So I was talking to a wonderful photographer this evening about a lens she just purchased, and our conversation made a terrible turn towards the nerdy. I realized that many photographers out there are making great photos, but don't necessarily understand a few key optical traits when it comes to their lenses... specifically the limitations that zoom lenses actually give us. We think that slapping "One Lens To Rule Them All" on our camera is all we have to do... but what if I told you it's stifling your creativity? What if I told you it's making you lazy? What if I told you it's limiting your options and forcing you into a box? If you are passionate about photography in the slightest, please follow along. While talking about portrait and prime lenses (lenses that are a single focal length and don't zoom), we're going to cover two technical topics that are interrelated. Those are "compression" and "how your aperture (f-stop) relates to your focal length" (the "mm" number, like 50mm).
Before we begin, please note that all focal lengths are in 35mm equivalent. That means If you're not using a film camera, D700, D3, 5D MkII, or 1Ds... you need to multiply these numbers by roughly 1.5x. A 50mm lens on a Nikon D90, for example, would look the same as a 75mm lens would look on a film camera. If you're still confused, don't worry. It's really the relationships between different focal lengths that are more important here for now. So, let's begin:
What's going on with this photo?
If you answered "Well, of course, that's an alien", you're wrong. But I think we can agree, that while entertaining, this isn't exactly a portrait a client is going to want to be remembered by. Okay, now look at this photo:
Would you consider this a pleasing portrait? If you answered "No" then I didn't really want to be friends with you either. But anyway, what makes the first one weird and the second one pleasing? It's a photographic concept called compression. The first image is very uncompressed. The background looks REALLY far away, and the foreground looks REALLY close. The effect is SO pronounced at 14mm (the first image), that the tip of the nose is noticeably closer to the lens, and the back of his head is so far away, that his ears are hidden behind his cheek bones. Now, granted, I had the lens about 5" from his face so it's as exaggerated as can be, but it does illustrate the importance of compression when it comes to photographing people. Looking at the second image, notice how everything looks nice and flat. Very two-dimensional. The background is at a nice distance and fits very well with the entire composition. The second image was taken with an 85mm lens.
You may have heard the term "portrait lens" before. All it means is that a particular lens has a focal length long enough to make generally appealing portraits... this is basically anything from 75mm to 200mm. But that's not to say 300mm is bad. In fact, there are some that argue that the 300mm f/2.8 is the greatest portrait lens ever. I do a LOT of portraits at 200mm for the compression. I'll have my 70-200mm on my camera, set the zoom to 200mm and LEAVE it there... and then walk backwards till my composition is correct. <THIS IS THE REASON zoom lenses suck. Moving your feet changes perspective, forcing you to make more compelling, creative images. Turning a zoom ring not only just changes framing, but also changes how your background relates to your subject in both focus and compression. Your depth of field is also dependent on focal length. For example: 200mm f/2.8 gives you approximately the same amount of background blur (bokeh) as 85mm @ f/1.8, but the difference is the background seems closer. Take a look at these two images:
Both of these images are at f/5.6... but they sure don't have the same depth of field. Let's take what we know about compression and analyze what we have here. Notice that the distance between the foreground/background in the first image appears to be about 25 yards, when it's actually around 100 yards... and the second image appears to be at least 300 yards when it's half of that. Now let's look at depth of field and bokeh. Notice at the SAME f-stop we have lots of bokeh in the first image, and absolutely none in the second image. The longer your focal length, the more bokeh can be produced.
What if we had switched lenses for these two shots? The first one would have had every single person in focus, and the ones in the background would have been so small you could barely tell what they were... and the ones in front would take up most of the frame. The IDEA of this image was that of anonymity and "being lost in a sea of people." If I had zoomed out, I wouldn't have had more depth of field and less blurring. With the second image, a long focal length would mean that the sense of environment is gone, as we'd have to pick a more selective focus. It's no longer about country life. We'd get the two boys playing in the tire, but that's only part of the story. With the wide lens and the depth of field we get the wispy clouds, and the barn in the back... all sharply in focus. We also get the expanse of farm land giving us the open air and feel.
What I'm trying to teach here is don't just haphazardly zoom because that's where you're standing. Get an idea of how you want your subject to relate to the background, choose the focal length (yes, that means switching lenses) and aperture required to make that happen... then move your feet to create the framing you want. Now, am I saying that zoom lenses are bad? Absolutely not. Wedding photographers and photojournalists live and die by a 70-200mm zoom, because speed is of the essence. The problem is that it's so easy to rely on them to do work for us... when we should be making them work for us. The other problem is we've all grown up on cameras that zoom, and we're afraid that using ONE focal length is like cutting off all our limbs but one... but we'd be wrong. Think of a zoom lens as a jack of all trades, but an ace at none. Start using that ace a bit more... I guarantee you'll be winning more hands.
So, if you've followed along this far you are likely saying "thank you!" or "yeah, I already knew that" or "ADVIL. NOW." If you have any questions or want any clarifications, please don't hesitate to e-mail me at firstname.lastname@example.org, fill out the contact form, or message me on Facebook. I really enjoy spreading the technical knowledge that I understand can be difficult to grasp. Stuff like this really requires you to go out and just take pictures. Try different things. Shoot in aperture or manual, use the same f-stop regardless of your lens, and experiment with different compositions. If you don't own a prime lens, please RUN, don't walk to picking one up. Regardless of what brand you shoot, pick up a 35, 50, or 85 with an f-stop number lower than f/2. I know Nikon and Canon both make 50mm f/1.8 lenses than can be picked up for UNDER $100. If you've only shot with zoom lenses, it will change your life.