Diffraction! it reduces the sharpness and contrast of your image, thus the overall resolution - isn't it scary?
You will have diffraction issue if using a too small F-stop. Few years back when I first learn about it, I started to limit my aperture setting to what could avoid it all together despite any given photography situation. Back then I have two lenses, so I got to test them to know what is the 'too small' value for these lenses:
1. Canon EF 100mm f/2.8 USM Macro and
2. Canon EF 16-35mm f/2.8 L II USM.
I found that the images begin to appear softer at F8 in the former, and F9 in the latter. So I stop shooting beyond these limits.
Today, I have changed my mind about the factors to consider when setting the F-stop.
Yes, deffraction can reduce the overall resolution of the image. But there are more to consider when 'creating' a photo.
At a glance, how these two photos differ to you? Which one do you like more (assuming both of them have the birds on the roof, so those birds are not the deciding factor)?
At small size you can hardly tell any difference isn't it?
Due to diffraction, the one (above) with F22 appears softer, and provides lesser details, especially at the focal plane (the wooden wall facing the viewer). However, it does provide much greater DOF (depth of field).
See the 100% cropped side-by-side comparison and you'll know what I mean:
After the detailed comparison, what do you think?
For this landscape shot, I preferred the grass in the foreground to be in focus, so I don't mind to sacrifice some loss of resolution at the focal plane.
Btw, if I didn't show the 100% cropped, I doubt anyone will notice the diffraction issue when viewing the smaller picture, which is often the case when we share something on the internet.
Another situation when I don't mind to have a little diffraction is when I want to create the star effect in night-time photography. To me, the dazzling touch of the star effect in exchange of some lose of resolution at the focal plane is definitely worth it.
The star effect starts to show at F5.6, but even at F8.0, it is still too weak to make an impact to me. I personally like to use F16, which create a big-enough star effect while the image didn't suffer so much from diffraction issue.
Perhaps a better example to illustrate the impact of star effect in night-time photography is through a picture with bigger light sources - didn't the starry street lights catch your eyes?
You will have diffraction issue if using a too small F-stop. Few years back when I first learn about it, I started to limit my aperture setting to what could avoid it all together despite any given photography situation. Back then I have two lenses, so I got to test them to know what is the 'too small' value for these lenses:
1. Canon EF 100mm f/2.8 USM Macro and
2. Canon EF 16-35mm f/2.8 L II USM.
I found that the images begin to appear softer at F8 in the former, and F9 in the latter. So I stop shooting beyond these limits.
Today, I have changed my mind about the factors to consider when setting the F-stop.
Yes, deffraction can reduce the overall resolution of the image. But there are more to consider when 'creating' a photo.
At a glance, how these two photos differ to you? Which one do you like more (assuming both of them have the birds on the roof, so those birds are not the deciding factor)?
At small size you can hardly tell any difference isn't it?
Due to diffraction, the one (above) with F22 appears softer, and provides lesser details, especially at the focal plane (the wooden wall facing the viewer). However, it does provide much greater DOF (depth of field).
See the 100% cropped side-by-side comparison and you'll know what I mean:
 |
| Focal plane: Left - No diffraction at F8, sharper image and better colour contrast. Right - At F22, image is softer due to diffraction. |
 |
| Background: Left - better resolution. Right - softer image, although not as obvious as at focal plane. |
 |
| Foreground: Left: DOF is shallow - blurry foreground. Right: With F22, the DOF extended to the foreground. |
After the detailed comparison, what do you think?
For this landscape shot, I preferred the grass in the foreground to be in focus, so I don't mind to sacrifice some loss of resolution at the focal plane.
Btw, if I didn't show the 100% cropped, I doubt anyone will notice the diffraction issue when viewing the smaller picture, which is often the case when we share something on the internet.
Another situation when I don't mind to have a little diffraction is when I want to create the star effect in night-time photography. To me, the dazzling touch of the star effect in exchange of some lose of resolution at the focal plane is definitely worth it.
 |
| F5 (above) and F16 (below). |
 |
| 100% cropped: F5.6 (left) and F16 (right). |
 |
| 100% cropped: F8 (left) and F16 (right). |
Perhaps a better example to illustrate the impact of star effect in night-time photography is through a picture with bigger light sources - didn't the starry street lights catch your eyes?
 |
| F16; 6s; ISO160 |
