Lenses, The Basics: Part I: Lesson 1

The basics of understanding lenses are fundamental to selecting and using a specific lens for your photography project. For example, for a landscape scene, you may want a wide view to exhibit the expanse of the land, while for a portrait you probably want a lens that is more narrow that can portray your subject without distortion and similar to what the eye sees.

Older Film and Newer Full Frame Lenses

In the previous lesson, I discussed the Full Frame, ( and DX (Nikon) and APS-C (Canon) formats. The full frame cameras have a sensor that is essentially the same as the 35mm film cameras before DSLR’s. This means that nearly all lenses manufactured for film cameras can be used on full frame camera bodies with the same field of view as you would expect if shooting through a film camera. Note that there are some very good older lenses, as I own a few, that are cheaper now and produce wonderful photographs.

For the DX/APS-C cameras, they can also use these older and newer full frame lenses, although because these are crop sensors, the field of view will not be the same as if it were on a full frame camera. Another way to think of this is that the image is zoomed in. For example, in bird photography, a lens would differ on the full frame vs. the DX/APS-C. On the DX/APS-C cameras, the bird is looking closer because the sensor is smaller and the image is cropped.

Full Frame

Nikon D750


Crop Sensor

Nikon D7000

DX and APS-C lenses

The DX and APS-C lenses have the same nomenclature as the full format lenses. A 35 mm DX/APS-C lens is also a 35 mm on a full frame and vice versa. A significant difference is the lens opening is smaller to accommodate the smaller sensor. The full frame lens has a larger opening and any light passing through it will cover the entire sensor on a DX/APS-C camera body. A DX/APS-C lens by virtue of having a smaller lens opening will not cover the entire sensor on a full frame format camera body. This leaves the corners of your images very dark and cutoff. Fortunately, most full frame camera bodies automatically recognize the lens on your camera and will change settings so the image is not cut off and having very dark corners. This lens correction lets you use your DX lens even on a full frame, though the field of view will not be the same.

DX/APS-C lens on a Full Frame Camera

Manual (M) and Autofocus (AF) Switch

Most camera lenses you see today have a switch on the side of the lens. The switch is marked M/AF or something very similar for Manual focusing and Autofocusing. When switched to Manual, you can grab the focus ring and manually focus the lens. Switched to autofocus the lens is focusing the lens. If for any reason you seem to be having trouble with your autofocusing, ensure the switch is activated to AF if autofocusing.

Vibration Reduction (VR) Image Stabilization (IS) Optical Stabilization (OS) Switches

Depending on the lens manufacturer your lens may come with a switch for Vibration Reduction (Nikon), Image Stabilization (Canon) or Optical Stabilization (Sigma). You will see these on many newer DSLR lenses. They all mean the same thing. When the switch is activated it can allow you to use a slower shutter speed that would normally cause motion blur from camera shake. This is a great option although it may add to the cost of your lens. I have a whole section on how to get tack sharp photos and how this switch works and plays a part. The Normal and Active switch on this Nikon lens below is part of the Vibration Reduction system. The Normal switch is for camera shake as you are holding it while the Active switch is for shooting from a moving car or some other unstable platform.

Switches on most newer lenses

Parts of a Lens

Exterior parts of a camera lens
Exterior Lens Parts

One of the most noticeable differences in the lenses above is the one on the left has an aperture ring. The right lens has no aperture ring. The DX lens on the right also has a switch for M/AF and VR which the lens on the left does not have as it was manufactured in the 1990″s before that technology was available. I will refer to these parts of the lens again in the next installment.

Lenses, The Basics: Part I: Lesson 1
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Welcome! My interest in photography spans 40 years and started with the purchase of my first SLR. Since then my passion has grown to landscapes, beach scenes, and travel photography primarily. Photography techniques I particularly enjoy are long exposures, and what I call splash art. You can see these on my gallery page if it interests you. Currently, I live on Amelia Island in Northeast Florida with my beautiful wife and our wonder dog, Fuji.