This is a subject I don't see mentioned much, so I'd like to finally kick off the discussion to bring some visibility.
As many of us are using an increasingly long tail of densitometers of various generations and models, and are turning to mismatched and/or 3rd party sources of calibration materials for them, this is something that's becoming all too easy to get mixed up and confused on.
Here are the top-level bullet points:
So how do you know which direction the emulsion is supposed to face?
In my own survey of densitometers I've paid close attention to, here's what I've found:
One example of a common way to mix this up is when calibrating your unit with a reference strip designed for a different densitometer. For example, the X-Rite 301-27 reference is easy to find new, and clearly labeled to be measured emulsion-side-up. But if you're using it to calibrate an emulsion-side-down instrument, you need to measure it upside-down. If you don't, you will get slightly incorrect readings.
Now to make all this clearer, I decided to go ahead and do a little date collection experiment. Using a fresh X-Rite 301-27 calibration strip, a Stouffer T2120 step wedge, and an X-Rite 810 densitometer, I tested 4 configurations:
But if you plot the differences between the 4 configurations, then the differences become quite obvious:
(This graph is showing the differences between the "correct" configuration and the other 3.)
As many of us are using an increasingly long tail of densitometers of various generations and models, and are turning to mismatched and/or 3rd party sources of calibration materials for them, this is something that's becoming all too easy to get mixed up and confused on.
Here are the top-level bullet points:
- Every densitometer has a preferred orientation for the film emulsion to face when taking measurements.
- Film emulsion direction is sometimes mentioned in the manual, but not always
- Calibration references are labeled for the densitometer they're intended to be used with, which may not match the densitometer you are using them with
So how do you know which direction the emulsion is supposed to face?
- If its in the product documentation, then go with that. It might be a few pages into the manual, and easy to miss.
- If the densitometer has a polished opal diffuser, then the emulsion should face that diffuser.
- If the densitometer does not have a polished opal diffuser that you can see, then the emulsion should probably face the sensor.
In my own survey of densitometers I've paid close attention to, here's what I've found:
| Densitometer | Emulsion Direction | Is it in the manual? | Notes |
| X-Rite 810 | Facing down | No | 810 and 820 are the same optical mechanism, polished opal diffuser and sensor elements in the base |
| X-Rite 820 | Facing down | No | |
| X-Rite 361T | Facing up | No | |
| X-Rite 301 | Facing up | Yes | |
| Tobias TBX1000C | Facing up | Yes | Polished opal diffuser and sensor elements in the head |
| Heiland TRD-2 | Facing down | Yes | |
| Dektronics Printalyzer Densitometer | Facing up | Yes | Acrylic diffuser in the base, sensor in the head, but calibrated to compensate for measurement artifacts. |
| Dektronics Printalyzer UV/VIS Densitometer | Facing down | Yes | Polished opal diffuser in the base, sensor elements in the head. |
Now to make all this clearer, I decided to go ahead and do a little date collection experiment. Using a fresh X-Rite 301-27 calibration strip, a Stouffer T2120 step wedge, and an X-Rite 810 densitometer, I tested 4 configurations:
- Calibrate emulsion up, Measure emulsion down
- Calibrate emulsion up, Measure emulsion up
- Calibrate emulsion down, Measure emulsion down (The correct configuration)
- Calibrate emulsion down, Measure emulsion up
But if you plot the differences between the 4 configurations, then the differences become quite obvious:
(This graph is showing the differences between the "correct" configuration and the other 3.)
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