Timeline for How do I calculate the “effective focal length” of a cropped photo?
Current License: CC BY-SA 3.0
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| Aug 1, 2017 at 18:56 | comment | added | Michael C | Also: What is the difference between perspective distortion and barrel or pincushion distortion? | |
| Aug 1, 2017 at 18:52 | comment | added | Michael C | Please see this answer to Is there a difference between taking a far shot on a 50mm lens and a close shot on a 35mm lens? | |
| Aug 1, 2017 at 13:29 | comment | added | scottbb♦ | Foreshortening is not an illusion — it's a real effect, it only happens if the distance between the camera and subject changes along with focal length. If you keeping the same framing of a human subject (i.e, head-and-shoulders shot), and move the camera back to keep the framing as you increase focal length, you will see background compression, and flattening of facial features. But by moving the camera, you have changed perspective. | |
| Aug 1, 2017 at 13:26 | history | edited | Martin | CC BY-SA 3.0 |
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| Aug 1, 2017 at 13:25 | comment | added | Martin | I just found this helpful article which supports both mattdm and scottbb. patricktaylor.com/1988. It seems that your position is an important factor. There can be the impression of foreshortening with a longer focal length, but this is an optical illusion. Thanks for your patience! | |
| Aug 1, 2017 at 13:17 | comment | added | Martin | I hesitate to disagree but I want to understand better, and it seems to me that the "crop factor" involved with different sensor sizes is a different kind of "crop" from cropping down an already-rendered image. In the latter case we're talking about trimming the outer edges from an existing image, whereas in the former we're talking about how the image will be rendered differently because of the sensor size. | |
| Aug 1, 2017 at 13:01 | comment | added | scottbb♦ | "A longer focal length foreshortens the perspective in your image such that the effect of distance is rendered differently." This is not true. As long as you are shooting the same scene, cropping is exactly the same as increasing the focal length (ignoring the fact that actual lenses often don't have the exact focal length that is printed on them). This is exactly how the effect of crop sensor cameras is calculated. The sensors are 1.6x (Canon) / 1.5x (Nikon) smaller than 35mm full frame sensors. Lenses on crop cameras have a FoV-equivalent focal length of focal length times the crop factor | |
| Aug 1, 2017 at 12:57 | comment | added | mattdm | This isn't right; the perspective will be the same if you stand in the same place, no matter what focal length you use or how you crop. Zooming or cropping (assuming sufficient resolution and identical viewing size) should will produce identical "foreshortening" or "flattening". | |
| Aug 1, 2017 at 12:05 | review | First posts | |||
| Aug 1, 2017 at 13:01 | |||||
| Aug 1, 2017 at 12:02 | history | answered | Martin | CC BY-SA 3.0 |