The equivalent focal length relates to the crop factor of a smaller sensor relative to a full format sensor. This is probably the least disputed topic of the whole discussion.
Some of you may already shout in agony but let's swallow this for now. a Micro-Four-Thirds camera with a 150mm f/2.8 lens.an APS-C format camera with a 200mm f/4 lens.a full format (35mm) camera with a 300mm f/5.6 lens.Equivalence is a SYSTEM discussion, not only a lens discussion.įor the sake of simplicity let's pick a concrete example that we'll use throughout this article: A lens makes only sense in the context of a camera and THIS is where things are getting complicated when comparing different SYSTEMS. A naked lens is nothing more than an expensive paperweight. Whatever we mention in our review, these physical characteristics are NEVER disputed. No matter what we are going to discuss below - the focal length and aperture of a lens isn't going so change. The lens aperture is usually specified as an f-number, the ratio of focal length to effective aperture diameter.
The aperture determines how collimated the admitted rays are. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. Aperture: In optics, an aperture is a hole or an opening through which light travels.For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. Focal length: The focal length of an optical system is a measure of how strongly the system converges or diverges light.I mention the obvious here because some people are really getting religiously defensive when it comes to a discussion about system equivalence.īefore diving into the details let's make a clear statement first - the focal length and aperture are static physical values. YOUR preferences are the only ones that matter to YOU. All systems compromise on something (size/weight/image quality/handling)- the important thing is that a system is right for YOU. In fact, I am not using full format cameras by choice whenever I can. This article is NOT an article promoting full format cameras. This will surely not end the discussions but it illustrates our view on this - take it or leave it. For the sake of efficiency, it was about time to write an article about it. Over the last few years we have received several messages asking about and disputing the system equivalence that we are mentioning in our APS-C and Micro-Four-Thirds lens reviews. Equivalent Focal-Length, Aperture and Speed of Camera Systems
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