Lens Categories

In my last two articles I talked about why Minolta Glass is still popular and which of those lenses are still popular today. Before decided which lenses to buy to add to my two kit lenses I did some research on lens catogories. There are dozens of different types of lens available, designed for use in a wide range of circumstances. The most important factor in any camera lens is its focal length. This determines which type of lens it is, and what subjects it will be able to photograph. Focal lengths range from just a few millimetres up to over a metre, and can be loosely grouped as follows:

Lens Categories
Focal Length Lens Type Common Subjects
8mm – 24mm Ultra wide angle (fisheye) Wide panoramas and skyscapes, artistic
24mm – 35mm Wide angle Interiors, architecture, landscapes
35mm – 85mm (50mm common) Standard General purpose
85mm – 135mm Short telephoto Portraits, candid
135mm – 300mm Medium telephoto Close sports, action
300mm+ Super telephoto Far sports, wildlife, nature, astronomy

Lens focal lengths are specified for a camera with a “full-frame” 35mm sensor. My Sony A65 use a smaller sensor, and this has the effect of cropping off the edges of the photograph, resulting in an image which is more “zoomed in” than it would be on a full-frame sensor. This cropping makes it seem as though the lens has a longer focal length than it really does. The Sony A65 has a crop factor of 1.5x, meaning that a 50mm lens actually has an effective focal length of 75mm when fitted to this camera.

The table below shows the focal length for a 35mm FF sensor, the APS-C (A65) equivalent and the smaller FF length required to get the 35mm equivalent:

Lens Focal Length Chart
Category FF mm APS-C APS=FF
Ultra Wide-Angle 8–24mm 12–36mm 5–16mm
Wide-Angle 24–35mm 36–52.5mm 16–23mm
Normal 50mm 75mm 33mm
Short-Telephoto 85–135mm 127.5–202.5mm 57–90mm
Telephoto 135–300mm 202.5–450mm 90–200mm
Super-Telephoto 300mm+ 450mm+ 200mm+

In addition to focal length there is another important measurement called aperture. Aperture determines how much light a lens lets in. When a lens has a wide aperture, designated by a small number called an f-stop (e.g. f/1.8), it captures more light. When a lens has a narrow aperture, designated by a larger number (e.g. f/5.6), it captures less. Wide apertures allows photos to be taken with less light because the lens can see more of the light. With a narrower aperture less light could pass through. Also, narrower apertures provide a greater depth of field, meaning that more of the image, such as a landscape, will be in focus. A wider aperture would make the landscape appear less sharp.

Now with an understanding of focal length and aperture as well as an understanding what different types of lens categories there are I was ready to pick additional lenses, more about that in my next article.

Related articles:
What makes Minolta Lenses such a great option for Photographers
Minolta Lenses to look for
My Minolta Maxxum Lenses
Minolta AF 500mm Reflex Lens
My other Lenses
Confusing EXIF Lens ID Information