How do you get an 800mmor even a 1200mm zoom lens on a point and shoot bridge camera?
Bridge cameras are well named. They’re a bridge between compact cameras (with often limited specifications) and more fully-featured system cameras such as DSLRs. Like compact cameras they’re not as big as a DSLR (though they’re not necessarily small either). And, like compact cameras, they also have a fixed lens (fixed in the sense that it can’t be removed, not in terms of focal length - of which more in a moment). However, like DSLRs, bridge cameras typically feature modes such as aperture priority and manual for greater control of exposure.
The Sony DSC-HX300. A new bridge camera with a lens that has an equivalent zoom range of 24-1200mm.
A recent trend in bridge camera design has been the superzoom bridge camera. These cameras have lenses that are the full-frame equivalent of a 28mm to 800, even 1200mm, zoom lens. As a full-frame DSLR user I find this seriously impressive. You’d have to have seriously deep pockets to be able to afford lenses that cover this focal length range. And it would have to be lenses plural. It would be economically impossible to design and build an equivalent zoom lens for a full-frame camera (if it were possible it would be a monster of a lens too).
The Panasonic DMC-FZ72. From the top it's possible to see how neatly superzoom bridge camera lenses fold up.
So how come a humble bridge camera can manage the feat in an affordable, smallish package? Well, it’s all down to sensor size. Bridge cameras (and compact cameras for that matter) have smaller digital sensors than both APS-C and full-frame cameras. The smaller the sensor the smaller the focal length of a lens needs to be for a given angle of view.
It's the size of the sensor that determines the angle of view of a lens
Let’s take a 50mm lens as an example. On a full-frame camera a 50mm lens has a (diagonal) angle of view of approximately 46°. However, fit a 50mm lens to an APS-C camera and the angle of view is reduced to 30°. This angle of view is closer to an 80mm lens fitted to a full-frame camera. Essentially the 50mm is ‘longer’ on the APS-C camera than it is on the full-frame camera. However, it’s not the focal length that’s changed – just the angle of view. All the other characteristics of the lens such as depth of field at each aperture is exactly the same no matter what camera the 50mm lens is fitted to.
This image was shot with a 50mm lens on a full-frame camera. If I'd used an APS-C camera I'd only have captured the area within the red box. On a bridge camera a 50mm lens would have captured the area within the blue box.
This is the key to why superzoom bridge cameras can be made at all never mind relatively cheaply. The sensor in a bridge camera is typically 5.6x smaller than a full-frame camera. If you were able to fit a 50mm lens to a bridge camera, the lens would have an angle of view of 8.7° or the equivalent to a 290mm lens on a full-frame camera. So, you don't need that long a focal length lens to achieve the equivalent of a 1200mm full-frame lens on a bridge camera. You only need a 200mm lens in fact, which isn't that difficult to build (though admittedly I'd find it difficult).
Although a 1200mm lens may sound fantastic, it's good to have a specific use for it – such as wildlife photography.
However, even though the real maximum focal length is 200mm, when you shoot you still have to use your bridge camera as though you were using a 1200mm lens. Any movement, no matter how small will cause camera shake. This means using a tripod or a seriously fast shutter speed (certainly higher than 1/1000 when used at maximum zoom). Still, that's a small price to pay for such versatility.