The advantage of a point-and-shoot camera
Although compact digital cameras are generally less capable than larger Digital-Single-Lens-Reflex (DSLR) cameras, I'd like to note that small-sensor cameras can sometimes be advantageous. Pen photography is a case in point.
To explain, let's perform a thought experiment with three imaginary cameras:
- A Canon Powershot SX 160 IS,
- An APS-C camera with a crop factor of 1.6 such as the Canon 60D, and
- A full-frame 35mm digital camera.
In this experiment, we'll try to take the same pen photograph (same perspective, same depth-of-field, same field-of-view, and same exposure) with each. Then we'll see what camera settings we'll need to use to accomplish that feat. I'll try to keep the technical lingo to a miniimum.
Let's start with the SX160. It has a 1/2.3" sensor (a mere 6.17mm wide). That is about 1/5 the area (actually a bit less) of a full-frame 35mm camera. In photo terms, This camera has a "crop factor" of 5.2. Don't read too much into that, it's simply a way to compare the "field-of-view" that different cameras have. Anyway, let's say that we've taken a pen photo with the following settings:
- Distance - 3 ft away from the pen (to get approximately arms-length perspective).
- Lens Focal Length - 40mm so that the pen fills the frame.
- ISO - 100 for minimum digital noise.
- Aperture - f/4 so the entire pen is in focus.
- Shutter Speed - 1/30 second (given the available light).
Now let's try to take an identical photo with the APS-C camera. To get the same perspective, we'll have to put the camera at the same location (remember, perspective is solely a function of distance). In order to fill the frame (same field-of-view), we'll have to use a 135mm lens (crop factor 5.2 vs 1.6 - the sensor is bigger, so we'll need to zoom in). We'll keep ISO at 100. Now, here's where things get tricky. Depth-of-Field (DoF) is primarily a function of distance, focal length, and aperture. We've kept the distance the same, but increased the focal length. To match the DoF, we'll have to use a smaller aperture (higher f/ number). It turns out that the necessary aperture is f/16. See
A Flexible Depth of Field Calculator if you want to play with the numbers yourself. That is a difference of 4 f/stops - and each stop halves the amount of light transmitted. In order to achieve the same exposure, we'll have to use a 16 times longer shutter speed - or about 1/2 second. To recap, those settings are:
- Distance - 3 ft away from the pen.
- Lens Focal Length - 135mm.
- ISO - 100.
- Aperture - f/16.
- Shutter Speed - 1/2 second.
Switching to the full-frame 35mm DSLR, to take the same picture, we'd need to use these settings:
- Distance - 3 ft away from the pen.
- Lens Focal Length - 200mm.
- ISO - 100.
- Aperture - f/22.
- Shutter Speed - 1 second.
Let's talk about camera shake. The general rule of thumb is that if you're shooting handheld, then in order to avoid motion blur, you have to use a shutter speed of 1/(lens focal length) or faster. With image stabilization, that number gets smaller. The SX 160 IS does have optical image stabilization, so you should indeed be able to use a 40mm lens focal length at 1/30 second without blur.
There's no way (even with image stabilization), however, that you can handhold a 135mm lens for 1/2 a second, let alone a 200mm lens for a full second. You'll have to use a tripod (and either remote shutter release or self-timer). Moreover, those shutter speeds are also sensitive to shake from the mirror moving and vibrations from the floor. For best results, you'll also need to use mirror-lock-up and stand still during the exposure.
If you want a faster shutter speed with the DSLRs, you'll need more light - which translates to more expensive studio equipment.
So, I hope you see that a compact digital camera can have its advantages.
Regards,
Eric
