Lens Diffraction

(© Ian Plant) Without getting deep into the science of optics or physics (frankly, I don’t understand either), diffraction is basically a reduction in lens resolution that occurs when you use small apertures, for example f/16 or f/22. Is this something you should be concerned about?

In a nutshell, the answer is both yes and no, but mostly no. If you can avoid small apertures, you should do so to optimize image quality. On the other hand, loss of sharpness due to diffraction is typically not very significant, and since there are many good reasons why you may wish to use small apertures, diffraction shouldn’t be high on your worry list.

Small apertures may be necessary if you want to make certain types of images. For example, when incorporating the sun into your images, small apertures such as f/16 or f/22 are necessary to get the most attractive sun stars. Small apertures may also be useful for achieving long exposures that result in motion blur, although neutral density filters can be used as well. By far the most common reason for using small apertures is to get sufficient depth-of-field in order to achieve near-to-far sharpness. The photo posted below is a perfect example. I was literally inches away from the foreground branch with a wide angle lens. In order to ensure sharp focus from my foreground to my background, I needed to stop down to f/16. Although I lose a bit of overall image sharpness to diffraction at this aperture, the lack of sharpness that would have resulted from insufficient depth-of-field would have been much worse. I’ll trade diffraction for depth-of-field any day.

The bottom line is that in most instances, diffraction will result in an acceptable loss of image quality, one that can be more or less corrected by a little extra sharpening when preparing the image for printing. You might not be able to create a 40”x60” print from a diffraction limited digital file and expect to see lots of fine detail (then again, I've made some big prints from images taken at small apertures that look incredible in terms of sharpness and detail), but for most uses you likely won’t even notice. The bottom line is that although you should avoid small apertures when possible, never let concerns about diffraction get in the way of your artistic vision.

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    A small aperture may show some loss of quality but so will using a ND filter and as Ian points out, you do not get the depth of filed with the ND filter. Also remember, the optimal viewing distance for a 40×60 print is 9 feet so a little less detail is acceptable.

    You are a rebel.

    I was convinced I had to go naked to the south pole to shoot 28 images and then focus-stack them while eating seals. In your last articles you say I can just walk from the parking lot and shoot at F16? Ridiculous.

    Ian, nice article and fantastic image as well. I think sometimes its easy to get caught up in all the “rules” you read about and forget the important aspect of the image is that you convey the emotion you intended. Nice work!

    Although not the point of the article, I have to comment on your camera positioning. So critical the way you had the limb enter the frame draw you through the foreground and deliver you to the central tangle. Without it my eyeballs would be a bouncing around. (And I’m with ya about the diffraction in images where you need that front-to-back focus.) Another great photo.

    THis is a topic I’ve talked to a few different photographers about and they all seem to be of the same opinion as what you just wrote. I really like big prints but, as was already pointed out, you don’t stand 1 foot from them to really get the image. Nice article to cut through the fluff. Also, I’ve only been to the Olympic rainforest once and I found it very hard to get an unchaotic (is that even a word?) composition. I admire your photo a lot.

    Very informative and proves you can learn something new every day. Outdoor photography is the essence of God’s masterful creations and we are there to honor that and share with others. Keep shooting.

    That shot is even more off the hook than your “Sasquatch” photo.

    It’s refreshing to finally see a pro cut through some of the technical noise so that students of photography can focus on the important things (like composition). Sometimes I think that pros purposefully manufacture horror stories about diffraction and noise (for example) in order to get amateurs and beginners worried about stuff that has nothing to do with image making. Anything to slow down their competition. Know what I mean?

    Anyway, great article.

    Thanks! An interesting take on things. I do think that diffraction can actually be a serious problem for some images, and I don’t mean to be dismissive of those who are concerned about it. But not every image allows you to optimize all aspects of the photographic process — sometimes you have to make compromises: if you need extra depth-of-field, then you have to live with some diffraction. Although diffraction can be an issue, and should be avoided where possible, it should not be elevated as a concern to the point where one starts making bad choices about other technical aspects of the process. It certainly shouldn’t be something that causes someone to not take the shot at all.

    Excellent article and wonderful image. You have given me the inspiration (and courage) to shoot more scenes with a small aperture. Thank you!

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