Compact cameras and apertures. Why only f8?

[JohnN]

I must have too much time on my hands

I think I understand what limits the speed of a lens, but why is the smallest aperture (or largest "f" value) limited to f8 on my G16. Why couldn't those clever engineers at Canon give me an f22 (for example) ?

 

[JackConnick]

Aperture is a ratio of the lens opening size. Compact camera lenses are quite small as their sensor size is small. So the effective opening size at f/8 is equivalent to the much smaller aperatures on larger APS-C and FX sensors, etc.

Also remember that use of small apertures can lead to less sharpness after about a mid-way point due to diffraction. Most of the time a mid aperture is sharper.

 

[Barmaglot]

Why couldn't those clever engineers at Canon give me an f22

You have to remember that the aperture number that you see is relative - it's not 'f22' but rather 'f/22', where the 'f' represents the focal length, which you divide by a number to arrive at the aperture diameter. In addition, you need to keep in mind the crop factor - for G16, with its 1/1.7" sensor, it's 4.55. The focal length listed in its specs is 28-140mm equivalent, which means that it gets the same angle of view as a full-frame (35mm film, 36x24mm frame size) camera with a 28-140mm lens, but the actual focal length range on the G16 is 6.1mm to 30.5mm. Finally, you need to take into account diffraction - as the rays of light pass next to the sharp edge of an aperture blade, they get slightly deflected, which results in loss of sharpness - if most of the light goes through open aperture center, this is negligible, but if the center is very very small and a significant proportion of light passing through it gets affected by the edges, you will see significant loss of quality.
Now, for a full-frame camera with a 28mm lens, an f/8 aperture means 3.5mm diameter, which is pretty good, and f/22 means 1.27mm - entering diffraction territory, but still workable. However, with a 6.1mm focal length, f/8 is already a 0.76mm pinhole, and taking it to f/22 would result in just 0.277mm - barely larger than a hair, and quite useless for imaging. On a full-frame camera at 28mm, this aperture would be an f/100 or thereabouts.

 

[Interceptor121]

You need to think equivalent f/stops
The G16 sensor is 4.3 stops away from full frame so your f/8 is actually f/35 on full frame
This is the reason why, put aside autofocus challenges, it is easier to shoot macro on compacts
This also means you need less powerful strobes to achieve foreground illumination taking the whole set up to a more compact level

 

[Chris Ross]

Even f8 is well into diffraction on the small pixels of compact cameras. On the TG-6 you have f2/2.8 at the wide end as apertures and f8 is achieved with an ND filter for that very reason. Peak performance is going `to be around f4 which is f17 equivalent depth of field.