Base Fog Testing

[Annie M.]

Is there a standard for testing for base fog in film? Is is done on exposed or unexposed film... 1X 2X 3X the usual development time? What is the developer of choice for Tech Pan these days now that technidol is extinct... I have Agfa Rodinal, HC110, A49, D76 & XTOL on hand.

Thx... A

[Bill Burk]

Hi Annie M.

I don't know if it's a standard, but I would fix, wash and dry a piece of film unexposed, undeveloped, to determine Base.

I read Base + Fog from any unexposed portion of the film after the regular development process. Then subtract Base to discover Fog. Many people use electrical tape or something to cover part of the film on their test exposure to guarantee there will be a spot to read Base + Fog.

You might find fog undetectable at shorter development times, and as you develop longer Fog will increase.

For me, Fog is meaningful in conjunction with the development time that I expect to use. So I note the Base + Fog at the different development times I test, and am happiest with things when it is low at Normal development time.

[Nathan Potter]

I also do as Bill above suggests. Obtain a value for just the film base by fixing and clearing. Then I use a Stouffer calibrated step tablet over the film during exposure with a stick on opaque tab somewhere on the emulsion during a measured exposure. Pick a developer of choice (often to minimize fog on old film) and develop according to your standard procedure. Finally compare the unexposed tab area fog to the low density steps on the Stouffer to estimate the fog level. Just subtract the previous base density value from the unexposed tab.

A good densitometer of course would serve you well for such an exercise.

Nate Potter, Austin TX.

[Mark Woods]

I'm sorry to respectfully disagree with the above gentlemen. One needs to develop an unexposed film for the normal time, stop it (or water stop -- whatever your procedure is), fix it, wash it, dry it. It's important to do all of the steps on the unexposed film to duplicate the base plus chemical fog residual left from the processing.

[Leigh]

One needs to develop an unexposed film...
Sorry.

Using unexposed film will yield erroneous results because the activity of the developer is not normal.

Develop a properly-exposed scene using normal processing times and methods, then read the edge.
There's plenty of room since the densitometer aperture is quite small.

The activity and exhaustion of the developer with normal scenes and normal processing conditions is
one critical aspect of film testing that many people overlook. Then they can't figure out their results. :eek:

- Leigh

[Sal Santamaura]

...Using unexposed film will yield erroneous results because the activity of the developer is not normal...Manufacturers' minimum developer quantity specifications per film area are calculated so that there's sufficient active ingredient to process images of any scene, from pure white to pure black (i.e. unexposed film). Unfortunately, many people overlook, ignore or disparage developer manufacturers' specifications, variously commenting about alleged motivations to sell more developer, claiming to know better and often stating that "it works fine." :)


...Develop a properly-exposed scene using normal processing times and methods, then read the edge...This is perilous because flare can result in additional density above fb+f. With roll film, at least one blank frame is advisable. If unwilling to just develop an unexposed sheet, pull the slide no more than halfway.


...The activity and exhaustion of the developer with normal scenes and normal processing conditions is
one critical aspect of film testing that many people overlook. Then they can't figure out their results...Yes. And those people are the ones who ignore manufacturers' minimum quantity specifications, resulting in developer exhaustion. :) Those who follow the specifications have no need to be concerned about exhaustion.

The time to develop a fb+f test is however long one will typically be developing negatives. If "pushing," "pulling," "expanding" or "contracting" for specific shooting conditions, test for "zone zero" density at those times as well as your "normal" time. You'll need the information for all combinations to establish proper exposures.

[Leigh]

Wow, Sal,

Talk about an explosion in an assumption factory!
How many invalid and erroneous assumptions can you fit in one post?

Where did I mention "ignoring manufacturer's recommendations" or "pushing and pulling"?

Developers are chemicals. You use the proper amount at the proper temperature and for the proper time. Period.

Manufacturers' recommendations are based on normal processing of average scenes.
If you deviate from that you will get varying results, just like if you vary the temperature or time.

Chemistry 101.

- Leigh

[mandoman7]

Its the curve above the fb+f that matters, and the base fog test serves to establish a base measurement from which to draw the curve. Eliminating development is actually introducing an unnecessary variable rather than the other way around. Its pretty easy to see, in practice, where the clear portions of the negative are and where flaring might be a problem. Not a thing to stress about. :)

[Leigh]

Eliminating development...
I don't understand this statement.

How can you "eliminate" development? That's what produces the image and the fog.

- Leigh

[Sal Santamaura]

...Where did I mention "ignoring manufacturer's recommendations"...
You didn't. I didn't say you did. I simply explained that, if one uses a developer manufacturer's specified minimum quantity per film area, exhaustion won't occur and "erroneous results because the activity of the developer is not normal" won't be an issue.


...Where did I mention..."pushing and pulling"?...You didn't. The OP asked whether "testing for base fog is done...[at] 1X 2X 3X the usual development time?" I answered her question.


...Manufacturers' recommendations are based on normal processing of average scenes...No, they're not. Developer manufacturers' minimum quantity specifications are based on providing sufficient active ingredients to avoid exhaustion regardless of scene content.

Many people like to use less than the specified minimum because, with "average" (whatever that is for a particular photographer) scene content, they can usually get by without exhausting the developer. As I've posted here and elsewhere, many times before, if one is a gambler, that's a valid approach. I'm risk averse, so use the specified minimum quantity of concentrate (or stock solution) at all times. The choice is everyone's to make: confidence or crap shoot.


...Chemistry 101...In order to apply basic chemistry to this question, one must first avoid erroneous assumptions. Like "manufacturers' recommendations are based on normal processing of average scenes." :)

[Sal Santamaura]

...I would fix, wash and dry a piece of film unexposed, undeveloped, to determine Base...


...Eliminating development...


I don't understand this statement.

How can you "eliminate" development?...One "eliminates development" by, as Bill explained, fixing a piece of unexposed, undeveloped film. I don't see the necessity for establishing base density separately from development fog, but understand what he wrote.

[Leigh]

You didn't. I didn't say you did. I simply explained that, if one uses a developer manufacturer's specified minimum quantity per film area, exhaustion won't occur and "erroneous results because the activity of the developer is not normal" won't be an issue....
You didn't. The OP asked whether "testing for base fog is done...[at] 1X 2X 3X the usual development time?" I answered her question
Then why did you quote my text rather than the OP's?


Developer manufacturers' minimum quantity specifications are based on providing sufficient active ingredients to avoid exhaustion regardless of scene content.
That's absolutely incorrect as regards compensating developers. The compensating effect depends on localized depletion.

It may be invalid for any developer that achieves different effects through the use of different dilutions, since these also rely on depletion.

The statement is probably valid for developers that are used at stock strength, but that's not guaranteed.


Many people like to use less than the specified minimum because, with "average" (whatever that is for a particular photographer) scene content, they can usually get by without exhausting the developer. As I've posted here and elsewhere, many times before, if one is a gambler, that's a valid approach. I'm risk averse, so use the specified minimum quantity of concentrate (or stock solution) at all times. The choice is everyone's to make: confidence or crap shoot.
I fail to understand why you raise this absolutely irrelevant point, except to bolster your otherwise unsupportable hypothesis.

I never suggested using anything other than the procedure defined by the manufacturer, and in fact specifically supported that method.
Nobody in this thread, other than you, has suggested any deviation from that protocol.

- Leigh

[Leigh]

Its the curve above the fb+f that matters, and the base fog test serves to establish a base measurement from which to draw the curve.
Yep. In fact b+f is just a neutral density filter, identical in every respect* to changing the intensity of the enlarger bulb.

- Leigh

* disregarding color temperature

[Sal Santamaura]

… Using unexposed film will yield erroneous results because the activity of the developer is not normal...


Manufacturers' minimum developer quantity specifications per film area are calculated so that there's sufficient active ingredient to process images of any scene, from pure white to pure black (i.e. unexposed film). Unfortunately, many people overlook, ignore or disparage developer manufacturers' specifications, variously commenting about alleged motivations to sell more developer, claiming to know better and often stating that "it works fine." :) ...


...Where did I mention "ignoring manufacturer's recommendations" or "pushing and pulling"?...


You didn't. I didn't say you did. I simply explained that, if one uses a developer manufacturer's specified minimum quantity per film area, exhaustion won't occur and "erroneous results because the activity of the developer is not normal" won't be an issue...


Then why did you quote my text rather than the OP's?..If you look closely, I quoted you in places (including the two quotes after that one) where information responding to your post was appropriate. Please also note that my answer about fog vs. development time is at the end of the post, separated from responses to your posts by a paragraph break.


...Developer manufacturers' minimum quantity specifications are based on providing sufficient active ingredients to avoid exhaustion regardless of scene content...


...That's absolutely incorrect as regards compensating developers...Compensating development is a technique. If one wishes to dilute any developer sufficiently so it falls short of the minimum necessary active ingredients for full development and also modifies one's agitation regime, compensation can be made to happen.

The OP asked nothing about compensating development. I provided no information concerning compensating development. The developers in her list have manufacturers' specified minimum quantities unrelated to compensation.


...It may be invalid for any developer that achieves different effects through the use of different dilutions, since these also rely on depletion...Manufacturers' specified minimum developer quantities are unrelated to dilution. The minimum is the minimum for avoiding exhaustion regardless of dilution. The minimum concentrate or stock solution required must be maintained at all dilutions. Effects of varying dilution, such as changes in granularity, curve shape, etc., have no relation to depletion.


...The statement is probably valid for developers that are used at stock strength, but that's not guaranteed...It is without question valid for developers listed in the OP's question. As stated by the manufacturers.


...I fail to understand why you raise this absolutely irrelevant point, except to bolster your otherwise unsupportable hypothesis...I've posted no "hypothesis," just facts from developer manufacturers. Those facts are completely relevant to the OP's questions.


...I never suggested using anything other than the procedure defined by the manufacturer, and in fact specifically supported that method...What procedure are you referring to? In post #5, you incorrectly stated that "...Using unexposed film will yield erroneous results because the activity of the developer is not normal..." I responded to correct that error for the OP and anyone else in the community following this thread, now or later when reading it in the archive.

What's the problem, Leigh? I don't know everything, so defer to manufacturers who document their products. Why can't you?

[Leigh]

I don't know everything, so defer to manufacturers who document their products. Why can't you?
I always recommend following the manufacturer's instructions, and have never suggested anything to the contrary.

This whole discussion started when I told previous poster to avoid developing unexposed film because the results can be unpredictable,
and may be different than when processing normally-exposed film.
Do you have a problem with that? If so, what?

- Leigh

[Sal Santamaura]

I always recommend following the manufacturer's instructions, and have never suggested anything to the contrary.

This whole discussion started when I told previous poster to avoid developing unexposed film because the results can be unpredictable,
and may be different than when processing normally-exposed film.
Do you have a problem with that?...I don't "have a problem with that." It's simply incorrect. If one uses the developer manufacturer's minimum concentrate / stock solution quantity, developing unexposed film will be neither unpredictable nor different than when processing normally-exposed film. Nothing more, nothing less.

I've posted that repeatedly in this thread. It's fact-based. Asking about it again won't change the answer or the facts. :)

[Leigh]

Thats right, Sal. Your opinions to the contrary won't alter the facts.

- Leigh

[Sal Santamaura]

Thats right, Sal. Your opinions to the contrary won't alter the facts...What that I posted here are "opinions" and what "facts" are you claiming they alter?

[Andrew O'Neill]

Annie,

Will you be using a densitometre? Step wedgies? Are you making curves? If you are running development tests with a step wedge, just read a clear area for the B+F. B+F will increase with increased development. Always read film that has been developed.
As far as Tech Pan goes, you could try mixing up some LC-1B. I used it years ago with Tech Pan and it worked well. The working strength is 1:5 to 1:12 depending on the contrast the you like.


water 750ml 52C
metol 4 gr
sodium sulfite 120 gr
hydroquinone 4 gr
sodium bisulfite 30 gr
water to make 1 liter

[Bill Burk]

I'm interested in eliminating development to find "Base" which I could find by looking up the manufacturer's specifications. If it's higher than 0.04 or 0.05, I like to know that it came from the film base on purpose. For example 35mm films sometimes have a high base density for anti-halation purposes.

Then I'm not flabbergasted by scary Base + Fog readings.

I run into high Fog with old expired high-speed film. Here the fog is worse than a neutral density filter. It's grain and lost speed.

I also see Fog go up with longer development times (N+2), which I consider part of the deal when developing to get higher contrast.

I recently saw unexpectedly high fog when I mistakenly developed in Dektol. At first I blamed the Infrared scope's green light from the eyepiece. But since it turned out to be Dektol now I am not worried about the eyepiece any longer. But unexpectedly high Base + Fog was a sign that something was wrong.

I rarely see much Fog in low speed film, fresh or expired.

I get what Leigh is suggesting. Sensitometry tests which only expose a small portion of film might give misleading test results because the film has access to more active developer chemistry than a batch of normally exposed film would have. My tests are probably valid in this respect because I develop tests with real shots. I throw one sensitometry test sheet in with five pictorial camera shots, and I use 12 ounces of stock D-76 plus 12 ounces water.

[Sal Santamaura]

...I get what Leigh is suggesting. Sensitometry tests which only expose a small portion of film might give misleading test results because the film has access to more active developer chemistry than a batch of normally exposed film would have...Why would an excess of active developer chemistry give different results than the manufacturer's specified minimum stock solution / concentrate quantity (assuming a normal agitation routine)? Wouldn't one simply end up with unused active developer at the cycle's end?


...My tests are probably valid in this respect because I develop tests with real shots. I throw one sensitometry test sheet in with five pictorial camera shots, and I use 12 ounces of stock D-76 plus 12 ounces water.Assuming you're referring to 4x5 sheets, that 12 ounces of D-76 stock -- 355 ml -- is slightly less than Kodak's specified 375 ml (250 ml per 80 square inches times 1.5, since you've got 120 square inches of film). Assuming normal agitation and some scene density in the pictorial images, your tests are probably valid. To ensure absolute validity, throw in another ounce of D-76 stock and another ounce of water. :)

[Leigh]

Why would an excess of active developer chemistry give different results than the manufacturer's specified minimum stock solution / concentrate quantity (assuming a normal agitation routine)? Wouldn't one simply end up with unused active developer at the cycle's end?
I have a feeling you're just trolling, because you can't possibly be that dense (Dmax = 10+).

GET OFF THIS DILUTION NONSENSE.
You're the only one talking about violating the manufacturer's recommended dilutions, and you're doing it as a crutch for your specious arguments.

If you develop a blank negative you can up with a higher overall concentration of active developer over the development time than you would
if some of that chemistry was being used up, which could result in higher fog.

Any time you're testing the results of a chemical reaction you want to duplicate 'normal' conditions to the greatest extent possible
to ensure accurate results. This is a basic law of chemistry.

----

Bill's test protocol sounds reasonable. I don't use D-76 so I'm not familiar with its characteristics.

- Leigh

[Sal Santamaura]

Why would an excess of active developer chemistry give different results than the manufacturer's specified minimum stock solution / concentrate quantity (assuming a normal agitation routine)? Wouldn't one simply end up with unused active developer at the cycle's end?...


I have a feeling you're just trolling, because you can't possibly be that dense (Dmax = 10+)...I've been a member of this forum for almost 13 years, limiting my photography-related posts to those where I can make a positive contribution. I do not troll here or elsewhere. A long engineering career has resulted in good comprehension of technical issues. Ad hominem attacks debase only the attacker.


...GET OFF THIS DILUTION NONSENSE...You're the only one talking about violating the manufacturer's recommended dilutions, and you're doing it as a crutch for your specious arguments...I've made no posts about "violating the manufacturer's recommended dilutions." My inputs in this thread concern using less than manufacturers' specified quantities of developer concentrate / stock solution. I've made no "arguments," specious or otherwise. My posts have simply pointed out facts.


...If you develop a blank negative you can up with a higher overall concentration of active developer over the development time than you would if some of that chemistry was being used up, which could result in higher fog...Having more active developer (at the same concentration) than is needed to completely develop an unexposed sheet results in no higher fog than developing a negative with some exposure, given normal agitation. It does leave unused developer when the development cycle is complete.

[Annie M.]

More than you ever wanted to know about fog here... interesting that in some circumstances fog does not effect the image in a uniform blanket.

http://archive.org/details/TheTheoryOfThePhotographicProcess

Thank you for your lively responses.

Sal thanks for addressing the 1X 2X 3X... I thought there might be a possibility that pushing might be part of the parameters of determining acceptable fog levels.

I have done some primitive testing and it seems to me that TechPan fog can very dependent on the developer used.... almost clear base to the eye with HC110 Dil F & almost 1/2 stop with Rodinal 1:100... Without a densitometer I cannot be sure but the fog is not anywhere near eating the shadow detail while I still get bright whites & that is what is important to me.

[Mark Woods]

The shadow detail is on top of Dmin (B+F) in a "correctly" exposed negative. A more dense Dmin generally affects the tonal range -- particularly on expired film. BTW, I feel Sal is the more informed contributor.

[Sal Santamaura]

..Sal thanks for addressing the 1X 2X 3X...You're very welcome.


...Without a densitometer I cannot be sure but the fog is not anywhere near eating the shadow detail...Human vision is poor at determining absolute brightness levels but great when comparing adjacent brightnesses. You can perform a pretty good subjective evaluation as follows.

Expose half a sheet/frame at Zone I, i.e. four stops below what a gray card or incident reading indicates, with reference to your working exposure index. Leave the other half blank. Develop normally (be sure to use sufficient developer concentrate / stock solution :) ). Look at the resulting negative while it's evenly illuminated. If you don't have a light box, a large, smooth lamp shade can sometimes work. Failing that, completely overcast sky or a piece of white card illuminated by direct sunlight will do. If there is a noticeable difference in density between the unexposed and Zone I portions of the negative, your exposure index is low enough to avoid losing shadow detail to base+fog. You could repeat this trial with successively higher exposure indices until Zone I disappears into the fog, thereby finding the highest usable speed for that film.

Once you've established an exposure index, shoot some scenes that contain the brightest whites of interest. Evaluating/printing those will reveal whether the exposure index base+fog has forced you to use pushed the whites up to a point where the film shoulders and muddies them. A densitometer and sensitometric testing using it are efficient, but they're not necessary to obtain the working knowledge you're after.

[Annie M.]

Sal...Exactly what I needed to know... Thanks!

[Bill Burk]

Why would an excess of active developer chemistry give different results than the manufacturer's specified minimum stock solution / concentrate quantity (assuming a normal agitation routine)? Wouldn't one simply end up with unused active developer at the cycle's end?

I would guess the error or discrepancy caused by developing batches of mostly blank film would be only a few percent...

You're right there would be plenty of fresh chemistry. Especially if recommended capacity is followed.

Fewer reaction byproducts, perhaps?

Leigh's suggestion makes sense that it's important to make tests as "realistic" as possible.

I can give one example where my tests might depart from reality a bit. When making a curve family, I start with 6 sheets and pull a sheet out after 4 minutes, pull another sheet out after 5 minutes, etc. As the test progresses agitation changes. The 4 and 5 minutes tests are pretty close. But the 12 minutes and 15 minutes tests are likely inaccurate. Now I follow-up by running a 15 minute test amongst a batch of N+2 film, and I mark the new Time/CI point on my running Time/CI chart. Solves my problem in a practical way.


Assuming you're referring to 4x5 sheets, that 12 ounces of D-76 stock -- 355 ml -- is slightly less than Kodak's specified 375 ml (250 ml per 80 square inches times 1.5, since you've got 120 square inches of film). Assuming normal agitation and some scene density in the pictorial images, your tests are probably valid. To ensure absolute validity, throw in another ounce of D-76 stock and another ounce of water. :)

I did the math several times. Must be a rounding error. I probably rounded 2.11 to 2.

I was much worse off before. I was using 8 ounces stock to develop 7 sheets. (Because 16 ounces brings the 5x7 tray to a "nice" level... and seven sheets is a Grafmatic load plus a sensitometry strip). So I fixed that.

I imagine other people make similar mistakes. I've read stories about people breaking their Jobo lifts because they fill the tank with developer (where it wasn't engineered to be loaded "full" of liquid). Then realizing they can't fill the Jobo tank, they use less liquid and this change accidentally gives the film insufficient stock solution per square inch.

p.s. I work for Kodak but the opinions and positions I take are my own and not necessarily those of EKC.

[Sal Santamaura]

I would guess the error or discrepancy caused by developing batches of mostly blank film would be only a few percent...Even if it did exist, a few percent discrepancy would likely fall below measurement error on the log density scale.


...You're right there would be plenty of fresh chemistry. Especially if recommended capacity is followed.

Fewer reaction byproducts, perhaps?...Since you're continuously agitating film in a tray, if the minimum D-76 stock solution quantity per film area specification is met, reaction byproducts shouldn't affect your results. Continuous agitation continuously induces fresh developer into the emulsion, so bromides won't change the fog level of exposed film compared to blank film.

In any case, you seem to have your process under control. That's what counts.