You’ve probably heard about vignetting, chromatic aberrations or CA, and diffraction and you know that they have to do with deterioration of the image quality due to imperfections of the optic system of the majority of lenses.
And most probably you even know how to deal with them. But did you ever wonder how and why they appear? Today we will talk about what these three things are and teach you how to avoid them.
Vignetting is darkening of corners on the photo either due optics vulnerabilities or applied intentionally in editing software in order to channel the viewer’s attention to the center of the picture.
Vignetting is a very common thing peculiar to fixed lenses with a wide aperture and wide-angle lenses. In case of the former, the lateral light coming into the lens is partially blocked by the lens barrel since the aperture size is so large. In case of the latter, due to the optics characteristics the light hitting the edges of a wide-angle lens takes more time to travel to the camera’s sensor, causing image corners to darken.
How to fix it?
Let’s say that you are using a 35/50mm f/1.4 or f/1.8 lens. Just stop down the aperture by a step or two, making the aperture size smaller and letting the peripheral light enter, and you will have a lot less vignetting on your photos.
When it comes to wide-angle lenses or if you simply need to use the maximum aperture for shallow depth of field, use a feature built-in in your camera that minimizes vignetting or apply this feature in Lightroom.
Chromatic aberrations, or simply CA, are a common occurrence in the majority of lenses due to the lens dispersion, causing the light of different colors travel through the lens to the sensor at different speeds not coming to focus in the same place.
It works similarly to the rainbow when the light is dispersed and appears as different colors, exactly the same that happens on your photos in the corners or areas with high contrast and difference in colors. You see red, green, blue, or purple fringes.
The effect is most often seen in wide-angle, wide-aperture, and low-quality lenses, both prime and zoom. CA reduce the overall sharpness and contrast of the image.
How to fix it?
Try stopping down your aperture by a step or two in order to achieve a wider depth of field and put all details in focus, which will help you minimize CA. Apart from it, use the feature that removes chromatic aberrations in Lightroom on your every shot or apply automatic CA removal feature that may be built-in in your camera.
Some top-segment lenses fitted with special ED elements, standing for extra-low dispersion, minimize chromatic aberrations too.
Diffraction is a loss of sharpness and overall photo resolution that happens due to diffraction of light entering the lens through a small aperture hole, small f number. In this case the light rays become interfering with one another, which decreases the sharpness.
Want an easy example of how it works? Try closing your eyes tight and you will see everything less sharply. The same happens with your pictures when you shoot using small f stops.
How to fix it?
Depending on the size of your sensor and your lens, you will start seeing diffraction at various aperture sizes.
The best way to find out the optimal diffraction-less aperture size for you will be to shoot a piece of paper with some text on a colored background using apertures from f/3.5 to f/20. However, remember that in majority of cases diffraction effect becomes visible at apertures smaller than f/8 or f/11 so be sure not to close it down too tightly.
Now you know that vignetting and chromatic aberrations can be fixed in Lightroom and by stopping down the aperture by a step or two. However, everything is different in case of diffraction.
That’s exactly why every lens has a sweet spot of aperture, which lets the photographer reach the best result in terms of the image quality and avoid these three optical effects. We’ll speak about how to find your lens sweet spot in one of our next articles. Good luck!
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