How to compensate for Close-up images
Where the subject to lens distance is less than 8 times the focal length of the lens a corrective shutterspeed must be computed. In this computation, if the lens is given in millimeters convert it to inches by dividing the focal length by 25. (1 inch = 2.54mm)

EXAMPLE:
Assume your lens has a focal length of 8" (200mm), and you're using a shutterspeed of 1/125 second at f/5.6
Using the f/stop numbers as focal length numbers, (i.e f/8 will be focal length of 8") place the 8 on the f/stop scale below the 1/125 second shutterspeed.

Measure or estimate the distance of the bellows extension(Lens to film distance). Assume this distance to be 16" (400mm).
Now look on the f/stop scale and find the number 16 and directly above on the shutterspeedscale will be found 1/30 second.
This new shutterspeed (1/30) should now be used with the f/stop selected previously (5.6)
Align these two values on the meter dial and any of the exposure combinations aligned may be used, 1/60.,f/4, 1/125sec.,f/2.8 etc..

This computing can be done mentally also...
Work in mm for a change. EXAMPLE:
We are using a focal length of 135mm and the measured distance(Lens to film distance) is 270. Now we divide 135 into 270 and get 2. Square root = 4. Thus our compensation will be a factor 4.(2 f/stops) When we take the exposure combination from above (1/125 sec @f/5.6) this would result in 4x1/125 = 1/30sec. at f/5.6

Using the formula (M+1)2 it goes like this:
M is magnification. To find the magnification we will measure the distance from front of lens(More precise:Place of shutter) to the point of focus(Main subject)!
Assuming a lens of 50mm(A) and the distance to our subject as 50mm(B), we divide B:A =1. In our formula we replace M with 1, add 1 and take the square root=4. Thus the factor is 4 or 2 f/stops.


Sinar once brought a nice tool, it was called the Sinar Gauge
With tis tool you could visually compensate and read the stops or factor on the pencil.
The cap of the pencil should be placed at the point of focus in either vertical or horizontal position.
The pencil itself was then placed on the groundglass and the cap could be measured. The value indicated on the pencil expressed the terms of f/stop (The amount of light loss due to bellows extension)
The exposure or light level must be adjusted accordingly.

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