I have a 4x5 camera with approx 22 inches of draw. I have a 120MM Rodenstock MAcRo lens. I need t oknow some of the basics for macro photography. Am I correct in saying that if I am 240MMfrom the lens to the film plane and the same from the lens to the subject I should be in focus?????????? and I would have an object 1:1.

Also when discriibing results is the first number (1:1) the object or is it he image on the film. Thanks in advance... Jerry Rosenfeld

-- Jerald A. Rosenfeld (rosenfeld@ameritech.net), October 27, 1998

Answers

The easiest way to determine if you are precisely at 1:1 is to set up to photograph an object that you know is 1 inch long (say a ruler) and measure it's length on the groundglass. If you want to make sure that it is exactly one inch on the film, take a polaroid and then measure that image. then measure the distance from the inside edge of the rear standard to the inside edge of the front standard and write down the results on a card you keep with your camera. it is probably close to 240mm but may vary somewhat depending on the position of the nodal point of the lens.

-- Ellis (evphoto@insync.net), October 27, 1998.

Jerald, If you do close-up work in LF, Calumet Photographic sells an extremely useful little device, called The Exposure Calculator. It only costs about $10.

I've found it indispensable, not only for determining precise reproduction ratios when doing closeups, table-top work, and macro photography, but also for detemining precise exposure compensation increases when extending the bellows beyond infinity.

The device consists of a small 2"x2" plastic chip, with a focusing target on its surface, and a 6" ruler, with reproduction ratios/proportion percentages printed on one edge, and exposure compensation increases in 1/3 stops on the other edge.

Place the chip in the close-up/macro scene itself, at the precise plane of focus. Then focus on the chip target, till it is sharp on the groundglass. To determine the exact reproduction ratio, and the necessary degree of exposure compensation increase, measure the actual size of the chip on the groundglass with the ruler. Takes less than 5 seconds.

This measurement, taken directly from the groundglass, immediately tells you the reproduction ratio of your subject, above and below 100% (1:1), within a range of 13% to 250%. It also immediately provides the exposure increase necessary when extending the bellows beyond infinity, in increments of 1/3 to 3 1/2 stops.

Hope this helps, Sergio.

-- Sergio Ortega (s.ortega@worldnet.att.net), October 28, 1998.

Strictly speaking, you should measure from the object to the front principal plane, then from the film to the rear principal plane. For the first approximation, these are both just "the lens". Yes, with these two distances at 240mm, you will get 1:1 with a 120mm lens.

The ratio "1:1" is image:object.

-- Alan Gibson (gibson.al@mail.dec.com), October 28, 1998.