G1X: Shake Icon

At slow shutter speeds, a blinking orange icon is displayed on the lower left portion of the G1X display.  This icon is to warn you that shutter speeds may be too slow and that a tripod is needed.  Once you know what it is, you realize that the icon is a shaky camera.  So when does the warning appear?

I set up a simple experience in which focal length, shutter speed, aperture, Image Stabilization and ISO were varied and noted the fastest shutter speed for which the shake icon remained turned on.  As suspected, ISO and aperture were quickly eliminated as having an effect.  The shake icon activation logic is a simple function of focal length and shutter speed; however, Image Stabilization (IS) is definitely a factor.

There is an old rule-of-thumb of 35mm photography that says the slowest shutter speed that should be hand-held is 1/focal length.  For example, when shooting a 100mm lens, a tripod should be used if the shutter speed is slower than 1/100 second.  This “rule” was developed before the introduction of Image Stabilization.  Of course, it is not a law of nature – only a rough guide for pointing to the need for a tripod.  A little too much coffee and a tripod is always needed!

In very rough terms, the old 1/focal length rule applies to the G1X when IS is turned OFF.  With IS turned ON, the shutter speed can be 3x slower before the shake icon appears.  All these “calculations” (if indeed they are done) are then rounded off.  Strangely (to me), the effects of digital zoom are not a factor.  Also, the IS effect on shake icon activation is identical whether IS is for single shot or continuous.  “Power IS” does not seem to matter. 

I can remember the simple rule of thumb but here’s a chart of the data.

G12: Focal Lengths

The G12 has a 5 to 1 zoom lens with focal lengths ranging from 6.1 mm on the “wide angle” end to 30.5 mm on the “telephoto” end.  The lens is not infinitely adjustable; there are 14 different focal lengths.  The available focal lengths are:

6.1 mm	12.1 mm
6.8	13.8
7.4	15.7
8.1	18.1
8.9	21.5
9.8	25
10.8	30.5

These are the focal lengths needed to do depth of field calculations using programs like DOFMaster.  There is also a DOFMaster App for the iPhone that is very handy and accessible in the field. The iPhone App does not always have the precise G12 focal length as part of its database.  For those focal lengths, I just use the closest available value.

G9: Aperture variations with zoom

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The aperture in a camera’s lens is simply the opening through which light passes to strike the sensor or film. Instead of quantifying aperture size directly, for example, speaking of an 8mm opening, we usually speak of the “f-number” or “f-stop”. The f-stop is the relative aperture in comparison to the focal length of the lens; that is, the f-stop is the focal length of the lens divided by the diameter of the aperture. For example, if the focal length is 100mm and the aperture is 25mm diameter then the f-stop is 100 / 25 = 4. Since most people use aperture and f-stop interchangeably, we’d probably say that the aperture was “f4” in that example. For more details, check Wikipedia.

What about f-stops for zoom lenses? If the physical opening remains constant but the focal length changes, then the f-stop changes with the zoom setting. This is the situation with the Canon G9 and most digital cameras having built-in zoom lenses. By tinkering with my G9, I found the zoom points for which the maximum aperture (f-stop) changes and constructed the table below.




The table shows, for example, that the maximum aperture for the wide angle (7.4mm focal length) is f2.8 but near mid-zoom, say 25mm focal length, the maximum aperture is f4. At maximum zoom (44.4mm focal length) the maximum aperture is f4.8.

Notice that, contrary to the simple definition, the maximum f-stop for the G9 is not exactly proportional to the focal length. This apparent contradiction is an indication that the available physical aperture is also changing. If this were not the case, then the f-stop at 44.4mm focal length would be f16.8 instead of f4.8 !

Try this little experiment. Put the G9 (probably any camera) at maximum wide angle, Aperture priority (Av mode) at f8. Oh – you might want to turn off the focus assist light! Point the camera towards yourself and look deep into the lens. Push the shutter button halfway (you don’t have to actually take a picture) and watch carefully for a little bit of movement deep in the assembly. You’ll see a small circular opening become even smaller. Now change the f-stop to f2.8 and try again. You’ll see that the small opening doesn’t change. Now zoom to about mid-telephoto and repeat the tests. Notice that the initial size of the circular opening (the physical aperture) is somewhat larger at mid-telephoto. Zoom all the way in and repeat. Although it becomes more difficult to see deep into the lens, the initial opening becomes even larger at maximum telephoto settings and it changes from a large opening to a smaller one at f8.

Finally, remember that, counter-intuitively, a larger f-number (f-stop) actually means a physically smaller opening (aperture) that lets in less light.

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