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I have the Nikon D5300 and it comes with a kit 18-55mm. I've been looking to get a 50 prime, and my friend has two (1.4 and 1.8) which she let me try out yesterday.

So, my camera is not full frame, and has a crop factor of 1.5. Every single resource I've seen has told me that the focal length a full frame (non DX) lens would be multiplied by the crop factor, meaning that a standard 50mm lens should look like 75mm on my camera.

My friend has a full frame camera, and her lenses are not DX lenses, however when I took photos with her lenses and compared with mine set to 50mm, the object I photographed (coffee cup) took up the exact same amount of space out of the frame. My lens is a DX.

Why is this? Do lenses adapt to the camera's crop factor? Is the camera adapting? How come every resource I've ever read said that her lenses on my camera should look like 75mm?

Entity
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  • Are both photos taken from the same physical position and using the same lens? What model is your friend's camera? – Patrick Hughes Jul 22 '17 at 19:33
  • @PatrickHughes Both photos were taken using my camera from the same distance – Entity Jul 22 '17 at 21:53
  • The other question doesn't answer my question either... Is it saying that DX lenses are identical to standard lenses?? – Entity Jul 22 '17 at 22:07
  • My findings seem to go directly against this article. I would expect the non DX lens to be "cropped in" more than the DX lens because the image goes out past the sensor... http://www.nikonusa.com/en/learn-and-explore/a/products-and-innovation/the-dx-and-fx-formats.html# – Entity Jul 22 '17 at 22:08
  • If you want to see the crop factor in action, take photos of the same scene with the 50mm lens mounted on your camera and then on your friend's camera. You will see that the photo taken with the FF camera has a larger field of view (wider angle of view) than the one taken with the crop-sensor camera. If you could mount a 75mm lens on the FF camera and shoot the same scene, it would look like the 50mm photo taken with your camera. That's the meaning of the 1.5x crop factor. – chulster Jul 22 '17 at 22:30
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    As the others have said, all 50mm lenses, whether marked as FX or DX, produce roughly the same angle of view on the same sensor. What makes a DX lens a DX lens is not its angle of view relative to its focal length, but rather that its image circle (the circle of light projected out the back of the lens) can be smaller than that of an FX lens, since the image circle only has to cover a smaller area (the DX sensor). And that means it can be made smaller, lighter, and cheaper than an FX lens of the same focal length and max aperture. – chulster Jul 22 '17 at 22:39
  • @Entity 50mm FF lenses do not project the same field of view as a 50mm DX lens over a larger area. (That would mean they have lower magnification - such as that of a 33mm lens.) If they are the same focal length as the DX lens, they project a larger field of view at the same magnification as the DX lens. Since the magnification is the same, the center of the image circle projected by both lenses is the same. It's just that the FF lens shows a wider view of the scene and projects it over a proportionally wider image circle. – Michael C Jul 22 '17 at 22:57
  • @Entity Please see all of the similar questions linked in the answer to Why do my 50mm APS-C and 50mm FF lenses have the same angle-of-view on my APS-C camera? – Michael C Jul 22 '17 at 22:58
  • And this answer to Shooting 50mm EF vs EF-S – Michael C Jul 22 '17 at 23:08
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    To add to the confusion, some (all?) Nikon full frame cameras have a DX mode, where they will detection that the lens mounted is a DX type and use only the center of the frame, decreasing the field of view to match that of a DX camera with that lens. – mattdm Jul 23 '17 at 10:00

3 Answers3

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If your friends full frame camera has the "Image Area" menu setting set to DX crop mode that would explain the result you got. This video covers the details http://www.nikonusa.com/en/learn-and-explore/a/products-and-innovation/the-dx-and-fx-formats.html

Michael C
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Thomas Schumacher
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The focal length of a lens does not change, not even 1 millimeter when you mount it on a camera. This is true regardless of the camera’s format.

Your kit lens when set to focal length 50mm yields exactly the same image size and angle of view as the borrowed. A prime lens is one that has a fixed focal length and it is unchangeable. A zoom lens has a variable focal length, in your case the kit lens is adjustable 18mm thru 55mm. Now the prime lens likely has more acuity than your zoom. This will be especially true if you operate them at the same f-number (aperture setting). The real question is, can you see a difference is acuity between the two? Likely the differences will be hard to spot unless you view the two images side by side on a huge screen or make big paper prints.

That being said, the borrowed prime operating a f-1.4 or f-1.8 has far greater light gathering power than your kit lens which will be operating at f-5.6 when set to 50mm. the difference is the prime is 3 stops faster i.e it allows in 8X more light when set to its widest aperture (f-1.4).

So what does the so-called crop factor tell us? The full frame camera sports an image sensor that measures 24mm height by 36mm length. Your compact digital has a smaller sensor. How much smaller? 24 ÷ 1.5 = 16mm and 36 ÷ 1.5 = 24mm. We calculate your sensor as 16mm height by 24mm length. Another way to say this is 1 ÷ 1.5 = 0.66 X 100 = 66%. In other words your camera is 66% of the size of a full frame.

What does that mean as to the size of an image taken with a 50mm? Both deliver the same image size however the larger full frame (FX) will show more room around the subject because the sensor is larger. In other words, the angle of view between a full frame and compact digital (DX) is different. The FX angle of view with the 50mm is 40° and the DX angle of view is 27°. The difference is 40 X 0.66 = 27.

For my part, I wish the crop factor would go away. It is only important to those folks who use a full frame and know all about how it images with different focal lengths. Then they can apply the 1.5 factor to see what focal length on a compact will deliver the same angle of view. I think this is not particularly important to a fellow who never used a full frame. The thing to learn is “how do various focal lengths image on my camera.

Alan Marcus
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Crop factor does NOT affect the lens or its image in any way. Cropping the sensor cannot possibly change the lens.

Crop factor only changes the smaller frame size in the camera. So your coffee cup (with same lens, at same distance) will be the same size in either body, but the frame of the picture area will be cropped in DX, showing less of the table that the cup is on. The full frame shows a 1.5x wider view, showing more table around the cup. DX sensor is cropped, showing less.

What crop factor means is, to see the same table area in both bodies, the full frame needs to use a 1.5x longer lens (equivalent focal length, to crop a smaller picture the same as DX frame sees it). Or if using the same lens, the DX needs to stand back 1.5x farther in order to see the same wider view.

The lens is not affected in any way. The DX camera just has a smaller sensor and so it shows a cropped view. Like if you had cropped it to 2/3 size in your editor. Cropping is cropping. The cup remains the same size in that smaller cropped image, however, if then you enlarge it 1.5x more for the two pictures to appear the same size, then the cropped cup will appear larger too (only because you enlarged it more). Same idea as any way you can crop an image.

http://www.scantips.com/lights/cropfactor.html

WayneF
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