F-Stop Printing with Darkroom Automation's f-stop timer and enlarging meter - Enlarging Meter FAQ.


The meter measures both print exposure and negative density.

The meter measures the light falling on the easel to 1/100th of a stop, corresponding to measuring negative density to 0.003 OD. It uses a 2mm square Silicon-Blue photodiode for measurement and shows the results on a 4-digit 1/2" high red LED display.

The meter is calibrated so a full scale reading of 9.99 indicates a light intensity producing maximum black on Ilford MGIV #2 in a one second exposure. A reading of 0.00 indicates a light intensity producing maximum black in a 950 second exposure.

There are two pushbuttons: one for on-off and one for making ‘Delta' measurements. The meter turns itself of after 5 minutes of inactivity. It is powered by two AA batteries, and with the meter's ultra-low power technology the batteries will last over 3 years in average use.

The meter's unique delta mode finds the right grade of paper, determines dodge and burn exposures and reads negative density by measuring the light difference between two points in the image.

The meter displays negative density in stops over B+F when delta mode is zeroed on the clear negative. The combination of an enlarger and the meter forms a projection densitometer. For photographic purposes a reading in stops is more useful than a reading in OD.

For more detail on the meter's operation please see the instruction manual in the support files section of the website.


  • You make prints with less guessing at the proper exposure and paper grade. You make fewer test strips, waste less paper, and most important of all, waste less time.
  • You precisely determine the optimum paper grade to create the image you want, be it high key or low key, brilliant or muted.
  • You quickly and accurately find exactly the right dodge and burn exposures.
  • You measure the effective negative density in _your_ equipment.
  • You find the optimum film development and exposure index for your photographic vision, your equipment and your method of working - perfect for the Zone system for both negatives and prints


The meter works with Darkroom Automation's exposure system.

A basic principle of photography is

    exposure = light intensity * time.

When stops are used to measure light intensity and time, and the exposure needed to obtain a given tone is expressed in stops (as the 'paper speed' for a given tone/paper/grade) then:

    Paper speed in stops = meter reading in stops + timer setting in stops

To place any given point in the image on a given tone you only need to set the Darkroom Automation f-Stop timer so the meter reading + the timer setting is equal to the paper speed.

Charts of paper speeds for common papers ship with the meter and it is easy to make a paper speed chart for any paper desired.

Some current paper charts are available in Darkroon Automation's support files.


You can use the meter in any way you desire: You can use it as a comparator as you would an Ilford EM-10 for quickly making 'drugstore prints' by varying the lens aperature to control exposure. You can scan for highlites and shadows as you would with a conventional enlarging meter/analyzer to find paper grade and exposure.

The procedure below is for producing a print that precisely matches your visualization. For most prints, however, you may follow only a few of the steps.

The first order of business is to select the paper - Ilford MGIV RC, Oriental G, MGIV WT etc.. Once the paper has been selected you need to determine the grade.

Determine paper grade:

Select two important areas of the negative and determine the tone for each area: for a straight brilliant print this would be either black/white or detail shadows/detail highlights; for a low key portrait this may be the desired skin tone and the black backround; for trees in the mist it may be the gray of the tree bark and the lighter gray of the mist.

Using the meter's Delta mode measure the intensity difference for these two spots.

Using a paper speed chart find the grade that has a paper speed difference for the two tones you selected that equals the meter’s intensity difference reading.

You have now selected the paper grade that will accurately fit the most important portion of your image. As mentioned above, these tones are often not the brightest and darkest points, though bright and dark work well for a first working print or 'drugstore prints'.

Determine exposure time:

Meter either the darker of the two tones above - or any other tone if desired - and look up the paper speed for that tone and the selected grade of paper.

Set the Darkroom Automation f-Stop Timer so the timer setting makes up the difference between the paper speed and the meter reading. If you are using another timer then Darkroom Automation provides timing charts for digital timers and f-Stop timing dials for analog timers.

You now have an exposure that will accurately reproduce the first tone and the paper grade that will cause the second tone to fall just where you want it.

Insert the paper and make the print.


After pegging the exposure for the most important part of the image you may find that areas of background or sky need a different value.

The quick and easy way to determine burn and dodge exposures is to meter the intensity difference between the part of the image you want to adjust and a part of the image that has the tone you want.

Set the timer's dodge or burn setting to the delta reading above. The dodge/burn exposure will make up the exposure difference between the two points so they get the same total exposure and have the same tone.

A sky burn for clouds can normally be determined before any test prints are made: meter the difference between a foreground highlight and a cloud highlight; use this reading as the sky’s burn exposure.

The other method to get the tone you want from a burn or dodge is make a measurement and take the difference between the measurement and the paper speed for the desired tone: use this difference as the burn or dodge setting for the f-Stop timer.


The meter, in combination with your enlarger, makes a ‘projection’ or ‘micro’ transmission densitometer.


    Spot Size: 2000-120 microns
    Measurement range: 3.0 OD; 9.9 stops
    Resolution: 0.003 OD; 0.01 stops
    Linearity: 0.003 from 0.0 to 2.5 OD, 0.009 from 2.5 to 3.0 OD

For the money, that’s a pretty good one.


The advantages to using Darkroom Automation’s Precision Enlarging Meter over a bench densitometer are:

  • It measures the effective density of your negative in your enlarger. Diffusion, condenser and point-source enlargers produce different ‘effective’ densities. This is critical when finding the Exposure Index and development time to produce a correct Contrast Index illumination range on the paper.
  • The meter is useful with small negatives: it is impossible to read a 35mm step tablet with a bench densitometer because the measuring aperture is too large. It is almost impossible with a 2 1/4” negative.
  • Stops are a more useful unit of measure in photography than OD: opening the lens or increasing the exposure time in OD’s isn’t normal practice.
  • You have more bench space. You don’t need to move the negative back and forth between enlarger and densitometer. You can see the effect of the negative’s density on printing by simply slipping a sheet of paper in the easel.


Zero the densitometer on a blank bit of the film, such as the space between frames, using Delta mode.

Move the densitometer to the point to be measured. The reading is the negative density over B+F in stops.

To measure Base+Fog first zero the densitometer with no negative in the enlarger. Then meter the blank film. The reading is the Base+Fog density.