Full-Frame vs Cropped Frame – What’s the Deal?
I often get asked which lens I recommend……as if there exists a lens that can do it all, for everyone, in all shooting conditions. The fact is, you have to decide what kind of shooting you intend to do, and then figure out which lens can help you, and of course, how much it will cost. In the end, I always recommend either the Canon 50mm prime f/1.8 or the Nikon 50mm f/1.8. They are both full-frame lenses, which simply means the image circle they produce will accommodate a 35mm film frame size, which full-frame DSLR sensors are. Only the higher-end cameras have a full-frame sensor, and virtually no one who asks me about a lens has a FF camera. So why do I still recommend them?
Honestly, there is a ton of confusion and bad information about this subject floating around. Right off the bat, You ABSOLUTELY CAN put a FF lens on a cropped sensor camera!! In fact, there are several reasons why this can be a BETTER choice. It’s tough to make generalizations about lenses, but I don’t see a down-side the using a FF lens on any camera as long as you understand what the REAL angle-of-view (notice I didn’t say “focal-length”) will be in a cropped frame. So throw that FF lens on your Canon or Nikon cropped-frame camera and go shoot. It’s really not worth the time obsessing over stupid stuff like the perfect focal length. Personally, I like shooting with primes, and if I need to change the damn focal length I just MOVE! There’s way too much emphasis placed on technical specs, and if you know how to compose and get proper exposure, and you understand the technical limitations of your equipment, you’ll take great shots. Equipment doesn’t take photographs, people do! However, if you MUST know the why, the how, and the WTF, read on.
What Is a Cropped Sensor?
Most lower-end (non-pro) DSLRs come with a smaller sensor. I’ll refer to these as 1.6 size sensors, because 1.6, to put it in a confusing and misleading way, is the factor by which your focal length changes on a 1.6 sensor. Confused? Simply put, think of a 1.6 sensor as having less angle-of-view, and don’t worry about it any more.
A cropped sensor means that the sensor is not picking up as much image “real estate” as a FF sensor if you use a FF lens. In the 2 images that follow, I shot the lava lamp with both a full-frame camera and a 1.6 cropped-sensor camera using the same 50mm full-frame lens at the same distance:
The first image above appears closer than the second image, but it isn’t. The difference is caused by the larger sensor in the second image being able to pick up more of the image circle projected by the lens….which, don’t forget, was used for both shots.
In the following image, we see the image circle projected by a full-frame lens, with both a full-frame sensor size (in red), and a 1.6 sensor size (in yellow) superimposed onto the image:
So the yellow rectangle above is “seeing” less of the image than the full-frame red rectangle. The image itself hasn’t changed, but the angle-of-view in the smaller sensor has, so it appears as though the image in the yellow frame is closer, which make it seem like the focal length is larger…neither of which is true.
Let’s understand what we’re dealing with. The focal length number expresses the distance from the aperture to the sensor. So the 50mm focal length in a cropped-sensor camera and a FF camera is EXACTLY the same. What changes is is the sensor size, and consequently the angle-of-view. In terms of the image circle, the image quality, Depth of Field, EV (exposure values) are exactly the same on both cameras using that lens….you loose nothing but image real estate by putting a FF lens on a cropped-sensor camera. Check out the following image shot with a full-frame lens on my Canon 40D, which has 1.6 size sensor:
Now look at the same shot taken with my Canon 5D…a full-frame camera:
Both shots were taken with the same lens, and I tried to get the subject to fill the frame equally for both cameras as best I could by moving in closer for the full-frame shot. I was using a tripod, so the orientation was different for the full-frame shot as I couldn’t get the 5D close enough without changing the angle.
Addendum – 10/29/14
I don’t feel that I correctly addressed the issue of Depth of Field when I first wrote this article. If you look closely at the above 2 images, you’ll notice that the image shot with the 5D, a FF camera, has a narrower DoF than that which was shot with the 40D, a cropped sensor camera. That is the direct result of having to INCREASE the focusing distance when shooting with the 40D to achieve the same composition. Since the 40D was further back, as opposed to the 5D, the DoF was larger. Both images were shot at f/2.5. It turns out that in order to achieve the same composition with a cropped sensor, the equivalent DoF would be that of an f/4 aperture. So you’d multiply the FF f-stop number by the crop factor (2.5 x 1.6= 4) to get the equivalent DoF for a cropped sensor when shooting the same composition as a FF camera. If that’s confusing, forget the math. Just know that one way to influence DoF is via focusing distance. The further away the camera is from the subject (focal point), the LARGER the DoF all things being equal. Since you would need to move a cropped sensor camera back to get the same composition as that of a full frame camera, you’re INCRESING the size of the DoF.
Just Step Back
So there you have it. The only thing that I changed was the distance from the camera to the subject. That, in a nutshell, is the ONLY significant factor that you need to consider when putting a FF lens on a cropped camera. With a 1.6 camera, you’ll need to be farther away at any given focal length than you would with a FF camera. Now look at this image, shot with a FF 50mm lens from about 12 feet away:
Compare it to the following image, shot with my Canon 5D and the same lens from 8 feet away:
With the first shot taken with my 40D, I couldn’t get far enough away to have the model completely fill the frame. This is the only potential issue with a FF lens on a non-FF camera. The angle of view changes, so you are shooting at an equivalent of around 75-80mm instead of 50mm. However, if you know this, just plan your compositions accordingly……step back! Obviously I was out of room in the first full-body shot above, but that’s because I planned poorly by not setting up the seamless background far enough back to give me enough room to shoot!
If You Have a 1.6 Sensor, You’re ALREADY Shooting a Narrower Angle-Of-View!!
At this point, I’d like to clear up another area that creates a lot of confusion. You can buy lenses specifically made for 1.6 cameras. They project a smaller image circle that just fits a 1.6 sensor. They are marked with focal lengths, just like any other lens. What confuses people is that if a 50mm lens designed for a 1.6 camera has a focal length of 50mm, that focal length is exactly the same as it is on a full-frame lens……50mm is 50mm after all, so the distance from the aperture to the sensor is exactly the same for either the full-frame OR the 1.6 sized lens. Look at the following shot taken with my 40D and a Tamron 17-50mm lens designed for 1.6 sensors, shot at 12 feet:
Compare it to the first full-body shot above taken with the same camera and the FF 50mm lens. Do you see a difference in focal length? No, you don’t. Here’s why……in both cases, since we are talking about a smaller 1.6 sensor, the equivalent focal length is @ 80mm. As a result, it doesn’t matter whether you buy a FF lens at 50mm or a lens designed for the smaller 1.6 sensors at 50mm. If you put either lens on a camera with a 1.6 sized sensor, the focal length in both lenses is exactly the same. The image circle projected onto the sensor from the full-frame lens is larger, but gets cropped by the smaller sensor anyway, so the image projected by the 1.6 lens and the full-frame lens is exactly the same size…..the size of the sensor. Also, in both cases, since the image that gets picked up by the sensor is the only image that counts, in both cases you are actually shooting at the 1.6 crop-factor, which turns out to be @ 80mm, not 50mm. The ONLY way to get an image that is projected at a 50mm focal length to LOOK like a 50mm image is by using a full-frame camera! You can put the Tamron lens on a full-frame camera and see a true 50mm image size, but since the image circle is designed for the smaller sensor, you will also see that image surrounded by a black circle.
So we now know that you can put a FF lens on a 1.6 camera, but not the other way around, unless you want to get a very pronounced vignette in your image. We also know that if you use a certain focal length lens on a 1.6 camera, it doesn’t matter whether or not that lens is made for a full-frame or 1.6 sensor, the crop factor means you are shooting at a longer perceived focal length since your actual angle of view is less.
One more series of shots to beat this to death. Look at the following head-shot, taken with a full-frame 70-300mm telephoto lens on my 1.6 40D from 7 feet away:
Compare that to this one, shot with the same lens at the same focal length on my full-frame 5D from 4.5 feet away:
Once again, the images look exactly the same in terms of focal length, because they are. However, the first image (Canon 40D 1.6 sensor) was shot from 7 feet away, and the full-frame shot (Canon 5D) was taken from 4.5 feet.
As you can see, there is no problem putting a full-frame lens on a camera with a 1.6-sized sensor. All you need to remember is that on a smaller sensor, any given focal length will appear to magnify more than it does on a full-frame camera. You can simply adjust your composition accordingly. Rather than getting hung up on all of the numbers, conversions, and distances, just look in your viewfinder and don’t worry about it! The bottom line is, if you are a photographer, what you see in the viewfinder is all you need to know. That’s why all of your exposure info is available to you inside the viewfinder…..that’s where the composition is! I laugh when I see people looking at their camera settings on the rear LCD screen, or the info window on top of the camera body. They aren’t composing a shot, they’re worrying about numbers. Look in the VIEWFINDER folks! All the info you need is right there, and you never need to take your eye off the composition…..but I digress.
This is why I always recommend the 50mm f/1.8 lens for both Canon and Nikon people. Canon and Nikon make a very affordable lens (@ $100), that is very sharp and great in low-light. Both B&H Photo and Adorama carry these lenses, and they are super-great about returning stuff, if you aren’t happy, but you will be so no worries.
There is only ONE caveat, and it only applies to people with a Nikon D40, D60, D3000 or D5000. The auto-focus (AF) function will not work on this lens on your camera. For you guys, I recommend the Nikon 35mm f/1.8. It is NOT a full-frame lens, and it’s almost twice as much at $192, but it’s great in low light and still a good deal.
For everyone else the 50mm f/1.8 is really a great buy. Who cares if it’s a full-frame lens? Not me…I’ve been happily shooting a 50mm prime f/1.4 lens on my 40D for almost a year now, and couldn’t care less that the crop factor gives me an 80mm or so image magnification. I just adjust my distance as I compose the shot, and never even THINK about the crop factor. So think about it….all of the time you’ve wasted agonizing over what is essentially a non-issue by reading this article, you could’ve been shooting….which is way more important!Tags: cropped sensor, lenses, photography