Short Description
Large SLR Lens Collection
If you own an SLR and you're serious about photography you'll start a lens collection.
Håkan Dahlström's lens collection, via Flickr.
The easiest way to think about zoom is in terms of magnification, for instance a camera with a 4x zoom lens will allow you to magnify the image up to 4x bigger. Lenses get their zoom rating by taking the ratio between the longest and shortest focal lengths. So for example a 35-105mm lens will be rated as 3X ( 105/35 =3). The question you need to ask yourself though is magnified compared to what? That's a good question and we'll get to that in a second.
SLR vs Digicam
SLRs do not come with lenses built in, digicams do, that means you'll need a lens collection for your SLR, Although you may start with one you'll quickly feel the need to acquire more. Digicams on the other hand come with lenses built in, what they have is what you get.
Visual Difference Between Zoom Levels
When you hear 2X zoom you think twice as big, but that's actually not true. It's useful to understand zoom as a form of cropping. When you zoom in you take a crop of a portion of the scene and make it take up the whole image. Of course its done optically so you don't lose quality. When you zoom in 2X you capture 1/2 the height and 1/2 the width of your original scene. So 2X zoom means you can only capture 1/4 of the 1X image. The image below illustrates this difference - as you can see 8X zoom actually capture just 1/64 of the scene - which equates to a tonne of zoom - 64X the pixels of the zoomed in portion of the scene.
Visual Difference Between 1X, 2X, 4X and 8X Optical Zoom
The following image illustrates how much area each zoom level captures of a scene. 1X zoom captures 100% of the scene where as 8X zoom captures 1.6% of the scene - a huge difference! Remix of Photo by
Stuck in Customs via Flickr.
Examples of Different Zoom Levels
The following images each illustrates the zooms depicted in the scene above - illustrating the difference in a resulting photo.
Example of a 1X Lens
This is the scene at 1X zoom, In this case 1X is 14mm so there is negative magnification relative to the human eye but a field of view that is close to the human eye.
Example of a 2X Lens
This is the scene at 2X zoom, In this case 2X is 28mm so there is a slight negative magnification relative to the human eye and the field of view is smaller than the human eye.
Example of a 4X Lens
This is the scene at 4X zoom, In this case 4X is 56mm which is similar to the magnification of the human eye but a much smaller field of view.
Example of a 8X Lens
This is the scene at 8X zoom, In this case 8X is 110mm which is slightly more than twice the magnification of the human eye.
Travel Zoom Cameras
Here are some cameras, we refer to them as travel zooms, that are both compact and offer a high amount of zoom. These cameras represent an excellent compromise between size and zoom and are great for traveling. As you can see in the above example 8X zoom is quite significant and that is the minimum zoom we require for the travel zoom rating.
Understanding Zoom and Focal Length
Although there are technical definitions of what focal length means for the purpose of understanding a zoom rating its best to keep it simple. So we'll define focal length as the level of magnification you're getting, the more focal length the more magnification. On any given lens the shortest focal length represents the minimum level of magnification and the longest represents the most magnification, the ratio between them is the total zoom range of the lens. Most people would guess a 10x zoom lens would let them "see" 10x farther with their camera - but that's not true - you're actually getting less magnification than you think because part of the zoom rage is wideangle and has negative magnification - you need this for taking group shots and panoramic photos.
What a Zoom Rating Doesn't Tell You
Two cameras could both be rated 4x zoom and actually have different levels of magnification. For instance both these lenses are 3x zoom:
- 35mm - 105mm (105/35 = 3)
- 50mm - 150mm (150/50 = 3)
The problem is these are drastically different lenses - same magnification ratios but each covering different magnification spectrums. Not every camera has the same starting point (aka minimum focal length) and that's the best thing to look at.
Understanding Focal Length and Magnification
The best way to understand focal length is to use a point of reference. The best point of reference is the human eye. If you look through a camera and things appear about the same size than its convenient to think of that focal length as zero magnification - the focal length that corresponds to zero magnification happens to be about 50mm. If you look in and things are smaller its like negative magnification - you can fit more in the picture than you'd expect (we call that wide angle) - that's anything less than 50mm. Finally if you look in and things seem bigger than that's positive magnification - this is what you naturally think about when you think zoom, this applies to focal lengths great than 50mm.
Superzoom Cameras
Super-zoom digital cameras provide a minimum of 8X zoom with some cameras offering as much as 30X zoom, most offer at least 15X zoom. These offer incredible levels of optical zoom so that you can get close to the action regardless of where you are. Great for sports and wildlife photography when you're a significant distance from your subjects.
Digital Zoom
Digital zoom is not zoom, it is simply an automated way of cropping the picture and resizing it back up creating the effect of zoom by "zooming in on the image". This crop ends up creating the same effect as zoom but quality is sacrificed as only a portion of the sensors resolution is used. Optical zoom on the other hand uses all of the sensors resolution. We highly recommend you never use digital zoom and turn it off on your camera settings so it doesn't engage.
Optical Aberrations in Zoom Lenses
The greater the zoom on a lens the more likely there is to be some form of optical distortion, typically chromatic aberration and field curvature, and especially at the high end of the zoom range. Nonetheless, most consumers may not even notice the effects given gains made in construction techniques of compact lenses that correct reasonably well for problems. The alternative is to own an SLR and with a huge collection of lenses that will provide a equivalent range to a super-zoom, this is likely an order of magnitude in additional cost to a super-zoom and for most people spending 10x the amount isn't an option.
Conclusions
- 8X or greater zoom is significant - up to 64X the print size of a distant object
- The lens on most digicams is both telephoto and wide angle so the magnification relative to your eyes will be about 1/2 as much
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Cheers
"Of course its done optically so you don't ->loose<- quality."
"loose" should be "lose"