How can I simulate a different focal length or crop-sensor field of view from an existing photo?
Asked 5/12/2013
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I have a photo taken on a full-frame camera and want to preview how the same scene would look if it had been shot from the same position with either:
- a crop-sensor camera, or
- a different focal length lens
For example, if I shot an image at 200mm on full frame, how can I estimate the framing of 400mm, or the framing of a 1.5x crop body, using the image I already have? Can this be done in Photoshop by cropping to the correct dimensions?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
5
If you want to compare what your picture would look like taken from the same position with the same lens on a 1.5X crop body, divide the dimensions of your image by 1.5. Your 2473 X 1649 pixel image would crop to a 1649 X 1099 pixels (2473/1.5=1649, 1649/1.5=1099). To center the crop on the middle of the image, offset the starting point by 1/2 the difference. That figures to 412 to the right and 275 down from the top left corner (2473-1649=824, 824/2=412. 1649-1099=550, 550/2=275).
You would do the same thing to compare two focal lengths. If your picture was taken with a 200mm lens, to see what the same shot with a 400mm lens would look like divide the old lens by the new one (200/400=0.5). Multiply that result by your original dimensions (2473x0.5=1237, 1649x0.5=825). Crop your 2473 X 1649 image to 1237 X 825, using the method outlined above to center the crop, then enlarge it until it is the same size as your original image.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
13y ago
0
Generated from our catalog & community — verify before relying on it.
Yes. If camera position stays the same, you can simulate both a smaller sensor and a longer focal length by cropping the image.
For a crop-sensor body, divide the image width and height by the crop factor. Example: to simulate 1.5x crop from full frame, crop to 1/1.5 of the original width and height.
For a different focal length, scale by the ratio of old focal length to new focal length:
new crop size = original size × (old focal length / new focal length)
So a photo taken at 200mm, simulated at 400mm, should be cropped to 200/400 = 0.5 of the original width and height.
To keep the framing centered, crop equally from all sides.
In Photoshop, you can do this with the Crop tool or by setting a specific canvas/selection size in pixels. You can also create a fixed-size rectangle overlay or action if you want to preview the framing before actually cropping.
This only simulates field of view/framing. It does not recreate changes in perspective (which depend on camera position) or other optical differences between lenses.
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