How can a lens have a 'speed'?

This week's Photography Fundamentals column answers a question that came to me as an anguished plea in my Twitter feed from a relative newcomer to photography. In short: How can a lens have a speed? Whilst he knew that speed equated to aperture and that a 'fast' lens was one with a large aperture, the terminology felt far from intuitive. How could an opening behind a lens be described in terms of 'fast' or 'slow'?

I'm guessing that if he were perplexed by the use of the the word 'speed' in conjunction with 'lens', there are a few other people out there who find the concept that lenses can be 'fast' puzzling, too. Or illogical. Or something that's accepted terminology. Or something that made sense many years ago but has since become obsolete. This might help.

It's not actually as illogical as it sounds to refer to lens speed. It's more a case of joining the dots.

We know that large apertures are referred to as 'fast'. A lens with a large maximum aperture, let's say ƒ/1.8 for the sake of an example, is described as a 'fast' lens. We know that the larger the aperture, the more light is able to reach the sensor (or film, if you're old school). We know that by the virtue of the exposure triangle, the more light that is able to hit the sensor, the shorter the time the sensor needs to be exposed to capture the image and the faster the shutter speed we can use. The shorter exposure time is a direct result of the larger aperture. The larger aperture allowed for a faster image capture, hence a large aperture is a fast aperture.

If you were wondering, yes, it's for this reason that higher ISOs are referred to as fast ISOs: increased sensitivity allows for faster capture.

A lens can have a 'speed' then, because it refers to how fast it can allow you to capture your images, which I hope isn't nearly as illogical as it first seemed.

Rule of thirds << Photography Fundamentals >> Time-lapse

Book review: The Canon 6D Experience

The Canon 6D Experience is part of Douglas J. Klostermann's series of e-book guides to Canon's and Nikon's dSLRs. There are ten Canon books and five Nikon books, ranging in price from $7.99 for guides to the oldest models of camera to $14.99 for the latest cameras. I've been taking a flick through it and seeing how it fits in with my use of my Canon 6D.

The best way to describe the Canon 6D Experience is as an augmented instruction manual. It doesn't just explain what a function is and how to operate it, but what effect or impact it will have on your photography. It shows you how to expose and re-compose your images, provides examples of different apertures and ISOs, and explains about metering. It covers a great many of the functions that I never use in my camera because I almost always shoot in Raw and almost never venture into liveview mode. Towards the end of the book it moves away from the camera itself and covers composition and discusses lenses.

This, then, is perhaps where this book falls down, or falls between two stools. For someone new to dSLRs and still finding their way in photography, would they be starting out with a 6D? In the book's introduction it says: 'If you are relatively new to dSLR photography and are still in the process of learning all the controls of a dSLR and the exposure concepts of digital photography, you have perhaps ventured towards the proverbial deep end of the pool by choosing the advanced 6D!' Of course there will be some beginners who've gone straight for the 6D, but they're not the camera's intended market. This guide will suit them well, but I'm not sure how many will be needing it.

For anyone who's comfortable with Canon cameras and is a competent photographer, a lot of the book's content is superfluous. It isn't that there isn't useful material in there, but that it's buried amongst the information we already know. Having a smaller, more dense publication that looks at the high level functions of the camera and compares it with other models might be more useful.

All of this leads me to think that if the books in this series that cover the lower specced models are written with the same attention to detail, they would be extremely valuable guides for people finding their way in dSLR photography.

On a very picky production level, I would have liked to have seen references to other chapters in the book numbered, or even hyper-linked. It is an ebook, after all. That would have made navigation a great deal easier.

My verdict, then? At $14.99 I can't really recommend the Canon 6D Experience; I just don't think it offers enough to kind of photographer who'd be using this camera. (Unless you really have thrown yourself in at the deep end.) If you're newer to photography and have a Nikon D5200 or a Canon 700D, for example, do check out the other books!

The Canon 6D Experience, by Douglas J. Klostermann, published by full stop and available for download from Dojoklo.