Confused about aperture and depth of field

[droad]

I’m new to the DSLR world having made the leap from a point/shoot (Nikon S9100) to a Nikon D5300. I’ve been experimenting with various ISO, aperture, and shutter speed settings to see the effect of each on a similar photo setup. I have a question on the aperture front. I clearly can see the impact to depth of field when I use a large aperture (less of the photo is in sharp focus). My thought was using a smaller aperture would always result in a longer depth of field resulting in more of the photo being in sharp focus. I generally use the Nikon 18-140 kit lens. The lens will do stops at 18mm from f/3.5-22 and at 14mm f/5.6-38. What I’m finding is that once I get to apertures smaller that f/8-13 my images are less sharp. That seems counter to “smaller apertures providing great depth of field”. Am I getting introduced to diffraction or is there some other magic about smaller apertures that I need to learn about? Said differently is there a general rule of thumb that f/8-11 is all you need for good depth of field for normal landscape photos?

 

[robbins.photo]

Once you stop down a lens (decrease the aperture) beyond a certain point, depending on how much light is available, you start running into diffraction. I don't do much with landscapes myself, I'm sure there's a lot of landscape shooters here abouts that can probably give you better advice than I can on that topic - but in general I've found that apertures somewhere in the F8-F11 range usually work pretty well.

 

[john.margetts]

For landscapes (which is what I mostly do) I use F/5.6 to F/11. That gives me a good compromise between the lens' 'sweet spot' and a good depth of field. The actual aperture will depend on light conditions on the day, of course,

Personally, I do not get carried away with sharpness. So long as the picture is in focus there are far more important things to worry about. A lot of people zoom right in to the picture on the computer and panic about detail that is not normally visible particularly when printed on paper.

 

[KmH]

Diffraction Limited Photography: Pixel Size, Aperture and Airy Disks

Depth of field is determined by more than just the lens aperture.
The lens focal length, the point of focus distance, and the size of the image sensor in the camera also affect the depth-of-field.
Understanding Depth of Field in Photography

Understanding Camera Lenses

 

[fmw]

I think it is simpler than diffraction. Assuming some sort of auto exposure mode, as you decrease the aperture (use a higher f number) your system compensates by increasing the exposure time. At some point you get to the point where hand holding the camera results in motion blur. Most lenses are at their sharpest at f8 or f11. Mount your camera on a tripod and you will see what I mean.

Remember, every change in an exposure element has a consequence. Aperture affects depth of field, shutter speed affects motion blur and ISO affects digital noise. You always need to find the best combination of the three to achieve your goal.

 

[JoeW]

First, if your setting is on "aperture" and you set it to f11 or f18, what it likely does is slow up the shutter speed (b/c so much less light is being let in to the camera). This results in a slower exposure and everything is not as sharp.

Second, most lens have sweet spots where they are particularly sharp, no vignetting. The 18-140mm kit lens is good for a kit lens but....it's simply not going to be as sharp as you get closer to the extremes.

Last of all, it's a kit lens. A kit zoom is not going to be as sharp as a prime lens or a higher quality zoom. Take a look at the Nikon 35mmDX f1.8...an inexpensive prime lens but it will be significantly sharper than what you're using...primarily b/c it's a prime lens.

 

[table1349]

Digital Photography Tutorials

 

[DScience]

Hyperfocal focusing !

 

[Ido]

It sure sounds like diffraction, but it could also be one of a several different things. For example, if you were shooting handheld and compensated for the change in aperture by slowing down the shutter speed, what you see could also be camera shake. The effects of diffraction can be subtle in one situation, and quite severe in another, so it's not necessarily what you saw.

It would be best if you upload a full-resolution image for us to see. Maybe one shot at f/8 or thereabouts that you feel is sharp, and one at a narrower aperture that you feel is soft.