# Photography: Why do some lens hoods have such deep notches?

**URL:** <https://boards.straightdope.com/t/photography-why-do-some-lens-hoods-have-such-deep-notches/775097>\
**Category:** Factual Questions\
**Created:** [December 19, 2016, 12:24am UTC](https://boards.straightdope.com/t/photography-why-do-some-lens-hoods-have-such-deep-notches/775097 "2016-12-19T00:24:22Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![jayjay](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jayjay/32/6765_2.png) [@jayjay](https://boards.straightdope.com/u/jayjay)\
**Post date:** [December 19, 2016, 12:24am UTC](https://boards.straightdope.com/t/photography-why-do-some-lens-hoods-have-such-deep-notches/775097/1 "2016-12-19T00:24:22Z")

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Someone on my FB friends’ list just posted an article about a very large camera lens. The photo with the article looked like the lens hood had notches/extensions 8 inches long. What is the purpose of such long extensions on camera lenses?

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**Author:** ![Giles](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/giles/32/60_2.png) [@Giles](https://boards.straightdope.com/u/Giles)\
**Post date:** [December 19, 2016, 12:38am UTC](https://boards.straightdope.com/t/photography-why-do-some-lens-hoods-have-such-deep-notches/775097/2 "2016-12-19T00:38:24Z")

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You need the lens hood to block all light except what will intentionally fall on the sensor/film inside the camera. So the shape of the lens hood is essentially a projection through the lens of the rectangular image inside the camera. The notches are the four corners of that projection of the rectangle.

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**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\
**Post date:** [December 19, 2016, 12:41am UTC](https://boards.straightdope.com/t/photography-why-do-some-lens-hoods-have-such-deep-notches/775097/3 "2016-12-19T00:41:25Z")

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This picture illustrates it:  
[![](https://i.stack.imgur.com/rg1A9.png) ](https://i.stack.imgur.com/rg1A9.png)

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**Author:** ![jayjay](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jayjay/32/6765_2.png) [@jayjay](https://boards.straightdope.com/u/jayjay)\
**Post date:** [December 19, 2016, 1:34am UTC](https://boards.straightdope.com/t/photography-why-do-some-lens-hoods-have-such-deep-notches/775097/4 "2016-12-19T01:34:55Z")

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Perfect explanation, folks! Thank you so much!

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**Author:** ![Mean\_Mr.Mustard](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mean_mr.mustard/32/3865_2.png) [@Mean\_Mr.Mustard](https://boards.straightdope.com/u/Mean_Mr.Mustard)\
**Post date:** [December 19, 2016, 2:30am UTC](https://boards.straightdope.com/t/photography-why-do-some-lens-hoods-have-such-deep-notches/775097/5 "2016-12-19T02:30:31Z")

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Lens hoods have an added benefit of protecting the lens from damage when it’s bumped against an immovable object.  
mmm