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Transitioning from Point-and-Shoot to DSLR: Understanding Full Frame vs Crop Frame Sensors

Gear Talk

Upgrading from a point-and-shoot camera to a digital SLR camera can be daunting, especially when you start hearing people carry on about what kind of sensor to get and you have no idea what they are talking about! The following will help you understand sensor size and how it can be a factor in your photography. This information will better equip you with the knowledge you will need to successfully choose your next camera.

What is a Sensor?

SensorComparison-1

A visual comparison of the Crop Sensor on a Canon Rebel T4i (left) and a Full Frame Sensor on a Canon 5D Mark III.

Every digital camera, even your point-and-shoot, has a sensor inside of it. In the simplest of terms, all these sensors do is convert an optical image (light) into an electronic signal which can be read as digital information–an image you download and can see, edit, and share. Your point-and-shoots have tiny, little sensors inside of them and for the most part they do a good job of converting light into digital information you can use–a photograph!

Some of you may have heard people carry on about the “size” of their camera’s sensors. The reason they care about this is because dynamic range and low-light sensitivity generally improves as the size of the sensor increases.

Defining Crop Sensors and Full Frame Sensors

135film

35 mm (1.4 in) wide film (36×24 mm). Image courtesy of Wikipedia.

A piece of 35mm film measures approximately 36 x 24mm in size, and that’s the size of the sensor in Full Frame cameras like the Nikon D4 and the Canon 5D Mark III. Full frame sensor cameras are among some of the most expensive DSLRs you can buy. However, you can buy a DSLR camera with small sensor and still experience much greater image quality than you can from your average point-and-shoot. Cameras like the Nikon D7100 and the Sony A77 have APS-C-sized (or “cropped”) sensors that measure about 23.6 x 15.7mm (this varies slightly among manufacturers) vs the average point-and-shoot sensor which runs about 11mms when measured diagonally.

Something else you should know about Crop Sensor Cameras

One of the fun things about advancing from your point-and-shoot to a DSLR is the ability to change out your lens. Lens types are described in two ways: focal length (size of the lens) and max aperture.

The max aperture, the f/stop reading when the lens is “wide open”, stays the same regardless of camera. Shooting at f/1.2 is the same no matter what kind of camera you use. You are letting in more light than when the lens is set to shoot at f/8.

The focal length of a lens, however, is subjective. On a Full Frame camera, like the Canon 5D Mark III or Nikon D800, a 50mm lens is a 50mm lens. That’s because the focal length of the lens is measured based on the standard 35mm film size–a size that lenses are built to accommodate.

However, on a Crop Sensor camera, like the Nikon D7100 or Canon T4i, your 50mm lens becomes, effectively, a 75mm lens (sometimes even 80mms if the sensor is even smaller). Since the sensor is smaller, it’s only seeing a portion of the image the lens is trying to project onto it. In effect, the smaller sensor is “cropping” the image being transmitted to it by the lens – hence the term Crop Sensor. This change in size is not a physical one–your 50mm lens is still a 50mm lens no matter what it is attached to. However, the results are different depending on your camera’s sensor and that is what it means when you hear that a lens of a certain length is “effectively” another length.

MoaiSensorComparisonBLFB

Sometimes you will hear the term “Magnification Factor” when referring to Crop Sensor cameras and the effect they have on perceived lens length. The lens isn’t shooting at a focal length that is any longer than what the lens actually is. The image appears magnified on the smaller sensor producing a narrower angle of view. Again, your 50mm is still a 50mm–but the resulting image is not what we think of as 50mms when shot on a Crop Sensor camera.

LensCropFactor

A Full Frame sensor (35mm) sees the entire tree. The Cropped Sensor sees only part of the tree. The lens remains the same but the angle of view, and what we see in the final image, is different. Image courtesy of Wikipedia.

So Crop Sensor Cameras are Worse than Full Frame Cameras?

Not necessarily. Sure, Full Frame DSLRs are receiving more information than Crop Sensor ones are and they certainly make the math on what lens to choose a no-brainer. But some photographers strategically choose Crop Sensor over Full Frame.

For one, Crop Sensor cameras tend to be cheaper but still pack a lot of quality punch, Nikon’s D7100 and Canon’s 60D being notable examples. Also, photographers who like doing telephoto photography enjoy the extra bump having a Crop Sensor gives to the lenses they use. If you are out birding, having a 70-200mm lens read like a 112-320mm (or thereabouts) lens is certainly a good thing! And, above all, even a Crop Sensor DSLR is going to provide a huge jump in quality for the average point-and-shoot user.

I’m Using a Crop Sensor Camera – How Do I Figure Out the “Length” of my Lens?

Warning: math. However, it is very easy math. If you know you have a Crop Sensor camera and it is a Canon, you can multiply your lens’ length by 1.6. For Nikon and Sony, it is 1.5. There are only two exceptions to this rule and that is for the Canon 1D Mark III and the Canon 1D Mark IV, for which you use 1.3.

MathBL

Don’t panic. Finding your focal length on a Cropped Sensor camera is easy.

Let’s say you have a Canon T4i. This is a very popular first DSLR for beginning photographers. Let’s say you want to use the also very popular Canon 24-70:

24 x 1.6 = 38.4

70 x 1.6 = 112

Your 24-70mm lens just became a nearly 40-112mm lens!

This is good to know because if you are shooting a wedding and you are in a very small chapel, the 24mm would be perfect but having nearly 40mms instead might be too tight to capture the scene. However, if you are shooting from the balcony and need to photograph the couple’s kiss, 112mms is likely more useful than 70mms.

So, in short, as a general rule: Crop Sensor cameras make lenses appear less wide than they say and also longer than what they say. This is one of the appealing things about a Full Frame camera–what you see is what you get in terms of lens focal length.

Conclusion

We hope this gives you a better understanding of what a Crop Sensor camera will mean for your lens selection versus a Full Frame camera. We also hope that this information has better equipped you with the knowledge you will need to help you successfully choose your next camera.

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Alexandria Huff is a portrait photographer based in San Francisco. Her tutorials can be found here on the BorrowLenses Blog, 500px, Shutterfly, Snapknot, and SmugMug. She specializes in studio lighting. Follow her work on 500px.

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Comments

  • D~C says:

    What is the crop factor math for Sigma DSLR cameras, particularly the SD1M and the SD15?

  • Alex 2.0 says:

    For the Sigma SD15 = 1.7x. For the Sigma SD1 Merrill= 1.5x.

  • Drew Hoover says:

    I think it would be helpful and appropriate for this article to discuss pixel pitch as well, since it severely affects image quality and what glass is appropriate for your camera. I use a D7000 (16MP APS-C) and a D700 (12MP FF), and at any given equivalent focal length, the D700 outperforms the D7000, even though the latter is a more recent design and packs more MP. It was hilarious to me that everyone freaked out about what glass can resolve the 36MP on a FF D800 when it has almost identical pixel pitch to the D7000, which was released years prior.

  • Perhaps just a technicality but you should mention that the focal length “difference” between crop and full frame is really just a matter of Field of View or FOV.

    That is, the focal length, being a mechanical function of the glass, never changes for any lens on any body. Rather, the FOV is tighter on a crop sensor (hence the crop) and so it gives the impression of seeing “further.”

    Something else that doesn’t change is perspective. The center portions of an image captured with an 85mm lens on a crop and full frame sensor will have identical perspective due to the mechanical focal length of the lens.

  • Daren Morgan says:

    Additionally, the output size from the crop sensor results in an image size the same as the full frame. Example: Suppose you were printing out a picture in a 4 x 6 size taken from a full frame cameras, and then took the same picture from the same position with a crop sensor camera. The resulting image at a 4 x 6 size would be the same as if you cropped the full frame image and then out put it to a 4 x 6 print,

  • Jacob D says:

    The article is good as written. Presumably this is intended for people who are relatively new to photography or digital cameras; delving too far into the tech (or semantics) tends to be cause confusion for anyone who’s not specifically looking for that type of stuff.

    That aside, the quality of today’s APS-C make it hard to argue that FF is a necessity except in a few very specific circumstances. It’s still a nice luxury though :) I do miss the days of shooting with my 5D and some wonderful, fast glass.

    On the topic of choosing your next camera, here’s something you might find interesting…
    http://hikeitlikeit.com/2011/photography-and-backpacking-3

  • kathryn3sons says:

    Well written article! I had learned this in bits and pieces on the Internet. Well done,

  • For any of your readers that are still interested in point and shoots, I created a comparison chart to make it easier to find the best point and shoot cameras. I also have several camera reviews on my site. I hope that some of your readers might find it useful! http://bestpointandshootcameraguide.com/

    Although after reading this article, I might be buying a DSLR next!
    Thanks –
    Will

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