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Determining life-size (1:1)

Ross Odom , Jan 28, 2007; 07:56 p.m.

What does "life-size" mean? and how do you determine if you're taking a "life-size" image of the object you're photographing? I've seen this referred to as a 1:1 relationship.

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Mike Earussi , Jan 28, 2007; 08:06 p.m.

If the object you're photographing is 1" long and the image on the camera screen is also 1" long then it is lifesize, i.e. the image on the film is exactally the same size as the real object. 1:1 is just the fraction representing 1 over 1. 1:2 =1/2 1:4 =1/4 etc. It's just convention.

tim swaback , Jan 28, 2007; 10:13 p.m.

So on 35mm film a 35mm object will cover all the way from left to right? Ive often wondered about this too.

Mike Earussi , Jan 28, 2007; 10:25 p.m.

Yes.

Philip Greenspun , Jan 28, 2007; 11:19 p.m.

To make it a little more concrete, if you are photographing a subject that is 5" tall and the subject fills the long dimension of a 4x5" negative, that was a life size or 1:1 exposure.

Alan Davenport , Jan 29, 2007; 03:14 a.m.

<I>So on 35mm film a 35mm object will cover all the way from left to right? Ive often wondered about this too.</I><P> Well, actually, no. A 35mm object will only cover 35mm of the frame, which is 36mm wide...

35mm film is named for the dimension across the roll (including the sprocket holes and edges.)

Bob Salomon , Jan 29, 2007; 05:42 a.m.

"So on 35mm film a 35mm object will cover all the way from left to right? Ive often wondered about this too."

No. If the object being recorded is 36mm long and it fully fill the long dimension of 35mm film frame then it is 1:1. If an object is 24mm long and is 24mm long in either direction of a 35mm film frame then it is 1:1.

Kelly Flanigan , Jan 29, 2007; 08:07 a.m.

In printing it can also mean the objects size on the print is life size.

Example 01: Like if one of BOB's buddies drags out a high school annual and we make a standup gag image of Bob S. for his birthday, or April fools, or a Photo convention roast party. Thus if Bob is 6ft tall; and the image in the annual is only 2 inches tall we force Bobs height to be 1:1 on the print. Thus Bobs gag image might be a cuttout 6ft tall and just his body; or maybe Becky Sue too the cheerleader!:)

Example 02: enlarging a dress, quilting pattern, bird house, lawn furniture drawing/sketch out of a boob, magazine, pattern book so that the chap/gal can start quilting, using the jig saw with a PATTERN done 1:1

Ross Odom , Jan 29, 2007; 10:32 a.m.

Thanks everybody for your answers. I wouldn't have guessed it was as straightforward as that.

Lynn Jones , Jan 29, 2007; 11:35 a.m.

I don't want to belabor the point, but I teach a 3 cred. hour, 96 contact hour college course in CU-Macro.

The relationship that is properly shown as a ratio is the image to object ratio. Life size is 1:1 (same as the fraction 1/1). Twice life size is 2:1 while one half life size is 1:2.

To predict or calculate macro ratios (which will tell you the magnification), measure the film to lens aperture distance, divide by the focal length and subtract 1, for example, a 100 mm macro lens divided by a bellows draw of 200 mm would equal 2, minus 1 or an image size (magnification) of 1, or 1:1.

To predict an image size, multiply the desired magnification by the focal length, add 1 and that will become the bellows extension. For example, with a 100 mm lens and a magnification of 2, add 1 or 3 and multiply the focal length by 3 (300mm - about 12") and this will be the bellows distance needed for a 2:1 magnification.

BE+Bellows Extension, F=Focal Length, M=Magnification

BE/F-1= M M+1xF = BE M+1 = f stops of exposure increase

Lynn


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