Digital Photography Gear: An Introduction to Interchangeable Lenses-Part III

April 25, 2013

Digital Photography Gear: An Introduction to Interchangeable Lenses-Part III

So let’s continue our discussion from our last post.


A macro lens allows you to shoot objects up close, creating an image that shows tiny details of small objects like flowers and insects.

digital photography lens

A true macro lens is a prime lens—a lens with a single, fixed focal length and, therefore, no zooming capability—gives you nearly a 1:1 magnification, producing images that are life-sized or nearly life-sized.

Macro lenses are particularly suitable for folks who are interested in nature digital photography, and especially shooting flowers and bugs. But a 70-100mm prime macro can also be a great lens for shooting portraits.

BTW, there are some zoom lenses are labeled “macro” by the manufacturer. But these aren’t true macros because you can’t get life-sized images from them. That’s not to say that these lenses aren’t worth considering. A zoom “macro” lens typically allows you to focus relatively close and that can produce some fun images too.

Crop Factors

So now we’ve talked about a number of different types of lenses available for digital photography. And it all seems pretty straightforward, right?

Well, yes and no…

There is one complication here. You see, the focal lengths that we’ve been talking about are for cameras with a full sensor, a sensor that’s the same size as 35mm film. “Full frame” digital cameras have a sensor that is as large as 35mm film, but these are generally high-end professional models. Most consumer-level digital cameras have a sensor that’s smaller than that. And, since the sensor is smaller than standard 35mm film, the images that the camera takes are “cropped” to the smaller sensor size. So the image taken with the smaller sensor camera will show a smaller area of the scene. And that means that the focal length of the lens is effectively increased due to the smaller sensor size.

That’s where crop factors come in. Digital cameras have a stated crop factor that’s based on the size of their digital image sensor and you can use that factor to adjust the focal length of your lens to find out how that focal length will act on your camera. So, for example, say that your camera has a 1.5x crop factor. On that camera, a 50mm lens will capture images like a 75mm (50mm x 1.5) lens would on a film camera. If the camera has a crop factor of 1.3x, the 50mm lens will act more like a 65mm lens on a film camera.

And, to add to the confusion here, the size of digital camera sensors (and therefore the crop factor) varies by manufacturers and sometimes even by camera model. For that reason it’s important to find out the crop factor for your particular camera and to keep that factor in mind when looking at lenses.

For reference, we have a table of the crop factors for many of the popular DSLRs and MILCs on the market today here. here.

By the way, some manufacturers label the focal length on their lenses in such a way that it’s already adjusted for crop factor. So if you see the focal length of a lens marked as ” 35 mm equivalent focal length”, you don’t have to worry about applying the crop factor because that’s already been done for you.

One More Thing

When looking to purchase a new lens, be sure to get one that has the appropriate mount to fit your camera. Each camera brand has its own specific mount. So, a lens made by Canon won’t fit on a Nikon camera.

There are several third party lens manufacturers such as Sigma, Tamron and Tokina who make lenses with mounts to fit the different camera brands.

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