Short Description

Crop factor applies only to 35mm SLRs, other camera segments may have crop factors but their lenses are rated as 35mm equivalents. The crop factor applies to SLRs who's sensors are smaller than a full frame 35mm sensor(36x24mm) but still use 35mm lenses. The crop factor illustrates how much larger a 35mm film is versus the smaller sensor along a single dimension. The ratio is also known as the focal length multiplier which illustrates the relationship between focal lengths of a lens when used with different sensor sizes.

For instance a 35mm sensor diagonal is 1.5X bigger than an APS-C sensor diagonal (the most common dSLR sensor) - thus its focal length multiplier is also 1.5X. Because the sensor is smaller than a full frame sensor the lens projects more image than the sensor can cover - hence the projected image is cropped and thus the name - crop factor. The focal length multiplier allows you to figure out how much is cropped by providing the equivalent focal length of magnification. For instance an image taken on a APS-C camera at 50mm will look like the same image taken on a full frame camera at 75mm - 1.5X magnification. This means smaller sensor SLRs get built-in zoom with a given lens relative to a full frame camera but they also loose the ability to go as wide angle as the full frame camera.

Visualization of Crop Factor

The following diagram shows the image projected by a lens and the relative differences between how much a full frame sensor is capturing and how much an APS-C frame captures. As you can see the smaller sensor captures less, but if it has the same number of pixels than on a relative basis the effect that is caused is basically zoom. If the full frame sensor was to capture the exact same image as the APS-C sensor you can see that the projected image would need to grow - in fact it would need to grow by exactly 1.5X - the same as the crop factor.

Illustration of Crop Factor on a Full Frame vs APS-C
illustration of a projected image being captured by full frame vs aps-cThe photo illustrates the difference between what a standard 35mm full frame sensor captures and a smaller APS-C sensor. It also illustrates the relative zoom afforded by the APS-C sensor and the wider angle afforded by the full frame sensor.

Top Full Frame Cameras

The following SLRs are some of the best full frame digital 35mm cameras available.

Nikon D750
Nikon D750
from $1,585
Low light performance Low noise at high ISO Help
2,956 ISO
Overall image quality Great image quality Help
93.0
Dynamic range Wide dynamic range Help
14.5 EV

Learn more about the Nikon D750

Nikon D810
Nikon D810
from $2,340
Low light performance Low noise at high ISO Help
2,979 ISO
Overall image quality Great image quality Help
96.0
Color depth Great color depth Help
25.7 bits

Learn more about the Nikon D810

Canon EOS 5DS
Canon EOS 5DS
from $2,896
Low light performance Low noise at high ISO Help
2,381 ISO
True resolution High true resolution Help
50.3 MP
Cross type focus points Many cross-type focus points Help
41

Learn more about the Canon EOS 5DS

Canon EOS 5DS R
Canon EOS 5DS R
from $3,100
True resolution High true resolution Help
50.3 MP
Low light performance Low noise at high ISO Help
2,308 ISO
Cross type focus points Many cross-type focus points Help
41

Learn more about the Canon EOS 5DS R

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Top APS-C Cameras

The following APS-C cameras are some of the best available.

Nikon D7200
Nikon D7200
from $829
Overall image quality Great image quality Help
87.0
Low light performance Low noise at high ISO Help
1,333 ISO
Screen resolution High resolution screen Help
1,228k dots

Learn more about the Nikon D7200

Nikon D5500
Nikon D5500
from $525
Low light performance Low noise at high ISO Help
1,438 ISO
Overall image quality Great image quality Help
84.0
Movie format Full HD Help
1080p @ 60fps

Learn more about the Nikon D5500

Pentax K-3 II
Pentax K-3 II
from $850
Movie format Full HD Help
1080p @ 60fps
Screen size Large screen Help
3.2"
Continuous shooting Rapid fire Help
8.3 fps

Learn more about the Pentax K-3 II

Pentax K-S1
Pentax K-S1
from $314
Viewfinder size Large viewfinder Help
0.63x
Light sensitivity High ISO Help
51,200 ISO
Movie continuous focus Movie continuous focus Help
Makes it easy to get in-focus movies

Learn more about the Pentax K-S1

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Discussion

Showing 3 comments

Johnsmith (7:34 AM, April 05, 2012)
Canon APS-C have a 1.6x crop factor (smaller sensor) so your 18mm = 28.8mm 
 
Roy Amrullah (9:16 PM, September 09, 2011)
550d seems to have 1.5x cropfactor then 18mm x 1.5 = 27mm. CMIIW
 
Avatar for Justin Ji Justin Ji (4:32 AM, June 15, 2011)
Nice! I was wondering why a 18mm lens on a 550d (APS-C) had less wide angle ability than a 26mm equivalent Nikon P100! : )