Digital Photography

On Being Digital

Using a Canon EOS350D. 8Mp sensor, probably the same as they use in the EOS 20D. This is a semi-professional camera. They probably cut corners on the body, tough plastic rather than alloy. But the sensor is good, it starts up fast to the point where it is not really an issue (by the time the viewfinder reaches your eye itņs ready), it can shoot about 3fps which is good enough for everything except professional sports photography. What a lot of people donņt understand is how these digital SLR cameras are fundamentally different from the point-and-shoot models. The sensor works in a different way using a real shutter to control the sampling of the incident light on the sensor. The point-and-shoots are giving a continuous reading so the lcd display can give a continuous image - thatņs why we see people holding the camera out in front of them - far enough to focus on the lcd screen. In my case that now means holding the camera pretty much at armņs length. P&S users rarely seem to use the viewfinder even though most cameras are equiped with one.

On the SLR the sensor is covered by the shutter curtain and only comes into play when you take the photograph. The viewfinder and the metering are done separately just like in a film SLR. The sensor in the SLR is a CMOS sensor - different design and has better performance in low light - that means you get less noise for an equivalent ISO rating. P&S use a CCD - they basically shift the data out so there is a bit of electronics with each sensor to hold a charge and this takes up sensor space and compromises design. Also the P&S sensor is smaller with correspondingly smaller lens. That means less light capturing, other things being equal. The more light, the more information and relatively less noise.

Issues that confuse:

Another knowledgeable shop assistant in a specialist camera shop - is the 18-55 cheap bundled lens any good? He shows me three A4 prints of shots taken of the street outside - one is the 18-55 lens worth about £50, one is the 17-85 IS lens costing about £500, one is an L series lens probably costing £1500 (no need to bother checking). Could I tell them apart? could I hell. I rated the IS lens the best, the other two I couldnņt distinguish. So why buy a more expensive lens? Well, the test was not a good one. Both photographs were taken in bright daylight, and almost certainly at f8 or smaller aperture. The fact is that at f8 even a poor lens will look okay - any fool can design a lens that performs well at f8 or f16, in fact if you stop down far enough you get a pinhole camera and you donņt need a lens at all!. In addition, at very small apertures, diffraction effects become more of a throttle on resolution. So all in all, at f8 you probably wonņt be able to tell them apart. But open up to f5, say, and you will see a big difference as light starts to bounce around inside the cheaper lens. And the subject will also hide any chromatic aberration. Use a test card and it will be a different story, I assure you. On top of all that, Iņll bet thereņs been some image sharpening going on, which further masks the differences. Remember that however good your digital post-processing, you want your optics to capture as much information as possible. If you want to compare optics you need to do it before any sharpening. And remember itņs not just about resolution - contrast is also important and any light bouncing around inside a poor quality lens will destroy that. Resolution and contrast together are responsible for that feeling of "crispness" in a technically good photograph. Sometimes that technical quality can make a mundane subject really jump out so that you see it in a new way.

We did our own tests, with a proper resolution test image. We compared a 50mm prime lens and the 18-55 EF-S zoom. At f8 it was almost impossible to distinguish at image centre, at edges the weaknesses of the zoom began to show. At f5 the zoom lens results were horrible, the prime was about the same as at f8. At 28mm the zoom also faired badly when compared to a prime lens. At 18mm it wasnņt bad at all. Maybe Canon realised that most users would already have a number of lenses in the 28-50mm range so they put the effort into the 18mm end (which is also where the short back focus comes into play).

So how to get that crispness, that technical quality, setting aside any artistic considerations? Well, you need to get a number of things right. Get one of them wrong and you will have a technically ordinary photograph. Just the slightest camera shake will negate the advantage of the best lens in the world. Let auto-focus pick up the wrong subject and it doesnņt matter how many megapixels you have. Compose incorrectly and no amount of work in Photoshop will save the day.

Technically, it is really all about getting as much information as possible out of the camera and lens. To get technical perfection, you need to get all of the following right:

If subject is static, and unless you need a shallow depth of field, aim for f8 and a longer exposure. If lens is an inexpensive one, f8 will put you almost on a par with the red ring brigade (no it wonņt!).

Before you spend £1000 on a better lens, spend £100 on a good solid tripod and a lens hood.