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Thread: Question about lens image circle size

  1. #1
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    Question about lens image circle size

    Just curious about something in relation to the size of the image circle of a lens. If you reversed the orientation of a lens so that light passed through from the opposite direction, would the size of the image circle remain the same or would it be different? For example, under normal use, a slide projector lens collects light from behind and projects the light through the front element. However, if you reversed the lens so that lights enters through the front element and passes out of the rear element and maintained the same distance from the screen, would the image circle size be the same?
    Last edited by tribal-warrior; 16th August 2019 at 09:35.

  2. #2
    Senior Member darr's Avatar
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    Re: Question about lens image circle size

    The outcome will be dependent upon lens design.

    I suggest you visit the Large Format Forum and ask this question over there. There are a few members at that forum that are lens collectors and lens builders and they would be more interested in answering your question IMO.

    Kind regards,
    Darr
    Website: photoscapes.com
    Photo Blog: darrlene.com

  3. #3
    Senior Member JoelM's Avatar
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    Re: Question about lens image circle size

    Quote Originally Posted by tribal-warrior View Post
    Just curious about something in relation to the size of the image circle of a lens. If you reversed the orientation of a lens so that light passed through from the opposite direction, would the size of the image circle remain the same or would it be different? For example, under normal use, a slide projector lens collects light from behind and projects the light through the front element. However, if you reversed the lens so that lights enters through the front element and passes out of the rear element and maintained the same distance from the screen, would the image circle size be the same?
    To keep the answer simple, it would be different. The optical formula has changed when you reverse the lens so it wouldn't be the same. Look through a pair of binoculars or a rifle scope, or even your lens and you can draw this conclusion. (I was a theoretical physicist that studied optics and solar astronomy).

    Joel
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