When all else fails
Are you still unhappy with the sharpness of your images? Isn’t it too much you want?
A digital camera is basically not capable of providing absolute sharpness. Most photo sensors are equipped with a special anti-aliasing filter that slightly blurs the image so that any point of the original scene in all cases is perceived by more than one photodiode. This is called antialiasing (antialiasing) or smoothing and is necessary to prevent moiré-striped artifacts that can occur when photographing fabrics and other items that have a periodic, repetitive structure.
The use of a Bayer filter in the design of most cameras also does not add sharpness.Each photodiode of the matrix with a Bayer filter is responsible for only one of the three colors (red, green, or blue), and the full image, in which each pixel contains information about all three colors, is formed as a result of interpolation, whose algorithms are very clever, but still not all-powerful.
Lenses are also far from ideal. Beautiful MTF curves do not guarantee absolute sharpness. In fact, curves only help us roughly compare lenses with each other, taking into account only their frequency-contrast characteristics.
It should be remembered that ringing-sharp images are always obtained by artificially increasing the sharpness using either the camera itself or the image editor. Reducing the resolution of a multi-megapixel image also visually improves its clarity.
Almost all lenses are cut in the center, especially when they are set to one or two steps. Most lenses lather around the edges if the aperture is wide open, but this makes absolutely no difference. No one will shoot at a large aperture in bright light, and at dusk or indoors, when you are forced to open the aperture, the corners of the frame do not bother you much, since they are usually dark and do not contain important details. If you open the aperture in the light, then most likely you need a small depth of field and, therefore, the blurring at the edges is only to your advantage, because it helps to better highlight the subject. Finally, a good photographer always tries to avoid sharp, contrasting objects on the periphery of the frame, as they distract attention from the plot center.
Don’t think about being too sharp. You risk losing sleep, rest, and appetite without any reward.
How do I check the sharpness?
If you are inclined to scrutinize your photos for sharpness, first make sure that you are doing it correctly. What does right mean? Here’s what:
Always view images at one hundred percent magnification. Any scale other than 100 % is generated based on the original image using resampling algorithms, which are not always good, and worst of all, differ from the different programs you can use to view it. You can increase the image to 200 or even 300%, but only if you use the nearest neighbor interpolation method (also known as step interpolation). If the program does not allow you to select this algorithm, stop at 100 %.
Use the native monitor resolution. It only provides per-pixel sharpness. By reducing the resolution, you may make the image larger, but you will inevitably blur it to some extent.
The VGA cable that connects the monitor to the video card, due to its analog nature, can distort the information transmitted over it. Do not forget to sync the monitor with the video card signal, since this can be done automatically on most monitors. An even more progressive solution is to use a digital DVI connection.
If your monitor is configured correctly, each pixel of this image should be clearly visible. The presence of bands is not allowed.
With regard to the verification of photographic equipment, I highly recommend you don’t use a test table. No lens, except for macro lenses, is designed for photographing flat surfaces. Our world is at least three-dimensional. When you shoot flat tables, the curvature of the image field does not allow for uniform sharpness at the same time at the center and edges of the frame, because the center and edges are at different distances from you. This is especially evident when the depth of field is low. You run the risk of being disappointed in a lens that might have shown its best when shooting real, three-dimensional scenes.
When testing the lens, shoot distant objects in such a way that the focus falls on infinity. This will ensure the most uniform sharpness throughout the frame, even at large apertures. It is best to shoot trees and other natural objects arranged on the principle of a fractal, i.e. parts of which repeat a single whole. You need the same level of detail at any zoom level. Man-made objects, especially primitive test tables, do not have this property.
When hunting for front-or back-focus, don’t forget that many lenses are characterized by certain compromises. For example, a zoom lens may have a small back focus in the teleposition and an equally small front focus in the wide-angle position. The focus accuracy may also vary depending on the focus distance. If these errors are small and the focus falls within the grip area, then you should have no reason to worry. In any case, you need to believe first of all the results of real shooting.
For the same lens, the sharpness may float depending on the focus distance, and for zoom lenses, it may also float depending on the focal length. This is normal – the more versatile the lens, the more compromise solutions used in its design.
It is necessary to distinguish defects in photographic equipment from design features. For any lens, you can choose the conditions under which it will not show its best side. This is not marriage. You just went beyond the capabilities of your hardware. Now you know what not to do with it, what aperture values, focal lengths, and other parameters are good and what are not. To make the most of this information is an opportunity that is shamefully neglected.