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mattdm
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It's hard to really tell from the small versions here — which is a lesson in itself, because at 1280x850, which is a perfectly fine online viewing size, the differences really don't matter that much.

However, in this case, I think Auto probably did make some better choices.

Shutter Speed

You picked ¹⁄₆₀th of a second. This is fine, but probably slightly susceptible to blur from camera motion shake or subject movement due to wind. Auto mode picked ¹⁄₄₀₀th, which will better freeze things.

ISO

You picked 200 and the camera picked 400. Like most modern largish-sensor cameras, there's not much difference between 200, 400, or 800 on this camera in terms of noise, but I suspect the auto mode enabled the expanded dynamic range option (where the camera actually shoots at a lower ISO and then brings up the shadows in internal post-processing). Because of the way that works, this is only available at higher ISOs than the base 200. (The difference isn't super-visible in the result, but I can imagine a little more detail in the shadows.)

Aperture

This is really the big one. You picked f/18, and the camera picked f/8. All camera-lens systems are subject to diffraction, which means that while the narrower aperture gives you more depth of field, there's less sharpness overall. See What is a "diffraction limit"? for more. In general, it's better to not go beyond f/8 except in special circumstances.

Overall Exposure Value

It's helpful to think of exposure differences in terms of "stops" — that is, poewrs of two. (See What is one "stop"?). Between f/8 and f/18, there are 2⅓ stops — going in that direction, darker, so we'll call it negative 2⅓. And between ¹⁄₄₀₀th and ¹⁄₆₀th is just about the same: 2⅔ doublings (which is 2⅔) — but in the direction of more exposure. So these things should just about cancel out. (See What is the relationship between ISO, aperture, and shutter speed? for more on this).

One would expect, therefore, a ⅓-stop change in aperture to get to exactly the same place. But 200 to 400 is a full stop, so that's a ⅔-stop discrepancy, which is kind of a mystery (that would normally result in a visibly brighter exposure), but I think that this is because of the dynamic range expansion effect I mentioned. (A change in the light would be another explanation, but that seems unlikely with no clouds in the sky, the same general framing, and less than a minute apart.)

mattdm
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