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How to buy cameras and PCs

Posted by Graeme in Uncategorized at 9:09 am on Monday, 28 January 2008

Having previously complained about how consumers are too confused to choose complex technology, I am doing my bit to improve the situation with a little explanation, and some useful links.

Computers

First, computers. This is fairly easy as I just point you to the Linux Documentation Project’s Hardware Buyer Howto. Despite the source, the advice is good even for those planning to use Windows or MacOS, or any other operating system. This is partly because much of the advice is of general application anyway. Even the advice on Linux compatibility should be followed by those planning to use Windows for two reasons:

  1. It keeps your options open, and,
  2. Windows only hardware is very often cheapo rubbish that bogs down your computers with special software to make up for its deficiencies.

It is written by Eric Raymond who is both a very talented programmer and an influential writer on software. It is quite likely that your email is, at some point, handled by software he wrote.

Many people will ask whether they need to go to so much trouble. I would say yes, with one qualification.

A computer is the most complex device that most people buy: more so than a car. It is also (like a car) something on whose functioning people rely. Doing a little reading is worth the effort. At the very least it will prevent salesmen making use of your lack of knowledge to sell you something that is more expensive than you need.

The qualification is that if, like many people, all you do is read your email, browse the web and write letters and other basic functionality, it is different. PCs are now so powerful that performance is irrelevant to you, and you should probably buy purely on price: a $200 PC with a cut down version of Linux is the cheapest option and is more than adequate.

(Compact) Cameras

Digital cameras are stunningly complex devices. Not only do the contain a lot of electronics (in fact fairly powerful onboard computers), but they, uniquely, also have precision mechanical components and precision optical components.

The first thing most consumers need to be told is that more mega-pixels is not necessarily better. With compact cameras it often means worse pictures.  The essential message is that the number of pixels should go up in line with the size of the sensor and lens.  The size linked to above also shows the relative sizes of different sensors. Bigger is much better.

The six mega-pixel optimum is about right for most compacts. It should be much lower for very small cameras (such as those built into mobile phones) and much higher for SLRs.

One measurement I like to make with compact cameras is the actual physical aperture of the lens. A higher aperture means the lens collects more light, which improves the picture. This is not the published f-number, which is the aperture proportionate to the focal length of the lens.

The number we want is fairly easy to calculate. Start with the focal length of the lens. This is the actual length, not the 35mm equivalent that is what is usually marketed. It is usually a smaller number that is printed on the end of the lens. When comparing cameras online I often find I have to resort to looking for photographs of the cameras to find this! For a zoom lens you want the lowest focal length number.

Next we want the f-number. Again, this is usually on the end of the lens, but it is slightly better publicised than the real focal length. Again, for a zoom lens, take the lowest number. This will typically be 2.8 or better for SLRs,

Divide the focal length by the f-number. Square the result. This tells you the effective area of the lens, and therefore how much light it will gather, at the widest zoom.

This is a little unfair as it favours cameras with wide zooms. Personally, as wide zoom is so useful I can live with this. If it bother you, it is relatively simple to interpolate the numbers to estimate the aperture at the equivalent of a standard lens (35mm equivalent of 50mm).

I have only looked aperture for compact cameras (or SLR lenses), and sensor size for both SLRs and compacts. There is a lot more
to it, but the other issues (image stabilisation, zoom range, etc.) are not really a problem for consumers. The issues of real aperture and sensor size are both critical and not widely understood.

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