What is an internal zoom lens, and do you need one?

When Nikon launched its new Nikkor Z 24-70mm f/2.8 S II professional standard zoom for its Z-mount mirrorless cameras, it made a great play on its internal zoom mechanism. So what is this, and why is it so important now?

An internal zoom lens is one where the lens barrel doesn’t extend or contract as you change the zoom setting. Instead, all the zooming is done my moving groups of lens elements within the lens barrel, which stays the same length all the time.

This is a pretty expensive way to make a lens, as reflected in the $2,797 / £2,599.00 launch price of the Nikkor Z 24-70mm f/2.8 S II, though there are other improvements to this lens that will account for some of this cost too, including a revised optical formula with dual-sided aspherical lens elements, new Silky Swift Voice Coil Motor (SSVCM) AF, a de-clickable control ring and an all-up weight of just 675g. The original Nikkor Z 24-70mm f/2.8 S is still a very good lens, but this new version has several key advances.

So what’s the big deal about internal zoom lenses? Here are two key advantages:

• The center of gravity stays constant. This may not be a big factor for regular photography, but it does mean that if you’re using this lens on a gimbal stablizer, you won’t have to keep rebalancing the gimbal for different zoom settings. It also means that you won’t have to keep adjusting the counterbalance on a video tripod head.
• Dust and moisture sealing is easier. With no extending lens barrel, it means there are fewer ways for dust and moisture to get in, and Nikon does say that its new lens has better sealing as a result. This doesn’t necessarily apply to all internal zoom lenses, but it is a better design in this respect.

Internal zoom designs do sound like a win-win situation, but apart from the potential cost increase, there is another less obvious downside. Internal zoom lenses don’t get longer as you zoom in, but they don’t get shorter as you zoom out. You’re always packing and handling quite a long lens, regardless of your zoom setting. It’s interesting not that Canon chose a more compact extending zoom design for its pro-level RF 70-200mm f/2.8 L IS USM, which is only 146mm long when retracted.

Internal zoom lenses are nevertheless desirable in the broader ‘storytelling’ and ‘creator’ markets. In other words, for people who shoot video, and this is an increasingly important sector in the camera market and perhaps even the most important today.