qqqwucheng
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I think the decrease of sharpness is due to the lake of pixels (when enlarge it to a certain size) rather than the minimal difference of DOF, is it right?
Depth of field Full frame vs Crop?
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sk66
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It depends... The reduction in sharpness due to enlargement is essentially *only* due to cropping/enlargement (reduction in COC). But the particular characteristics of what is sharp/unsharp will vary with the resolution (lens/sensor)... there's not necessarily "less resolution" for the DX/smaller image if a different camera/sensor/lens is used.
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sk66
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That's because it's overly complicated and highly subjective. And I personally don't like "equivalence" because there are too many variables, you can't ever really get to exactly equivalent, and for most it's not much of a concern.
But DOF/sharpness considerations are actually pretty simple. The more critically an image is going to be viewed (enlargement/display size relative to viewing distance), the more sharpness/DOF you need.
Digital makes it a bit more confusing because we tend to think of "image size" in terms of megapixels... but in relation to DOF, megapixels are irrelevant. However, image resolution (megapixels/sensor/lens) is not irrelevant in terms of the specific characteristics of the resulting image w/ a given DOF.
HoppyUK
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It's worth bearing in mind that when it comes to depth of field (the limit of acceptable sharpness, according to the DoF standard) you don't need many pixels at all - just over 1m, 1270 x 847 = 1.08m to be precise. That does not mean to say anything over this is worthless, not at all and of course it's not that simple, but it's certainly true that when you get over say 10m, you'll be hard pressed to see any improvement without both big enlargements and close viewing.
Most people put too much emphasis on pixels (resolution) and not enough on contrast that is the key factor in the perception of 'sharpness'. You get much more of that from top quality lenses and larger sensor formats, than simply from tons of pixels.
Most people put too much emphasis on pixels (resolution) and not enough on contrast that is the key factor in the perception of 'sharpness'. You get much more of that from top quality lenses and larger sensor formats, than simply from tons of pixels.
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sk66
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I do agree that most of this is just academic, and pretty much irrelevant for most... use what you have and forget about it.
However, I do not think it is entirely academic if you are choosing what gear to buy/use.
With sensors of similar MP count, what I find is that the character of the OOF portions (bokeh) often tends to be "busier" and more annoying with the smaller sensor (same/similar DOF). This is due to the greater resolution (pixels/area) used to record it (the blur radius of a point may be the same, but there are more of them and they are smaller). And often, what is actually in focus is sharper with the larger sensor, partly because you are able to stop down farther (equalizing the DOF's) and partly because larger sensors (pixels) are less demanding (different DOF's).
These differences range from inconsequential to quite notable... but typically more towards inconsequential. Especially if you start with a more acceptable BG, and an adequately sharp lens/aperture.
In other words, technique and other choices matter more... it's only when you don't have choices that it makes much of a difference. I.e. you can usually get close enough to "equivalent" with most systems... is it worth the costs for those few times where you can't?
But if you want to take it to extremes, try comparing macro shots of the same composition with a tiny sensor vs a FF sensor... the tiny sensor will generate a much more "usable" image with greater detail/DOF, even after enlargement. The only way to duplicate it is to stack images from the FF sensor. Granted, a FF stack *can* be much better, and there are many other tradeoffs being made at the same time (ISO performance, diffraction limits, etc). But it's why I often prefer to use my 1" Nikon1 over any of my DSLRs for macro/closeup work, particularly for moving subjects (but sometimes for product work as well).