How do I calculate whether a lens hood or front attachment will appear in the frame?
Asked 11/25/2020
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I make front-of-lens attachments and need to know when a hood or attachment will start to show at the edges of the image. How can this be estimated for a given lens? I assume it depends on focal length, front opening size, and sensor/film size, and possibly focus distance or aperture. Is there a practical way to calculate this, or at least test it reliably?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
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Angle of view is determined by (real) focal length and sensor/film size. That's your starting point.
AoV=2*arctan(d/2f)
where:
- AoV is the Angle of View
- d is the size of the sensor/film in the direction measured
- f is focal length (in the same units as d)
For a circular hood you would use the diagonal measure of the sensor/film
For a "petal" hood you would need to calculate based on the width and height as well as the diagonal of the sensor/film.
For many lenses aperture and/or focus distance can also play a part if lenses "breathe" (change focal length) as they are stopped down to different apertures and/or focused to different distances. Sometimes this can be rather significant. The AF-S Nikkor 70-200mm f/2.8G VR II, for example, gives an angle-of-view when zoomed to 200mm and focused at the minimum focus distance that is equivalent to a 140mm lens focused at infinity!
An alternative to calculating fields of view and angles/lengths is to download patterns for different lenses from the following:
Even if you can't find your exact lens, lenses with similar focal lengths/angles of view and front element diameters should be similar.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
5y ago
0
Generated from our catalog & community — verify before relying on it.
Start with the lens’s angle of view, which is set mainly by focal length and sensor/film size:
AoV = 2 × arctan(d / 2f)
where d is the sensor dimension in the direction you care about and f is focal length. Use the diagonal for a round hood; for a petal hood, check width, height, and diagonal separately.
A hood or front attachment will become visible if it intrudes into that viewing cone. So the key is whether the opening of your attachment is wide enough, at its distance in front of the lens, to clear the lens’s angle of view.
In practice, also allow for lens “breathing”: some lenses change effective focal length with focus distance, and sometimes with aperture, so the safe dimensions can vary.
A practical test method is to make a simple viewing jig matching your sensor/film size at the correct flange distance. Looking from the back through that cutout into the lens, no part of the hood/attachment should be visible. If it is, it will vignette. This is a useful real-world check even if the math says it should fit.
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