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# Thread: Subject to lens Distance at 1:1

1. ## Subject to lens Distance at 1:1

Hi,

I was wondering what the ratio of subject to lens compared to lens to film distance is at 1:1? If I have any lens, in this case lets use a 210mm on a 4x5 camera, and I extend my bellows to 420mm, what distance will my subject be from my lens? My guess was it will be the same as the extension of the bellows, but how is one to figure this out?

-Josh

2. At 1:1, subject to focal plane = 4 * FL

3. plus inter-nodal distance.

4. In addition to above, a few more more heuristics for 1:1:
Lens coverage is double
Angle of view is half
Bellows draw is double focal length
Lens to film and lens to subject are same
Lens is two stops slower
Airy disks are twice as big
Depth of field and depth of focus are the same

5. A quick review indicates that all of these answers is true.
However if you want a quick and dirty method of focusing to 1:1, both the lens to film and the lens to subject distances need to be 2x the focal length of the lens. If you measure to the middle of the shutter, you will be very close.

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