There're many things which can affect Depth of Field (DoF), which as we've seen can radically affect overall sharpness; from the point of view of your camera the main items are:
Focal length of your lens
Distance from lens to subject
Aperture used for a photo, and ...
Size of FILM or DIGITAL SENSOR.
ALL these items are interrelated; changing any one will affect DoF.
The one item over which you have NO control is Film or Sensor size (except when you buy the camera, and you don't really have a lot of choice anyway).
Depth of Field is quite a complex subject when you investigate in depth (pun intended); one day I'll write a little tute with the maths involved, but for now I ask that you simply accept the following.
The smaller the Film / Sensor size, the greater is DoF, MOST OTHER THINGS REMAINING EQUAL.
The larger the Film / Sensor size, the smaller is DoF, MOST OTHER THINGS REMAINING EQUAL.
Have a look at the following table:
| Film/Sensor size | 120-6x6cm | 35mm (24x36mm) | Digital Sensor* 15x22mm |
| Lens (Equiv. to "standard" lens) | 80mm | 50mm | 27mm |
| Aperture used | f8 | f8 | f8 |
| Distance, camera to subject | 5m | 5m | 5m |
| DoF Near | 3.84m | 3.58m | 2.66m |
| DoF Far | 7.15m | 8.28m | 39.42m |
| Total Depth of Field | 3.31m | 4.69m | 36.75m |
*The figures provided for Digital Sensors are for an "average" sensor, as there are many different sized sensors in common use.
The lenses used for our examples are those that are regarded as the so-called "standard" lens for that size film / sensor. A "standard" lens is regarded as approximately equal in focal length to the diagonal of the fim / sensor size.
As you can see from the table, you don't have to worry too much about there being "not enough" DoF with your digital camera, rather, most owners complain that because of the inherent greater DoF, they can't get a sufficiently SHORT DoF when they want it for creative photography.
This table should also explode the myth that, "Digital cameras have better Depth of Field". They do, but ONLY if they use a small sensor, and it has nothing to do with being "digital"; a film camera with similar film/lens specs would exhibit the same properties.
The Last Word: