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Crop Factor (Focal Length Multiplier)

The Crop Factor is a term that can be heard quite often in the world of digital photography. What does it mean that a camera has a crop factor of 1.6x and how does it affect your focal length? We try to untangle this issue and describe it as clearly as possible.

The subject of crop factors and focal length multiplier can be a bit confusing and hard to understand at first — I will try to explain it as simple as possible but yet informative enough for you to get the entire picture.

The size of the sensor is what controls the crop factor, and it’s always compared to a 35mm film size. So when people talk about Full Frame they are talking about cameras that have a sensor the same size as a 35mm film (24x36mm).

As you can see in the illustration above, a body with a crop factor captures only the center part of the image. The image itself is round because that’s what the lens produces, and the sensor only picks up the light that reaches it. A full frame sensor will capture edge to edge of what the lens capture.

It’s important to know that the crop factor changes the field of view, it doesn’t actually change the focal length, since that is something that is decided by the design of the lens. The same results could be produced by taking a photograph with a full frame camera and crop it to only show the center — however it would require a camera with a good enough sensor that such a small crop would still produce a good quality image. These high-end sensors are currently only found in the top of the line cameras from Nikon and Canon.

What it also means is that the perspective doesn’t change with the crop factor, if you stand on the same spot and take a photograph with a full frame camera with a 50mm lens and then take another photograph with a 1.6x crop factor camera you will get the exact same perspective (the 1.6x camera will however not have the same view of field).

When people say that a 50mm lens is the natural focal length they talk about perspective in relations with the human eye, and as stated above, this is the same even on cropped bodies, a 50mm lens still produces a natural looking photograph. To test this, use a 50mm lens and look through the viewfinder with one eye and have your other eye open, you will notice that the perspective looks the same for both eyes, no matter if you’re using a cropped body or not.

Lenses designed for Crop Factor cameras

To counter this issue, most lens manufacturers have designed some lenses that are only meant to be used on cameras with a crop factor (i.e. not on full frame bodies). These lenses often produces a smaller image circle so if they were used on full frame bodies they would create a black edge, much like circular fish eye lenses do. Since the problem with crop factor is mainly negative with wide-angle lenses it’s almost entirely that focal range that has designated digital lenses.

Here is a list of the name camera manufacturers call their digital only lenses.

  • Canon — EF-S
  • Nikon — DX
  • Sony — DT
  • Pentax — DA
  • Sigma — DC
  • Tamron — Di-II

One thing to remember is that the crop factor is still in use even on these cameras and you must multiply the given focal length to get the “correct” focal length. For example, Canon has an ultra wide EF-S lens that has a focal length of 10-22mm, on a body with a 1.6x crop factor the focal length corresponds to a 16-35mm. So don’t believe that you do not need to multiply the focal length just because you have a lens designed from cropped bodies.

How it affects your photographs

There are both positive and negative affects with the crop factor, let’s talk about the positive aspects first.
To get the “correct” focal length you need to multiply the focal length with the crop factor. When I say correct I mean the focal length that the lens acts like, not what it truly is. My camera has a crop factor of 1.6x and that means that a 50mm lens is a 80mm lens (50×1.6=80). It also means that a 100-400mm lens is actually a 160-640mm lens. That’s a very good thing in most situations. You loose 60mm on the short end but gain 240mm on the long end — rather significant. With telephoto lenses the crop factor is often desirable, since it extends your “reach” quite a bit.

Another positive affect is that almost all lenses are much sharper in the middle and softer on the edges. How can this be a good thing? Well with a camera that has a crop factor you only get the center of what the lens sees (unless it’s a lens designed for crop factors as described above). So with a crop factor you only get the center and therefore the best performance from your lens.

Now over to the not so good aspects of the crop factor. Wide-angle lenses, this is a big minus on the bodies with smaller sensors. As the example above, the 10-22mm ultra wide turns into a 16-35mm lens, and for example a 17-40mm lens turns into a 27-64mm lens. You simply do not get the same wide angles with a crop factor, the edges are cut off and field of view is more limited.

Another negative affect is that the extra focal length you gain also means that you increase the risk for blur due to camera shake. The rule that you should have a shutter speed of 1/focal length is no longer true. For this rule to be true you first need to multiply your focal length with the crop factor of the body.

Full frame camera often have a larger viewfinder as well. When I’m comparing my old 35mm film camera with my 1.6x crop DSLR it actually makes me a little bit sad inside. The viewfinder on the 35mm camera is so large and bright where as the DSLR’s viewfinder is although bright still very very small.

There is one more thing a smaller sensor affects, but it would be hard to classify it as either good or bad. Different sizes of sensors change the depth of field. A smaller sensor will give you greater depth of field (more in focus) and a full frame sensor will give you a narrower depth of field (less in focus). If this is good or bad is dependent on what you desire, either you want as much as possible in focus or you want to isolate your subject as effective as possible.

I hope I didn’t confuse you too much. This is an important part of digital photography to understand, at least the very basics of it.

28 Comments

  1. Add point Subtract point

    Photoshop tutorials, from beginner to advanced. photo manipulation, icon design, text effects, interface, layout, painting, photo effects, psd tuts, maxon cinema 4d, designing.
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    “Idiots November 9, 2010″

    “This is the stupidest tutorial ever” (see previous post)

    Only Idiots post pointless and unhelpful comments. This instruction and the others on this site will be very helpful to photography novices, unfortunately it will be of no benefit to “Idiots”

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    Jonatan (2 Points) October 16, 2010 at 2:50 pm

    AMAZING AND CLEAR EXPLANATION!!!!!! THANK YOU SO MUCH :)

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    ايفون (1 Point) September 22, 2010 at 11:25 am

    great tips with good comparison

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    Wisconsin Motorcycle (1 Point) June 22, 2010 at 2:44 pm

    Very nice cropping advice. Thanks for sharing your knowledge.

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    Thank you very much, for good words.Here is my entry into the blog,lucy

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    Web Design (1 Point) April 26, 2010 at 8:11 pm

    nice pointers thanks for sharing

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    เพลงใหม่ล่าสุด (1 Point) February 3, 2010 at 4:03 am

    great i never seen before.56

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    โหลดเพลงmp3ฟรี (2 Points) February 1, 2010 at 10:57 pm

    great i never seen before.49

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    แจกเพลง (1 Point) February 1, 2010 at 12:07 am

    great i never seen before.44

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    เพลงใหม่ล่าสุด (1 Point) January 30, 2010 at 7:55 am

    great i never seen before.

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    Robert Gates (1 Point) November 10, 2009 at 11:55 pm

    At the beginning of the article you state that crop factor does not change the focal length of the lens, just the field of view and I understand that. Later in discussing the negative effects on camera shake you say, “…the extra focal length you gain…” This is confusing to me. My Nikon has a 1.5 crop factor and I’ve always believed that if using a 100mm lens I don’t have the extra reach of a 150mm lens but I simply have the same FIELD OF VIEW I would have if I were shooting from the same spot with a 150mm lens on a 35mm camera. My 100mm does not have the longer reach of a 150mm, just a cropped field of view relative to a full frame sensor and movement of the lens in that smaller field of view would create more blur. Do I have it right?

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    new and confused (1 Point) September 27, 2009 at 6:12 pm

    Thanks that really helps me! Finally more simplified explanations for beginners. Are all crop factors the same for digital? I have a sony a350 would that be the same if not how do i find out my crop factor?

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    Amol Temghare (1 Point) September 20, 2009 at 3:17 am

    wat a perfect explanation Fredrik…. it dint confused me, even a bit…… i m now clear to this part…..
    i had been hearing ot this part but dint know wat exactly it meant…..
    but it is crystal clear to me now…. thanks a lot

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    Rob Barker (1 Point) February 24, 2009 at 4:42 pm

    I think your assertion that crop factor does not change perspective is misleading. Perspective is related to FoV and the ‘normal’ or ‘natural’ focal length of 50mm only applies to the 35mm full frame format. The same 50mm focal length is a moderate telelphoto on a ‘crop sensor’ or APS-C camera and a moderate wide angle on medium format. The focal length doesn’t change, but the FoV is different.

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    Thank you so much for explaining the crop factor, it was as interesting as it was informative, and I appreciate the elucidation. Great tutorial!

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    jonathan (1 Point) August 28, 2008 at 4:36 pm

    Concise explanation..In particular i was unsure about the crop factor as it applies to “digital only” lense… My canon rebel XT has a 1.6x crop factor irregardless of which type of lense i use. For example sigma has the DC line up which can only be used with the rebel & d20 through 40 series but will have the same crop factor as the DG series which will fit a full frame sensor mount or the smaller APS-C type .

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    David Jenrette (1 Point) August 11, 2008 at 7:28 am

    from Frederick: David, I actually have never used a medium formal camera and I don’t know that much about them – so I really can’t comment much on that. But as far as I do know, the current medium format lenses are considered to be some of the best lenses in photography. Also, Hasselblad’s latest medium format camera have an incredible, 36×48mm, 50 megapixel sensor in it – if anything that camera will magnify every little weakness in a lens.
    (end quote)
    Yes, medium format lenses can be excellent on medium format size sensors, because the images are not magnified as much. The same lenses on 35mm format, where they are magnified much more, are not nearly as good. If a medium format lens resolves 40 lines/mm, that is really good — but you wouldnt accept that resolution on a 35mm camera.

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    I like Theo have just bought a DSLR and found this article informative and in no way confusing.

    Excellent

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    Great article Frederic! No you didn’t confuse at all, it’s all very clear to me now! I just bought myself a DSLR this week and wasn’t entirely sure what they ment by this, but now I do! Thanks-a-lot!

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    @David, I actually have never used a medium formal camera and I don’t know that much about them – so I really can’t comment much on that. But as far as I do know, the current medium format lenses are considered to be some of the best lenses in photography. Also, Hasselblad’s latest medium format camera have an incredible, 36x48mm, 50 megapixel sensor in it – if anything that camera will magnify every little weakness in a lens.

    @Peter, I’m assuming you meant the Four Thirds system (4/3)? Well I didn’t mention them since all the lenses for that system are “digital”, with a focal length multiplier of around 2x. If all the lenses you can use for a camera have the same “crop factor” this becomes rather irrelevant, at least in my eyes.

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    Peter Brockbank (1 Point) July 16, 2008 at 6:43 pm

    Why no mention of Olympus two thirds system.

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    David Jenrette (1 Point) July 16, 2008 at 10:53 am

    Going back to film days: when you compared 35mm lenses with med format lenses, the 35mm lens had higher resolution. Why? Because, to make an 8×10 (for example) the 35mm negative had to be enlarged 8 times, but the 2-1/4 negative was enlarged (for the same 8×10) only about 4-1/2 times. This meant that the med format lens didnt have to be as good as the 35mm — which is a good thing because it would be harder to make such a lens and quite expensive.

    My point is that some of the lenses for the smaller sensors on most DSLRs may actually be better in those centers than the full frame lenses of the same focal length.

    Even smaller sensors, the quality of my coolpix cameras is amazingly good. What do you think? Is my point relevant or pointless?

    David Jenrette

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