- Hide menu

Crop-Factor Myth – misconstrued misnomers and disseminated confusion.

Photo taken with a D5ll with a full frame sensor, the green line would be what a 1.6 camera sensor would have recorded.

Are we confused yet? Many of us with a foundation from the photography of yesterday seeking an understanding of a new paradigm of digital photography have been unintentionally misled. With the switch from film to the original camera sensors we had to get a new understanding of our equipment both new and old. The first digital camera sensors as well as most sensors today recorded an image on a smaller recording surface than the 35mm film image of yesterday. Our images shot with wide-angle lenses of our film days no longer appeared to be wide-angle images. Our telephoto lens images appear to have more magnification. Yes, this was disconcerting so we attempted to understand. Well meaning camera techno geeks explained in terms intended to simplify concepts but only confused. To make matters worse, in the quest to explain, misleading explanations have misinformed those who have never put a film camera to their eye so incorrect construal of Crop-Factor conception is universal as old hands shared bogus information to those who had never known film.

Photo of Grizzly Bear cub taken with a full frame camera with a 500mm lens, green line would have been the (1.6 crop) if shot with my 7D. The in camera crop gives the illusion of magnification. Regardless of sensor size the 500mm is a 500mm.

Crop-Factor is a term that is used often in the world of digital photography. The terms Crop-Factor and focal length multiplier were coined by techno geeks while attempting to help SLR film photographers who weren’t techno geeks understand how their existing ranges of lenses would perform on newly introduced DSLR cameras that had sensors smaller than the 35mm format, a recipe for misunderstanding, confusion and delusion.

Consequently, many; otherwise, intelligent and knowledgeable people still “believe” in the myth and misnomer of the Focal Length Multiplier, believing the Focal Length Multiplier actually multiplies magnification – it doesn’t!  It should be called the Cropping Factor and that is all it is, but Crop-Factor still needs to be understood better. In the techno geeks, honest effort to transpose old variables to a new paradigm technophiles confused instead of clarified.

I am far from being a techno geek, but the idea that my 400mm could be a 650mm didn’t make sense to my rudimentary understanding of physics so I delved deeper, and I found physics still remained constant. My 400mm is still a 400mm.

What does it mean that a camera has a Crop-Factor of 1.6x and how does it affect your focal length? I’ll try to untangle this issue rife with confusion and describe it as clearly as possible. The ‘Focal Length Multiplier’ is the most misunderstood characteristics of DSLR cameras and so lets look at this aspect of DSLR imaging and attempt to lie to rest some of the myths and misunderstanding.

Another example of how the smaller camera sensor crops the photo to give the illusion of magnification

The size of the image sensor is what controls the crop factor, and the sensor is compared to the traditional 35mm film dimensions = 35mm X 24mm; by comparison a 1.6 ratio sensor is only 22.2 mm x 14.8 mm. So when people talk about “Full Frame” camera sensors they are talking about cameras that have a sensor the same size as 35mm film cameras of yesterday.

When you put a 500mm lens on a EOS 7D (1.6 crop factor) you do not get a 811mm lens – it is still a 500mm lens. The focal length; hence, the magnification of a photographic lens is fixed by its optical construction, and does not change with the format of the sensor that is put behind it. It should be noted that the lens casts the same image no matter what camera it is attached to.

When you mount a lens to a camera, it projects a circular image onto the sensor. The lens projects the same size image despite which camera it’s mounted on. When the image hits the film or sensor, a rectangular portion of the round image is registered. A 1.6x sensor has less sensor surface to capture the image than does a full frame sensor therefore less of the projected image is captured on the smaller sensor.

Because of the smaller format of many DSLR sensors, telephoto lenses have a narrower angle area of image registration than the same lens on a full frame sensor. ‘Crop’ is a good term because the imaging area is physically smaller; hence, an auto crop. It is in no way “magnified”. However, the image takes up a larger proportion of the (smaller) frame and so it is easy to see why some people call it a magnifying effect because it is an “in camera” crop that incorrectly alludes to the illusion of magnification. Nothing changes about the lens; it’s simply the amount coverage of the image projects upon the camera sensor.

Lens Crop Factor graphic

sdf

The first part of this video I shot with my D5ll wishing I was shooting wit h the 7D, later I swiched to the 7D which made the bears appear closer, not because they were magnified more but because the image was registered on a smaller sensor.

What I don’t hear people speak of is how Crop-Factor manifests itself with wide-angle photography.  After buying my first digital camera, a Canon EOS 30D (1.6 crop) I was enthralled with my new ability to stitch photos together to get great wide-angle photos.  A few years later I bought a Canon EOS D5ll (full frame) and all the sudden I found I didn’t need to stitch as many photos together as I did with my 30D. I then put two and two together and figured out my new full frame sensor in my D5 ll acted as a de facto, wide angle image recorder. I was thrilled.

I often talk to photographers who buy Canon 7D’s and other smaller sensor cameras when they could afford full frame cameras but choose the cropped sensor models solely for the “Focal Length Multiplier” effect.  I cringe when I hear this because they could achieve the same crop in post processing had they purchased the full frame sensor with close to the same resolution. This would also have the benefit of choosing a more suitable crop in post processing. The reason I cringe is because they have short changed themselves of the wide-angle benefit of the full frame sensor and post processing flexibility. Yes it has come to my understanding since publication that some photographers choose smaller sensors for pixel pitch  and pixel density but that isn’t the discussion here.

There are a slew of different sensor sizes besides the 1.6 I used for my examples but regardless of sensor size my point remains the same.

Soon after acquiring my D5ll I discovered HD video function and loved it.  I have often found when wildlife was out of range for good still photography, it still made compelling video. My video library grew. Post processing video doesn’t allow cropping; I then deduced a smaller sensor could give my video a tighter in camera auto crop. I then bought a 7D for video work for when my subject was too far away. I do switch bodies back and forth as needed for video depending on desired composition or proximity to my subject.

I live in the Greater Yellowstone Region and am lucky to have a plethora of wildlife and embarrassment of riches of landscape right out the door.  While cruising for photos I have my landscape gear on my D5ll (full frame) and my telephoto on my 7D.  I have to switch them sometimes, but this is the best setup to start a shooting day. Occasionally wildlife will be too close for the registration on the smaller sensor but that usually isn’t the case.

I hope I have cleared up a confusing topic!

Daryl L. Hunter leads photography tours

The Hole Picture Photo  Safaris

My portfolio Slide Show

  

 

 

 

 

 

 

 

 

22 thoughts on “Crop-Factor Myth – misconstrued misnomers and disseminated confusion.

  1. Jeff Clow says:

    Outstanding explanation, Daryl…!

  2. Donald Quintana says:

    Great explanation!I’ve had this discussion many times trying to explain the difference. You did it magnificently!The images really help to convey your message. Enjoyed the article.

  3. I never considered this until I actually got my full-frame dslr. Then it dawned on me that the same result could be had by cropping the image with software.

    • Yes Steve, that was my experience, but before that I had many telling me my 400mm was much more and it just didn’t make sense to me so I investigated. Then after much coffee I attempted to explain 😀

  4. Nice post, Daryl. I agree that a full-frame DSLR is better for landscape shots. I am one of the 7D users you spoke of, mainly because that’s what I could afford, but the advantage I see in the crop factor is when I am shooting wildlife. If I have to crop an 18mb RAW file to bring the subject a bit closer, I may end up with a 10mb file. Still big enough to print at larger sizes. I also don’t own anything larger than 400mm lens.

    If I have to crop an 18mb RAW file of wildlife from a full-frame camera (assuming I am the smae distance from the subject as above), I would end up with a much smaller file, hence, print sizes would be limited.

    My next body purchase will definitely be a full-frame. Am I thinking correctly here as far as the file size remaining after cropping?

    ps. Keep up the brilliant work!

    • Daryl Hunter says:

      Thanks Aaron, I see your point about a post processing crop if it were an apples and oranges comparison such as a Canon 1D X (18 megapixel) vs a canon 7d (18 megapixel) but that departs from my point of how sensor size doesn’t extend telephoto length.

      As I said in the article there are other valid reasons for choosing a cropped sensor camera.

  5. Shiv Verma says:

    Daryl, You are 100% correct. I would like to add one caveat – make sure when cropping a full frame image you have a decent equivalence of pixels. a 20mp full frame cropped to a 1.6x factor sensor will give you only 12.5mp. Just something to keep in mind.

    • Shiv Verma, thanks for your input. This is a factor but separate issue. A 12 megapixel image still provides a 36 megabite file, great for most publishing needs and adequate for small to medium size fine art production.

      It was an honor to have an analyst like Shiv comment – see his about page.
      http://www.shivverma.com/about

  6. Alex Dickson says:

    I have often talked about this same subject, and have had a hard time explaining it to people. Finally, someone can put it in words that makes sense. It doesn’t matter what sensor your capturing on, a 500mm is a 500mm, its simply cropped in camera. In no way is there any compression change on a cropped image. The true test would be to take a picture with a 500mm on a crop sensor and an 800mm on a full frame. They will be “zoomed in” to the same point, but the compression will look very different. Good article Daryl.

    • Thanks Alex, I am glad I was clear because the topic has become so convoluted, as I wrote I didn’t know if I was succeeding. Too often I have spoken to folks making purchases because of bogus explanations and hopefully this article and hopefully many more written by others can put this canard to rest.

  7. […] Crop-Factor Myth – misconstrued misnomers and disseminated confusion. […]

  8. Thank you for the simple, yet complete explanation of this subject. I initially thought I was getting a “new” free zoom lens when I purchased my first Nikon, “cropped factor” camera. Then reality set in and I began to understand it when my photography guru explained it to me. I then understood it, mainly by comparing sensor sizes and image sizes…and then finally by my comparing the results from my D200 thru the D7000 and finally to the D800E.

    Thank you, again.

  9. Derek Bown says:

    The crop on the full frame does reduce quality when comparing sensors of the same MP range. So there are advantages to the smaller sensor size. However there is a secondary effect not covered here.

    Light. Simply put the crop sensor has a smaller portion of the light coming through the lens falling on it. So you end up with a tighter crop but a “dimmer” image. Obviously you can compensate with ISO etc but full frame will always give better performance when light / exposure time limits are a factor. ie low light or fast movement.

    Personally I have a crop sensor camera and have found I often need to push the ISO higher than i’d like to capture crisp sports images.

    • Derek, I don’t believe you are right here. The lens delivers the light, that would be the same amount of light for either sensor; however, the smaller sensor would capture less light only because of its smaller capture area. That said; that smaller capture will have the best light the lens has to deliver because it wouldn’t be capturing light the weaker light were there is “light falloff” from the periphery of the lens.

  10. Dave Peeters says:

    Your photos are outstanding, just ran across your site when searching for an explanation on the crop factor myth. I needed something to send to a friend, knew what you wrote was the case but you did a great job of summarizing and explaining with photos, thanks for taking the time to do this

    • Thanks Dave, I hope it makes some sense to your friend and thanks for the referral. Clarity was tough to achieve on this one but the attempt also taught me a lot.

  11. Celina Ledger says:

    Thanks for the clarification of the misleading hype, it was definitely informative.

  12. Naushad says:

    There are more areas to this crop factor puzzle.

    First. One can ask everything being equal I shoot with FX 500mm and then I shoot with a DX 800mm. Consider both camera sensor has the same resolution. No post processing nothing. I print or display the photo. What is the difference? This is actually the most important question to be answered in my opinion.

    There isn’t any difference. One can say the smaller sized sensor providing the same resolution may suffer from image quality but that is only in theory.

    Second Question. This is something I have been just started to think about. Not yet came to any solid conclusion.

    Crop Factor: 1.5x
    DX 16mm vs FX 24mm
    frame taken from the exact same point.
    They look almost identical.
    But Is there any perspective difference?
    I am betting there is perspective difference. If that is not the case there would never be any need for making lenses of all kinds of focal length. Just make one lens with x focal length because you can always crop to get the angle of view of whatever focal length you need (to simplify things imagine our sensors are of a gigantic resolution so big that cropping of any factor wouldn’t make any difference).

Leave a Reply

Your email address will not be published. Required fields are marked *