Digital SLR’s - A Quick and Cautionary Guide to Lens Selection

If you are thinking about moving into digital underwater SLR photography, you need to be aware of some of the issues surrounding lens selection. Almost all of the digital SLR cameras that can currently be housed have an imaging chip that is smaller than a 35mm film frame. When you use a conventional lens designed for a 35mm camera on one of these digital bodies, its like adding a 1.5 x teleconverter.

For macro photographers, this is usually a benefit. If you use the popular 60mm or 105mm Nikon Micro lenses, you’ll be able to shoot around 1.5:1 - one and a half times lifesize - instead of just lifesize. Because you don’t have to add a close up lens your focus range is unrestricted and by avoiding the use of a seperate teleconverter, your autofocus is unaffected. The only downside is that your lens will have a longer focal length, typically turning a 60mm into a 90 and a 105mm into a 160mm. This might be longer than you want for some subjects.

For wide angle photographers, using digital SLR’s will usually mean you need new lenses. For example a 20mm, the “standard” focal length for many underwater film photographers, becomes a 30mm on most digital cameras. A few wide angle lenses developed specifically for the digital format are available, chiefly from Nikon for the D70, D100 and Fuji S2 Pro. So if you do want to take wide angle pictures it is vital to check on availability of lenses for your intended camera.

The way lenses are being sold can also be misleading. Because film and digital SLRs can share the same lens mounts, they can have, in effect, two focal lengths. It is often unclear whether the focal length applies to a digital or a 35mm camera. Recently a client of ours was sold a lens for his digital SLR for wide angle work. It was a 21 - 35mm - a nice range on a film camera. But on his digital SLR this became a near useless 32mm to 52mm. Our advice is to use a specialist photographic dealer to ensure you don’t get stitched up. Also bear in mind that all housings have resrictions on the lenses they will accept and you should check with your housing dealer to ensure compatibility.