Just got an EG&G Sensitometer

[Bill Burk]

You find a film's speed by seeing how much light it takes for the film to begin to respond to light.

So after developing a test and graphing it, look at the curve where film density crosses 0.10 above base plus fog.

Then you try to figure out how much light hit the film at that point.

From that amount of light, you get the speed.

There's more detail to it, but basically that's how you figure out film speed.

I use a graph, calibrated to my EG&G to study film. The top scale is where I look up the speed.

That top scale on my graph is set to how much light my EG&G puts on film through the step wedge, at the 10 to the -2 setting with the 1.84 neutral density filter "in the well".

If you want to use my graph, that's fine, just cut that top strip off and slide it left and right as needed...

Basically, if you develop the film just right and "hit the ASA triangle" with a fresh film, you can slide that scale until the factory box film speed is directly above the point where the curve crosses 0.1 above base + fog.

http://www.beefalobill.com/imgs/sensitometrymarkvi-6.pdf

 

[mr_coffee]

Great!
Thank you both!!

Now it's much more clear, the Kodak reading is a good reference and also the Bill's graph!

 

[Nodda Duma]

Such great timing sometimes on threads. I am in the process of generating the characteristic curve and determining the speed of my emulsion in a more controlled manner than I've done in the past. I have been doing in-camera exposures, but of course the snag is measuring lux in a satisfactory way (for reference, I've spent a significant part of my career doing radiometry .. it's one of the subjects in optical engineering that my expertise is very deep on). A sensitometer makes a lot of sense, but I don't know which model would accommodate my glass plates. Any suggestions?

My other thought was to use the enlarger, which allows me to make an illuminance measurement that I can believe and use the setup in a repeatable manner. My only concern is I don't know what's going on in the UV part of the spectrum where my emulsion is most sensitive, but I am pretty sure I can tie the indoor measurement to an outdoor setup by replicating the enlarger setup's light levels at the plate outdoors and comparing the effective speeds.

 

[Photo Engineer]

I have used an EG&G, a camera and an enlarger to determine both speed and curve shape. They all work, but the camera method is the least effective.

PE

 

[ic-racer]

If you use times greater than 1 second, then an old contact printer, UV lamp, enlarger timer and step wedge could make a good sensitometer for plates.

 

[Bill Burk]

An EG&G would work for you but I see they are pretty expensive... would eat up a lot of your profits.

How would you feel about using film for control. Here's what I'm thinking.

Make a jig that holds a piece of control film and test plate with step wedges in contact. Ensure there is a marking device that keeps pairs identified as belonging to each other.

Expose film and plate at the same time.

Develop the film in D-76 for the time that gets it as close as possible to meet ASA contrast. This confirms the exposure (gives you a reference key to the x-axis).

Separately develop the plate any way you want. Make several pairs of exposures and develop the plates for different times or different developers to get a full family of curves.

But always develop the film in D-76 to ASA contrast.

Graph the result locking the x-axis of each plate to where the corresponding film revealed about the exposure.

Advantage: You can expose your tests in camera, in daylight conditions with vintage lenses and shutters that are not calibrated or consistent, yet your test results can always normalize the exposure.

 

[ic-racer]

The software I developed generated the ASA triangle and calculates various speed points.

 

[Bill Burk]

Awesome!

 

[ic-racer]

Well, many years later I have an update on my Wejex sensitometer. I needed replacement glass for the step wedge that was 0.5mm thick, and that was very hard to find back then. Now just about every smart phone screen protector is made of it. It took some searching to find one that wasn’t tempered glass since cutting that is practically impossible, but the cheap knockoff stuff worked pretty well.

The original setup had the glass between the film and the wedge causing the wedge to be less than sharp and significant bleed from one section to the next. I moved the wedge under the glass so it is in contact with the film and now it works great. I hope to use it for some film and/or developer comparison videos in the near future.

Yes, basic sensitometery video would be great. Putting the wedge between the film and glass is probably the best way. That is how the EG&G works. You just tape your wedge on the glass.

 

[ic-racer]

EG&G Sensitometer with plastic cover removed to see the underlying chassis:

 

[ic-racer]

EG&G Light Chamber and film stage.
Notice how there is no diffuser between the lamp and the film stage. It seems light falloff at the extremes of the film stage are minimized by reducing the cosine angle due to the distance of the film stage from the lamp. You can see from the underside picture above that the lamp is at the bottom of the unit, and the film stage is at the very top of the unit. The film stage is inserted into this opening.
A foam-lined lid presses down on the film and when the lid touches the button in the middle of this picture, the flash is ignited.

 

[ic-racer]

The clear filter shown above can be removed and attenuation filters placed. This is because the three capacitors (that control the three flash durations) produce three different intensities. The filters equalize the Lux-second exposure between all three settings.

Allowing one to test a film for reciprocity failure against three different exposure times with the same overall Lux-second exposure.

 

[ic-racer]

The EISCO sensitometer is much smaller and it used a number of diffusion strips to even the exposure across the film stage.
According to the technical support team, the diffusion material needs to be replaced in the same order.

 

[ic-racer]

I did tests showing that in my Darkroom, sensitometer light color does not change my results. However, if one is comparing B&W film of highly different color sensitivity spectrum, white light might be better. You can see that replacing these LEDs with different ones would not be that difficult of a task.

 

[ic-racer]

Even though EG&G and WEJEX sensitometers are used as standards in many tests, there is another level of precision, an order of magnitude higher in price.
The $20,000 Agfa Avisense 2000 sensitometer uses carbon step wedge (instead of silver emulsion film step wedge) and has a very sophisticated light system.

 

[ic-racer]

For most all purposes of fine-art photography, calibration of one's sensitometer with name-brand fresh film will be sufficient. Trying to calibrate to an ISO standard with a ISO calibrated meter (like Agfa's ISO 9001 certified calibration lab) has its own sources of error in reading the film stage. This is exemplified here in the instructions on calibrating the Avisence 2000:

 

[ic-racer]

Also, of note, even on the $20,000 sensitometer, the steps are 0.15 log d apart and there are only 21 of them. (just like almost every other sensitometer out there.)
As you know the toe is going to be on the left in the above picture (the dense steps). There are not enough steps to the right show the shoulder. This is a clear example of why one almost never sees the shoulder of published H&D curves:

 

[ic-racer]

Just to continue the conversation, in the example above, the "BAR" notation can be confusion, so re-plotting the same values as MILLILUX-SECONDS gets rid of the bars.

ISO 100 film (shown here) will always have POINT A at 0.9 Log millilux-seconds (or 8 millilux-seconds) by definition.
Film Speed ISO = 800/millilux-seconds

 

[ic-racer]

So, in terms of sensitometer calibration, all sensitometers will produce a density of 0.1log D above film base plus fog on ISO 100 film when they give the film a 0.90 Log Millilux-Second exposure.
This converts to an 8 millilux-second exposure.

So, when you put (properly processed) ISO 100 film on you sensitometer, the step on your sensitometer that produces 0.1 log density on the film is giving 8 millilux-seconds exposure.

 

[ic-racer]

I think it works with any DC voltage (don't need regulated voltage). The AC circuit of the device likely provides a regulated 300v or so to the capacitor irrespective of the input voltage. Just like any other flash, a low voltage battery just makes the capacitor take longer to charge, but once it is charged, the flash output should be the same as if you had a fresh battery.

Since you have a good densitometer, you should be able to test the film stage for even illumination. I'd say the farther away from the film stage, the better the illumination. I don't have pictures off hand of the inside of my Wejex, but the majority of the bulk of the device is to provide distance between the lamp and the film stage.

 

[StrangestStranger]

I managed to come across an EG&G sensitometer for just the cost of shipping. The problem was that it was tested prior to shipping and I was informed by the shipper that it was no longer working. Based on the information in this thread I decided it might be simple enough to diagnose and find out what was wrong. The first thing I did was order a new bulb . The socket that the bulb plugs into is a standard vacuum tube socket, so i order one of these (https://smile.amazon.com/gp/product/B00E1P1QD0/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1) to solder the new bulb into.

Still no luck, all I got was a very small arc of the bulb, barely noticeable in the dark. I then started to investigate the circuit. I was getting 430V out of the power supply, so that told me it was good. I also got 430V after the rectifier, so everything was good up to that point. All of the resistors looked good as far as I could tell.

In old circuits, i assume capacitors are the things that fail first. These high voltage capacitors aren't easy to find, but I managed to find one for the trigger circuit and two for the 1/100 and 1/1000 circuits. I first replaced the trigger circuit capacitor (https://smile.amazon.com/gp/product/B0745KCJ76/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1), still same problem. I decided to put the original capacitor back since it had a much lower ESR value and I didn't want that affecting the trigger voltage.

I also thought that maybe the spark coil was bad. The problem is I didn't have enough information on the spark coil to know what to replace it with, so I ordered several different types. I noticed that they had an FT-118 bulb (https://www.xenonflashtubes.com/spi.../ft-118-spiral-60ws-photo-flash-lamp_163.html), too, so I figured what the heck and included that bulb in the order. It turns out the original spark coil was perfectly fine.

My next step was to replace the 1/100 capacitor (https://www.ebay.com/itm/Capacitor-...e=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649), but since its the same type as the 1/1000 circuit, i decided to replace both at the same time. Still no luck with bulb. I decided to put the original bulb back in to see if it produced a different result and it did, the flash was much brighter, just not bright enough.

So, I'm still confused as to what might be wrong. The original bulb produced more light than the new replacement bulb, which got me to thinking that maybe the original bulb is bad, and the replacement bulb may not be the correct bulb. So, I wired the socket to the second bulb I ordered using patch wires and low and behold, the bulb flashed with an intensity that hurt my eyes. The problem was a combination of the 1/100 and/or 1/1000 capacitors and the bulb.

So if you are looking to fix an EG&G, I included links to all the parts I purchased that got the unit working again. Hopefully this post will help somebody in the future.

 

[Bill Burk]

I managed to come across an EG&G sensitometer for just the cost of shipping. The problem was that it was tested prior to shipping and I was informed by the shipper that it was no longer working..

Wow what a project! The flash at 1/100 is intended to be fairly dim to the eye, as it only outputs a few meter candle seconds in that hundredth of a second.

1/1000 and 1/10000 are brighter - so you should expect them to 'hurt' your eyes but 1/100 shouldn't.

 

[StrangestStranger]

Thanks bill. Actually on my model the 1/100 circuit puts out 1000 MCS, the 1/1000 puts out 5000 MCS, and the 1/10000 puts out the lowest of 130 MCS. So everything seems to be working according to spec.

 

[Bill Burk]

Stouffer has a step wedge that fits if you call them. It’s not in their catalog or on their website but it’s not expensive

 

[StrangestStranger]

Yup, I've had one since I did sensitometry in college. I don't think its a Stouffer, maybe Kodak, but it's 21 step. I calibrated it in college, but I plan to re-calibrate it with my current densitometer, an X-Rite 810.