Friday, January 13, 2006

Zoom Zoom Zoom

I'm not talking about Mazda, sorry.

I've been lusting after a DSLR (Digital Single Lens Reflex) camera lately to replace my Sony DSC F717. The 717 has served me very very well and I'm rather fond of it as a general media-capturin' machine but the amateur photography nerd in me has become unsatisfied with its speed and response. It has a decently fast lens but somewhat slower focusing and shot-taking speed. It's also not (of ocurse) on an interchangeable lens system so I'm stuck with the one lens.

So a DSLR it is. The problem with most entry level DSLRs (the only ones I can afford at the moment) is that there is a "crop factor." Imagine a piece of 35mm film, the standard against which most other things are relevant. A 1.5 crop factor DSLR camera contains a piece of digital film that is 2/3 the size of a 35mm piece of film. Said in reverse, we have to multiply the area of a digital piece of film by 1.5 to reach the normal size of 35mm film. But what is a "digital piece of film"? It is a rectangular sensor which converts light to electronic signals which are then sent off to be processed into a digital picture. The two main technologies right now are CCD and CMOS and while each has its own advantages and disadvantages, they are both sensors which convert light into electronic signals.

If you take a look at camera prices and specifications, you'll notice that a Canon EOS 5D is priced around $3k while the new (and in many respects much better) Nikon D200 is priced at around $1700. What's the deal and is the Nikon that much of a better camera? Well yes and no. The D200 certainly has a faster burst speed (5 frames per second), for example, but the 5D is a full frame DSLR while the D200 is still at a 1.5x crop factor. This means that for any given lens at any focal length, the D200 will only see the middle 2/3 of what a 5D will see.

This is a disadvantage for the D200 in some ways. Let's say we couple the 5D with a 12-24mm lens. In 35mm terms, a 50mm lens is about what the standard human eye sees, a 12mm lens is very very wide and a 200mm takes the human field of vision and "zooms in" roughly 4 times. On a 5D, the 12-24 is a very wide angle zoom lens. The lens can send the same information to the D200 but the since since all lens measurements are based on the 35mm standard, it is really sending a 12-24 field of vision to a 35mm piece of film. Remember now that the D200 can only see about 2/3 of this "film". The center 2/3 of a 35mm piece of film seeing things through a 12mm lens is about 18mm, hence the 1.5x factor. This is true for any focal length so all of a sudden the 12-24 lens becomes an 18-36 lens. Still wide angle, but not as wide. This is a big disadvantage in buying lenses because really nice, fast, wide angle lenses cost a lot of money. If you just dropped $2k on some kind of wide angle 10mm, you don't want the crop factor to all of a sudden bump it up to 15mm.

The reverse is almost true for telephoto shots. On a 5D, a 70-300mm lens will get you 300mm at full telephoto. On a D200, because of the 1.5x crop factor, you'll get a 105-450mm (!!!) range, effectively. It is not entirely true though because it is like saying you can get the same range on a 5D just by ignoring the outer 1/3 of the frame. However, since, area wise, the D200 has a higher pixel density than the 5D, you'll probably get a bit more resolution with a D200 at "450mm" than a 5D at "450mm".

Most people would probably much rather better wide-angle capabilities than super telephoto capabilities. Why? The more you zoom, the slower a lens gets and the less light it can gather. So at really high levels of zoom, you can only shoot brightly lit objects. A fast super telephoto zoom (such as ones used for sports photography or wildlife photography) is ridiculously expensive too. So in other words, the higher end of zooms aren't useful for most people, even amateur photographers, unless you specialize in sports or wildlife. A wide angle, on the other hand, allows people to get a lot into a shot and then crop as needed. It also solves the problem of not having enough space to "foot zoom" when one is indoors. In short, there tend to be more subjects for the very wide angle lens than a super telephoto lens.

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