This article will explain what aperture is an guide you on how to get sharper urbex images from your DSLR setup, sharper images make cool images.
What is an aperture?
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at the image plane.
If the admitted rays also pass through a lens, highly collimated rays (narrow aperture) will result in sharpness at the image plane, while uncollimated rays (wide aperture) will result in sharpness for rays with the right focal length only. This means that a wide aperture results in an image that is sharp around what the lens is focusing on and blurred otherwise. The aperture also determines how many of the incoming rays are actually admitted and thus how much light that reaches the image plane (the narrower the aperture, the darker the image) (ref1)
Why is this important?
Diffraction and circle of confusion – there are multiple indepth articles available for these. Two things affect the sharpness of an image, focus and diffraction – we will leave focus for another day and just look into diffraction in this article. Diffractions can be explained as when light comes through a small opening, how much light spread is observed. This is important as the more diffraction, the softer the images becomes.
Moving away from geek stuff, selecting the optimum aperture will provide you with with a sharp image.
Sigma 17-70 – aperture settings below. All images 500x crop at 55mm
Just on this practical test you can easily see the difference, F22 and F16 hold the sharpest results. F4.2 is pretty poor and even F8 is soft. The cost of shooting with aperture stopped down is a longer shutter speed, this is why we need a tripod when urbexing
Tokina 11-16mm – aperture settings below. All images 500x crop at 11mm
The Tokina shows a different set of results, sharpness seems to peak around F8, even F2.8 is pretty damn good. F22 and F16 looks a touch soft however no where near as significant as the Sigma.
Test your lens, test it to find the optimal aperture setting that fits your normal style of urbex. The Tokina and Sigma are different types of lenses and in differing price brackets so no conclusions are being made in direct comparison. The point here is that there not all lenses are made equal.
#ref1 – credits here