Photographers have a dilemma. If you want your photographs to have the largest possible depth of field – from the foreground to infinity – a small aperture is absolutely necessary. At the same time, though, a small aperture causes your photograph to lose sharpness from diffraction. So, where’s the sweet spot? In this article, I will cover how to choose the sharpest possible aperture for such a photograph, including mathematically accurate charts (free for printing) that are easy to use in the field.
When photographers talk about lens diffraction, they are referring to the fact that a photograph grows progressively less sharp at small aperture values – f/16, f/22, and so on. As you stop down your lens to such small apertures, the finest detail in your photographs will begin to blur. With good reason, this effect can worry beginning photographers. However, if you understand how diffraction impacts your photographs, you can make educated decisions and take the sharpest possible photographs in the field. In this article, we will explore the topic of lens diffraction in detail and talk about different techniques you can utilize to avoid it.
A decentered lens contains one or more optical lens elements that are either moved or tilted from the principal axis of the lens. Such shifting or tilting of lens elements can potentially lead to blurring / softness of parts of the image due to divergence of light rays. While very slight decentering of optical elements can be observed in many lenses, especially on superzooms, severe decentering and tilting can render the whole image blurry, with the lens unable to achieve good sharpness across the frame.
When light rays coming from a bright source(s) of light (such as the sun or artificial light) directly reach the front element of a camera lens, they can reflect and bounce off different lens elements, diaphragm and even off the sensor, potentially degrading image quality and creating unwanted objects in images. Better known as lens “flare”, the effect can impact images in a number of ways: it can drastically reduce image contrast by introducing haze in different colors, it can add circular or semi-circular halos or “ghosts” and even odd-shaped semi-transparent objects of various color intensities. Flare is not always undesirable in photography though – sometimes in is used creatively to add artistic elements to images. In fact, lens flare is often deliberately added to movies and computer games to add a sense of realism and boost the visual experience of the viewer.
Vignetting, also known as “light fall-off” (sometimes spelled “light falloff”) is common in optics and photography, which in simple terms means darkening of image corners when compared to the center. Vignetting is either caused by optics, or is purposefully added in post-processing in order to draw the viewer’s eye away from the distractions in the corner, towards the center of the image. Depending on the type and cause of vignetting, it can be gradual or abrupt. There are a number of causes of optical vignetting – it can naturally occur in all lenses, or can be caused or increased/intensified due to use of external tools such as filters, filter holders and lens hoods. In this article, I will talk about each type of vignetting and also discuss ways to reduce or increase the amount of vignetting in photographs using post-processing software like Lightroom and Photoshop.
In photography, there are two types of distortions: optical and perspective. Both result in some kind of deformation of images – some lightly and others very noticeably. While optical distortion is caused by the optical design of lenses (and is therefore often called “lens distortion”), perspective distortion is caused by the position of the camera relative to the subject or by the position of the subject within the image frame. And it is certainly important to distinguish between these types of distortions and identify them, since you will see them all quite a bit in photography. The goal of this article is to explain each distortion type in detail, with illustrations and image samples.
When my article on field curvature was published a while ago, where I talked about how one could do a quick analysis of lens MTF data and determine if it exhibits any field curvature, some of our readers expressed interest in understanding how to read MTF charts. Since we talk quite a bit about lens performance and MTF data here at Photography Life, I decided to write a detailed article on the subject and do my best to thoroughly explain everything related to MTF curves, charts and all the verbiage that comes with them.
A fellow photographer recently asked me how much image degradation one would see with each Nikon teleconverter. As a nature photographer, I have been wondering myself about this for a while, but never had a chance to actually quantify what the image degradation figures would look like when using the TC-14E II, TC-17E II and the TC-20E III with Nikon lenses. I have been relying on field use and my vision so far and here is what I have thought about each teleconverter.
Field Curvature, also known as “curvature of field” or “Petzval field curvature”, is a common optical problem that causes a flat object to appear sharp only in a certain part(s) of the frame, instead of being uniformly sharp across the frame. This happens due to the curved nature of optical elements, which project the image in a curved manner, rather than flat. And since all digital camera sensors are flat, they cannot capture the entire image in perfect focus, as shown in the below illustration:
If you are wondering about how to calibrate lenses, this article has detailed explanations and different methods of AF fine tuning. Due to the nature of the phase detect autofocus system that is present on all SLR cameras, both cameras and lenses must be properly calibrated by manufacturers in order to yield sharp images. Various factors such as manufacturer defects, sample variation, insufficient quality assurance testing/tuning and improper shipping and handling can all negatively impact autofocus precision. A lot of photographers get frustrated after spending thousands of dollars on camera equipment and not being able to get anything in focus. After receiving a number of emails from our readers requesting help on how to calibrate lenses, I decided to write this tutorial on ways to properly fine tune focus on cameras and lenses. Lens calibration is a complex topic for many, so my goal is to make this guide as simple as possible, so that you could manage the process by yourself, while fully understanding the entire process. In addition, I strongly recommend to follow these tips every time you purchase a camera or a lens in order to identify and address any potential focusing issues. But I have to warn you – this article is NOT for beginners. If you just got your first DSLR, you might get very quickly frustrated with the calibration process.