then choose aperture based on how much of the face you need sharp. Focus on the near eye for best portrait results.
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