Ever wondered why full frame lenses go to much smaller f-stops than MFT lenses?
Even if you don’t know what diffraction is, you might still want to read this article. Every photographer knows, if you shoot your lens wide open, it is not as sharp as if you step the aperture down a little. But if you step it down too far, you get another problem: your photos will start to lose sharpness, but that is due to another effect called diffraction.
Now I don’t want to write one more article on the topic of diffraction in general, because other people have done so already and much better than I ever could. So instead I will just link to the fantastic article of photographylife. If you want to know in-depth what diffraction is, just read their article – it is time well spent.
Furthermore: diffraction is a problem that affects all lenses and cameras, so you may be wondering: Why is this article specifically targeting Micro Four Thirds cameras?
WARNING: Simplification ahead!
This is because diffraction (and when it starts to become a problem) is related to the size of the pixels, which are usually smaller in cameras with smaller sensors, due to the fact that people still want a lot of megapixels. If you increase the megapixels at the same sensor size, or if you decrease the sensor size at the same megapixel count, the size of each pixel has to shrink.
Now on a full frame camera, I would usually still be fine with shooting at f16, not having to worry much about diffraction. It starts to slowly affect the image quality for pixel-peepers, but the effect is so minimal that it usually doesn’t matter. However, on APS-C (or very high megapixel full frame cameras) I would already not go beyond f11 and on MFT I always recommend people to not go below f8, unless they have a good reason (i.e.: forgot an ND filter and the ISO is already at its lowest setting).
However, instead of me telling you what to do, just use the following example to see for yourself. By clicking on the f-stop numbers, you will see a 100% crop of the same image on an Olympus E-M1 Mark II, with a 12-40 f2.8 Pro lens, shot at all major apertures. The camera was on a tripod and wirelessly configured as well as triggered. So the only change is the aperture.
The image I used for this, was an iPhone 6S package. This is not because I particularly like iPhones (I don’t, I use an Android phone), but because I needed small, sharp text, where sharpness changes would be very obvious.
It is also important to state that, depending on how large you print or how magnified you look at your image, you may be able to get away with smaller apertures without visible deterioration in image quality. The loss of contrast that starts at f11 is still easily compensated, but the loss of sharpness becomes rather extreme at f16 and smaller.
In some situations a loss of sharpness is not even a problem, if you are shooting at high ISO, you are losing a lot of information anyways and a small loss in sharpness might not be so noticeable as well.
At the end of the day it is important to know the limitations of your camera and why images can lose sharpness at small apertures. It doesn’t mean you should never use those apertures. You can and sometimes compromise on the sharpness to get the shot exactly the way you want it. And that’s totally ok.