Transmission densitometers and the importance of emulsion orientation

[dkonigs]

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:

• 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.

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:

• 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

If you plot the raw density values for the step wedge measurements, things appear somewhat close:

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.)

 

[Alan9940]

The manual for my Gretag D200-II doesn't mention film direction for any of the measurement modes, but I've always placed the film emulsion down.

 

[Saganich]

For the Macbeth TR-524 it is emulsion facing UP, on page 1-6 (j).

 

[MattKing]

Warning - pedantry alert!
Don't you mean emulsion orientation, rather than emulsion direction?
To me, direction implies movement.

 

[grahamp]

Interesting. That might explain some odd behaviour with my old Photronix Delta III (light in the base, sensor in the arm above). Needless to say, it came my way years ago without instructions!

 

[dkonigs]

Warning - pedantry alert!
Don't you mean emulsion orientation, rather than emulsion direction?
To me, direction implies movement.

Pedantry accepted, within reason.
Thread subject changed, but I didn't upload new graph screenshots.

 

[dkonigs]

Interesting. That might explain some odd behaviour with my old Photronix Delta III (light in the base, sensor in the arm above). Needless to say, it came my way years ago without instructions!

Even when there are instructions, I think a lot of people miss this part.

One of the test users for my new densitometer model got this wrong on some of his early tests, and suggested that I mention the emulsion orientation in the included quick start guide.

It is mentioned in the quick start guide, and the regular user manual, and even on a slip of colored paper included in the box for extra visibility.

 

[MattKing]

Pedantry accepted, within reason.
Thread subject changed, but I didn't upload new graph screenshots.

The graph screenshots are fine as they are.
And I'm not sure why, but the thread seems so much better now

 

[Milpool]

Pedantry accepted, within reason.
Thread subject changed, but I didn't upload new graph screenshots.

What you meant was obvious to everyone except the pedant.

 

[MattKing]

What you meant was obvious to everyone except the pedant.

You seem to forget that this is an international site, where many people do not use English as a first language, and a reasonable percentage of people actually have to use computer translation in order to understand every single English post they read.
Not to mention the people who are just learning the first things they have ever learned about densitometers.
My first reading of the thread title made me think that it referred to the direction that the film was inserted, not whether the emulsion was up or down. It was easy for me to realize quickly that that wasn't what was meant - I have enough familiarity with densitometers to have been able to figure that out - but why would you assume every other person reading this thread would be coming from the same point of understanding?
Pedantry does, sometimes, lead to better understanding and clarity you know.
Not posted as a Moderator per se, but I have been observing how people interact here for a long time, and I have certainly seen a fair few misunderstandings during that time too.
I've even helped straighten a few of those misunderstandings out!