More Silly Numbers: The UltraZooms

March 25, 2010

As someone who rarely photographs sports or wildlife, the world of long-zooms is not one I pay much attention to.

But there’s trouble brewing lately, in the “bridge camera” market; and it’s reached a point even I can’t ignore.

Yes, just as with megapixels, camera makers have launched another numbers race—this time over zoom range.

Currently, bragging rights go to Olympus, with their SP-800UZ (“ultrazoom,” geddit?). While it shares an alarming 30x zoom range with Fujifilm’s HS10, the Oly is biased more towards the telephoto end. And so, the SP-800UZ wins the zoom war with a zany maximum of 840e!

Olympus SP-800UZ

Olympus: My Numbers Are Biggest!

The outsized lens makes the SP-800UZ one rather odd-looking camera. And despite the SLR-ish hump on top, there is actually no eye-level viewfinder. You must frame using the back LCD—holding the camera away from you.

Now, for those who photograph birds, zoo animals, stadium sporting events, etc., I’ll admit the handiness of having a long zoom range.

But 840e is getting into crazy-magnification territory. Just locating the subject will be a challenge (especially with  unsteady arms-length viewing). For reference, we’re talking more than double the magnification you would typically buy in binoculars.

Needless to say, aggressive two-stage antishake becomes mandatory in UltraZoom cameras. Even so, you’d better pray for strong sunlight to keep shutter speeds brief. And once your subjects are really in the distance, no lens will remove the milky haze of the atmosphere itself…

Nonetheless, all the major camera makers are now cranking up their UltraZoom specs. (Panasonic is being the most conservative, with “only” 18x on their FZ35.)

The styling of UltraZooms usually mimics the serious look of a DSLR. But in fact, all of these models employ the same little trick:

The imager in these cameras is nowhere near the APS-C format found in DSLRs. In fact, it’s under 8% of their sensor area. (A so-called 1/2.3″ chip is approximately 4.6 x 6.2 mm.)

This lets camera makers scale down all the lens dimensions by the same proportions. So, a focal range that would require a bazooka-like barrel on APS-C can be made smaller than a beer can instead.

And the volume of glass required for a given lens design (and thus, its weight) shrinks even more dramatically—to almost 1/40th. You can see why camera makers became so fond of this little gimmick.

But small sensors are prone to all the curses this blog has talked to death already: Picture noise, and ugly noise-reduction; poor dynamic range; and susceptibility to diffraction blur.

Also recall that the “brightness” of a lens (its widest f/stop) is actually a ratio: f/numbers are the focal length divided by the aperture diameter.

The physical diameter of the glass limits the second number; so as you zoom in, lens brightness drops. The Olympus SP-800UZ lens specs are 5.0–150 mm focal length; f/2.8–5.6 in aperture. That’s right—you sacrifice two whole f/stops at the long end of the zoom range.

In the case of the Olympus SP-800UZ, this raises another troubling question. To cram 14 megapixels into such a small sensor, each one can only measure 1.44 microns across.

But when your lens is set at f/5.6, diffraction creates an Airy disk almost 7.6 microns wide.

So when you’re fully zoomed in, how sharp can your photo even be? The smallest point of light theoretically possible smears across a dozen pixels. And this is before considering lens aberrations (which are probably significant too, at the extremes of the zoom range).

So if an UltraZoom is what you need, don’t let me stop you from buying one.

But just don’t expect it to rewrite the laws of physics.


4 Responses to “More Silly Numbers: The UltraZooms”

  1. […] a backside-illuminated sensor uses it. It seems particularly popular in today’s nutty “Ultra Zoom” market […]

  2. theinfernal Says:

    I’d like it if you pointed out that since 2X digital zoom sacrifices a spot of light, and APS-C is bigger than 1/2.4″ by fourteen times, therefore a camera with APS-C can digitally zoom 3.75X before the sensor becomes cropped to the same size as the one in the superzoom and theoretically have the same image quality.

    For example the f2.8 24mm eq. lens in the NEX system can zoom up to 90mm before a compact camera becomes comparable to it. Bear in mind the pixel pitch in the NEX is bigger and only the centre (the optically best part) of the lens will be used, so the NEX should still beat the compact.

    I’m particularly addressing the NEX + 16mm because this combo is almost as small as a large compact.

    • petavoxel Says:

      I take your point; but the exact numbers are a little hazier. In principle, a lens designed to cover a smaller image format can (and needs to) achieve a higher resolving power. Whether that actually happens in practice (given the tolerances of manufacturing and assembling those lenses) is a different question.

  3. petavoxel Says:

    I don’t think it’s an accident that in DP Review’s latest roundup of Ultrazoom models, it was two cameras with a less extreme 18x and 20x zoom range which got their top image-quality scores.

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