The main difference between these two camera types is the sensor size. Interchangeable lens cameras tend to have larger sensors than compact cameras. There are some exceptions to this rule, though, for example the Pentax Q system, which has a small sensor in a camera body with changeable lenses, and the Canon G1X, which has a large sensor in a fixed lens camera body.
I recently acquired the Olympus TG-310, a compact, rugged camera with a small sensor, for use when swimming, skiing, and so on. And I was interested in seeing what the real world difference between this camera and my Panasonic GH2 is. The two cameras are shown below, with the Olympus TG-310 to the right:
As mentioned, system cameras and compact fixed lens cameras tend to have different sized sensors. To illustrate that, here is a comparison of the relative sensor sizes of the Four Thirds sensor and the 1/2.3' sensor in the Olympus TG-310 compact camera:
The smaller sensor means that the camera manufacturer can cram more features into the lens more easily. So while the Lumix G 14-42mm kit lens seen on the GH2 above only has a 3x zoom and no macro mode, compact cameras tend to have much a larger zoom ratio, and a macro mode to boot. I write about this difference in the introduction to my Micro Four Thirds lens buying guide.
The specific compact camera still has fairly unimpressive optical features, though. This is because it is a rugged compact, designed to be waterproof, shockproof and freezeproof. Because of this design choice, it has a relatively small lens assembly, to keep the size and weight down. This dictates employing only a 4x zoom ratio.
I bought the camera very cheaply, since it has recently been obsoleted by the newer Olympus TG-320. It appears to share some components with similar cameras from Panasonic, most notably the Lumix DMC-TS10.
Looking at some of the specifications of the two cameras used in this test, we see that they are not altogether that different:
GH2 + Lumix G 14-42mm
|Focal length range (equiv)||28-84 (3x)||28-102 (3.6x)|
|Minimum focus (normal)||0.3m||0.6m|
|Minimum focus (macro)||N.A.||0.03m|
|Image stabilization||Optical||Sensor shift|
But these are just the specifications. Let's see what the difference is in terms of image quality.
I started with taking a basic landscape photo. I set both cameras to full auto, which is probably what a newbie would do. The zooms were both set to the widest setting. The cameras were handheld. Here are the two images, scaled down a bit, click to enlarge:
GH2, ISO 160, f/4.0, 1/160s
TG-310, ISO80, f/3.5, 1/60s
To compare them better, here are some 100% crops from the images:
While the scaled down images look fairly similar in terms of image quality, it is very clear from the 100% crops that the GH2 in fact has a huge advantage in terms of resolution.
Indoor photo with flash
To further look at the image quality differences, let's look at some images taken indoor with the built-in flash. The subject here is the LEGO Technic 9392 model. Again, I used full auto on both cameras.
GH2, ISO 160, f/5.2, 1/60s, f=33mm
TG-310, ISO100, f/4.7, 1/60s, f=11.8mm
We don't need to look at any crops here, we immediately see that the GH2 image is vastly better. One thing to note, though, is that more of the model is in focus from the Olympus TG-310. It has a deeper depth of focus. This is due to the smaller sensor, which keeps more of the subject in focus. This effect can be both positive or negative, depending on what you want.
Finally, I have tried to take night exposures with both cameras. I put them on a tripod, and still left them in full auto, at the widest setting. Here are the results:
GH2, ISO 160, f/5.6, 6s
TG-310, ISO100, f/3.5, 1/30s
In this case, the GH2 noticed that it was on a tripod, and gave me a long exposure of 6 seconds, straight from the full auto mode. This surprised me positively, I had guessed it would push the ISO up to expose it as much as possible during a short shutter time. It also stopped down the aperture to f/5.6, for better depth of focus, and set base ISO. Well done! Just what I would have done myself.
The Olympus TG-310, on the other hand, illuminated the scene with the flash, which gives a pretty good exposure of the handrail in the foreground. But the rest is pitch black.
For the sake of fairness, I gave it another chance, and turned off the flash, while still using full auto. Here is the result, at ISO320, f/3.5, 1/4s:
This image is barely usable, but still much worse than the results from the Panasonic GH2.
A compact camera can be small, cheap, and sport an impressive zoom and macro range. But the image quality tends to be much worse than an interchangeable lens camera with a larger sensor. Of course, there are enthusiast compact cameras too, with a somewhat bigger sensor than basic compact cameras, better and faster optics, and better image processing. But in demanding situations, they still cannot compete with larger sensor cameras.
Another item to point out is the ergonomics. The GH2 is a fairly small interchangeable lens camera, and some complain that the buttons are difficult to operate, being so tiny. But the Olympus TG-310 has even smaller buttons, and requires more dexterity to be operated. It also has fewer buttons, and requires more menu access to change common settings.