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I rarely have time to get out from large city, so large buildings are the main theme of my photos. I still wonder if using the Manual mode instead of Auto in my D5100 can give any benefit. I made two photos with the largest and smallest possible Exposure/Aperture ratio of this scene:

enter image description here

But I do not see any difference:

enter image description here enter image description here

except that white edge is a bit blurred to the right, but it is probably some random motion glitch because of suttering or I don't know.

So since there is no difference between that two extreme presets, does it make any sense to use them, if Auto mode (the first image) already looks fine?.

Here are RAWs:
https://drive.google.com/file/d/0B3BLwu7Vb2U-TVYtVHhFNk5sM0U/view?usp=sharing
https://drive.google.com/file/d/0B3BLwu7Vb2U-YmpSMUc2bzQ2Ymc/view?usp=sharing

  • There is a difference. At f/4 your suffering from CA, the softness around bright edges. At f/25, you have eliminated the CA. That is one of THE reasons to stop down, to reduce optical aberrations and achieve diffraction limited performance. To get optimal results, since depth of field changes do not have a recognizable impact on the image, you should use the maximum F# that does not reduce resolution...which is likely around f/8 rather than f/25. – jrista Mar 16 '15 at 19:04
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Note that there are differences between the two shots. You assume the blurry edge is due to shake, but it doesn't look like that. Actually, at maximum aperture, your lens likely does not behave at its best.

A wide aperture will get you various image defects like blur, chromatic aberration, distortions etc.

Likewise, a narrow aperture like f/25 will suffer from diffraction problems!

Lenses will generally behave their best at some aperture a few stops above the widest setting, eg f/8.

For detailed tests, see eg. http://www.dxomark.com.

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So since there is no difference between that two extreme presets, does it make any sense to use them, if Auto mode (the first image) already looks fine?

That depends. If you are interested in the artistic side of photograph, experimenting with different setting just to see what effect they have on the photograph makes sense. However, if it is just too time consuming to change settings, then just taking photos on Auto mode will help you. On Canon (at least the 550D, I assume it is the same for others) it is possible to change the settings on auto mode by rolling the control wheel. THer MAY be a similar thing available on Nikon that can allow you control over the depth of field and exposure time, while still gaining the benefit of Auto exposure. You can also use the Aperture priority mode, which is the A option in the MASP secion of the dial on the top of your camera.


Below is an explaination of why you see no difference between the photos in terms of focus

When you are a large distance from your subject, the Depth o Field (i.e. the area that is in focus) in the image becomes quite large, even with wide apertures (i.e. small f/ number). In fact, once you focus past the hyperfocal distance, everything from a point between you and your subject and infinity is in focus.

For your lens and camera this distance is about 7.2 metres at f/4. Since the buildings are MUCH MUCH more than 7.2 metres away when you focus on them, the vast majority of your image is in focus (from about 7 metres to infinity, assuming the buildings are 500m away). Since a smaller aperture produces a larger depth of field (given the same conditions and other settings) at f/25 the hyperfocal distance is 1.2 metres and your Depth of Field would be from 1.1 to infinity.

Since the entirety of your scene is within your depth of field both times, you will not be able to tell the difference between the apertures based on focus. However you may be able to tell the difference with other factors produced by different apertures.

To calculate these distances I used this calculator.

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    Note that the calculator you've linked to by default gives values for what appears to be in focus when viewing a small print. If you view the image at 100% on a computer screen the depth that appears to be in focus will be much smaller. – Matt Grum Mar 16 '15 at 15:05
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If you feel like you get good results from Auto mode, you don't need to shoot in manual. Shooting in full manual just gives you total control over all the details of your shot, most significantly exposure and depth of field.

In this case, when you shoot a cityscape or landscape, you'll generally want a small-ish aperture to maximize the depth of field so you can get as much of the scene sharp as possible (e.g. f11, f16). At a large aperture such as 1.8, you'll notice that your foreground and background elements will be out of focus due to the shallow DoF. If Auto mode picks an appropriate aperture for the situation, then there's not really any reason to switch to Manual. If you don't trust the camera to choose the correct aperture (for an important shot, I sure wouldn't), then you can switch to Aperture priority and dial in the setting that you want, and the camera will adjust shutter speed and ISO to balance the exposure.

The blurriness you see in the shot at f4 is most likely because you're at the maximum possible aperture for your lens (f4 at 24mm). In general, lenses will produce softer images at their maximum apertures, which is why you'll often hear photographers talk about "stopping down" a lens to produce sharper images - you'll usually hit the sweet spot of sharpness around f8 for most lenses.

TL;DR: If you know any subset of the settings you'll need (aperture, shutter speed, ISO), dial those in manually so the camera doesn't pick incorrectly, and let the camera adjust the other settings automatically to balance exposure. If you don't really care, or you trust the camera to pick the right settings for the situation, shoot away in Auto.

  • Remember that there's a ceiling on f-number beyond which you actually lose sharpness due to the edge distortion. – yo' Mar 16 '15 at 18:00
  • Remember also that even at wide apertures if the object(s) focused on are further than the hyperfocal distance for a particular focal length and aperture then everything past the point of focus will be within the DoF. – Michael C Mar 17 '15 at 23:47

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