Just got an EG&G Sensitometer

[ic-racer]

After reading the EG&G manual I now understand the special light filters that are missing for my unit. Since the light output for the three flash speeds is so different, they had the equivelant of Neutral Density filters to make the 10-2 and 10-3 speeds the same intensity as the 10-4 speed.

Rather than relying on gelatin or acetate filters that may fade with time, or rather than the expense of pure carbon filters they used a very simple solution.

The filters are just sheets of plexiglass that are black or painted black and they have a series of lines on them to controll the light intensity.

One filter has 3 slits and the other has 19 slits.

Last night I cut 2 pieces of plexiglass to the appropriate size and then painted one side of each with semigloss black paint.

Today I will mark out where I want the slits to be and just scrape the paint away using the blade of a fine screwdriver. I can then fine tune them by adding or removing more paint as directed by flashmeter measurements.

 

[ic-racer]

I made my 'filters' the other day. I was not shure how large the lines were to be. My first filter used lines about 2mm wide. I made 3 lines and it was too bright for the 10-3 setting. I tried it on the 10-2 setting and it seemed to be just right.

For the next filter I used 0.5 mm lines. I started with just one line and it was too dark. Then I added a second line and it was just right for the 10-3 setting.

I also replaced the Radio shack flash tube with the new FT-118 replacement. The replacement is not an exact replica. It is a little smaller than the original. I suspect either the Radio Shack tube or the replacement FT-118 will work fine.

Now I am ready to start to do some testing. I am probably just going to test the Wejex and EG&G as I have been unable to get an X-rite on ebay for $25. I guess I need to put out some posts about how they are totally unsuited for panchromatic film so people stop bidding them up

 

[ic-racer]

I did some research and it seems that the resolution of conventional film radiography is a little better than the 'film-less' radiography and this makes conventional film somewhat better for mammography. In mammography, one needs good film resolution to detect microcalcifications and subltle spiculated lesions that might be masked by the surrounding breast parenchyma. I suspect that as digital gets better this will all change. But this continued use of conventional film for mammography is, I believe, the reason that there are still high prices on the x-rite sensitometers. As 'film-less' imaging takes over the field of mammography I suspect these x-rite sensitometers will really come down in price.

 

[ic-racer]

Amazing Eye for Brightness

Did my first H&D curves with the EG&G.

I exposed a strip of film to each setting on the EG&G. The first segment was 10-2 with my filter with 3 wide slits. Next was 10-3 with the filter with 2 narrow slits and finally 10-4 with no filter.

Now, I don't have a flash meter. So I use my eye to match the intensity of the 10-4 flash to the others and kept scratching lines in the black paint on the filters until the intensity matched up to my eye. I thought I could get to 1 to 2 stops.

Well, I plotted the three H&D curves and they almost superimpose exactly! WOW!

Here is some of the raw data:

[Step #] [10-4 (no filter)] [10-3 (3 wide slits)] [10-2 (2 narrow slits)]

18 1.32 1.31 1.31
17 1.38 1.38 1.38
16 1.47 1.46 1.45
15 1.56 1.54 1.54
14 1.65 1.62 1.62
13 1.74 1.70 1.71
etc...

 

[ic-racer]

EG&G on e-bay

I have no affiliation with this item, nor can I vouch for its quality, however, if someone is looking for an EG&G sensitometer, this looks like a working example of a mark VII.

http://cgi.ebay.com/EG-G-Mark-VII-S...QQssPageNameZWDVWQQrdZ1QQcmdZViewItem#addimg1

 

[ic-racer]

I see there is another EG&G Sensitometer on ebay now:
http://cgi.ebay.com/EG-G-PH-10-Mark...ltDomain_0?hash=item51910612e2#ht_3834wt_1167

 

[Photo Engineer]

That is an old model. The latest ones have 4 buttons and an even later model has an arched or curved exposure plane to give more uniformity. That value listed is way out of sight IMHO.

PE

 

[ic-racer]

That is an old model. The latest ones have 4 buttons and an even later model has an arched or curved exposure plane to give more uniformity. That value listed is way out of sight IMHO.

PE

Price is crazy. The one I got at the start of the thread (3 years ago) is the same model...$35

I noticed everything that seller had on ebay also said "or make offer" so I presume he knows he won't get that much.

 

[ic-racer]

I never got around to posting the innards pictures from when I serviced mine, so here they are:
I have also decided that the regulated power supply is probably due to the transformer being a ferroresonant transformer as there is no electronic voltage regulation circuit present.

 

[Stephen Benskin]

I got my Mark VI back when EG&G was still doing calibration. They might still be, but around ten years ago I heard the price had gone from $300 to $1200 just for the calibration. That lead me to believe EG&G didn't want to do them any more. But when they did, they would read the exposures, check the electronics, change the power cable, and include new compensators and a step tablet (uncalibrated).

Mine read
10-2 (.001sec flash duration) = 765mcs
10-3 (.0001sec flash duration) = 3728mcs
10-4 (.00001 flash duration) = 60mcs

I always used 10-2 for exposing film because of the lower illuminance and practical exposure time. 10-3 was way too bright and 10-4 might start showing problems with reciprocity.

With the 10-3 compensator, the exposure for 10-2 was 20.3mcs. I then used ND filters to adjust for the different film speeds. I used .6 NDs. They brought the exposures down to 4.78mcs for 100 speed films, 1.18mcs for 400 speed films, and 0.28mcs for TMZ and Delta 3200.

I've also worked with a Mark VII that had
10-2 = 681mcs
10-3 = 3440mcs
10-4 = 59.4mcs
10-5 = 29.2mcs
10-6 = 6.85mcs

The manual has a phone number for EG&G, but I also wrote down a number that might be one for the then calibration department. It is (800) 950-3441. They might still sell the compensators. BTW, I talked to EG&G once about finding a meter that could be used for the calibration of the sensitometers. For that kind of accuracy, it would have run around $4000 dollars. There is a lot of good information that can come out of a calibrated light source. It was well worth the $300.00 extra dollars for the calibration.

Steve

 

[Kirk Keyes]

I never got around to posting the innards pictures from when I serviced mine, so here they are:

That looks great!

 

[Photo Engineer]

Thiis is the most accurate method of getting the characteristic curve of your film or paper.

PE

 

[Photo Engineer]

Not really. The Sensitometer is calibrated for time and light output and so is more accurate for all purposes. Units like this are used by EK, Fuji and Ilford to test films and papers. Our lab had several EG&G units.

PE

 

[ic-racer]

I calibrate mine with name-brand film (of course this is a 'quick and dirty' calibration). But think about it, film is cheap and available and has extremely hight quality control for it's light sensitivity. And, with respect to speed, all I really want to know anyway "is this new film/developer combo faster or slower than Tri-X in D76 processed to a .7 gamma"

Also, I don't post my H&D curves with the calibrated axes.

 

[ic-racer]

With the 10-3 compensator, the exposure for 10-2 was 20.3mcs. I then used ND filters to adjust for the different film speeds. I used .6 NDs. They brought the exposures down to 4.78mcs for 100 speed films, 1.18mcs for 400 speed films, and 0.28mcs for TMZ and Delta 3200.

I have also done that mis-matching of the compensators to help fit the film range to the wedge with the limited ND filters I have.

I really like the concept of those compensators. They will be almost as stable throughout time (unless the plexiglass yellows or something) as a carbon filter, at an order of magnitude less in production cost.

 

[ic-racer]

Here is the Wejex sensitometer I wrote about earlier in the thread. I did not have a digi camera when I had it apart, so no pictures to post. But it is night-and-day different inside compared to the EG&G:

 

[Stephen Benskin]

I really like the concept of those compensators. They will be almost as stable throughout time (unless the plexiglass yellows or something) as a carbon filter, at an order of magnitude less in production cost.

The compensators are on film or acetate. The lines are clear but not cut outs. Mine haven't yellowed yet.

Greg Davis: This is the most accurate method of getting the characteristic curve of your film or paper.

The idea is to make it knowable, repeatable, and produce the smallest number of variables. That way you are confident the results reflect what you are testing for. Contacting eliminates flare. Optical conditions can be integrated into the interpretation of the data later. The color temperature of the light source represents daylight balance, and the repeatable exposures guarantees that any difference you see in density between samples is the result of the processing or film and not the exposure. If you are using film samples from the same batch, then you know you are testing mostly for the processing. A calibrated step tablet guarantees knowable densities. Most commercial densitometers are accurate to +-0.01 or +-0.02. The possible degree of error with combining the variance in the confirmation of the densities of the step tablet and the variance in the reading of the resulting film densities can be fairly large. A calibrated step tablet eliminates one of the variances. If I know the amount of light falling on the step tablet and the density of the different steps, I am able to know the about of light striking the film at each of the steps. This allows for actual log-H values instead of relative log-H and speed is calculated using actual log-H.

Interestingly, the EG&G sensitometer isn't acceptable for use in ISO testing. The standard requires a "non-intermittent illuminance-scale type". EG&G uses a flash unit. It appears that one person's accurate is another's not-so-much.

Steve

 

[ic-racer]

The compensators are on film or acetate. The lines are clear but not cut outs. Mine haven't yellowed yet.

Ok, I see. Mine did not come with any, so I made them based on the [poor] pictures in the manual. Mine did come with one clear plexiglass plate with a black painted border, so I figured the others would also have been clear plexiglass with black paint.

I'll have to post some pictures of my home-made filters. I used trial and error to scrape lines in the paint until I had a similar 'speed' from the film at each of the 3 settings. I know that is not the way they were supposed to be calibrated. The original filters were calibrated to intensity, and small differneces in film speed were then ascribed to high-speed reciprocity failure.

 

[sanking]

Here is the Wejex sensitometer I wrote about earlier in the thread. I did not have a digi camera when I had it apart, so no pictures to post. But it is night-and-day different inside compared to the EG&G:


In addition to a Mark VII I also have a Wejex. The basic exposure of the Wejex is about 2.5 seconds and you must adjust with ND filters. If I were calibrating film for long time exposures the Wejex would be a better choice than the EG&G.

Stephen, how did you make the mcs readings with your EG&G?

Sandy King

 

[Bill Burk]

This is a good discussion for me because I have to make (or buy) line filters or ND filters for the EG&G that Steve sold me.
Seems to me a good test would be to flash same piece of film twice (work and turn) at the same (10-2) setting - one with and one without the line filter that I'm making. Then the displacement of the curves between "with" and "without" would be the density of the filter. I could scritch away until I hit a reasonable whole log value.

 

[Stephen Benskin]

Stephen, how did you make the mcs readings with your EG&G?

I just find the transmitted light using

Transmittance = transmitted light / incident light

Transmittance is the reciprocal of Opacity and Opacity is the antilog of Density. I find the step tablet density that I want to find the mcs for and calculate the Transmittance of that density and plug it into

transmitted light = Transmittance * incident light

Fortunately, I've incorporated it into my program so I don't have to do the calculations by hand every time.

Or you were wondering how I got the initial values for the different settings. That was done by EG&G. I sent them the NDs too so they could do the tests with them. I figured there would be some light loss from reflection and absorption within and between the filters. I also make sure that the filters are stacked in the same order each time I test to assure consistency.

As a side note, those using sensitometers should also take the hold time for latent image keeping into consideration. All the accuracy and repeatability of the sensitometer would be worthless without a consistent hold time.

Bill,

That idea strikes me as brilliant.

Steve

 

[sanking]

Interestingly, the EG&G sensitometer isn't acceptable for use in ISO testing. The standard requires a "non-intermittent illuminance-scale type". EG&G uses a flash unit. It appears that one person's accurate is another's not-so-much.

Steve

Interesting.

And by extension the EG&G sensitometer would not be useful in film testing where exposures get into the reciprocity failure range.

Sandy King

 

[Stephen Benskin]

Interesting.

And by extension the EG&G sensitometer would not be useful in film testing where exposures get into the reciprocity failure range.

Actually, I think that's the one area it has the advantage over the other types. The Mark VII has two settings that appear to be practical only for short exposure reciprocity testing.

This is only a guess, but I believe the reason why intermittent sensitometers aren't preferred is partly because of short exposure reciprocity failure. I also think it's because of the inconsistency of the light over the period of discharge. You know, build up and fall off from peak intensity and any possible shifts through color temperature as that happens. I remember reading something about having the non-intermittent light source on for a few minutes before testing so that the color temperature and intensity fluctuations equal out. The timing device for the exposure for this type of sensitometer is a rotating pie wedge.

Steve

 

[sanking]

Actually, I think that's the one area it has the advantage over the other types. The Mark VII has two settings that appear to be practical only for short exposure reciprocity testing.


Steve

Not sure I understand. Does the Mark VII have some system for long exposures, say longer than one second?


Sandy

 

[Stephen Benskin]

Not sure I understand. Does the Mark VII have some system for long exposures, say longer than one second?
Sandy

No, I was thinking reciprocity failure on the other end of the scale - ie short. Either way, reciprocity failure doesn't fall within the parameters of the ISO standard. But it must be nice having the ability to test for long exposure reciprocity.

I just looked up Wejex. Sounds like a nice little device. They mention the choice of a blue or green filter. That sounds like it was designed for X-Ray film testing. Do you know the color temperature of the light source?

Steve