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Lens Diffraction vs Image Quality

Edward1064
Enthusiast

While recently attempting some panoramic photography, I was using f-numbers of f/11 to f/16 to increase the DOF. Later I wondered whether light diffraction was spoiling some of the image quality. My equipment was a 7DII and Canon 16-35 mm IS USM f/4 lens.

 

Using some basic optics, even with a perfect lens, each point on the object is not focused to a point on the sensor, but to a blurred area roughly 2.44*f*lambda/D, where f is the focal length of the lens, lambda is the light wavelength, and D is the lens's aperture diameter. Since the f-number is defined as f/D, the blur reduces to 2.44*lambda*f-number. My camera's pixel size is 4.1 micrometers. If my math is correct, and assuming an average wavelength of 0.55 micrometers, even at f/4 the blur is 1.4 pixels. At f/16 it is 5.2 pixels.

 

What I don't know is how much this matters to image quality. In the future I plan to examine my photos closely to see whether the theoretical blurring vs f-number actually matters. Has anyone looked into this? I would appreciate some experienced feedback!

 

Many thanks,

Ed

 

(Trying to watch Giants vs Dodgers while writing!)

 

 

 

 

 

24 REPLIES 24

Thanks, EB. I do know about the need to rotate the camera around the lens’s entrance pupil to eliminate parallax. I’ve made some panos in the backyard to show the issue. Using Lightroom to stitch. Will get a nodal slide if I really get into this!

I tried to edit my first reply but the forum is being contrary. Won't let me edit!  There is a mistake in the description of the second example. It is one shot, not three.  A straight shot from the 24mm lens. I posted it for comparison. Same lens used in different ways. You decide.

EB
EOS 1DX and 1D Mk IV and less lenses then before!


@Edward1064 wrote:
Thanks, EB. I do know about the need to rotate the camera around the lens’s entrance pupil to eliminate parallax. I’ve made some panos in the backyard to show the issue. Using Lightroom to stitch. Will get a nodal slide if I really get into this!

For most landscape shots, parallax should not be an issue.  It does not become an issue until there are elements in the foreground that you wish to capture, which are relatively close to the camera compared to more distant subjects in a typical landscape shot.

--------------------------------------------------------
"The right mouse button is your friend."

"For most landscape shots, parallax should not be an issue."

 

Nothing is or is not an issue depending on, "...how is the photo going to be used."  For the end purpose of my shown pano, I took no special treatment. It is/was hand held and simply merged in LR.

 

 

EB
EOS 1DX and 1D Mk IV and less lenses then before!

johnrmoyer
Whiz
Whiz

I have found this usefull: https://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

 

GMIC Richardson/Lucy deconvolutiion will remove some diffraction.

 

Digital Lens optimization in DPP removes some diffraction.

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