Sphericalaberration and chromatic aberration

Last week we looked at using shutter speed and how it controls motion in your image. For that effect we used the Shutter Priority mode, for creating shallow depth of field we use the aperture so we’ll switch over to Aperture Priority mode.

If you’ve ever wanted to create images with a beautiful, soft out of focus background this article will give you some tips and guidelines to do just that. We’re going to look at how to use Depth of Field (which is simply how much of your image is in focus) and what settings to use to optimize this effect.

Sphericalaberration formula

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Sphericalaberration in a lens

You can use the widest aperture, and the longest lens but if you put your subject right up next to the background you’ll never get it blurred. The further away from the background the subject is, the more out of focus you can make it.

In this example, you can really see how the background starts to come in focus as you close the aperture down to a smaller and smaller opening. Look at the patio and the snow on the railing, compare the first and last images in that area. In the image using f1.8 the snow is so out of focus, it has almost started to become circles of white (ironically called circles of confusion, go figure!). Notice how far away that background is, and how widely out of focus I can throw it and have a good result, even using an aperture like f5.6

Notice how different the last shot above looks than the first one! Keep in mind you do NOT have to buy expensive $2000+ lenses to get this look. Sure you can if you feel rich, but if wanna save your pennies opt for a less expensive fixed lens with a wide aperture such as a 50mm f1.8 (less than $150 usually) or an 85mm f1.8 (around $600 or so).

What issphericalaberration and How can it be corrected

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I prefer the slightly longer 85mm because, besides using a large aperture, the focal length also plays a part in how much the background gets blurred.

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Coma aberration

Sphericalaberration diagram

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If you want to make a nice out of focus background, and utilize shallow depth of field choose a large aperture opening, the biggest you have on your lens. Aperture settings can be a bit confusing because they are inverse of what you’d expect. The largest aperture opening is actually represented by the smallest number. An example of that would be f1.8 or 2.8. Choosing a small aperture like f22 of f32 will give you a large depth of field where it’s possible to get your entire scene in sharp focus. Each setting has applications in certain scenarios, it’s important to know which aperture to use to get the affect you desire.

The three factors that affect background blur are: aperture, focal length, and distance of the subject to the background

On a Canon camera you will want to choose the Av (which means aperture value) setting, and on Nikon choose A. That will put you in aperture priority where you will be choosing the aperture setting and the camera will be choosing the shutter speed to make the correct exposure.

What issphericalaberration in Physics

The three factors that affect background blur are: aperture (using a wide one), focal length (longer lenses enhance the affect), and distance to subject and subject’s distance to the background.

The following images were all shot with an 85mm f1.8 lens (that just means the largest aperture possible on it is f1.8). With such a lens it is possible to get the background way out of focus.

So DO go try this at home. Try it with something close to the background, then far away. Try it with a 12mm lens, 50mm lens, then a 200mm and see what happens. Share your results in the comments section and please share this article using the social media links below if you enjoyed it.

Sphericalaberration example

So what can we take away from this experiment? Go out and try doing this yourself. Set your camera on Aperture Priority and run the full range. Make sure then when you get to the smaller apertures (f11, 16 or 22) that your shutter speed isn’t getting too slow for hand holding. If you need to, use a tripod to steady the camera. Don’t let your shutter speed go lower than 1 over the focal length of your lens (so using a 200mm lens you need to shoot at 1/200th of a second or faster to get no camera shake) . I pushed that a bit here using 1/60th with an 85mm lens but it still came out relatively sharp. I could have used a tripod or increased my ISO to give me a bit more shutter speed room.

Let’s do one more example, using that subject to background distance factor I mentioned above. In the following images I focused on the tree which was fairly close to me. The background house, yard, etc, is quite a distance away. Let’s see how the same settings we used above play out in this scenario.

Have you ever noticed everything you shoot with wide lens all seems to be in focus? While the depth of field mathematically is actually the same as with a longer lens – the wide makes everything appear more in focus, partly because of distance to subject.

Spherical aberration is an imperfection of the optical system of the human eye. The role of spherical aberration of the human eye in the quality of vision and pseudoaccommodation is reviewed. Spherical aberration is an imperfection of the optical system of the human eye. In most cases, due to well-developed neuroadaptation, it is insignificant for the perception of the image. Nevertheless, its role in modern ophthalmology is far from straightforward. On the one hand, there are clinical scenarios in which an excess of spherical aberration degrades the retinal image and leads to a high dissatisfaction rate among patients.©Recently, there is a growing interest in the modulation of spherical aberration in the clinical setting. Modern intraocular lenses as well as laser refractive procedures are aimed at interfering with spherical aberrations of the optical system in order to increase range of pseudoaccommodation. Here, we review the role of spherical aberration of the human eye in the quality of vision and pseudoaccommodation.