One of the benefits of owning a DSLR is having the freedom to change lenses according to your needs. We’ll look at the basics of what a lens is all about from focal length, to aperture, to wide vs telephoto, to demystifying all those strange symbols. Today, let’s look at focal length.

Focal Length

When light rays hit a lens, they converge at a single focal point. In it’s simplest sense, the distance from the middle of the lens to where the lines converge is the focal length of the lens denoted in mm. Lenses range from 10mm at the wide end up to 300mm for a consumer telephoto lens.

There are two types of lenses:

Prime - These lenses have a fixed focal length. As such, they usually have a larger aperture than zoom lenses. Some notable lenses include 30mm f/1.4, 50mm f/1.8 or f/1.4, 85mm f/1.8 or f/1.4.

Zoom - A zoom lens has the ability to vary its focal length and as a result, can give you different angles of view.

Lens manufacturers produce many different ranges of focal length but they usually fall under three categories:

Wide Angle - Lenses wider than 50mm (eg. 10-22mm, 14-24mm)
Normal - 50 mm
Telephoto - Lenses longer than 50mm (eg. 70-200mm)

You may have seen the words “35mm equivalent” when talking about focal length. This is simply a comparison to 35mm film cameras, not to be confused with focal length of a lens. (The film used in 35mm cameras were, surprise surprise, 35mm wide!)

So why do we need to bother with knowing the 35mm (full frame) equivalent? It’s used more as a standard so we can make comparisons. Most DSLR’s have a crop sensor (except for full frame DSLR’s like the Nikon D3, Canon 1Ds and 5D) meaning compared to a 35mm camera, we only see a crop of the actual field of view. Different camera companies use different crop sizes. The crop value is referred to as the Focal Length Multiplier(FLM). My Nikon D300 has a crop factor of 1.5. This means that compared to a full frame camera like the D3, I see 50% less with my D300 than I would with a D3.

So, if I am using a 50mm lens on my D300, that would be equivalent to using a 75mm lens on a D3 because 50mm x 1.5 = 75mm.

I found this great drawing here that shows you the differences between a full frame and crop sensor. This one uses a crop factor or FLM of 1.6, which is what Canon uses.

The RED box represents a full frame sensor and the BLUE box a crop sensor.

Now, don’t get confused with all the numbers. A 50mm lens is still a 50mm lens regardless of which camera body it’s used on. The focal length doesn’t change but the field of view varies according to the sensor size.

Here’s an example:
To get the same field of view as a 50mm on a D300, I would need a 75mm lens on a D3. (50mm x 1.5 = 75mm)

Or, to get the same field of view as a 15mm on a D3, I would need 10mm on a D300. (15mm / 1.5 = 10mm)

So what does this all mean to you? Well, if you have a crop sensor body, which most of us do, you will have more “reach” or telephoto than if you were using a full frame body. Most photographers like to use an 85mm lens (on a 35mm camera) for portraits. If you have a crop sensor body, you can get a 50mm lens and it will be close to 85mm on a 35mm film camera. Therefore, you will like using your 50mm lens as a portrait lens.

Next up, lenses and aperture!

Laura is a Vancouver wedding and portrait photographer. Visit laurahana.com.

focal length: 32 mm
shutter speed: 1/200
aperture: f/2.8
ISO: 400
flash: none

This photo made me laugh out loud. The expression in her eyes and the obvious, object in her mouth just makes for a funny picture. While I was searching my files for today’s daily pic, I came across this one and laughed. Catching our kids doing their zany little things can brighten up someone’s day. Do you have photos of your kids doing silly things that make you smile?

This happened under Daddy’s watch. Am I surprised? Not really.

Laura is a Vancouver wedding and portrait photographer. Visit laurahana.com.

focal length: 24 mm
shutter speed: 1/30
aperture: f/2.8
ISO: 800
flash: none

Being upside down is fun! So are photos of kiddies hanging upside down from playground sets to chairs to Daddies. Try shooting your kids while they are swinging about, hanging, sliding and doing things they love to do. You’ll get genuine smiles and a cute picture!

Sophie just loves it when we do this to her. Sometimes it’s the only way to get her in position for grandparents to give her a peck on the cheek!

Laura is a Vancouver wedding and portrait photographer. Visit laurahana.com.

focal length: 24 mm
shutter speed: 1/80
aperture: f/2.8
ISO: 800
flash: none

I usually advise others to get in close but there are times where a larger field of view has its purpose, even when shooting portraits. For example, in the today’s daily pic, you can see someone walking by to the left of my subject. My husband took a series of photos and we liked the one with the man’s legs in the frame as if gave the image scale. By scale, I mean that we are now able to see how tall Sophie is compared to the adult as they are in close proximity to each other. Do you have any images where you framed in an object to show the scale of what you photographed?

It’s really amazing how quickly children develop their new found skills. Not long ago, she was just taking tiny baby steps. Now she’s walking so much faster that I can’t keep up with her anymore.

Laura is a Vancouver wedding and portrait photographer. Visit laurahana.com.

focal length: 24 mm
shutter speed: 1/200
aperture: f/2.8
ISO: 800
flash: none

For the last few years, I had been exclusively using my 50mm f/1.8 prime lens until I got my zooms. Although it took a bit of getting used to not having to zoom in and out with my legs, I’ve learned to appreciate the versatility of my new lenses. Because I’m always crouching on the floor in awkward positions, it’s difficult to move backwards quickly enough to properly frame a moving subject when using a lens with a fixed focal length. I had a lot of cut limbs and fingers back in the day due to my lack of agility. Now, I just have to rotate my lens to get a wider field of view without even moving! However, the one danger in that is objects seems farther than they appear and I have to be careful she doesn’t hit my lens!

There’s just something so sweet about a baby hug. Have you had one today?

Laura is a Vancouver wedding and portrait photographer. Visit laurahana.com.