Cameras.co.uk: Buying Lenses for an SLR camera

Wednesday, 11 July 2007

Buying Lenses for an SLR camera - Compatibility

Care needs to be taken when buying a lens to ensure it is compatible with your camera body. There are two factors to look out for.

Each camera body has a specific lens mount. Each lens will fit onto a specific lens mount. For example a lens made by Canon will fit a Canon lens mount, but cannot be fitted onto a Nikon camera and vice versa. This gets slightly confusing as some other camera manufacturers, such as Fuji, use lens mounts from other manufacturers. Therefore you need to know the lens mount your camera has and buy lenses that are compatible with the mount.

Next you need to make sure that the lens is compatible with the type of camera (digital or film) you have. This is because some lenses made for film cameras are not compatible with digital cameras and some lenses are made specifically for digital cameras and will not work with film cameras.

Lenses made recently for film cameras tend to work perfectly well with digital cameras, but some older lenses may not work at all or suffer from certain restrictions. Therefore it is advisable to check with your dealer before buying. If you are still not completely certain then check directly with the manufacturer.

There is one other point to consider when buying lenses made originally for 35mm cameras to use with a digital camera. This is that a conversion factor needs to be applied to the focal length of the lens in most cases. This is because the sensor in most digital SLRs are smaller than those in film cameras. The knock on effect of this is that when you attach a 35mm lens to a digital SLR it increases the zoom capacity of the lens while decreasing the wide angle capability. The exact conversion factor to apply depends on the sensor size of you camera, but normally works in the range of 1.5 to 1.6 times. To illustrate the difference this can make I will use a 200mm lens. If the conversion factor for your camera is 1.5x this increase the focal length of the lens to the equivalent of a 300mm lens.

Labels: Buying Lenses, digital SLR camera

1 Comments:

At 04 August 2007 18:21 , chris said...: This blog post is a bit vague. The limitations on lens / body compatibility vary greatly from manufacturer to manufacturer - Olympus digital SLRs, for instance, are limited to lenses designed in the last few years as they adopted a new bayonet lens mount when they first started introducing digital SLRs. Canon adopted a new bayonet lens mount when they launched their first autofocus SLRs in 1988, so any earlier lenses need an adaptor, with one of two required depending on the lens. At the other extreme, Pentax digital SLRs can accept virtually any bayonet mount Pentax lens. With these cameras and lenses, the 'restrictions' mentioned have little to do with image quality or the capabilities of the lenses - just that the older lenses have fewer automatic controls, so take a bit more work to use.

One thing I'm surprised isn't mentioned above is lens coating. Almost all lenses have a coating of some form, however newer lenses designed with digital cameras in mind tend to have a different coating to older lenses designed when only film cameras were available. This can give photos slightly inaccurate colours, though this is an easy fix in Photoshop. Some manufacturers, such as Sigma and Tamron, have taken to labelling their lenses to clarify the coating on them - some of their lenses may be designed to suit the size of a film negative (which is larger than most digital SLR sensors), but have the coating that digital SLRs require.

The last paragraph is a bit misleading - the conversion factors discussed apply to 'digital' lenses as well as 'film' lenses. An 18-55mm 'digital' or 'film' lens mounted on a digital SLR has a range equivalent to a lens of about 28-80mm mounted on a film SLR. The paragraph reads as though this conversion factor is only applicable to 'film' lenses mounted on digital SLRs.