Aperture question

thisispants · Jan 23, 2009

Can I ask a dumb question...if I'm shooting outside on a sunny day, and I take two photos.....one with an apature of 4, and the other with an apature of say 16....and I let the camera take care of the shutter speed....other than depth of field, what difference will it make to the end photo?

Anscojohn · Jan 23, 2009

Theoretically, the f/16 should be less "sharp" because of diffraction.

bdial · Jan 23, 2009

The shutter speed will be quite a lot faster at f/4 than it would at f/16, so you might have better sharpness due to less camera shake. You will have less or no motion blurring in a moving subject.
OTH, depending on the lens, it might produce a sharper image at f/16 than at f/4.

Chuck_P · Jan 23, 2009

Should not be any difference. Basically, when in "Aperture Priority" mode, you are in control of the depth of field and the camera finds the shutter speed to maintain the exposure equation: exp = light intensity (aperture value) x time (shutter value). The camera is finding the equivalent exposure. The camera is still subject to the pitfalls of reflective metering, though. If the subject/scene does not contain roughly equal proportions of light areas and dark areas (i.e. average) , the meter will try and make it average, and this could make for a drab end result.

Q.G. · Jan 23, 2009

CPorter said:
Should not be any difference. [...]

... but only if you are shooting a static subject from atop a sturdy tripod.

And even then, though perhaps not immediately visible, the "less "sharp" because of diffraction" answer applies.
Else the difference will be what the other answer says as well.

Chuck_P · Jan 23, 2009

Q.G. said:
... but only if you are shooting a static subject from atop a sturdy tripod.

And even then, though perhaps not immediately visible, the "less "sharp" because of diffraction" answer applies.
Else the difference will be what the other answer says as well.

I made an assumption that the OP recognized the slower shutter speed, I was responding from a different angle-----bad assumption.

Steve Smith · Jan 24, 2009

Generally, on a bright sunny day with ISO 100 film, setting the aperture to f16 should give you a shutter speed of 1/125. An aperture setting of f4 gives four stops more light so needs four stops less of shutter opening. In this case, 1/2000.

The 'slower' shutter speed is still fast enough to get a decent, shake free picture without a tripod although for the sake of comparison, a tripod should be assumed on a test like this.

Steve.

Christopher Walrath · Jan 25, 2009

In regards to total amount of exposure applied to the surface of the film with the camera making proportionate and reciprocal adjustments to the shutter speed setting.

NO DIFFERENCE.

JBrunner · Jan 25, 2009

It's spelled "aperture". I can do this because my spelling and grammar sucks.

In terms of exposure, as Chris said, no difference. That's reciprocity at work.

In terms of sharpness and depth of field, yes, there are differences, and the differences will vary depending on format, but follow the same general direction. Smaller apertures will result in greater DoF, at the risk of diffraction at the smallest apertures. In real world terms diffraction generally isn't something to worry about with 35mm until about f22 for an 8x10 print, although it is measurable at that point.

Q.G. · Jan 25, 2009

Diffraction is such that maximum attainable reslotion just about halves every two stops the aperture is made smaller. And it does so when going from f/1.4 to f/2.8 as much as when going from f/22 to f/45.
That's quite something. Readily measurable. And not just at small apertures.

But it's right that in real world terms, whether you'll notice depends on what it is that is limiting resolution most. And it usually is not diffraction.

Shows a thing about DOF too, by the way: it increases faster than the DOF-folklore predicts, because the sharp bits get less sharp quite rapidly, and with that, of course, also the difference between sharp and unsharp diminishes at haste.
Less difference between sharp and unsharp = more DOF. And not just because the CoC gets smaller.

Aperture question

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