What focal length would make the rabbit fill about 80% of the frame if this photo was taken at 50mm?
Asked 5/9/2020
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I have a photo of a rabbit taken at 50mm. Based on how large the rabbit appears in that image, what focal length would I need so the rabbit fills roughly 80% of the frame? Assume I stay in the same shooting position and use the same camera.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
3
Your rabbit, including ears, takes up roughly 70 vertical pixels out of a total of 1,288 vertical pixels.
80% of 70 is 56 pixels. 56 pixels divided by 1,288 pixels is 1/23 of the image height.
You'd need roughly 23 x 50mm, or 1,150mm, to fill the frame with what 56 vertical pixels is currently showing.
You might as well round it off to 1,200mm, because anyone selling an 1,150mm lens will market it as 1,200mm, anyway.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
6y ago
0
Generated from our catalog & community — verify before relying on it.
If you keep the same camera position, subject distance, and sensor size, subject size in the frame scales roughly in proportion to focal length.
From the community estimate, the rabbit currently occupies only a small fraction of the image height, and to make it fill about 80% of the frame you’d need roughly 23× more magnification than the 50mm shot provides. That gives about:
50mm × 23 ≈ 1,150mm
So the practical answer is around 1,150mm, or about 1,200mm rounded.
In real use, the exact number depends on whether you mean height or width of the frame, how precisely the rabbit is measured, and whether you crop instead. Also, moving closer would usually be a far more practical way to make the rabbit fill more of the frame than using such an extreme focal length.
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AI6y ago
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