Aperture and Image Quality – Lens Diffraction

landscapes stock photography | Storm Clearing at Sunset at The Walls of China, Mungo National Park, NSW, Australia

In different landscape photography articles I often see a recommendation to use very small aperture like f/22 to get maximum depth-of-field (DOF) have every thing in focus from “you nose till horizon”. (This also known as “near-far composition”). While this is absolutely right I cannot agree with that advice. Why? Simply because the quality of the picture will be much worse than with using aperture f/8 or f/11. All lenses are designed to have the best possible image quality at so called “sweet spot”, which is around f/5.6 – f/11. That applies to old lenses and that applies to modern super-quality lenses like Nikon 14-24/2.8. The graph that illustrates the quality of the images at different apertures is below.

This graph is not for a particular lens. But all lenses behave in the same way Carl Zeiss, Nikon, Canon, you name it. As you can clearly se we have quality degradation at f/22. How much? That depends on the lens. Quality degradation is caused by diffraction around aperture blades. Also that depends on the medium we are using for capturing photos. Back in old film days photographers could easily use f/22 to get max DOF because the only diffraction they had was around aperture blades.

Now in modern digital world we have diffraction in CCD/CMOS sensor in cameras as well. And the amount of diffraction depends on pixel dimensions. Pixel dimensions depend on the size of the sensor and amount of pixels. The bigger your sensor the bigger pixels the sensor has and therefore the smaller aperture you can use. But at the same time more megapixels you have on the sensor then the smaller your pixels the sensor has and therefore the larger aperture you have to use to prevent diffraction. If you haven’t read about that please check article on “Lens Diffraction and Photography” on Cambridge in Colour photography tutorial site. It has a nice calculator so you can check your sensor against different apertures. Note, the Canon EOS 5D Mark II camera has pixel size 6.4µm and pixel area ~41 µm2. It’s not in the list in the calculator, but you can use Canon EOS 20D/350D instead with roughly the same pixel area 41.2 µm2. If you wonder why Canon EOS 20D/350D have the same pixel size as Canon 5DMkII please bear in mind that even if it has full-frame sensor it has much bigger resolution that makes pixels smaller.

The image above shows diffraction in Canon EOS 5D Mark II sensor at different apertures. Again as you can see stopping down to f/22 causing image quality degradation. I can clearly see the difference between f/11 and f/16. I don’t want to compromise photo quality in landscape photography and therefore I do not use apertures smaller than f/16. Usually it is f/8 or f/11. So what is the solution if we do need to have max DOF?

Well… there are 3 options:

  1. Get sharp foreground and leave horizon slightly out of focus. That works quite well due to peculiarity of human perception.
  2. Get closer and shoot with wide lens. By using wider lens you are increasing DOF.
  3. Capture a few frames with different focus and then stack them in Photoshop. Its complicated but it gives excellent results. As an example this photo of Cascades on Eurobin Creek was made from 6 frames at 100mm and f/11. How to stack images you can find on NaturePhotographers.net site in great article “Blending Exposures in Photoshop” by John Williams.

Hopefully this information helps you to achieve better quality with maximum depth-of-field and using best lens apertures.

PS. Also if you want to read more about maximising Depth-of-Field and better understand hyper-focal distance please have a look at the following article: The best and useful “Depth of Field” explanation.

PPS. This post was already ready and scheduled in my blog when I saw an article “Lens Diffraction” by great landscape photographer Ian Plant. Well… that’s just a coincidence.

By the way he has a few great eBooks on landscape photography, composition and light. Definitely worth reading.

Improve your photography skills with eBooks from Ian Plant.

 

 

 

Ilya Genkin is a Sydney, Australia photographer whose subjects include the Pacific coast, Australian outback and deserts, rainforests, lakes and rivers, urban landscapes, night photography, and more.
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  • Chris - July 27, 2011 - 2:38 am

    Good Article, good job on explaining what every photographer should know.

  • Ilya Genkin - July 27, 2011 - 8:29 am

    Thanks a lot, Chris! Very much appreciate!

  • Lee Duguid - July 28, 2011 - 12:26 pm

    Interesting read, thanks for sharing. Are photography buyers discerning enough to notice? I’m not sure. Of course you wouldn’t want to or really need to go higher than F16 but for the most part good sharpening techniques can bring back some detail.

  • Ilya Genkin - July 29, 2011 - 9:05 am

    Valid point, Lee! Thanks for that! Yes, I agree that for small and may be medium size prints it doesn’t really matter. Also most buyers probably will not notice anything, but if we are talking about large prints it is quite visible. When you need to enlarge up to 300% then you the best quality you can get otherwise prints will be blurry.

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