Sunday, 24 June 2012

Smaller lenses, smaller apertures

When the Panasonic G mirrorless interchangeable lens cameras were introduced in 2008, two kit zoom lenses were initially available. They were the Lumix G 45-200mm f/4-5.6 tele zoom lens, which is still in production, and the Lumix G 14-45mm f/3.5-5.6.

The latter was rather quickly replaced with the lighter and cheaper Lumix G 14-42mm f/3.5-5.6 in 2010. The newer lens has a 13% smaller front lens element, while retaining the same aperture specifications. Not bad!

2011 saw the announcement of newer zoom lenses in the premium X series: The Lumix X 45-175mm f/4-5.6 and the Lumix X 14-42mm f/3.5-5.6. See them below:



Front, from left to right: Lumix X 14-42mm, Lumix G 14-42mm
Rear, from left to right: Lumix X 45-175mm, Lumix G 45-200mm

The newer X lenses are smaller than the original zoom lenses, and retain the same aperture specifications. In fact, The Lumix X 14-42mm has a 35% smaller front lens element, in terms of diameter, compared with the original Lumix G 14-45mm lens. This corresponds to an almost 60% smaller front lens area, see the diagram below:



How is this possible?

One answer is that the lenses do not have the same maximum apertures. Sure, the end points are the same, f/3.5-5.6 for the kit zoom lenses and f/4-5.6 for the tele zoom lenses. But in the middle of the zoom ranges, the maximum apertures are smaller for the newer lenses. See the diagram below for an illustration of this fact:



The diagram uses logarithmic scale. As you can see, the maximum apertures are only the same in the start and end points of the focal length ranges. Inside the ranges, the newer lenses have a smaller maximum aperture. The Lumix X 14-42mm lens has a constant aperture of f/5.6 from f=32mm to the longest end.

This fact is generally not revealed in lens announcements or reviews. So, is Panasonic fooling us? Perhaps. By using "traditional" zoom end point apertures, Panasonic is not drawing attention to the fact that the newer lenses are in fact slower than the ones they replace.

Olympus appears to have chosen a different approach. Some of their premium lenses clearly feature slower zoom end points, e.g., the Olympus M.ZD 12-50mm f/3.5-6.3 and the Olympus M.ZD 70-300mm f/4.8-6.7.

Does this matter? I'd say hardly. Those who are interested can read about it here or in other sources. And since the difference is fairly marginal, much less than one stop, it will have very little practical impact. Modern cameras handle high ISO fairly well, so the loss of some aperture doesn't matter.

All in all, I've found the newer X branded lenses to give better image quality than the older lenses. So I am happy. It is the image quality that matters.

Quite recently, Panasonic has launched another tele zoom lens. It is the Panasonic Lumix 45-150mm f/4-5.6:


Again, we see the same aperture range as the other tele zoom lenses: f/4-5.6. And again, it has a smaller front lens element than the preceding lens. This time, though, the maximum focal length is smaller, at 150mm, which in part explains this.

But I would not be surprised if Panasonic again use the trick of having a more limited aperture as you zoom the lens over the focal length range.

I'm guessing that this new lens will replace the Lumix G 45-200mm f/4-5.6 as the entry level tele zoom lens. This will make more sense from a market perspective, since it will be easier for the sales personnel to explain why the 45-175mm lens is the more expensive, when it also has the longer zoom range. The current situation is a bit counter intuitive, where the 45-200mm lens is the cheapest, but has the longest zoom range.

4 comments:

  1. This is only partially true--or at least, it is only true for some lenses and not others. If you look at the aperture range of the non-power zoom 14-42 compared to the older 14-45, you'll find that the newer kit lens is actually faster in the middle of the range.

    14mm
    14-42 is f/3.5
    14-45 is f/3.5

    18mm
    14-42 is f/4
    14-45 is f/4.5
    25mm
    14-42 is f/4.5
    14-45 is f/4.9
    35mm
    14-42 is f/5
    14-45 is f/5.6
    42mm/45mm
    14-42 is f/5.6
    14-45 is f/5.6

    Granted the 14-42 still needs to be stopped down to get the same level of sharpness, most of the time to f/8, but even still the 14-42 is faster even though it has a smaller front element.

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    Replies
    1. Yes, you are quite right. I noted this fact in my article about the differences between the 14-45 and 14-42.

      I actually think the cheap Lumix G 14-42mm lens is a fine kit zoom lens, especially for the price.

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  2. This small pancake is charming indeed but I'd like it cheaper ;) half cheaper or sth ;) compared to dslr kitzooms it's just sooo expensive...

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  3. I nominated you for a Liebster! Check my blog’s home page.

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