topic Re: Lens Diffraction vs Image Quality in EF & RF Lenses

Lens Diffraction vs Image Quality

Edward1064 — Sat, 09 Oct 2021 04:13:16 GMT

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,

(Trying to watch Giants vs Dodgers while writing!)

Re: Lens Diffraction vs Image Quality

Waddizzle — Sat, 09 Oct 2021 10:22:08 GMT

The range of focal lengths of your 16-35mm lens is WAY too short for capturing a set of mages for a panorama.

Re: Lens Diffraction vs Image Quality

Edward1064 — Sat, 09 Oct 2021 14:15:43 GMT

I don't understand what you are trying to say.

Re: Lens Diffraction vs Image Quality

jrhoffman75 — Sat, 09 Oct 2021 14:30:34 GMT

See discussion here (info about 7D Mark II):

Top 6 Reasons Why Your Images May Be Blurry (the-digital-picture.com)

Re: Lens Diffraction vs Image Quality

Waddizzle — Sat, 09 Oct 2021 15:10:34 GMT

@Edward1064 wrote:
I don't understand what you are trying to say.

How did you arrive at the conclusion that aperture size and settings is the reason why you images seem soft. I don't think you have properly identified the issue. But, post a sample photo of the issue, so that we can better understand what it is that you are seeing.

Ultra wide angle lenses are not known for capturing sharp details of distant subjects, most particularly landscapes, which tend to be dozens or hundreds of yards/meters from the the camera. A UWA lens tends to make distant objects appear smaller, which reduces the resolution of the landscape shot.

I capture most of my panoramic shots using a 70-200mm lens, with the camera rotated to the portrait mode orientation. You can capture one row of sample shots, or multiple rows of shots to create a even larger final composited image.

Re: Lens Diffraction vs Image Quality

Waddizzle — Sat, 09 Oct 2021 15:20:50 GMT

@Edward1064 wrote:
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.

Is stopping down the aperture to f/11 to f/16 an issue? It certainly does not help. Check a DoF table or app to see just how much depth of field you can get at f/4. You might be surprised by the results. The hyperfocal distance is relative close to the camera, even at f/4, when it comes to shooting landscapes.

Re: Lens Diffraction vs Image Quality

ebiggs1 — Sat, 09 Oct 2021 18:58:47 GMT

WA and UWA lenses have smaller aperture diameters at any given f-stop than longer lenses. This causes them to exhibit more diffraction than longer lenses. It is best not to stop down past f8 or f11 with a UWA lens. However you must decide whether the need of extra depth of field (DOF) is more important.

I do lots of panos. I used WA and UWA lenses and generally use f8. Here is a seven shot pano I did recently with a 24mm WA at f11.

Here is almost the same shot only using three photos.

Of course I have no idea what you are shooting or what your goal is but with this type of photo IQ isn't the most important spec. My ef 24-70mm f2.8L is a very sharp zoom. It will guess it has better IQ than the 16-35mm f4 zoom does. One thing to keep in mind that as distance increases lens resolving power also decreases.

Re: Lens Diffraction vs Image Quality

Edward1064 — Sat, 09 Oct 2021 21:45:49 GMT

John,

Thank you for the link. There is a link within that link that has image comparisons for different cameras and lenses, and I will spend enough time there to understand it.

Re: Lens Diffraction vs Image Quality

Edward1064 — Sat, 09 Oct 2021 22:14:59 GMT

Hi Waddizle,

Thank you for your responses. I guess I should tell a little of the backstory.

For several years I have been a bird photographer, using the 7DII and a Canon 100-400 mm II lens. While hiking, we met another hiker who was doing panoramic photography, and I became interested. Something else to learn. So I set about photographing a unique Monterey Cypress tree at Point Lobos, near Carmel, Ca. I wanted to make a panorama that included a little of its surroundings, on a cliff above the ocean. It was an experimental adventure, camera handheld in portrait orientation, using a couple of ideas I had gleaned from online reading. Namely, shoot at high f-numbers for DOF (not really so relevant in this case since the subject was not so close) and in manual mode with fixed focal length. It turns that a panorama does not enhance the Cypress tree. See the Monterey Cypress below. It has a name: the Old Veteran.

I also took single shots of the Cypress at f/8 that looked a little better than the ones that were to be part of the panorama, taken at higher f-numbers, which got me thinking about diffraction. Thus the derivation that shows the diffraction depends on lens f-number in a straightforward way.

Yesterday I received an L-bracket for the 7DII and will use it on my tripod for the next reound of tests with various f-numbers.

Re: Lens Diffraction vs Image Quality

Edward1064 — Sat, 09 Oct 2021 22:31:14 GMT

EB,

Thank you. Those panos of yours are really interesting. Yes, and image quality is not as important as it is with, say, bird photography. My interest here is to get the best quality photographs that my equipment can muster, not so limited my skills!

About different lens focal lengths, the diffraction blurring does not depend on the lens focal length, but only on the f-number. This is because the f-number (image distance/lens iris diameter) contains both the lens opening and the image distance. So it is easy to think about.

Please see my comments to Waddizzle. The tree photo was shot at a zoom of 23 mm and f/8 and 1/125 sec.

Re: Lens Diffraction vs Image Quality

ebiggs1 — Sun, 10 Oct 2021 03:58:04 GMT

Ed,

This is not correct.

"the diffraction blurring does not depend on the lens focal length, but only on the f-number."

Diffraction is worse with WA and UWA lenses because of the short FL. Why? Because the hole in the diaphram is smaller at any given f-stop compared to the same f-stop in a normal or tele typle lens. In a WA/UAW the light path is bent at a greater angle.

Another factor is sensor size and pixel size. A camera like the 7D Mk II has fairly small pixels. Its going to be affected sooner than a camera with larger sensor and pixels.

It becomes a photographers decission as shooting at wide open apertures all lenses suffer form optical aberrations. This is one reason most all lenses show their best when stopped down one or two stops. Diffraction is usually even where aberation is not. This makes diffraction less destructive to lens IQ.

How about DOF. DOF affects different parts of a scene with differing amounts. Remember we said diffraction is even, however, DOF is not. The farther away from the focal plane you are, the more blurry your picture will get.

Diffraction is easy to correct in Photosop with smart sharpening and/or unsharp mask. Resolving power of most lenses is at its highest or best in the f4 to f8 range. Just anoher factor to consider.

Re: Lens Diffraction vs Image Quality

Edward1064 — Sun, 10 Oct 2021 05:08:15 GMT

EB,

How do you do a pano, composed of several shots, with movimg subjects?

Re: Lens Diffraction vs Image Quality

Waddizzle — Sun, 10 Oct 2021 11:15:29 GMT

@Edward1064 wrote:
EB,

How do you do a pano, composed of several shots, with movimg subjects?

Ed

I have never purposely tried it. But, you can probably pull it off using a high frame rate, provided your subjects are neither moving quickly or close to the camera.

For example,I have captured pano shots of a bridge with moving vehicles, The individual frames are fine, and are free of any motion blur from moving vehicles. The only potential for real issues would occur at where the images overlap. The stitching algorithms tend to throw away differences, and keep what is similar.

Provded your subjects are not moving any significant difference across the frame from one shot to the next, you should be fine under those circumstances.

Re: Lens Diffraction vs Image Quality

Waddizzle — Sun, 10 Oct 2021 11:44:09 GMT

@Edward1064 wrote:
Hi Waddizle,

Thank you for your responses. I guess I should tell a little of the backstory.

For several years I have been a bird photographer, using the 7DII and a Canon 100-400 mm II lens. While hiking, we met another hiker who was doing panoramic photography, and I became interested. Something else to learn. So I set about photographing a unique Monterey Cypress tree at Point Lobos, near Carmel, Ca. I wanted to make a panorama that included a little of its surroundings, on a cliff above the ocean. It was an experimental adventure, camera handheld in portrait orientation, using a couple of ideas I had gleaned from online reading. Namely, shoot at high f-numbers for DOF (not really so relevant in this case since the subject was not so close) and in manual mode with fixed focal length. It turns that a panorama does not enhance the Cypress tree. See the Monterey Cypress below. It has a name: the Old Veteran.

I also took single shots of the Cypress at f/8 that looked a little better than the ones that were to be part of the panorama, taken at higher f-numbers, which got me thinking about diffraction. Thus the derivation that shows the diffraction depends on lens f-number in a straightforward way.

Yesterday I received an L-bracket for the 7DII and will use it on my tripod for the next reound of tests with various f-numbers.

Ed

You should not need an L-bracket with the 100-400mm, or a 70-200mm. With those lenses you should be using the tripod foot, not an L-bracket, anyway. Rotate the camera to portrait mode within the lens collar.

I shot the bridge using a 70-200mm, and rotating the rig within the tripod ring on the lens. Capturing a panorama does not capture more detail, at least not exactly. I could capture a similar angle of view shooting the bridge at 24mm. But, I can create a higher resolution final image by capturing a series of pano shots while zoomed in on the details. I shot at 7

I shot the bridge with a 20MP 6D. The final image was 38MB. The pixel resolution of the final pano image was, of course, much higher than the 20MP image shot at 24mm.

It seems like you were some distance from this beautiful tree. Capturing a pano image of the tree and its immediate surroundings with a long lens should have more detail than a single photo with a similar angle of view captured using a shorter lens.

But, the individual samples captured for a panoramic shot will not look any better than a single still of the same scene that was shot at the same focal length. The longer lens allows you to zoom in on the details that elude a wider angle lens.

[EDIT] I forgot to add the reason I posted the bridge photo. It was shot in Av mode, at ISO 100. Each frame used an 8 second shutter speed. My shooting position forced me to have a sidewalk between me and the bridge. I could not set up camp in the middle of the sidewalk.

During the course of capturing the shots, a couple of joggers passed in front of the camera, as well as a couple that walked past the camera. Seeing how I was piddling with my smart phone while the shutter was open, they never realized that I was capturing a shot. I reshot the sequence. But, the original shots showed no trace of anyone having crossed in front of the camera, which is no doubt due to the long shutter speed.

Re: Lens Diffraction vs Image Quality

ebiggs1 — Sun, 10 Oct 2021 15:00:51 GMT

Ed,

"How do you do a pano, composed of several shots, with movimg subjects?"

You really can't. Or at least, you need to be aware of some compromise. The bridge photo, which I have seen many timers on here is beautiful, for sure, but you notice there is no definition in the water in the foreground. That is probably due to the fact it was moving waves or ripples.

A person or animal in a single frame will still remain sharp unless it is next to a seam area. If there is too much motion in the various shots Lightroom will not merge them.

I don't necessarily agree with a multi-shot pano being better IQ. It is certainly a bigger file but the individual shots are no more higher IQ than any one single shot. This would greatly depend on camera, lenses and conditions. Panos are different than multi-focus stacking which can increase IQ. Panos take multiple shots and puts them together using LR, or some other software, to allow a wider final photo. Usually because it can exceed what can be contained within just a single frame.

What you may not know is panos also have issues with parallax. A way to correct for parallax error is to use a nodal slide. I don't bother because I am not interested in the highest IQ of these shots because of their final usage. Which is another factor in your decission making, how is the photo going to be used. In fact the two shots shown were hand held using my 1DX, 24-70mm f2.8L lens @ f9.5 (using P mode), SS 1/350 and ISO 200.

Re: Lens Diffraction vs Image Quality

Edward1064 — Sun, 10 Oct 2021 15:08:07 GMT

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!

Re: Lens Diffraction vs Image Quality

ebiggs1 — Sun, 10 Oct 2021 15:12:30 GMT

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.

Re: Lens Diffraction vs Image Quality

Waddizzle — Sun, 10 Oct 2021 18:58:58 GMT

@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.

Re: Lens Diffraction vs Image Quality

ebiggs1 — Mon, 11 Oct 2021 14:32:55 GMT

"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.

Re: Lens Diffraction vs Image Quality

johnrmoyer — Tue, 12 Oct 2021 14:41:22 GMT

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.