You might notice that the zone behind the subject is reaching toward the background. As a result, while little changes between the photographer and the subject, the background is becoming increasingly more “in focus.” This can be a desirable effect if one is taking pictures while sightseeing, or anywhere that the environment shares an equal interest with the subject placed within it. However, if it is your desire to create a focal point, where the subject is the primary detail you wish for the audience to pay attention to, then the depth of field in the first example may be preferable. With a 50mm lens set to f1.4, the background,and all of the foregrounds becomes softly out-of-focus–leaving the audience cued towards our model.

If you're still learning the fundamentals of photography, I really highly recommend you take a minute and read through my photo basics series.  It's a collection of 8 posts I wrote for newer photographers.  It'll walk you through getting a good exposure, how to set your camera up to get crisp sharpness, composition, and more.  Read the photo basics series here.

Nikon, Fuji, and Sony crop sensor cameras have a 1.5x crop factor.  Canon crop sensor cameras have a 1.6x crop factor.  So if someone recommends a 200mm focal length, you can rightfully ask whether they mean full frame or crop sensor.  However, the focal lengths photographers talk about are usually in full frame.  So you can do some simple math to know what focal length you should use to achieve the same field of view as 200mm on a full frame camera.

Three factors weigh heavily on how depth of field occurs in an image: aperture or iris size (f-stops), Lens focal length (mm) and camera to subject distance—sometimes referred to as focal distance. For the sake of this conversation, we will concentrate primarily on the iris and its effects on depth of field.

After you've taken a picture, almost all cameras will save the focal length information in the metadata of a picture.  So if you want to go back and see what focal length you used to get a certain look, then you can go into the properties of the photo and see that.

With the camera at one end of this example and the subject positioned at 5-feet from the photographer, there is a narrow zone of acceptable focus around both sides of the subject. Here, we are using an f-stop(aperture) of f1.4. This selection must be mademanually on a cinema lens.

You need to understand that point to select a proper focal length for portrait photography.  In the (horrible quality) animated gif above, I took four pictures of my wife from different focal lengths.  After each shot, I STEPPED BACK and zoomed in.  By doing this, her face remains the same size in the picture, but as you can see, the photo looks COMPLETELY different!

As the variables adjust, using Depth of Field Simulator, you see the effects in real-time. By changing the lens focal length, camera-to-subject distance, and f-stop respectively, incremental changes can be seen taking place involving the background. Its apparent distance, and degree of sharpness changes in direct proportion to the size of the aperture! This makes the choice of aperture both an aesthetic consideration, as well as an exposure imperative.

Focal length ofmirror formula

In short, the focal length of the lens is the measure of how “zoomed in” your lens is.  Much like looking through binoculars, you may be at 40 mm and be able to see an entire mountain, or zoom in to 400mm and only see one tree on the mountain.

Thank you for this interesting article. You mentioned that there is no advantage of full frame sensor over the crop sensor. Now what about shooting in low light and the impact on the noise level ?

It may help to think of these f-stops as fractions of the maximum possible aperture in which a lens may “stop open.” If f1.0 is a wide-open lens aperture, then f16 is something like 1/16 the resulting size of the original aperture opening. Since f-stops are measured by dividing the effective diameter of the iris—as seen through the rear lens element—by the focal length of the lens, it makes sense that we would think of these measurements as fractions. Therefore, the formula for calculating an f-stop looks like this: F-stop = focal length/aperture diameter.

Best photography article I’ve read in quite a while.. I never get clear explanations about focal length but this one explained it in a way I could actually understand… Especially the meaning of “wide” with face portraiture.. THANK YOU!

Every photo/video lens has a diaphragm inside. The size adjusts by way of a menu system inside the camera, a series of buttons on the camera, or an f-stop ring on the outside of the lens. The consequences of each selection have an effect on exposure. Therefore, carefully consider choices for the aesthetic effect, versus the effect on the exposure that results.

excellent tutorial on photography HARMER sir, my good wishes to you. SHASHI KUMAR MOGHE

Because depth of field is relative to specific f-stops, it can be a consideration when calculating the proper exposure of an image. Depth of field also plays an aesthetic role in how an image looks. Do you prefer dreamy, out-of-focus backgrounds in a portrait, or do you like to see details in the background that reveal a subject’s location? Your preferences become tied to aperture choices affecting over-all exposure. Therefore, the resulting f-stop of an exposure decision allows depth of field to be a compositional choice as well.

I wrote an entire article about how the crop factor affects field of view, which you can read if this isn't quite sinking in yet.

Have you ever noticed how your pupils react inside to low light? They get bigger, to allow more light to pass to the retina. However, outside our pupils get smaller with abundant light. This is how to control exposure using the lens aperture. For more on thatsee our article on the exposure triangle. If you are a beginner, this advanced concept may require additional study and research.

Focal length is something that we talk about constantly as we discuss different lenses and styles of photography in our weekly free podcasts.

aperture – the diaphragm inside a lens, comprised of tiny thin blades, that create a measurable hole for light to pass through during exposure.

exposure triangle – a principle that defines proper image tone/balance by discussing manipulation of the lens iris, camera shutter, and the sensitivity of the recording media. Visit the link embedded in the text above for a deeper explanation.

If you understand this principle, it can save you a lot of money on lenses!  When I suggest to newer photographers that they buy a wide-angle landscape photography lens, they sometimes say something like, “Why would I spend $500 on a 10mm lens when my camera already came with an 18mm lens?”  Aside from the optical quality differences, the difference between 10 and 18mm is HUGE and will make a significant difference in how much of a landscape fits into the frame.

However, if you are interested in shooting sports photography and you already have a 250mm lens on a crop sensor camera, it would be mostly worthless to spend $500 on a 300mm lens (assuming the optical quality is the same) because it will barely make a difference in the magnification and field of view.

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The point is that full frame cameras are not capable of shooting any wider or more telephoto than a crop sensor camera.  The difference just means that if the same focal length is selected on the lens, the full frame camera will produce a wider shot.

plane-of-focus – the “slice” of an image that exists at the precise point of focus. This slice runs parallel to the camera’s image, or sensor plane–extending infinitely left or right–and moves forward, or recedes from the lens based on lens size, f-stop, and subject distance to camera.

All this means is that on the wide end of your lens, zooming in 5mm will dramatically impact the field of view (how much scene you can fit into the frame).  However, when you're zoomed in tight, zooming in 5mm will only make a minute difference in how much scene is in the picture.

background/foreground – areas behind, or in front of a subject, that contain details relevant to the image’s overall composition and framing – affected by depth of field.

If you shoot a crop sensor camera (Nikon D3300, D5500, D7200, or Canon Rebel, 70D, 7D, Fuji XT1, or Sony A6000 just to name a few), then your camera's crop factor will make your camera more zoomed in when compared to full frame cameras at the same focal length.

Now, here is where it can be a little confusing. When we refer to an aperture as “large,” we signify that adjustment with a low number like f1.4. When we refer to an aperture as “small,” we signify that with a higher number like f16. These numbers relate to a series of aperture “blades” that form the “diaphragm” inside our lens. As these blades open and close, they form a hole where light can pass through the lens and strike our image sensor—or film plane when using photographic emulsion.

Now let’s take a look at how the zone of focus around our subjects can change, based on the aperture (a.k.a. f-stop, diaphragm) we select. Here are some detailed illustrations from Michael Bemowski’s internet application, “Depth of Field Simulator.” You can access Michael’s app here.

Howto calculatefocal length ofconvexlens

Here is another example where the f-stop changes to an f2.8. Do you see an increase in the zone of focus? Let’s try another setting.

Given this example, as we resolve the subject—the object we want to be in sharp focus—we create a “zone” around that subject where the image is in apparent focus. The zone consists of the area in front of and behind the point of focus, where-in our subject resides. This zone is directly related to the f-stop we select on our lens. We do this by adjusting the lens iris, or aperture (like f2.8 or f16) that controls the diameter of the opening inside the lens. It works a little like the pupil in our eye.

Landscape photography (10mm to 18mm) Full body portrait of a person (24 to 45mm) Headshot (55 to 140mm) Night photography (10 to 18mm) Close-up photography or macro photography (70 to 150mm) Wildlife photography (200mm to 850mm) General lens for shooting family and kids (35 to 90mm) Outdoor sports photography (200 to 400mm)

I also want to make sure it's clear that you can achieve the same wide angle of view on a crop sensor camera as on a full frame camera just by using a wider lens, so there is no advantage to a full frame camera for landscape photography.  And on the long end, it can be handy to have a crop sensor camera because it makes a 400mm lens turn into a 640mm lens without paying thousands and thousands of dollars on a lens that long.

What is depth of field? Let’s start by determining what it is not. Depth of field is not a tangible thing. Depth of field changes depending on the way one takes a photo or shoots a video. Understanding depth of field is essential in cinematography, where the focus is manipulated to achieve the desired look.

Please understand that full frame cameras are neither superior nor inferior to crop sensor cameras.  They both have benefits and drawbacks.  I used to shoot a full frame Nikon camera, but ended up switching to a crop sensor Fuji XT1 camera which I'm really enjoying right now.  Don't let anyone tell you that a full frame camera is better.  It's simply different.

It can be a bit confusing as a beginner to understand focal length because there are a few twists and complexities, but I'll do my best to explain it in 5 minutes or less.  I'll start with the most basic information and then build up to the more advanced stuff.  Be sure to read the entire article because there are some cool examples down lower that will help you get the right focal length for when you're taking pictures of people.

The caveat is that the focal lengths necessary for micro 4/3 will be wider than those required by the full-size sensor. Thus, to get shallow depth of field, the m4/3 user will be required to get closer, or further from their subjects as the aesthetics demand.

The actual measurement of focal length is the distance, in millimeters, between the convergence point and the imaging sensor.  The convergence point is the point at which the light rays combine in the lens.  No worry, though, you'll never need to know that again.  There's no pop quiz at the end.

If you shoot at 20mm and the person you're photographing is 30 meters away, the person will be small (magnification) and you will see a lot of area around the person (field of view).   However, if you zoom in to 300mm, the person will be large in the picture (magnification) and there won't be much scenery on the sides of the model showing in the frame (field of view).

Now that you've read through this handy cheat sheet of focal lengths for different situations, you should really consider checking out my free lens finder.  It asks you 5 questions about what camera you use and what you want to take pictures of and your budget, and it gives you my personal recommendation of the perfect lens for you.  Find your perfect DSLR lens here.

Wider lenses show more distortion (unnatural bending of objects in a picture–especially around the edges of the frame).  Also, the wider field of view of a wide lens (10 – 18mm) will make objects which are close to the camera seem much larger, and objects further from the camera much smaller.

What isfocal length of lens

This is really a great information for beginners. Today I learnt something new and informative. Thanks so much, keep posting.

I love this article! Truly excellent and easy to read. I study photography at Chicago Photography Academy and found this extremely helpful.

Your work is amazing. Thank you. I’m just starting to educate myself, but it took me a while to find someone I wanted to learn from.

Focal lengthformula for concavelens

By manipulating the size of the aperture, we create a narrow zone around our subjects using a wide-open (large) f-stop. While narrower (small) apertures produce the opposite effect. Did you ever squint your eyes to make distant objects appear sharper? This is the principle behind the lens aperture that controls depth of field.

The above image shows how narrow the depth of field is around our subject placed at 5-feet away from the camera. Notice how little is in focus in front of, and behind our subject? It is the shaded area that will change as we adjust our aperture size.

A camera with a full-size sensor will require lenses that cover a 24X36mm projection area. A camera with a micro 4/3 sensor will conversely require lenses that need only cover an area of 13X17mm in total image size. If one matches the image circle of the lens to the area of the sensor, the depth of field results is comparable.

The focal length measurement tells the photographer what the angle of view will be.  The angle of view means how wide of an area is visible in the picture.  It also conveys the magnification of far-away objects in the photo.

image field – all the areas in the foreground, middle-ground, and background of an image that reside within the visible frame. The image field is a factor determined by the lens size, or angle of view.

When on the wide end, you see much more of the backyard around her.  You see the side of the house, all of the fence, and you can't even see the trampoline because she's covering it.  However, as you scoot back, you see much less of the yard (narrower field of view).  Also, notice that the face looks badly distorted when shooting with a wide angle lens up close, but as you scoot back and zoom in, everything looks normal and proportional.

With respect to the size of a camera’s image sensor, there are no discernible differences among brands on the matter of effects (if any) imposed on depth of field. Because image sensors of different sizes require different image circle projections, it is possible to experience similar depth of field characteristics if one selects the lenses that offer the appropriate coverage for a given sensor. In other words, match the sensor to your lens system.

What isfocal length of lensClass 10

One last thing to notice, and this one is a bit more advanced, is that the background appears blurrier and blurrier as the focal length increases, despite the camera settings staying the same for all of the shots.  To learn more about that, read my article on the many things that impact depth of field.

However, most photographers stick to the standard of the 35mm imaging sensor (full frame).  So if you hear a photographer recommend shooting at 200mm, they probably mean 200mm on a full frame camera.  35mm has long been the standard.  The good news is that you can use some very simple 3rd grade math to know exactly the focal length equivalent on your camera.

What isthe focal length of a lensPhysics

angle of view – the observable point of view of a lens, described by its size in millimeters, and defined by the image framing.

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So suppose I take a picture of a building on a crop sensor camera at 18mm.  If I put the same lens on my full frame camera and shoot at 18mm, the full frame picture will be much wider.  However, I could easily get a 13mm lens and put it on my crop sensor camera to match the exact same field of view as the full frame camera.

Focal length is measured in millimeters, but the measurement is not of the actual physical length of the lens, but rather the magnification properties of the lens.

Focal length, or the strength of your lens described in millimeters, can also affect depth of field. Wide-angle lenses–those with a broad field of view, and low millimeter designations—appear to demonstrate more depth of field. While lenses with higher magnification and higher millimeter designations appear to demonstrate less depth of field around a subject. This can be very handy when one wishes to direct the attention of the audience to specific items within the image frame. In this way, depth of field can be a powerful storytelling tool.

All lenses show the focal length right on the lens.  First of all, you'll see the range of the focal length that the lens can achieve in the name of the lens.  If your camera came with an 18-55mm f/3.5-5.6 lens, then you know that the widest your lens can go is 18mm and the most zoomed in your lens can go is 55mm.

There is one last thing you need to understand about focal length in order to have the basics under your belt.  Here it is: As focal length increases, the change of the field of view decreases.  As focal length reduces, the change in the field of view increases.  Or in other words, there is an inverse exponential relationship between focal length and the change in field of view.  Clear as mud?

Focal lengthexamples

As you listen to the Improve Photography podcasts each week or watch our Youtube videos, you'll often hear us discussing different focal lengths for different purposes.  In this article, all the examples of focal lengths I've used have been with crop sensor cameras, because that's what most of you will be using on your cameras.

If you have a crop sensor, I recommend you at least have a 35mm or 50mm f/1.8 in your arsenal. Very affordable fast primes.

All of the focal lengths below are the common focal lengths for crop sensor cameras, since the vast majority of the people reading this article will be shooting crop sensor cameras.  These are rough numbers, intended to give you an idea of what focal length you'd want).

Jim, I have been taking professional pictures for over 10 years and still do not understand “focal length”. I pick the lens in my kit that I know would work best for my needs and shoot. Do I really need to know all this?

Focal length ofconcavelens

As you turn the barrel of your lens to zoom in, you can look at the scale on the end of the lens that connects to the camera to see what specific focal length you are shooting at.

You should notice a gradual increase in the area around the subject. This is the depth of field. It is a zone that extends from just under four feet from the camera and extends out to over seven feet from the camera–with the subject set at five feet, and an aperture of f5.6 on a 50mm lens. Let’s look at one final example. Then, we want to point out some unique aspects of this depth of the field phenomenon.

Depth of field relates to something called the plane of focus. Imagine a photo as a 3-dimensional projection with the camera at one end of the projection, and the subject(s) arranged within the “field” of the projection. It’s like a big “slice” of our image field, that gets thicker as we open, or close down our aperture (iris). This “slice” also moves toward, or away from our camera based on our lens size, and subject distance. Here’s an example:

Given the following suggested focal lengths for different situations above, what is the ideal distance between the photographer and the subject? I am new into photography, I am sorry for my noob question.

This last example shows the most demonstrative change in the zone of focus, or “depth of field,” around our subject, using the same 50mm lens set to f11. At this point, something interesting is happening. Notice the rate of change in front of the subject versus behind the subject, as the aperture gets smaller? This change exists proportionately at a rate of nearly 1/3 in front, and 2/3 behind the subject.

It is more accurate to think of depth of field as a condition resulting from a set of conditions relating to a photograph and its visual arrangement. It describes an area of acceptable focus around a subject placed at a specific distance from the lens. This phenomenon occurs within the lens diaphragm—comprised of tiny thin blades that open and close to create an aperture.

Keep in mind that not all lenses can zoom (change the focal length).  Some lenses are prime, which means they cannot zoom in.  A common lens that cannot zoom (one which you likely own) is a 50mm f/1.8 lens.  It's a fantastic lens, but it cannot zoom in or out.  It's a fixed focal length lens.

Is it true that when using a crop sensor your 1.8 lens is then doubled to a 3.6? In other words, are your f stops all doubled?

We have seen how aperture affects “dof” directly. Now let’s discuss subject distance, and lens focal length. Using the depth-of-field simulator, change the camera to subject distance at the bottom of the application desktop. Notice how, as the distance increases between us and our subject, the zone of focus around that subject increases? At the same time, as our camera to subject distance increases, and focus increases, the background becomes more and more in focus. This is a proportional relationship. The further the subject is from the camera, the more the background comes into clarity. Therefore, if you want soft out-of-focus details behind your subject—move closer!

Thank you so much for explaining focal length in so much detail! I am a new DSLR owner (crop sensor) so this article was super helpful for me. I was particularly interested to understand what the mm measurement actually means because that just baffled me and I hadn’t found a clear explanation anywhere else. I think I’m probably going to have to keep coming back to this article as I practice to get my head around it all, but thanks for giving me a giant leap forward in my understanding! 🙂

200mm on a full frame camera is the same thing as about 135mm on a crop sensor Nikon camera, because the Nikon has a crop factor of 1.5x.  On a Canon crop sensor camera, however, it would be 125mm.

There is no “right” or “wrong” focal length for any given situation.  It's all a matter of personal preference and what you want to capture.  However, there are certainly norms of the focal lengths typically used in different situations.

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