Is Your Camera Diffraction Limited?
Is Your Camera Diffraction Limited?
When photographers think about diffraction, we tend to think about lens diffraction. For some reason, we seem to ignore the part the camera sensor plays. I too made this mistake, until recently, when I was plagued with soft images. Following lots of head scratching, I discovered that my lenses weren’t the cause and that I was suffering from camera diffraction.
To help understand what was happening, let me share my story.
My Camera Diffraction Story
It all started for me when I bought a new Fuji XT5 camera to upgrade my aging Fuji XT3.
Knowing that I was about to buy an XT5, a couple of friends sent me links to reviews and articles. These suggested there were focus problems with some of the lenses in my Fuji system. Additionally, I found a Fuji article listing the lenses capable of “resolving the detail” in the XT5 sensor; quite a few of my favourite lenses didn’t make the list.
I did watch a few video reviews, and all seemed to be viewing the Fuji RAW files in Lightroom. I’ve been down this road before and seen poor results when processing Fuji XT RAW files in Lightroom, so I was suspicious of the results. I also viewed the Fuji article with suspicion as it seemed more like a way to sell their latest lenses. Then to back up my suspicions, others contacted me to say that they have achieved great results with the “problem lenses”. That was the final push that I needed to purchase an XT5.
After some initial photography with my new XT5 I was very happy with the lens performance.
Diffraction Problems Creep In
Up until this point, most of my photography using the Fuji XT5 was around a city. This was a mix of shooting with prime and zoom lenses. It was only when I came to use the camera and zoom lenses for landscape photography that I noticed a problem.
It seemed that in a lot of my shots, I wasn’t achieving enough depth of field and the distant objects were soft. Based on what I was seeing, I shifted my usual point of focus, moving it further away from the camera. This appeared to improve the results. I even wrote about it in the May 2023 issue of my newsletter.
After that, I didn’t give it much thought. That was until I recently bought a used Olympus EM5 Mark III.
Olympus EM5 III High Resolution Mode
I initially bought the EM5 Mark III for trekking. Although I already had a Panasonic G9, the EM5 is much smaller making it ideal. It also has a High-Resolution mode like that of my Panasonic G9. But when I came to try this out on the EM5, I was completely underwhelmed. The images were far too soft and very poor in comparison to the G9.
This sent me off researching ways to improve the performance of the High-Resolution mode on EM5. What I found was a Diffraction Calculator on the Photo Pills website which I’ve embedded later in this document.
The Diffraction Calculator
Here are the results when I enter my Fuji XT5 details into the calculator.
Two things stand out to me:
- When viewing the image at 100% magnification, diffraction may become visible at f/6.3. When I look at my work, I seem to be in the habit of shooting at f/13.0. What’s silly is that I know this is too small an aperture, but I think I’ve become lazy.
- The calculator needs the number of Megapixels as an input to determine if diffraction is an issue. In other words, the camera is part of the diffraction problem, and it isn’t just the lens.
Testing Camera Diffraction
Once I realised all of this, everything that I was seeing seemed to make sense, so I decided to take some test shots. Let’s look at the first one which was shot using the Fuji XT5 and Fuji 10-24 lens at 14mm. This is the first-generation Fuji 10-24 lens rather than the new lens. It’s also one that Fuji says won’t resolve the detail the XT5 sensor can capture.
You can click the images below to enlarge them.
I’m not sure how well this will show on the website, but I’ll try to explain what I see on my monitor. You can also click the image to enlarge it.
Both sections are from images shot with the same camera, lens, and settings. The sections are from the top right of the frame, and nothing has changed between the shots other than the aperture. When I look at this, image 1 shows more and clearer detail.
Now let’s look at example 2.
This time the section is from the foreground (bottom left) of the same images. Again, image 1 appears to show more detail and sharpness.
The difference between the two images? Image 2 was taken at f/13.0 whilst image 1 was f/6.4. On my screen, image 1 is clearly better than image 2.
What Changed to Correct the Diffraction
The first factor is obviously the aperture. Limiting my aperture to f/7.1 produced sharp images with almost no visible diffraction and f/6.4 was even better. I was quite shocked at how sharp this lens is.
My next problem was that if I was only shooting at f/7.1 or wider, how could I achieve enough depth of field? The answer was simple, move the point of focus a little further from the camera than I had been using. When I stood back from my tripod and checked the distance to the focus point, it was too near to my camera.
I then discovered another problem which I can’t yet explain. When I place the point of focus towards the side of the frame, the shots come out softer. Focussing nearer to the centre of the frame produced a noticeably better performance.
When I was careful to follow these points, my images came out much sharper.
How To Limit Camera Diffraction
Whilst I mention camera diffraction above, this is the same thing as lens diffraction. I’ve decided to refer to it as camera diffraction because the camera is what’s changed. When I use the same lens on my XT3, I don’t notice the diffraction because the sensor doesn’t have enough pixels.
I would suggest a three-step process to avoid camera diffraction:
- Use the diffraction calculator linked below to understand the limits of your camera.
- Based on this, limit your aperture. This will limit your depth of field, which is where the third point comes in.
- Identify the best point of focus. Check that it’s far enough from the camera but still close enough for sharp focus. Also place it near to the centre of the frame rather than to the edges. Better still, try focussing manually and checking the edges of the frame at 100%.
The Diffraction Calculator
You will find the Diffraction Calculator I used on the PhotoPills website along with some great articles and other photography resources.
If you would like to know more about the high-resolution mode mentioned in this article read my assesment.
More Photography Tutorials
You’ll find more high quality, free tutorials on my Landscape Photograph Tutorials page.
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