X-Rite 334 Sensitometer: Inspection and Analysis

[ic-racer]

With the demise of film medical radiography, sensitometers have hit the used market. Currently on ebay there are about 80 sensitometers and about 80 transmission densitometers. But the sensitometers are about ten times less expensive.

I found a seller with six working X-Rite 334 sensitometers for $19 each.

I bought one to analyze.

My first impression was how small the unit was. Somehow the pictures on ebay make it appear larger thinking it will take a whole piece of xray film. Actually, its light stage is perfectly suited to 35mm film.

As a size comparison, I have photographed the unit next to a 35mm camera.

 

[ic-racer]

The bottom of the unit has the on-off switch and the DIP switches to adjust the light output.
The bottom is designed to be removed with 4 screws to replace the battery. Removing the bottom also allows one to investigate the innards.

Torroidal coil is interesting. Turns out I thought this was a LED unit (as many sensitometers are) but I was mistaken. More about the light source and its need for the coil to come...

 

[ic-racer]

The foam to keep the battery from rattling was a goopy mess so I took the opportunity to replace it with fresh foam rubber.

 

[ic-racer]

The light source is not evident from the bottom of the unit. The top has to be removed. To have access to the screws to see the light source, the hinges for the top cover need to be un-coupled. This involves tapping the hinge pins outward. One needs to work from under the top cover.

 

[ic-racer]

4 screws affix a bar that holds the step wedge and its underlying diffuser in place. The item on the far right is a photodiode sensor to monitor the light intensity of the device with a feedback loop during the exposure.

The unique "calibration monitor" circuit provides repeatable exposures from month-to- month and from instrument-to-instrument. X-rite 334 Manual

 

[ic-racer]

With the diffuser and step wedge removed, the light source is evident. It is an electroluminescent lamp.

 

[ic-racer]

My understanding is the electroluminescent lamp in this device uses Sylvania Type 814 phosphor consisting of zinc sulfide and copper which generates a blue color at 60, 400 and 6,000 Hz with a peak wavelength of 452 nm.
It also generates a green color by altering the driving frequency of the lamp. The color shifts from green to blue as the excitation frequency driving the lamp increases.

 

[ic-racer]

The electroluminescent panel in this device is constructed somewhat similar to a capacitor with a dielectric matrix between the panels in which phosphor crystals are embedded. The torroidal coil encountered earlier is part of a DC to AC circuit that drives the lamp. Applying alternating current to the device will activate the phosphor crystals and emit light of certain wavelengths depending on the crystals.

This lamp may be the ideal lamp for a sensitometer. It has uniform brightness over a flat area. It is inherently thin and durable. The brightness and color can be controlled by altering the amplitude and frequency of the driving voltage.

 

[ic-racer]

An example of the change in color from blue to green with change in frequency:

 

[ic-racer]

With the step wedge removed from the device, its values were read with my densitometer. These will be the X values plotted on the H&D curves.

 

[ic-racer]

The foam on the lid that holds the film flat had deteriorated and was replaced.

 

[ic-racer]

The lid was re-attached and the hinge pins re-inserted.

 

[ic-racer]

Website image of the 334 from the Wayback machine:

 

[jvo]

i knew i didn't need to know this, and found it fascinating as i read through the clear explanation - thanks.

jvo

 

[tih]

Thanks! - this is fascinating, and useful.

Question: with my 334, I've found that it gives a little less exposure than I'd like, but the green setting works best with normal B/W films. Still, I've ended up using it at the "5" intensity setting for 400 ASA film, "7" (maximum) for 200 ASA, and then holding the film steady while exposing two times for 100 ASA, and four times for 50 ASA. Can you tell if it might be possible to recalibrate the unit to deliver more light at each setting, making it more suitable for our use?

 

[ic-racer]

Without a schematic, modification is not easy. To increase the time, first the DIP switches need to be decoded and figure out how they control the time via the timing chip. Sometimes the datasheets for the IC chip has a suggested circuit showing how timing is controlled.

What might be easier would be to modify the switch, so one can keep the lid closed and provide the needed multiple exposures. The ESECO works like that. The exposure button is on the side and not linked to the lid. Same with the Wejex. In both of those multiple exposures are easy, without opening and closing the lid.

 

[acoma]

Thanks! - this is fascinating, and useful.

Question: with my 334, I've found that it gives a little less exposure than I'd like, but the green setting works best with normal B/W films. Still, I've ended up using it at the "5" intensity setting for 400 ASA film, "7" (maximum) for 200 ASA, and then holding the film steady while exposing two times for 100 ASA, and four times for 50 ASA. Can you tell if it might be possible to recalibrate the unit to deliver more light at each setting, making it more suitable for our use?

Just a thought, would it be possible to insert an ND filter between the sensor and the diffuser (wratten or some similar thin material)? Of course this assumes that the light source is capable of producing an appreciably increased output. Settings for higher speed films would need to be shifted down the intensity scale, if this approach works.

 

[acoma]

Ic-Racer - thanks for the teardown. Mine should arrive Thursday.

 

[ic-racer]

Just a thought, would it be possible to insert an ND filter between the sensor and the diffuser (wratten or some similar thin material)? Of course this assumes that the light source is capable of producing an appreciably increased output. Settings for higher speed films would need to be shifted down the intensity scale, if this approach works.

The sensor shortens the time and I tested this, but I did not test if it can lengthen the time. This is certainly worth a try.

 

[dkonigs]

From the info you've shared, I went and got myself an X-Rite 396. Its very similar, but the electronics look more modern. (Its likely that it works the same way, however.)
One thing that's missing from the documentation, is anything about what amount of light exposure (in standard units) each of the DIP switch settings actually corresponds to. Don't we need to know some form of this if we're trying to characterize film?

I saw the limited notes that "tih" posted on this, and that can be an okay starting point (if accurate to other models), but it would be nice to have a better idea.

 

[ic-racer]

Bill Burk and I had a thread on the value of sensitometer calibration a while back. I use "FILM" to calibrate. So in essence I use all my sensitometers like a "Balance," rather than a "Scale." There is always some film used as the comparison. You can also use your "Standard" film's given ISO and work backwards to find the light intensity if you process it via ISO rules.

Calibration of a sensitometer with "control stock film" is the same method used by the USAF:

Requisition the sensitometer calibration package for the type of sensitometer to be calibrated at least every 12 months.
• Calibrate the facility standard sensitometer according to TO 10-1-6-2, and as supplemented by instructions in the calibration package. Once you calibrate the facility standard sensitometer, use its calibration for all remaining facility sensitometers. Do this every 12 months.
• Produce exposures on control stock film using the facility standard sensitometer during calibra- tion. Use these exposures for later calibrations and certifications.
AIR FORCE INSTRUCTION 14-202 28 MARCH 1994
Intelligence
STANDARDIZATION, EVALUATION, AND QUALITY ASSURANCE FOR US AIR FORCE RECONNAISSANCE IMAGING SYSTEMS

 

[ic-racer]

Another way to put it is that a control strip sensitometer alone is NOT used to find a value to set on your exposure meter. Usually one will adjust the exposure index setting of one's exposure meter based on IN CAMERA testing. Then, knowing the IN CAMERA exposure index number and the speed number arrived with the sensitometer, you can have a conversion factor to find baseline settings for an UNKNOWN film. You can do this at night in your darkroom and not have to go outside and do the IN CAMERA tests on the UNKNOWN film.
There are many other uses, many for fun and learning to. It is fun to make H&D curves even if it is not something that will affect the way you make images.

 

[ic-racer]

Example:
I know I like HP5 8x10 exposed at index 200.
I got Shanghai film in the mail and exposed a strip of HP5 and Shanghai in the sensitometer that night. I could have used any of them, they all work the same.
The test showed Shanghai was 3 stops slower, so EI 25.

Next day I went out and thought,"25 is pretty slow" exposing at EI 50.

Images under exposed. SO... believe the testing!!!

 

[ic-racer]

From the info you've shared, I went and got myself an X-Rite 396. Its very similar, but the electronics look more modern.

Yes that looks like a nicer one, I'd like to see the innards on that one if you plan on opening it to check.

Main reason I got the 334 was to open it up and show here for interest; my own interest and maybe everyone els's too.

 

[ic-racer]

BTW EG&G Did give the exposure at the film stage, but really this is just an estimate. That was never a "Calibrated Exposure" listed in the manual.

...the 10^-3 second light pulse emits a nominal 5000 MCS, the logarithm for which is 3.7.... EG&G User's Manual 1985