# Selecting a lens for concert/ auditorium

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### #1 Joe B Jowers

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Posted 12 September 2008 - 12:05 PM

Are there charts or formulas for determing what lens length to use when taping a performance on stage. I'll be shooting an awards show and I've been on several of these shoots before but never had to determine what lens to use. One the scout I'll be able to measure the distance from the camera position to the stage. How then do I know if I'll need a 40x 50x or 75x.

Thank you.
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### #2 Chris Keth

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Posted 12 September 2008 - 07:18 PM

Once you find out the distance from the stage, figure out the angle of view you'll need for the tightest shot you'll want. Then, with a field of view table, find out what focal length that corresponds to on your format. Bingo, you know the long end of the lens you want. Remember to measure to the furthest side of the stage, since it could be many more feet from you then the close side.
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### #3 Daniel Porto

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Posted 14 September 2008 - 01:02 AM

Once you find out the distance from the stage, figure out the angle of view you'll need for the tightest shot you'll want. Then, with a field of view table, find out what focal length that corresponds to on your format. Bingo, you know the long end of the lens you want. Remember to measure to the furthest side of the stage, since it could be many more feet from you then the close side.

Correct me if I am wrong but the DOF only changes by altering the aperture and increasing or decreasing the focal length only increases the visibility of this DOF (depending on the aperture). Thus with a bigger focal length the 'visible' DOF is smaller.

Assuming that this is the case I gather that the field of view table measures the DOF in terms of the visible DOF??? I am a little confused on that.

Thanks
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### #4 Chris Keth

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Posted 14 September 2008 - 01:59 AM

Correct me if I am wrong but the DOF only changes by altering the aperture and increasing or decreasing the focal length only increases the visibility of this DOF (depending on the aperture). Thus with a bigger focal length the 'visible' DOF is smaller.

Assuming that this is the case I gather that the field of view table measures the DOF in terms of the visible DOF??? I am a little confused on that.

Thanks

Field of view really has nothing to do with depth of field, other than usually being proportional. It is an angular measure of what a particular focal length can see. For example, a wide lens may have a field of view of 100 degrees, that is the frame encompasses 100 degrees of space in front of the lens. A longer lens, on the other hand, may have a field of view of 10 degrees, or even far less. A "normal" lens for any format (one with a focal length equal to the diagonal of the format) usually has a field of view of around 50 degrees.

In figuring out what lens the OP wants, he might decide that he wants to be able to go as tight as a choker. Using your trigonometry, you would find the angular size for the height of someone's head at the distance the camera is from the stage. By looking up that angular measure on a field of view table (it would be the vertical field of view) you could find out what lens would give you that shot.

It's a bit of a nerdy, textbooky way to solve the problem but I would rather be sure than get there and be screwed.
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### #5 Daniel Porto

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Posted 14 September 2008 - 04:58 AM

Field of view really has nothing to do with depth of field, other than usually being proportional. It is an angular measure of what a particular focal length can see. For example, a wide lens may have a field of view of 100 degrees, that is the frame encompasses 100 degrees of space in front of the lens. A longer lens, on the other hand, may have a field of view of 10 degrees, or even far less. A "normal" lens for any format (one with a focal length equal to the diagonal of the format) usually has a field of view of around 50 degrees.

In figuring out what lens the OP wants, he might decide that he wants to be able to go as tight as a choker. Using your trigonometry, you would find the angular size for the height of someone's head at the distance the camera is from the stage. By looking up that angular measure on a field of view table (it would be the vertical field of view) you could find out what lens would give you that shot.

It's a bit of a nerdy, textbooky way to solve the problem but I would rather be sure than get there and be screwed.

Thanks for the clarification Chris!

The 'nerdy textbook' way for something like a concert in which you could only use primes sounds like a pretty smart idea to me!!
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