Saturday, 20 July 2013

Smaller lenses, smaller apertures

Panasonic recently launched their third tele zoom lens, the Lumix G 45-150mm f/4-5.6. It is impressively compact considering the specifications:

LensLumix G 45-200Lumix X 45-175Lumix G 45-150
Max aperturef/4-5.6f/4-5.6f/4-5.6
AnnouncedSep 12, 2008Aug 26, 2011Jul 18, 2012
Filter thread52mm46mm52mm
Front lens element diameter37mm32mm27mm

So, how can Panasonic design a smaller lens with a smaller front lens diameter, and still retain the same aperture range, f/4-5.6? The answer is simple: They cheat.

Well, "cheat" may be a bit too strong word, as the aperture range is indeed f/4-5.6 for all of them. But what the specifications don't tell you, is that the aperture between the short and long ends is different. This diagram sums up my point:

If you took the average aperture over the focal length range, then you would see that the newer lenses have a smaller average aperture. Hence, while the specifications look the same, the smaller lenses are giving you a smaller aperture on average. I guess there is no way to avoid this: Panasonic cannot cheat the laws of physics. If they make a smaller lens, then the aperture must be smaller.

The same also goes for the kit zoom lenses. Here are the four kit zoom lenses from Panasonic:

Lumix LensG 14-45mmG 14-42mmX PZ 14-42mmG 14-42 II
Year released2008201020112013
Filter thread52mm52mm37mm46mm
Front lens element diameter45mm30mm21mm25mm

I only have the two in the middle, but for them, we again see a clear correspondence between the front lens diameter and the aperture range:

The most recent kit zoom lens is remarkably compact, and has a very small front lens element. With this in mind, I would guess that the aperture is not linearly decreasing as you zoom, but looks more like the Lumix X PZ 14-42mm in the diagram above.

So, is this a problem? Based on my own experience, I tend to use the zoom lenses the most in the very short or long end. And in those positions, I get the aperture from the specifications, so there is no change. However, when using the lenses somewhere between the short and long ends, the newer and smaller lenses will give a smaller aperture.

But the difference is not huge. At the very most, it is one half stop. But mostly far less than this. So I think few users will notice any change.

On the other hand, the size of the lenses is important to many people. After all, if size was not important, why would we stick with the Micro Four Thirds format? For example, the Sony NEX system cameras are not a lot larger, but feature a larger APS-C sensor. It is the lenses, though, where the main difference in size is. And this is where Panasonic can make a difference. The cameras cannot be made significantly smaller, given that there must be some grip surface and a screen. But, as they have demonstrated, the lenses can be miniaturized even further. That is one way to differentiate themselves from the competition.


  1. It'll be interesting to see the new Panasonic 14-140 compared to the old. I suspect the same "spec cheating" may be happening on that lens as well, although the wide end of the zoom is actually faster (f3.5)!

    I agree that for the extremes focal lengths, the specs are the same, which is often where you might be using a kit zoom. But on a longer telephoto zoom like the 45-XXX lenses, I at least find myself using the middle of the range quite frequently.

    I'm surprised that few review sites disclose this information, as it would be useful in comparing zoom lenses. SLRgear usually has it listed, but not many others.

    1. One could say that the original 14-140mm already does this: The max aperture is f/5.8 for a large part of the zoom range. I think that very likely, this will apply to the new 14-140mm as well. But it gets f/5.6 as the upper aperture range, which is better.

      I'm still anticipating that the 14-140mm becomes a very good lens. Panasonic have had a lot of experience since making the first one, which is not very good, in my opinion. At least the new one will be more portable.

      And that is one of the big problems with the original one, as I see it: It is too big and heavy.