BTZS Testing on negatives developed in Pyrocat-HD

[sanking]

I think you'll find that filter wasn't for the absorption of Ultra Violet (very little of a tungsten source spectrum is UV) .. but for the other end; Infra Red ... there is quite a bit of that ... and its' alter ego - heat.
IR filters are very common in optical system .. they are commonly called "heat glass" or heat filters".

Yes, the IR filter is common in this type of system and in fact I still have one of these filters installed in the Bes 23-C II that I use for film testing. It is in the form of some type of acryllic of about 1/32" thickness. But I also had a UV filter in there at one time, of that I have no doubt, and to the best of my recollection it either came with the enlarger or was recommended by Beseler. I can not say how much UV the tungsten-halogen bulb in my Beseler 23-C radiates, if any, but I have tested other bulbs of this type with UV processes and and they definitely emit some UV radiation.

And BTW, Cool-Blue and Daylight fluorescent tube, which most people don't expect would provide mucy UV radiation, are almost as effecive in exposing dichromate colloid processes as real "UV" type tubes, i.e. BL, BLB and SA.

However, let me make this perfectly clear. I am not claiming that the tungsten lamp in my Best 23C II system is radiating enough UV radiation to affect exposure of panchromatic film. I simply put it out as an idea that deserves some consideration and I intend to test it myself as soon as I have the materials required to do so.



Sandy

 

[gainer]

Yes. Kirk, I studied these characteristics of human vision while working in simulation and human factors at NASA Langley Research Center. My question was not about the human resonse curve, but about the response curve of the visual filter in certain densitometers. If it is supposed to duplicate the human response curve, then it should not be used in the kind of work we are talking about in this thread. Nowhere in the system do we have the human resonse curve duplicated by any of our sensitized materials.

 

[Kirk Keyes]

Sandy, the BLB (Black Light Bulbs?) tubes you mention - I understand there are at least two types of these tubes. One has a main emission at around 370, and the other aroud 350. Is this correct, and which type do you use?

Kirk

 

[Ed Sukach]

Yes, the IR filter is common in this type of system and in fact I still have one of these filters installed in the Bes 23-C II that I use for film testing. It is in the form of some type of acryllic of about 1/32" thickness.

I don't mean this to be a win/ lose argument. It is entirely possible for an enlarger manufacturer to do any number of things with the construction of their equipment. Somewhere in this PC, there is a bookmark of a lamp manufacturer's site (Osram??) complete with spectrograhic charts of the output of their lamps. It is true that there is *some* UV emanation from Tungsten and Halogen lamps - but not much. The higher the color temperature of the lamp - the more UV .... That is why most "studio" flash systems - balanced to daylight ~ 5000 - 6000K have "UV" coating... to eliminate fluorescence from fabric "brighteners" and such.

I DON'T know about Beseler. I DO know that my Omega 5500 does NOT have UV filtration in the optical system of its Color Head.

It really suprises me that an IR - Heat Glass filter would be made of acrylic. This would be the first plastic heat filter I've ever encountered. The special glass ones I am familiar with (@#$% expensive!! - 50 US$ for the Omega) are very effective - that is, they get HOT!!! Are you sure it was an acrylic filter? If I remember - one of the ways to identify plastics was to burn them ... Nitrocellulose burns very well, a clear, yellow flame... I can't remember what acrylic does, but I think it was either a flame or smoldering and bubbling.

 

[sanking]

Sandy, the BLB (Black Light Bulbs?) tubes you mention - I understand there are at least two types of these tubes. One has a main emission at around 370, and the other around 350. Is this correct, and which type do you use?

Kirk

Kirk,

The BL and BLB tubes are essentially the same tube, the only difference being that the BLB has a filter that cuts off all light above about 420 nm. Since many alternative processes have some sensitivity to light above 420 nm the BL tubes print slightly faster than BLB. BTW, the correct name for these tubes is Black Light and Black Light Blue.

I have an article on UV light sources for alternative printing at http://unblinkingeye.com/Articles/Light/light.html. There are SPD charts for many of the light sources people are using for printing alternative processes.

You might be interested to note that the SA and AQUA tubes, which peak at around 420 nm, are also very effective for exposing Pt./Pd. processes. Some people actually find that they print faster than BL and BLB tubes, though that was not true with the tubes I tested. Some of the extra speed from the SA and AQUA tubes is likely due to the fact that glass passes a much higher percentage of radiation at 420 nm than at 350 nm.

The issues involved with exposing alternative processes are very complicated as you have to balance issues such as UV transmission of glass, the SPD of the light source, and the specific requirements of the process. The good thing is that if you just forgot all this you can make good prints with a rather wide range of light sources, some which in theory would not appear to be good candidates.

Sandy

 

[sanking]

It really suprises me that an IR - Heat Glass filter would be made of acrylic. This would be the first plastic heat filter I've ever encountered. The special glass ones I am familiar with (@#$% expensive!! - 50 US$ for the Omega) are very effective - that is, they get HOT!!! Are you sure it was an acrylic filter?

The filter is some kind of plastic, and it looks to be acrylic. But you may be right in that it is not an IR filter. I could have just assumed that it was when its only purpose might be to just support the filters that go into that slot.

Sandy

 

[Kirk Keyes]

Sany wrote, "I have an article on UV light sources for alternative printing at http://unblinkingeye.com/Articles/Light/light.html. There are SPD charts for many of the light sources people are using for printing alternative processes."

Sandy - thanks for the tip on the article. I guess that makes you the expert on that subject! :^)

So are you using the Sylvania BLB bulbs for which you have the spectra in the article?

 

[Kirk Keyes]

Patrick wrote, "Yes. Kirk, I studied these characteristics of human vision while working in simulation and human factors at NASA Langley Research Center."

Cool! Wish I was there back then with you.

"My question was not about the human resonse curve, but about the response curve of the visual filter in certain densitometers. If it is supposed to duplicate the human response curve, then it should not be used in the kind of work we are talking about in this thread. Nowhere in the system do we have the human resonse curve duplicated by any of our sensitized materials."

Patrick, that's true. The response has certainly not been "duplicated". But what is really more important is that some of these things that we are discussing have been standardized. Like the Status A and M filters used in color densitometry. We need to recognize that.

And where things may not have been standardized, like UV filtration of a densitometer, then finding out peak transmission and bandpass widths are needed too. Determining these things may help with this question, and being explicit about them, like Sandy was when describing his densitometer, will help too.

I'm sure you can visualize exactly what the properties of a 373 nm with a 45 nm width looks like.

 

[Kirk Keyes]

Sandy Wrote, "Yes, the IR filter is common in this type of system and in fact I still have one of these filters installed in the Bes 23-C II that I use for film testing. It is in the form of some type of acryllic of about 1/32" thickness."

Sandy, Ed is right. Acrylic resin is not going to to be a very good IR filter. Remember that IR will heat things up and that will warp or melt the plastic.
There are special types of glass designed for this purpose.

Acrylic will not even be a good UV filter. Actually, most organic materials that are colorless are probably going to transmit UV on down to about 200 - 300 at the highest. Not effective as a UV filter.

"I can not say how much UV the tungsten-halogen bulb in my Beseler 23-C radiates, if any, but I have tested other bulbs of this type with UV processes and and they definitely emit some UV radiation."

Yes, they do radiate some UV light. But when compared to the amount of visible light they are emitting, it is practically insignificant. I have a spectrophotometer that uses a tungsten bulb and it can read down to 320 nm. But in the design of the instrument, no glass has been allowed in the pathway for the light. Only front surface mirrors and quartz glass have been used to avoid filtering any of the UV.

I have no doubts that you could make an exposure on a material like Pt/Pd paper with a tungsten light source.

"I am not claiming that the tungsten lamp in my Best 23C II system is radiating enough UV radiation to affect exposure of panchromatic film. I simply put it out as an idea that deserves some consideration and I intend to test it myself as soon as I have the materials required to do so."

This could be demonstrated by combining a Wratten 18A filter with your tungsten light. The 18A passes UV from about 320 to 400 nm, centered around 360 nm and filters out visible wavelengths up to about 700 nm where it starts to pass IR. This alone would be ideal for testing your Pt/Pd paper as it will not respond to the IR. You could try it with some panchromatic film, as long as it was not sensitve past 650-680 nm. I have no doubt that you will loose a lot of film speed when compared to the tungsten light alone, daylight corrected or not. Please let us know what you find.

But practically, he UV component of a tungsten bulb is not sigificant when exposing a step wedge for use with panchromatic film.

Kirk

 

[Kirk Keyes]

Sandy - Side Note -
I've been looking at your UV light source article you recommended http://unblinkingeye.com/Articles/Light/L2/l2.html , and I have a question - you say, "Speed was determined by the first step wedge that provided maximum density"

Why did you pick that? Doesn't film testing convention say that you should have used the first step that showed any density? That's how regular film speeds are determined. And paper speed points are a middle grey. Why did you use maximum black?

Sorry for the side trip, but I'm curious.

 

[sanking]

Sandy - Side Note -
I've been looking at your UV light source article you recommended http://unblinkingeye.com/Articles/Light/L2/l2.html , and I have a question - you say, "Speed was determined by the first step wedge that provided maximum density"

Why did you pick that? Doesn't film testing convention say that you should have used the first step that showed any density? That's how regular film speeds are determined. And paper speed points are a middle grey. Why did you use maximum black?

Sorry for the side trip, but I'm curious.

Kirk,

In the sentence that you cite I was talking about the speed point of a print, not negative film speed. There is an ANSO method for determining the speed point for silver papers, and it is the exposure necessary to produce a print density of 0.6 over B+F.

Alternative printers use different speed points for their prints. Dick Arentz, for examples, calculates speed point at 90% of Dmax, taking into account the long sweeping toe of the Pt./Pd. process. I think that is a very reasonable choice for Pt./Pd. and also for the closely related kallitype process (not VDB but kallitype based on ferric oxalate). On the other hand with a process like carbon that has an almost absolutely straight line it makes more sense to me to establish the speed point at between 95% to 100% of Dmax.

However, to be precise about film speeds, they are not determined by using the first step that shows any density. There is also an ANSI standard for making this determination and it is based on the exposure value needed to produce a log density of 0.1 over B+F when development is such that an SBR of 1.3 will give a negative DR of 0.8. I pretty much quote from Davis above but other sources use very similar language.

Sandy

 

[Kirk Keyes]

Sandy writes, "Alternative printers use different speed points for their prints. Dick Arentz, for examples, calculates speed point at 90% of Dmax, taking into account the long sweeping toe of the Pt./Pd. process. I think that is a very reasonable choice for Pt./Pd. and also for the closely related kallitype process (not VDB but kallitype based on ferric oxalate). On the other hand with a process like carbon that has an almost absolutely straight line it makes more sense to me to establish the speed point at between 95% to 100% of Dmax."

Thanks - that what I was wondering about.

"However, to be precise about film speeds, they are not determined by using the first step that shows any density."

Yeah, I know. From the tables in the article it kind of looks like you were just visually comparing step densities. I don't think we would have made it this far into this thread if I was not familiar with this.

Thanks for the answer above.

 

[Kirk Keyes]

Another quick correction -

On page 8 I said:
"The Xrite 810 is designed to do Status M transmission RGB filters. These are designed for use with internegatives that will be printed on color neg paper. This is not the right kind of densitometer for measuring the materials under discussion here. Ideally, you should find a densitometer that uses Status A filters, e.g. the Xrite 811, 820 or 310."

This is not correct - densitometers with Status M filters are fine for this type of testing. Status A filters are recommended for measuring materials designed for direct viewing or projection, such as transparencies. Status M filters are recommended for measuring densities in film that are intended for printing, such as color negative and internegative films, as well as reversal films when used as originals for printing. The use of Status M filters in our situation is completely appropriate here.

 

[gainer]

Kirk,

Surely, if I know whether it is flat across that band, or if these are widths where the response is down 3 db or 6 db or whatever. I'm nitpicking, of course, but I'm also curious.

It was fun part of the time. I graduated from WVU with a BS in aeronautical engineering and went to work for NACA in 1952. Did analysis of maneuver loads flight test data, analysis of wind tunnel data, fatigue tests of B-47, and without moving from my desk became employed by NASA. I designed star charts for the Mercury astronauts to use as backup reentry guidance, worked on aerial combat simulations, measurement of eye movements for the purpose of improving instrument panel layout, worked on mathematical models of human operators. My last position description referred to me as " an internationally known expert in non-linear mathematical models of the human operator." Somewhere along the line, I took a couple of graduate level courses in Psychology at William and Mary. Now I'm resting.

 

[Kirk Keyes]

Patrick wrote: "I'm nitpicking, of course, but I'm also curious."

I'm curious too, as I hope you can tell. I was looking through my 1980 vintage Kodak Wratten Filter handbook today, and I noticed that they had no mention of the Status A and M filters. I had hoped that they were possibly part of that series. If you know of someplace to find absorption spectra for these, I'd love to see them.

You home-made your densitometer right? I can't remember if you said what sensor - Si photodiode? What did you do as far as filtration on it?

"It was fun part of the time..."

As I said, cool!

 

[gainer]

I had a long reply set to send and got disconnected from my server. I'm going to write it in notepad as I should have done in the first place.

It was fun while we were doing our own work on a tight budget. When it became mostly monitoring contracts, it was no fun.

 

[Kirk Keyes]

I hate when that happens!

Hey, isn't it the middle of the night where you are? I'm going to bed now here on the west coast so I'll see your reply in the morning.

Later, Kirk

 

[gainer]

Here it is, whenever you are.

I am using a silicon phototransistor in current mode. The sensitive

area is no bigger than a pinhead. It has sensitivity from UV to IR, but

the response is not flat, being higher in the red.

The meter uses the exponential relationship between current through a

semiconductor diode and the voltage drop across it. I use two op amps,

each with a diode as feedback. In this mode, the current into the

summing junction of one op amp comes from the photosensor and that into

the other op amp comes from a variable resistor. The output of the

first op amp is proportional to the log of the photocurrent. The

resistor is used to set level. The outputs of the two op amps are

summed in a simple resistor network into a potentiometer, the arm of

which goes to a digital panel meter. This pot sets the constant of

proportionality between the log of the photocurrent and the meter

reading. The two pots act independently of one another in that I can

set the level without affecting the scale, or the scale without

affecting the level.

This arrangement allows me to set the scale to read zones for any grade

of paper and the level to make the zone readings come true, at least

for two points on the paper's scale. There is one scale setting that

will read density. So far it has been of great use for comparative

tests and in printing. The use of two log channels provides at least a

first order compensation of temperature effects. The residual is taken

care of by the fact that I don't want to be in my darkroom when it is

too hot or too cold.

The probe is a simple affair on about two feet of twin lead. In

measuring projected density there can be a problem with flare in the

projection lens. I put a mask in the negative carrier just large enough

to pass one step of the step wedge, and slide the wedge into the slit

to make each reading. I block off extraneous light from other sources.

When I use it for printing, The same flare that the photosensor may see

will also br seen by the printing paper. In this sense, it has an

advantage over densitometers that are outboard of the enlarger on

negatives that are to be enlarged. My meter could be adapted to work

over a light table to measure for negatives to be contact printed, and

it could be equipped with an attachment to read reflection density.

Excuse the length, but I thought some of you might be interested in the

thing.

I do not currently have any set of filters for special purposes. If I

had my druthers, I would have a fixed, flat, wide band response with a

set of filters to modify the response as needed. If anyone knows of a

phototransistor with very low dark current that fits the basic

requirement, I would like to know about it.

It is interesting to note that when I worked for NASA, much of our

simulation was done with a large analog computer.You could fit maybe 6

of the op amps into an average bathtub. Of course, they operated with

voltage swing of + or - 100 volts, but they required constant

attention. The rectifiers and amplifying elements in these things were

vacuum tubes,and if the air conditioner ever failed, we couldn't use

the thing. It took about 9000 watts to run it. There were 100

amplifiers, some of which were dedicated integrators. They were

programed by wiring plug boards to connect various amplifiers,

integrators, resistors, capacitors, pots, and gadgets dreamed up by

Gadget Gainer. The other guys said they could always tell which board

was mine because it had something hanging on it that didn't come with

the computer.

Enough for now.

 

[gainer]

And I do not know how it came to be double-spaced. It was not so in Notepad. Maybe I shouldn't do these things at 3 AM.

 

[Kirk Keyes]

Patrick wrote, "I do not currently have any set of filters for special purposes. If I had my druthers, I would have a fixed, flat, wide band response with a set of filters to modify the response as needed. If anyone knows of a phototransistor with very low dark current that fits the basic requirement, I would like to know about it."

Good luck finding that! Let me know too if you do.

You did not mention your light source - I'll assume you are using a tungsten lamp of some sort. So a tungsten lamp, combined with your IR-loving photodiode is probably severely biased towards the IR. For making "visual" readings, you could add a temperature correction filter such as a 80A to take some of the excess red from the lamp out, and then perhaps a second 80A combined with a IR cutoff filter to take some of the red/IR response out of the photodiode. This would go a long way towards adjusting your system.

For making measurements of specific colors -R, G, B, or UV you could add a Wratten #92 for Red, a #93 of Green, a #94 for Blue. The 92/93/94 combo is used for densitometric measurements of color films and papers. The precision of these filters according to the guide is +/- 5%. The guide does recommend using a #301A Infrared rejection filter in combination with these filters as they all pass IR.

For more accurate measurements, there are Status A, D (?), and M filters, which according to the guide, "are carefully selected and calibrated to conform to close spectral tolerances. Their use allows more direct comparison of measured densities with other similarly equipped electronic densitometers." They must also be used with the #301A IR cut-off filter.

Kodak does not sell Status filter despite making them - they must be purchased from densitometer manufacturers (at least in 1980...).

Narrow band color filters could also be used - the #25 for red, #61 for green, and the # 47B for blue.

Partrick, for UV you could add the 34A I mentioned to Sandy yesterday IF you could find a way to filter out the blue that it passes. I would suggest looking for a dichroic filter for this though.

I suspect that the filters in Sandy's Gretag are probably not gel filters, but are dichroic filters because of the narrowness of the bandpass. This is actually better than a gel-based filter as the dichroic filters will essentially last for ever, do not fade on exposure to light, and can have much sharper shoulder's than the gels usually do.

Patrick - you mentioned "comparitive" measurements - what do you do for calibration?

 

[Kirk Keyes]

Sandy wrote, "BTW, I called Stouffer to discuss this situation and talked to one of their technicians. He told me that they neither test for nor attempt to control the UV absorption characteristics of their step wedges. He said that there was a UV densitometer on the premise and that they would pull it out and try figure out the reason for the discrepancy."

Hey, that's great - thanks for taking the initiative and calling! I'm, of course, interested in hearing what they find too.

When you get back to them, I hope this discussion has impressed a few thing on you that you will remember - please check with them and find out:
1) What model of densitometer they used?
2) How did they calibrate the densitometer?
3) If they know - what are the peak wavelength and band-pass width of the filters?
4) Did they have any control or check samples to compare readings with?

Knowing these things will help us compare their results with ours.

Kirk

 

[gainer]

For density measurements, I set the meter level to read 0 with nothing in the carrier, then set the scale pot to read the density of a 0.6 neutral density filter. There is nothing I can or should do about intermediate or higher densities, as the response of the meter is inherently logarithmic.

For printing, I print the step wedge on the paper I intend to use. I judge which steps should be, say, zones 2 and 8 and set the meter to read those numbers in the corresponding steps of the wedge. This can be made to work even on stained negatives if a stained copy of the step wedge is used.

 

[Donald Miller]

For density measurements, I set the meter level to read 0 with nothing in the carrier, then set the scale pot to read the density of a 0.6 neutral density filter. There is nothing I can or should do about intermediate or higher densities, as the response of the meter is inherently logarithmic.

For printing, I print the step wedge on the paper I intend to use. I judge which steps should be, say, zones 2 and 8 and set the meter to read those numbers in the corresponding steps of the wedge. This can be made to work even on stained negatives if a stained copy of the step wedge is used.

How would this respond a step wedge that is developed in a proportional staining developer?

 

[Kirk Keyes]

Patrick wrote, "...then set the scale pot to read the density of a 0.6 neutral density filter. There is nothing I can or should do about intermediate or higher densities, as the response of the meter is inherently logarithmic."

Patrick - I would suggest using a high cal point that is a bit higher than 0.6. You're using an ND filter right? Glass or gel? The smaller Wratten filters are allowed to vary density within +/- 5% across the surface of the filter. Also, as you are calibrating at the bottom end of the practical range of densities you will encounter in film testing (0.6 is only two stops of density), you may have some larger errors for readings outside of your calibration range. Remember it only takes a little error in the setting of your high point to extrapolate to a larger error farther out - it tweaks the slope of the response line.

It's best to have calibration points that "bracket" the range of values that you wish to measure. And since your diode has a pretty linear response, you can be reasonably certain that the values in between the cal points fall on your calibration curve. (But it is always best to use a check standard to verify!)

If you like, I can send you a copy of my Stouffer Step tablet. I sure I've got some that will have densities above 2.0, probably more. Of course I can also "calibrate" it by reading the RGB-Vis densities with my densitometer. Let me know if you are interested.

"For printing, I print the step wedge on the paper I intend to use. I judge which steps should be, say, zones 2 and 8 and set the meter to read those numbers in the corresponding steps of the wedge."

So you make adjustments so the your meter reads in "steps" instead of actual optical density?

"This can be made to work even on stained negatives if a stained copy of the step wedge is used."

Well, that indirectly relates to this thread. And I'm sure Sandy would remind you of the complications involved in reading stained negs, especially when the spectrum of the measurments is not controlled.

Sure, you could adjust it to read "effective stops" at two points, but I think the non-linear printing response of stained negs (at least on VC paper) will give you wacky results for the zones in between 2 and 8. Especially if you have no filtration on your densitometer - since it is going to be more red-sensitive than a densitometer than one that has a blue filter on it.

To respond to Donald's question - Because of the lack of filtration and the spectral resonse of the photodiode, I think that any readings made with Patrick's desnitometer on a stained negative would essentially be missing the stain since the red and IR portion of the spectrum are "blinding" the densitometer, so to speak.

Patrick - Thanks for the info.

Kirk

 

[sanking]

This could be demonstrated by combining a Wratten 18A filter with your tungsten light. The 18A passes UV from about 320 to 400 nm, centered around 360 nm and filters out visible wavelengths up to about 700 nm where it starts to pass IR. This alone would be ideal for testing your Pt/Pd paper as it will not respond to the IR. You could try it with some panchromatic film, as long as it was not sensitve past 650-680 nm. I have no doubt that you will loose a lot of film speed when compared to the tungsten light alone, daylight corrected or not. Please let us know what you find.


Kirk

Yes, I had already figured out that the transmission characteristics of the 18A filter would be about perfect for this type of testing.

But are UV filters only made in glass? The prices I have seen for18A filters are fairly intimidating.


Sandy