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:

Lens	Lumix G 45-200	Lumix X 45-175	Lumix G 45-150
Max aperture	f/4-5.6	f/4-5.6	f/4-5.6
Announced	Sep 12, 2008	Aug 26, 2011	Jul 18, 2012
Length	100mm	90mm	73mm
Diameter	70mm	62mm	62mm
Weight	380g	210g	200g
Filter thread	52mm	46mm	52mm
Front lens element diameter	37mm	32mm	27mm

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 Lens	G 14-45mm	G 14-42mm	X PZ 14-42mm	G 14-42 II
Year released	2008	2010	2011	2013
Length	60mm	64mm	27mm	49mm
Diameter	60mm	61mm	61mm	56mm
Weight	195g	165g	95g	110g
Filter thread	52mm	52mm	37mm	46mm
Front lens element diameter	45mm	30mm	21mm	25mm

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.