Understanding Crop Factor: Are You Being Scammed By Camera Manufacturers?

Perhaps you have heard the term “crop factor” before, but you’re not sure what it really means. If that’s the case, you’re probably also unaware of what an important part it plays in making the most of your digital camera. The camera settings we still use–ISO, aperture, and f-stop–were designed for film and do not take into account the wide variety of sensor sizes used by digital cameras; we use crop factor to account for these shortcomings in camera design. If you use a camera with a smaller sensor, the following video could completely change the way you shoot:

What is Crop Factor?

So, what is crop factor, anyway? As Tony Northrup tells us, it is the size ratio of smaller sensors to a 35mm film frame. For example, a Micro Four Thirds sensor is half the size of a 35mm frame, so it has a crop factor of 2. It might seem logical that full-frame cameras, whose sensors are the same size as 35mm frames, would naturally make better pictures, since they have a larger sensor and can take in more photographic information. However, Northrup shows us that this is actually a myth. And he tells us how to take photographs with smaller-sensor cameras that are just as good.

There are a number of camera settings that must be adjusted by the crop factor:

  • Focal Length – A camera with a smaller sensor will make an image appear closer, even with the exact same lens and focal length. Focal length must be reduced according to the crop factor to achieve the same angle of view.
  • ISO – The ISO standards were created decades ago and were meant for film; they measure the amount of light captured per square inch, not total light captured by the sensor. To account for this, divide a given ISO by the square of your camera’s crop factor.
  • Depth of Field – Smaller sensors give your camera more depth of field, even on the same f-stop as a full-frame camera. If you want a shallower depth of field, be sure to increase BOTH the aperture (by the crop factor) and the ISO (by the crop factor, squared), so that your camera receives the right amount of light.

To better understand these concepts, let’s take a look at some examples:

crop factor

Three photos of a white wall.

The above image shows three photographs of a white wall (which appears gray), taken with three cameras of different sensor sizes. The ISO, aperture, and shutter speed were exactly the same for all three. But as you can see, the smaller the sensor size, the noisier the image looks, because smaller sensors receive less total light.

crop factor

The same photos with crop factor applied.

These photos were taken with three different cameras as above, but the crop factor has been applied. The appropriate ISO makes it possible to take a relatively noise-free photograph, even with a small sensor.

adjust-for-crop-factor

Full Frame vs. Micro Four Thirds

Above is a great example of everything the crop factor can do, in one image. The photograph on the left was taken with a full-frame camera; on the right, with a Micro Four Thirds camera (with a crop factor of 2). The focal length on the left is 100mm; on the right, 200mm. As you can see, though the settings are different, the two photos have a similar viewing angle, depth of field, and brightness. They are not exactly the same, but they’re very close!

Are You Being Scammed By Your Lens Manufacturer?

Dishonest marketing by several camera companies fails to account for all aspects of crop factor. This leaves many photographers disappointed with their purchases and unable to get the results they’re looking for. Northrup suggests you stick with gear from Nikon, Canon, and Fuji, as these companies are more truthful in their advertising. But, by understanding crop factor, you can make smarter purchasing decisions next time you’re in the market for a lens from any manufacturer.

Applying crop factor also helps you get better photos using the gear you already own. Though full-frame digital cameras are more expensive and are often thought to be objectively “better” than those with smaller sensors, Northrup has debunked this myth by showing us that image quality doesn’t have to suffer if you do the right math.

“All you have to do is apply the crop factor appropriately, and you can get exactly the same image with small sensors.” – Tony Northrup

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9 Comments

  1. Willi says:

    “This is a great example of everything the crop factor can do, in one image. The photograph on the left was taken with a full-frame camera; on the right, with a Micro Four Thirds camera (with a crop factor of 2). The focal length on the left is 100mm; on the right, 200mm. As you can see, though the settings are different, the two photos have a similar viewing angle, depth of field and brightness. They are not exactly the same, but they’re very close!”

    The left one is MFT and the right one 35mm, not the other way around.

  2. Linda says:

    Thank you Tony! Great and very useful info!

  3. Gary R Hook says:

    Tony Northrup cleaerly had trouble with math in school

    It is mathematically/geometrically impossible to get the “exact same picture” from 2 different size sensors. Doesn’t matter which 2 you choose, it can’t be done, _technically_. To say so, unequivocably, is misleading.

    To mitigate the above statement, distance to subject can alter the relative impact of sensor size (which is what impacts the circle of confusion value) on the depth of field. Close-ups make the sensor size less relevant; long distance makes the CoF value of greater concern, and it is this fact that obviates Northrup’s assertion.

    Could we possible do some fact checking before publishing articles like this? Misinformation does nothing to help people.

  4. Anders Blomqvist says:

    Hi,

    Interesting article, and the video from Tony Northrup is excellent though a bit long. The concept of total amount of light is good, because this makes it easier to get similar pictures with different sensor cameras.

    However, I think you have picked the wrong picture for the Full Frame vs. Micro Four Thirds comparison – these are taken with same camera but different settings, and the DoF is thus different as can be seen from background.

    Regards,
    Anders

  5. Dan Richards says:

    I have shared this article with two photography groups, I am a member with.
    I noticed something I seen before. My 500mm mirrored lens has an f8.0. A while back I saw another one by a different company just like mine, no difference I could see, that they claimed was a f5.5. No way. Yes the mirror does increase the light a very small amount, but not that much.

  6. Clive Dickinson says:

    This video is very misleading and gives misleading information. It gives wrong information about the ISO standard, it fails to point out that noise is dependent not on sensor size but on the number of pixels per square inch and on the actual pixel technology.

    It is a shame that he gives a clear demonstration of the relationship between shutter speed, aperture and sensor sensitivity (ISO), but he wrongly asserts that the parameters used are outdated. I suspect that he wants a gimmick to make this video attractive. Therefore he tries to dumb down a fairly complex mathematical relationship by attacking the photography companies.

    The real problem is that crop factor does not change the focal length or aperture of a lens. It changes the field of view.

  7. Alvin Chandrin says:

    It’s true that ISO is a measure of absolute sensitivity, which can be interpreted as sensitivity per unit area, but that was true in film days too. In film days, a 35mm photo blown up to the same size as a print from a 4×5 negative would show more grain. There is no conceptual change when using a digital sensor. A smaller sensor yields more noise for equivalent prints.

    The ISO doesn’t change for a given exposure without also changing f-stop and/or shutter speed. This is clearly illustrated by the equivalent portraits shown in the article. Physics is physics, whether you’re using film or CMOS, a 4/3 camera or an 8×10 view camera.

    The trick for figuring equivalent ISOs, comparing lower ISOs from smaller sensors with higher ISOs from larger sensors, is a good one to know. However, it’s not new either. In the bad old days, you could achieve the same sort of comparison by taking your 35mm picture on 25 ASA film and comparing with a 4×5 on 200 ASA film.

    Can you get equivalent quality from a crop sensor that you can get from a full-frame sensor. Clearly, and as the article shows, the answer is yes. Can you get the same quality in extreme lighting situations? Will you have the same flexibility in approaching that extreme situation? In that case, the full-frame sensor wins hands down.

  8. Stefan Weilhartner says:

    The ISO-Values in digital-cameras are nothing but crap.
    they are approximated by some fictional formula. but in reallity the sensor does not change compared to different films in analog times. it maybe is some configuration change internally of the sensor chip where the range of the analog/digital-converter in the chip changes and therfore could be adjusted to low-light-conditions but the sensitivity of the senosr stays the same.
    i always use auto-iso-mode in my nikon ff dslr and it works well most of the times. only in very intense sunlight i have to use filters when i still want to stay at f/1.4

  9. James says:

    This has opened my eyes, I was about to fall for the apeture trick with the new Sony RX10ii (2.8 constant). I was going to say everyone should read this but then I saw the other comments which seem to disagre somewhat with the facts in this video. It would be great to hear responses to the commenters that have an issue with this video, just to clear it up once and for all.

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