Why we use different lenses and why we move

Zoom with my Feet

Zoom with my feet

Why do we have so many lenses or zoom lenses? Why do we move or not move?

I’m often surprised when I hear photographers talk about lenses and well even more surprised when I read photography blog articles about lenses and what they think “does what” when it comes to lenses and why we may choose one focal length over another. After all can’t we just “Zoom with our feet”? So why do we even have more than one lens, cuz really what would be the point? So this is a small excerpt from a larger article I had in mind to write to show; “What Does What” and why we need more than one lens and even why we may not.

So the basis of this article is the two main things as photographers we can control: Focal Length and Distance to Subject/our movement. I don’t think people fully appreciate Distance to Subject and our movement within the field we are shooting and how many things it actually affects. It can change things like: Depth of Field, the fall off of light, Perspective, Magnification, distortions and a multitude of other things. We are talking about capturing light and  distance just plays a big role in the physics of that.

So for this discussion we know the two main things we are concerned with now let’s take a look at a few definitions because how a word is defined is important to this discussion and also because these words can have varied meaning in and out of photography. So these are the definitions as they apply here.

Magnification: In the context of this, it means, the size an object appears within the image, whether that is our viewfinder an LCD screen or the print. So if we have an apple that fills our screen top to bottom in 3 images it would be of Equal Magnification regardless of how that Magnification was achieved and despite the image having a different appearance (I’ll get to that). We can magnify a few ways. Optically (Lens magnification) or simply getting closer (Moving/distance to subject) We can also of course crop to magnify in a sense but that’s outside of our discussion. When we understand that distance to subject also “magnifies” we can better understand why two 100mm lenses, one a standard telephoto lens, another a Macro lens can have different magnifications. It’s simply that the Macro lens allows for a closer minimum focus distance. Closer = More Magnified.

The Joshua Tree in this image is said to be of Equal Magnification despite begin shot with different lenses at different distances. As you can see the Field of View and Perspective are very different

Magnification

Field of View/Angle of View: This is simply the amount of a scene visible in our image. I actually like to use Angle of View better than  field, because angle is more fixed. “Field” can be left more to interpretation. But Field actually is the more common term. A Wide-Angle lens has a very Wide Field of View, it sees everything. A Telephoto Lens has a narrow angle of view, It sees less and if we have a defined subject may show less of the background surrounding it.

In this image we can see two different Field of View. The Wide angle on the left includes a lot of the mountain area surrounding the center Joshua Tree. The Telephoto image contains just parts of the central mountain. (Click to enlarge)

Field of View

 

Perspective: Perspective is a word that is used to mean many different things and often used incorrectly. But in the context of this article: It is the relationship of one object to another to show, size, distance and scale between the two. Often times we can have a “Natural” perspective and then also a “Forced” perspective. It’s something controlled by the photographer and can be used to portray things either how they are or even how they want them to appear. It’s far more important to an image than people know or even possibly think about but it can change what an image says. The basic tenant of this is : Things that are closer to the camera appear larger, those farther away appear smaller. Think of Telephone poles down a long road and you looking down the road.

In this image we can see how the perspective has changed. Look at the relative size of the cactus as compared to the mountain behind and how it changes (Click to enlarge)

Perspective

We now know the 3 things,  so what controls what when we talk about them in the Lens vs Movement arena?

Magnification is control by both. You can change lenses to magnify. Say we have a Bird in a tree at a distance. we can switch to a powerful Telephoto lens to bring that bird in and fill the frame. But Moving closer also magnifies that bird…even if it may fly away. So both changing lenses (Focal Length)  or “Zooming” affect magnification, but also moving closer can do the same thing

Field of View is control only by focal length/our lenses, although it is possible to move back to encompass the same area as wider lens, the look will not be the same nor will the actual “Angle” which is why I prefer, Angle of view

Perspective is only controled by moving. If we stand in one place and take images with different focal lengths, it will not change perspective, in fact if  you cropped in to an area that was equivalent to a longer focal length than a wider focal length (again without moving) you would see that that area looks precisely the same without any change in perspective. When we move even without a camera to our eye we can se how the perspective or the relationship of one object to another object or the background changes. That in itself is in plain sight.

So now that we know what affects what we can also dispel an very common myth that is repeated day after day: Zooming with your feet . If we accept that “Zooming” means changing lens focal lengths, then we know that moving will not truly replicate that and only changes one common thing; Magnification. The images, even though magnified the same will not look the same. No, Virginia, you cannot zoom with your feet

 

So let’s take a look at what we now know in practice.

This first example is “Zooming” or changing focal lengths (primes)

When we look at this we can see that Perspective has not changed while zooming because the relative size of the cactus to the Mountain has not changed at all. Our Field of View has changed.

Zooming

 

Next we will keep out focal length fixed at 40mm and simply move or walk forward. We can see that we will begin to magnify our subject and also the perspective will change as we get closer to the cactus. The cactus will grow larger in proportion to the mountain.

Moving

Now that we know what affects what. What does the “Smart” photographer do? 

As you can see both zooming and moving give us a lot of options for the composition of our image. WE can make these artistic decisions and our vision to show the scene how we want it to be. The smart photographer uses everything at his disposal and  uses by varying Focal Lengths (Zooming) and also moves  for the best Perspective

Let’s take a look at what it looks like if we keep magnification constant  (cactus size stays the same) and then both Zoom and Move

Zoom and Move

So how exactly do we decide on Perspective. What is right? Well it’s simple math: You Take Length x Width x The square root of the diagonal x π =….Ummm OK No. You simply look and walk. Use your eyes and walk forward and backwards until you have the perspective you desire. Then at that point you can choose a lens that best fits that perspective and includes as much of the field of view that you want and also any amount of negative space, if any at all. It’s all up to you and your vision.

Now after that you still have some more things you can change, You can decide to shoot lower or higher, you can angle the camera up or down, left and right. All these things will effect the final image but it’s best to start with Perspective and Field of View and then work from there. I’ll leave these other parameters to another article since I have a lot to say about them too.

Now I will admit there are times we want to stick with a fixed focal length and perspective. If I was shooting Street, I may want to keep a constant perspective  with my subjects. It’s why a 35mm lens is so popular a focal length with Street Shooters, It provides the perspective they want and the shooting distance they normally like working with but at the same time, allows the Field of View needed to place a subject within an environment.  I could also make the case of why a Portrait shooter should stand in one place, a distance where the subject has a natural perspective to their body/head ; Nose to eyes to ears. When you find that distance. You simply change focal lengths depending on the shot desired: Full body, 3/4, Head and Shoulders, Headshot etc.

 

I hope this helps you to better understand just why do we have Zoom lenses or multiple prime lenses (if you want to) and the effect they have and the effect your feet ACTUALLY have

Cheers, PT

2 Comments

  1. aris June 22, 2016 at 11:15 am #

    Hey there. Great article. The photos really illustrate the difference. We need more sites talking about perspective. If people understood it more, the whole full frame/crop sensor voodoo debate would stop.

    Question: isn’t standing in one place and zooming (longer focal length) simply and precisely magnifying the whole image?

    I understand that at the same time the image is just cropped to fit into the sensor rectangle a.k.a. changing the field of view. Is your sensor smaller and you want the same photo from the same position? Stay in the same place and zoom out a bit to reduce the image magnification, a.k.a. crop factor.

    I sometimes feel that people assign magical powers to terms like focal length and crop factor but really, all it is is just zooming and cropping. And YES! lenses vary a lot in other departments but when it comes to focal length it is just magnification to help you correctly frame the perspective from the position you are standing.

    Just an amateur.

    • Peter June 22, 2016 at 11:50 am #

      Hi,
      Thanks for the great comment. I agree about the Full/crop sensor debate. Very few people actually understand it. The thing we just need to keep in mind is that we are actually “Cropping the lens” Even though we have a smaller sensor, That is not what is being “Cropped” It’s the portion of the lens the sensor (regardless of sensor size) sees.(Full frame Nikon cameras do have the ability to Crop the sensor, Canons do not) It’s also why while Magnification changes with a Crop sensor, it doesn’t actually change Focal Length (because that’s not how focal length is determined) but it will also change Angle of view. To directly answer your question “Question: isn’t standing in one place and zooming (longer focal length) simply and precisely magnifying the whole image?” It’s magnifying a PART of the image since the field/angle of view will change

      So if you wanted to have the same image with a crop sensor that you do with a Full frame, standing in one place you simply need to zoom out the equivalent of crop factor. So if you are shooting Nikon FF with a 200mm, you would shoot a Nikon Crop at 133mm. Giving you the same Magnification, and Same Angle of view. and since you haven’t moved the same perspective

      And while you can’t Zoom with your feet, you can zoom with your crop. So if you crop in on an image that gives you the same “Effect” as zooming. The problem being at some point you will throw away far too many pixels

      Great questions, I wish more people asked thses questions. For “Just an ameteur” 😉 you’ve got a great handle on it
      Cheers,
      Peter

One Trackback

  1. By How Viewpoint changes an Image on May 10, 2016 at 12:56 pm

    […] Viewpoint is “Where we view our subject from” and in Art it is not synonymous with Perspective, although it is used that way in common use. Perspective is the relationship of one object to another to show depth as I discussed in my last article: Why we use different lenses and why we move  […]

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