When I was writing up my thoughts on Nikon’s 200–500 I started thinking about the way I think about zoom lenses compared to the way I generally see most people thinking about zooms. I don’t expect, or want, to change any minds here. Instead, what I’d like to invite you to be introspective for a moment, and think about how you use your gear and how that’s influenced by the way you think about the gear.

What I’m really talking about here are mental models. Wikipedia defines a mental model as an explanation of someone’s thought process as to how something works in the real world. It’s how our minds relate the world around us and it guides how we interact with things. One way of looking at this is that we may find something intuitive if our mental model and reality match up.

One mental model for a zoom lens could be of a lens that allows you the control to adjust framing or magnification of your subject as you see fit. If you want a looser crop, you zoom out a bit; tighter, zoom in. You could maybe say, a zoom is not so much a lens made up of lots of focal lengths, but one that’s adjustable over the whole range to your needs at the moment.

Another mental model could be of a lens that is really a replacement for a distinct set of primes—sure there’s still the fine grained variability but it’s a secondary consideration. A 24–70 is useful because it replaces a 24, 28, 35, 50, and closes in on replacing an 80mm lens too. It’s not that you look at the numbers and only shoot only at those specific focal lengths, but that primarily you think about the lens as a replacement for those other lenses you’d otherwise have to carry and change between.

The distinction may be all philosophical, and it may all just be in my head. However, I’d invite you to stop for a moment and think about how you shoot with a zoom when you use one. While you’re doing that, I’m going to tell the story of a zoom that doesn’t really zoom right.

In the history of photography there have been few lenses that have provided multiple focal lengths in one package, but didn’t arrange them such that there was a continuous progression from smallest to largest. One, if perhaps the only, example of this that I know of it Leica’s Tri-Elmar 28–35–50mm f/4 ASPH (also known many as the MATE short for Medium Angle Tri-Elmar).

Though Leica would point out that the lens was in fact a true optical zoom, the design of the lens, and the design of a Leica M range finder, resulted in it really only working easily at the 3 focal lengths listed. In no small part, this is because the zoom positions were arranged as 28mm, then 50mm, then 35mm as you turned the zoom ring. If you were at 35mm and wanted to zoom out to 28mm, you first zoomed in to 50mm before zooming all the way back out.

Would you find yourself massively annoyed by the behavior of the LeicaTri-Elmar 28–35–50 f/4 ASPH?

What about if the zoom positions were in order, but the lens simply didn’t produce a useable image at anything but those positions?

In many ways, I don’t really see a problem with the design of the MATE. But in much the same way, I frequently see a zoom lens as a collection of distinct primes with the continuous extra coverage being an added bonus.

Like I said, I didn’t set out to change any minds or make any great revelations. This was an exercise in thinking about how you think about things, at least that’s what I’d like to think.