4 October 2014

Canon recently announced the Powershot G7 X, which couples what appears to be the 1-inch detector from Sony’s RX-100 with a fast 24 to 100 mm equivalent focal length zoom lens. It’s all bundled up in a very compact package.

Canon GX 7

The Canon G7 X (from the Canon press kit)

I have a Canon G15, and while I love its portability, it is somewhat limited in image quality by its small 1/1.7-inch sensor. Is the G7 X the camera for me?

In ambient light, sure. However, the G7 X doesn’t have a hot shoe for an external flash, which means it’s pretty much limited to the built-in flash. The built-in flash is probably fine for a little fill to complement direct sunlight, but on its own it’s going to give the usual awful results. With my G15, I frequently use a little Speedlite 270EX II for softer bounce flash. It fits quite nicely in my man-bag alongside my G15.

Canon G15 and with Speedlight 270EX II

The Canon G15 with the Speedlight 270EX II

On the other hand, the G7 X is effectively much faster than the G15. The following figure shows the equivalent f-number of the two cameras against their equivalent focal lengths. For the G7 X, I took information from the DP Review first-impressions review, which shows the real aperture increasing roughly linearly from f/1.8 at 24 mm to f/2.8 at 50 mm and then staying constant out to 100 mm.

Plot of the effective aperture of the Canon G15 and G7 X

As you can see, the G7 X is about 1.5 stops faster around 24-28 mm and about 1 stop faster from 50-100 mm.

I normally don’t like to push my G15 beyond ISO 400; at higher ISOs the image noise becomes too prominent. That suggests that I could use the G7 X up to ISO 1000 at 24-28 mm and ISO 800 at 50-100 mm. (All other things being equal, when the equivalent aperture is one stop faster the exposure time can also be one stop faster without reducing image quality. The exposure time scales as the inverse of the ISO, so if the equivalent aperture is one stop faster, the ISO can be a factor of two larger.)

The problem of course is that in low light, even at ISO 1000, exposure times can be too long and images can be blurred by camera shake or unwanted subject movement. I’ve used my G15 to check exposure times indoors with normal lighting at ISO 1000 and f/2, finding typical exposure times of 1/30 to 1/60 of a second. That’s fast enough that image stabilization can eliminate camera shake, but not fast enough to eliminate subject motion when photographing kids, for example.

Furthermore, having a bounce flash allows me to work even in much darker conditions and to have some creative control over my light. I’d not have been able to take either of these two photographs with ambient light or built-in flash.

Example A Example B

All cameras involve compromises. The G7 X would a huge improvement over my G15 in ambient light, but the lack of a hot shoe would be a significant limitation; 90% of my photography would benefit and 10% would be impossible. It’s a close call, but for the time being, I’ll not be trading in my G15.


I said “pretty much limited to the built-in flash”. That’s not quite true. One could use the built-in flash to trigger off-camera flash, but you’d lose TTL and so would probably need several attempts to get the exposure right. That’s fine for a posed subject, but not in a more dynamic environment.


© 2014 Alan Watson Forster.