All in Focus or All Sharp – You can’t have Both

Summary – Depth of Field (the area in focus) and Diffraction (affects sharpness) are a basic photography tradeoff. In general, one comes at the expense of the other. Some illustrated examples (without the physics).

 


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So – you want the nearest to farthest points in a scene in focus

(this is depth of field)

You also want sharpness throughout

(diffraction can cause loss of sharpness)

Bottom line – you can’t have both

(unless the subject is a flat surface AND

you’ve aligned the sensor face with that surface)

.

Post based on an email from a reader
Who noticed I used f/51 on an image in a recent post
Asked about diffraction

.


This post assumes you know that

As you change your aperture to higher numbers

f/22 for example (not f/4)

Two things happen to the resulting capture

1. More of the scene (near to far) is in focus

2. Sharpness can be lost (blurriness sets in)

All else equal, the results are sensor size dependent

If you want a comprehensive discussion

Search the net on DOF and diffraction

My main intent is to show examples

Not to teach a course in physics 😉


The illustration subject is a camera bag

Lots of texture detail to judge sharpness

Tilted back from the camera to judge DOF

I focused precisely (Liveview X10) on the

Pointy-bottom at the center of the letter M

Keep your eye near here for diffraction effects

Aperture was changed in 1-stop increments

f/4, f/5.6, f/8, f/11, f/16, f/22

For this camera (Pixel Diameter: 5.5 µm)

Diffraction should become noticeable at about f/11

Nikon D300 + high quality Nikkor 105mm macro lens

Tripod & remote shutter release for stability

——————————————————-

Roll over for f/4 vs f/22 comparison

The DOF change is very obvious

(Recall that the bag is tilted away from the camera)

The loss of sharpness is nearly imperceptible

.

I focused on the M’s point in DOMKE

2014-04-23_9-52-33 2014-04-23_9-53-31

This next series is f/4 through f/22 in 1-stop increments

 Click on f/4 (top left) and step through via right arrow

To see the gradual change

Or – from f/4, toggle backward & forward to|from f/22

To see the big change  in DOF, but

The sharpness loss near the M is barely noticeable


Rollover for another view of the two extremes

You can actually see the loss of sharpness near M’s point

That’s a “big-whoop” (from cynical me)

2014-04-23_9-54-31

2014-04-23_9-55-51

 .

Conclusions?

Draw your own….

For my style

DOF (both shallow & large)

is very important

Diffraction concerns

aren’t foremost in my mind

If f/8 or less gives me the DOF I want

I won’t stop down further unnecessarily

Nor will I stay at f/8 or lower

If it doesn‘t provide the DOF I want

For my style, diffraction concerns are over-blown

For you, only you can decide

Test your gear and do it on a variety of subject matter

Macro, close up, landscape, portrait – the works

Do not, as some do, refuse to go above f/8

Simply because you read somewhere that was bad

Shoot for yourself – not theoretical-number-rules

For me & my style

Big DOF changes (in either extreme) are

Far more important (and noticeable)

Than slight changes in sharpness

Arty needs selective (shallow) focus

Landscapes need a large DOF (usually)

In neither case should diffraction concerns

Be over-riding (IMO)

Focus stacking software might be a consideration

I’ve never felt the need

Not anal-compulsive enough I guess 😉

 


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6 thoughts on “All in Focus or All Sharp – You can’t have Both

  1. Focus stacking is just a matter of taking multiple exposures and blending them in accordance with your vision. Think about macro, where this is a necessity whenever you want to have an image without substantial bokeh. Not exactly anal.

    • You, of course, are absolutely right. In fact, I’ve already written a follow-up post on focus stacking (check in 2-3 days) which illustrates your point exactly.

      I was carried away by the fact that my macros are usually florals and I prefer some (or a lot of) bokeh for those subjects. Different strokes for different folks.

      Thanks for speaking up.

  2. Another parameter in this equation is resolution. A some point high ISO will take away both sharpness and focus. Of course, a tripod and longer exposure can deal with this issue. Nick

    • There’s resolution & then there’s resolution. My D800E (full frame 36 megapixels sensor and reputed to be one of the best DSLRs in terms of image quality) is more susceptible to diffraction than my 12 MP D300 (DX sensor). By more susceptible I mean that diffraction will show up at a lower f/stop in the D800E than the D300. This is because the pixel pitch is smaller in the 800E (it’s all about Airy disks, Rayleigh resolution criterion, and a bunch of other physics stuff that dictates that smaller pixel pitch leads to diffraction at lower f/stops). But if you’re not shooting 1:1 or similar macros you’re probably not going to notice or care.

  3. Great examples. Thank you for the post.
    I can’t even imagine f/51. My camera only goes to f/29 and that is tiny. Must be a pinhole =:0

    It is interesting that your two cameras give differing results. I have heard different cameras (same make/model) can have different color reproduction.

    I am convinced I will have to try this out on my camera now, just to see…I wonder if I need to do all the lenses too?

    Brian

Comments are closed.