Densitometers are a valuable tool in the offset printing industry. If you are in this industry, then this is an essential tool for your printing press. I would like to show you four essential things that you need to know about this tool so that it can bring the quality in your press room to another level. Here is what I will show you:
- What a densitometer is.
- The different types of densitometers used in the printing industry.
- Where you can buy a new or used densitometer.
- How they work.
What is a densitometer?
In the offset printing industry, a densitometer measures how dark a printed image is. It cannot see color. A spectrophotometer on the other hand can see color, and though they look alike, the two are not to be confused.
The darkness reading of a printed ink will usually tell you the density. Since a densitometer cannot see color, the operator must tell it what color is being read. Many densitometers can automatically tell by the reading what color it is likely reading, but it is not with certainty.
A densitometer is designed to read a color bar that runs across the printed page. This color bar will tell you everything that is happening on the printed page. This is the primary tool used by a densitometer.
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| A densitometer reading the color bar. |
The different types of densitometers used in the printing industry.
There are three different types.
Reflection. This is the one most commonly used with an offset printing press. It measures the amount of light that is reflected from a printed surface. With this ability, other properties such as grayness, dot gain, or hue error can be read.
Transmission. Back in the days of film, this type of densitometer was used to measure how much light was transmitted through film. These days with imagesetters, film has largely disappeared from prepress departments. These densitometers are still being made, but not so much for the printing industry.
Combination. Does both of the above. However as mentioned, this type has become almost obsolete since the onset of computer to plate systems.
How densitometers work.
We will speak about reflection densitometers only from this point since they are the main type used in the offset printing industry.
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| How a densitometer works. |
Since a densitometer simply measures the amount of light that is reflected back, the components are simple and consist of the following:
1. A light source or lamp with stable output. As defined by the American National Standards Institute (ANSI) as well as the International Standards Organization (ISO). These standards are necessary for communication between sources.2. The filter/aperature and optics. These optics are designed to focus the light down to a defined spot on the paper.3. The color filter and sensor. These read the strength of the reflected light at a 45 degree angle. This angle is to minimize the glossy effect. Each color will have a filter built into the densitometer. The sensor sends the reading to the logarithmic amplifier.4. The logarithmic amplifier. The reading is interpreted as logarithmic to make it similar to the way we see light. For example, something twice as dark does not necessarily have half of light. Our eyes interpret in a logarithmic way. Ten percent less might be seen as something twice as dark.5. Display. This reading is then sent to the display of the densitometer.
Where can used or new densitometers be purchased?
There are 3 main suppliers of new densitometers for the printing industry. They will cost you $3500 or more. Here they are:
Used densitometers.
Here are some links to good used x-rite densitometers. They range anywhere from $300 to $1200. They are an economical start if your offset printing operation doesn't have one yet.
Conclusion
A densitometer is a basic start for any press in the offset printing industry. If you are serious about quality control, it is essential.
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