Choosing Your Format
The three common interchangeable lens camera formats based on sensor size, from smaller to larger are Micro 4/3, APS-C and full frame. All three systems have matured to include features like dual memory card slots, superb lenses in commonly needed focal lengths, weather and dust sealing, video recording and lots of accessories.
If your intention is to produce large detailed images with the greatest amount of creative control and the deepest choice of lenses and accessories, a full frame system is your best choice. The down sides of a large full frame system are its cost, substantial bulk, weight and obtrusiveness. This matters especially when you are carrying your own gear on long trips. My philosophy is I only take as much gear as I can fit in a single bag that I can comfortably carry myself.
As a traveler I am often rolling my suitcase with my gear on my back, walking long distances through airports and train stations, loading and unloading all my stuff at security checkpoints and standing in line for long periods of time at any hour day or night. That is why, after years of travel, I have converted to APS-C as my primary system.
APS-C systems are considerably smaller, lighter and generally less obsrusive than full frame systems and Micro 4/3 are smaller and lighter still. The down side of the smaller formats are increased noise at higher ISO, slightly less overall dynamic range and the reduced shallow depth of field that the lenses can produce. These are trade offs that need to be weighed carefully when considering which format to buy into.
Keep in mind that technology continues to improve with every new generation of camera sensor and processor and the amount on noise produced is really very mild and you have to pixel peep at 100% magnification for it to be noticeable. I have not found noise in my APS-C system to be an issue even at 8000 ISO.
Crop Factor
| Camera Type | Sensor Dimensions in mm | Current Max MP |
| Micro 4/3 | 17 x 13 mm | 20.4 MP |
| APS-C | 24 x 16 mm | 24.2 MP |
| Full Frame | 36 x 24 mm | 50.6 MP |
If you look at the column for sensor dimensions you will notice that a micro 4/3 sensor is about half the size of a full frame sensor and this influences the way the camera sensor “sees”. So between full frame and micro 4/3, there is a 2x crop factor when comparing lens focal length.
Looking at an APS-C type camera sensor, its dimensions are half way in between full frame and micro 4/3 so it “sees” with a 1.5x crop factor to produce an equivalent angle of view.
Here is an example of a “normal” lens and it’s equivalents in the three formats. The important thing to notice is that Angle of View is about the same on all three focal lengths.
| Camera Type | Lens Focal Length | Lens Diagonal Angle of View |
| Micro 4/3 | 25 mm | 46.8 degrees |
| APS-C | 35 mm | 44.1 degrees |
| Full Frame | 50 mm | 46.8 degrees |
However, the Micro 4/3 and APS-C lenses would be smaller and lighter than the equivalent full frame version making the lens and camera easier to carry and less obtrusive. This matters when walking around the streets, photographing people, and lifting the camera to make snap shots. Less weight equals less inertia, less neck, shoulder and back strain and a less obtrusive system. A smaller system draws less attention than a larger more noticeable one.
Depth of Field
Depth of field is the zone of acceptable sharpness a lens sees from near to far at a given aperture. For instance, a full frame 50mm lens has a depth of field at f/8 of about 6 feet. Therefore if you focus on an object 10 feet away, anything 3 feet in front of and 3 feet behind that object will be in focus. Make sense? The same lens opened up to f/2 will have a depth of field of only about 16.5 inches.
Taking a photograph with an APS-C camera and lens with the same angle of view, that is 44.1 degrees and 35 mm focal length at f/8, the depth of field is 8 feet 8 inches and at f/2 it is 1 foot 10.6 inches or just under two feet.
A Micro 4/3 camera and lens with the same angle of view of 46.8 degrees and 25 mm focal length, will have a depth of field of 15 feet 4 inches at f/8 and at f/2 it will be 2 feet 9 inches.
Again we see the effects of sensor size acting in a similar fashion to the way it did when looking at crop factor. A Micro 4/3 camera has about twice the depth of field of an equivalent lens at the same aperture with the same angle of view. The APS-C camera is about half way in between. But really it’s a function of focal length, a 35 mm lens is still a 35mm lens and a 25 mm lens is still a 25mm lens. It’s the cropping in as a consequence of sensor size that gives them a similar angle of view.
Depth of field is a creative choice and it’s various styles go in and out of fashion like the wind. Unless you are portrait photographer, don’t choose a system based solely on shallow depth of field. It is doubtful to play much of a factor at all in most travel photography.