Digital SLRs have different sized sensors. Some have the same sized sensors as a traditional 35mm film camera. These Digital SLRs are often referred to as "full frame" cameras. The majority of Digital SLRs have sensors that are smaller than traditional 35mm film cameras. Typical consumer level Digital SLRs have smaller sensors.
When buying lenses to go with your Digital SLR this matters because the majority of lenses are designed to work with 35mm SLR film cameras or with Full Frame Digital SLRs.
If you own a Digital SLR with a smaller sensor this has an impact on the focal length of a standard lens when you attach it to your camera.
When a lens is placed on a small sensor Digital SLR it has a multiplier effect. This increases the focal length of the lens.
To further complicate the subject different manufactures produces Digital SLRs with different crop factors. Some manufactures also use more than one sensor size within their ranges.
You normally see the multiplier quoted as either 1.3x, 1.5x or 1.6x. A camera with a crop factor of 1.3x will have a larger sensor than a camera with a crop factor of 1.5x. Even then a camera with a 1.3x crop factor has a sensor that is smaller than a full frame Digital SLR.
There are advantages and disadvantages to the crop factor. For example if your camera body has a 1.5x crop factor this works to your advantage when you want to zoom in closer to your subject. So for photographing distant subjects this is good news.
The opposite is true when you photograph sweeping landscape or cityscape scenes. For these shots you want a lens that can zoom out as far as possible to enable you to squeeze in everything in the scene. As the crop factor increases the focal length of your lens, you are less able to zoom out to capture this type of scene.
Staying with a Digital SLR with a 1.5x crop factor, this will turn a lens with a focal length of 400mm into a lens with a 600mm focal length. As you can see this can allow you to zoom in much further and can therefore come in very handy for subjects such as sports or wildlife photography.
The flipside is that an 18mm lens used for wide scenes becomes a 27mm lens. This has a major impact on the pictures you are able to take. To compensate for the crop factor you would need to buy a 12mm lens. An extreme wide angle lens like this would be much more expensive.
To help you get round this a series of lenses have been developed specifically for use with Digital SLRs with a crop factor. Look out for this type of lens if you want a cost effective way to overcome crop factors. These lenses are mainly aimed at solving the loss of true wide angle lenses.
For when you need a longer length lens you are best off using the standard lenses designed for 35mm film cameras and Full Frame Digital SLRs. That way you get to take full advantage of the crop factor.
If you own a 35mm film camera or Full Frame Digital SLR avoid lenses made for cameras with a crop factor.
Individual manufactures tend to stick to the same size sensors in their Digital SLR bodies. There are exceptions to the rule so the table below is best used as a rule of thumb rather than something set in stone.
1.6x (with some 1.3x models)
Camera Lens Introduction
Buying Your First Lens
Camera Lens Types
Camera Lens Brands
Buying Second Hand Lenses
Digital SLR Crop Factor
Caring For Your Camera Lens
Common Lens Faults
Camera Lens FAQs
If you are looking to produce professional level landscape or interior photographs then the likelihood is that a full frame Digital SLR would be a good choice. By going over to full frame you have the advantage of a highly specified Digital SLR plus all crop factor issues are wiped out. Some photographers keep a full frame Digital SLR camera for their landscape work plus a Digital SLR with a crop factor for their wildlife photography. That is certainly an expensive way to go about it, but they get the best of both worlds.
Aside from any lens issues Full Frame Digital SLRs produce better quality images owing to the ability of their larger sensors to hold a greater level of detail.
It is always difficult to predict what might happen in the future. But it is worth considering that there are a lot more Full Frame Digital SLRs than their used to be. Originally these were priced within the reach of professional photographers only. As they become more widespread and prices fall it may not be long before Full Frame options are widely available to hobby photographers. If this is the case and you believe you may switch to Full Frame in the not too distant future then it may be best to avoid lenses designed for Digital SLRs with crop factors. This is because when you switch to Full Frame these lenses will not be compatible with your new camera.
If this move does happen the second hand value of this type of lens is likely to fall.
The table below shows you the impact crop size has on a selection of focal lengths.