Enlarging Basics: Focus, Aperture and Exposure

Printing is where a negative becomes a photograph. It is also where the process stops being chemistry and becomes craft, because every decision after focus is an aesthetic one dressed up as a technical one.

The sequence is fixed. Follow it in order and you will get a printable image on the first or second sheet.

Step one: align and set up

Before the negative goes in, check alignment. Put a spirit level on the baseboard, then on the negative stage, then on the lens board. If any of the three is out, one side of every print will be soft and stopping down will not fix it.

Then set the magnification. Raise or lower the head until the image is the size you want on the easel, and lock the column. Set the easel blades so the image sits inside them with a border of at least 5 mm.

Step two: focus on the grain, not the image

Focusing by eye on the baseboard is unreliable. An edge can look sharp while the image is still soft. The only dependable focus reference is film grain.

• Place a focus finder on the baseboard in a mid-tone area with visible texture.
• Focus at the aperture you will print at — stopping down after focusing shifts the plane of focus.
• Turn the focus control until the grain is at its most defined, then check the corners.
• If the centre and the corners disagree, the enlarger is out of alignment.

Step three: choose the aperture

Most enlarging lenses are at their sharpest two stops down from wide open. On a 50 mm f/2.8 lens that means f/5.6 or f/8; on an f/4 lens, f/8.

Aperture also controls exposure time, and there is a practical range you want to stay in. A base exposure of 8–20 seconds gives you room to dodge and burn. Much shorter and you cannot control it; much longer and the session drags.

Step four: make a test strip

A test strip is five exposures across one sheet of paper, each a third of a stop apart. It costs one sheet and tells you the correct exposure to within a fraction of a stop.

• Set the timer to the exposure you estimate, then halve it — you want the first step to be too light.
• Cover four fifths of the paper and expose the first step.
• Uncover one fifth more and expose again. Repeat across the sheet.
• Develop, stop and fix. Read the strip under white light, not safelight.
• Pick the step where the highlight just holds detail, not the step that looks most correct overall.

Step five: set the contrast

On variable-contrast paper the filter changes the contrast grade. Higher grades expand the tonal range, lower grades compress it. The right grade is the one that gets both shadow detail and highlight detail onto the paper at the same time.

Changing grade changes the effective paper speed, so expect to redo the test strip when you change filters. Higher grades are usually slightly slower.

Step six: print, then adjust

Once exposure and grade are right, print a full sheet. Now the aesthetic work starts: dodging to hold back light in an area that is too bright, burning to add light where it is too dark.

This is where f-stop thinking pays off. A one-stop burn is a doubling of time. A half-stop burn is 1.41×. A third of a stop is 1.26×. Expressing every adjustment in stops means you can describe the print to yourself precisely enough to reproduce it next week.

Common printing faults and what causes them