DETERMINATION OF OPTIMUM FILM DENSITY

Now you know how to best expose and process the paper.  What's left is to figure out how to expose and process the film to produce a negative that matches the abilities and qualities of the paper.  First we must quantify the paper, in other words, measure the characteristics of the paper so that we can produce a negative to match those characteristics.

There are a few special tools needed to complete this set of tests.  However, some of these you may already have.  

First, you'll need a grey card to make visual comparisons.  Grey cards are made by several companies, are often easy to find for next to nothing at camera shows, and have several other photographic uses.  

Also, you will need a transmission step wedge.  You can think of step wedges as a set of "perfect" negatives with specific densities on them.  They are common place in the graphic arts industry and are made by several companies, such as Kodak (1-800-242-2424) and Stouffer (1801 Commerce Drive, South Bend, IN, 46628, 1-219-234-5023).  Make sure you get one with density steps of at least 0.05 (1/6 f-stops) or finer.  But be careful; the more steps, the more expensive, so don't go overboard.  The 0.05 steps is as fine-tuned as you need to be.  Try to get a step wedge that is the same width as the film under test.  If you are testing several film formats, try to get different step wedges.  You need to put the step wedge in the negative carrier, and you shouldn't cut the step wedge unless absolutely necessary.  It will make your life a LOT easier if the step wedge that you buy has numbers on each step.  This will help you identify the steps during the tests later on.  (If your wedge lacks numbers, you can place special marks on the steps to help in identification, such as dots and circles. ) The one I use is the Stouffer CT40 (they don't make this version any more) which cost about $25 and has 40 density sections that run from 0.0 thru 2.0.  Most step wedges come in calibrated and uncalibrated versions.  The calibrated ones cost more, and for our purposes, the uncalibrated ones will work fine.  You use the step wedge as a set of "perfect" negatives for these tests which are used as targets for your actual negatives.

Lastly, you'll need a way to measure the density of the step wedge -- and eventually, your negatives.  If you have access to a densitometer, that's great, but few of us do.  You can easily substitute a color analyzer, if you have one -- if it has a readout in seconds.  Many handheld, ambient light, exposure meters, such as those made Minolta and Sekonic, have adapters to use under the enlarger, and these will work fine, as well -- once again, as long as they have a readout in seconds.

1. Every type of paper has a different range of tones that it can reproduce. This is important to determine so that you will know how to correctly expose and process your film to fit within the limits of the paper.

• A. Leave your enlarger set up from the last test -- with no negative in it. 
• B. Turn off the lights, turn on the safelights, and put a piece of the paper under study in the easel.  Place the step wedge on top of the paper.  
• C. Make an exposure of the step wedge using the exposure determined in the last test.  Process it exactly the same, as well.
• D. After processing, compare the step table print to your grey card.  One of the steps will be very close to the grey card.
• E. Place the step wedge in the enlarger.  Make sure that the step that matched the grey card appers in the carrier opening.  If you are using a submini format of less than 35mm wide, you will probably have to cut the step wedge to get it to fit in the negative carrier.  An alternative is to use the 35mm carrier.  The print that was made with the step wedge directly on the paper just got us close -- this tests adds the effects of the enlarger and lens and will be more exact.  You will probably have to run multiple tests since the tiny submini carrier may only show two or three wedges at a time.   
• F. Make an exposure of the "grey card" section of the step wedge using your base exposure.  Process it exactly the same, as well.  The exact wedge that will produce a print that matches the grey card will vary according to your equipment.  If the resulting print is darker than your grey card, switch to a lighter section of the step wedge.  If the resulting print is lighter than your grey card, switch to a darker section of the step wedge.  Just make sure to keep the exposure and the development the same.  
• G. Compare the tone of the print to the tone of the actual grey card. The "color" of various B&W papers can vary from brown to neutral to blue. Ignore the "color" and concentrate on matching the tone that is closest to the grey card -- how light, dark or grainy the image is. For color paper, select the best density regardless of the color of the print and then attempt to change the filtration on subsequent test strips until the grey card is matched.
• H. When you find a step on the wedge that produces a tone as close to the grey card as you can get -- when using the same exposure and development as the earlier tests -- stop the test.  
• I. All that you have to do now is determine the density of the step that produces the grey tone.  You will use this as a target in the next set of tests -- determining how long to develop the film.  This is where you use your color analyzer, densitometer, hand-held meter, or whatever.  
  
  • 1. Mark or note which step on the step wedge produced the best print.  
  • 2. Remove the step wedge from the negative carrier.
  • 3. Place the meter probe in the middle of the easel.
  • 4. Turn off the lights. Turn on the enlarger.
  • 5. Without changing the f-stop on the lens, adjust the meter (on hand-held meters this is the ISO dial) to set the exposure exactly at 1 second.  If your meter does not have a 1 second setting, the 10 second setting can be used -- just multiple all future results by 10.  If you are using a color analyzer for these tests, make sure that you are using the exposure channel. If you are using a densitometer, follow its instructions.
  • 6. Now put the step wedge back in the negative carrier.  Make sure to place the same step of the wedge in the carrier that produced the best grey card print.
  • 7. Do not change the f-stop or meter settings.  Make sure the correct step on the wedge falls on the meter probe.
  • 8. Record the time (or density) that the meter recommends for this "grey card" section of the wedge.  It could be anywhere from 3 to 20 seconds depending on your equipment.  You will use this number again as a target when you determine the best development time for the film.  In a nutshell, you'll expose the film under study to a grey card.  Then you will vary the development until you match this density on the film -- which you already know produces a perfect grey card print at an exposure time that will also produce maximum black in the shadow areas.

Now that you what the density of your film should be, you're ready to move on to DETERMINATION OF OPTIMUM FILM EXPOSURE AND PROCESSING.

FRONT DESK.

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