One of the most important aspects photographers consider when choosing an optical lens is its sharpness. optical lenses do not always provide the same sharpness at all their apertures, which is why you need to consider the optimal aperture of the optical lens to get the best results. But what is the optimal aperture or sweet spot and how do you find it on every optical lens?
The optimum aperture of your optical lens
The optimum aperture of an optical lens is nothing more or less than the f-number (or f-stop value) at which the optical lens maximizes its sharpness and reduces distortion and chromatic aberration, in other words, the aperture at which the optical lens works best. For reasons of optical lens construction, the least sharp apertures are always the extremes, i.e. the most open and the most closed. This means that you should not abuse the most open aperture much if you want to go for quality, even if you love the blur produced by that f/1/8 optical lens.
Normally, even when you want a very shallow depth of field, you have to close the aperture at least one stop to gain sharpness. So, if you have an f/2.8 optical lens and want to use an open aperture, for example, try shutting down at f/4 to gain a little more definition. Relying on bright optical lenses is very important because this way it is much easier to avoid extreme aperture values. Closing the aperture all the way is even worse, because the effect of optical diffraction comes into play, producing even worse results in terms of sharpness.
A curious detail is that the maximum aperture or sweet spot is a term from racquet sports such as tennis or padel: the sweet spot is the central point of the racquet that provides greater control, as well as a more powerful impact and bounce. Athletes strive to always hit the ball at this spot because they know that’s where they’ll get the best results in the game. So, you’re starting to understand this concept better applied to photography, right?
How do you find the maximum aperture on your optical lens?
Ideally, you should know the optimal aperture of your optical lens beforehand. To do this, you can use tests and reviews or advice from the manufacturer. Unfortunately, you won’t always have access to this information and will have to find it on your own.
The quickest and most convenient way to find the optimum aperture for your optical lens is to use the intermediate aperture, usually between f/8 and f/11. Any of these apertures will give you the maximum sharpness available on your optical lens. So when you don’t care about the depth of field of a scene, try to always use an f/9 type aperture and that way you will maintain the optimum aperture, which will ensure the greatest sharpness from your optical lens.
Aperture sharpness test
If you have time and want to know exactly how your optical lens performs at each aperture to find out which is the sharpest when you shoot, you have no choice but to test them one by one. So do a f-stop sharpness test. The sharpness test is very simple, but it will require precision and attention to detail.
Place the camera on a tripod to ensure that you have the same frame for all the pictures you take. Next, select a frame that is composed of only one plane (so as not to confuse blur with lack of sharpness). A brick wall might be the ideal frame for this test, so that you have the same depth of field regardless of the f-stop you use.
Take a picture with each f-stop. You can see the difference using the extreme f-stops, but if you want to be more efficient, focus on the intermediate f-stops, which is where you’ll find the optimum aperture. As a rule of thumb, you can use the range between f/5.6 and f/16, but remember that the most likely optimum aperture is between f/8 and f/11.
Once you have the series of brick wall photos, use digital processing software to crop them to 100% and compare the shots taken at each aperture. The sharpest photo will tell you which f-stop your optical lens performs best at. That’s it! You now know the optimal aperture of your optical lens!
Closing the diaphragm
Remember that when you close the aperture a lot, the diffraction effect you want to avoid will appear. This creates a dilemma when you want to maximize the depth of field. The maximum aperture is indeed on an intermediate diaphragm. Fortunately, if you are careful and use an intermediate aperture, it is relatively easy to maximize the depth of field and the only thing you need to do is to take into account the hyperfocal distance.
Now that you know what the optimum aperture or sweet spot of your optical lens is, there is a question that must be on your mind: do I always have to shoot with the optimum aperture of my optical lens? The answer is no. Knowing the optimum aperture will help you to know which f-stops will give you the best sharpness in your shot, but whether you use it or not will depend on the type of picture you want to take or the light conditions you find.