Film-Pre-exposure/Post-exposure

[Claire Senft]

LORD I HOPE THAT YOU ARE DOING WELL!.

Patrick distressed am I indeed to learn that you have been ill. All kidding aside, APUG has received and been to recipient of a blessed benefit due to your contributions. I am certain that those small town folks in West Virginia realize how blessed they are from your presence.

Tonight I say a prayer of thanks because of your blessing to me.

 

[gainer]

Thank you indeed for your concern. I'm only 81, but I may be suffering a little from early onset Old Timer's disease. I have a lot of things stored in memory that are not as easily accessed as they used to be. Names of persons whose faces I can visualize sometimes escape me, then pop right up at other times. My father told me he once had that problem. An important woman named Mrs. Campbell was introduce to him at a faculty function. In looking for a mnemonic irrelevance to help him remember her name, he observed that she was rather plump which made him think of Campbell's Beans. The next time he met her, he greeted her "Oh, hello Mrs. Van Camp."

 

[Jim Fitzgerald]

Mr Gainer is completely correct except that it was an article written by Ralph Steiner and edited by Mr Vestal. A very fine article it was indeed. This article was the basis for the APUG article to which I referred.

For those of you who are unfamilar with Mr Steiner he was a chemical engineer by education...Dartmouth if my memory serves me correctly. He was a contemporary and friend of Walker Evans. I believe that the relationship between Mr Vestal and Mr Steiner was one of Mr Steiner being, among other things, friend, confidant and mentor to Mr Vestal.

Mr Steiner was a commercial photographer who also worked in cinema and was a very much respected member of the photographic community.

Claire, I just read this article a while back. Mr. Steiner was an amazing guy. I'm going to try this with some Efke 25 in 4x5 as a test to see what I can get. If I can shoot it at 200 and retain it's qualities that would be great. Going to expose 4 sheets. 25,50,100 and 200 then expose three pieces of film to my green safelight for up to an hour? Dark room and some distance from the light to the film if I remember correctly. Any help would be great as you seem to be ahead of the curve on this process. Thanks.

Jim

 

[Claire Senft]

Sorry...I just lost a 1 hours worth of preliminary answering of your question by having unintenionaly and still with out knowing what I did that caused the problem. The answer is gone...POOF...I will start again tomorrow. The short answer is to expect a speed of 50 from your film and when taking shadow readings to use 100 to accomplish that when taking an INCIDENT reading in the proper shadow area. Remember that my previous post made the assumption and was conditional on the readers were familar with BTZS systemology. I am too peeved and too angry to continue now. Will be at it tomorrow I guess. Night night.

 

[richard ide]

Making a pre or post exposure to raise the threshold has nothing to do with reciprocity. You can expose for a long time at a distance from the film but why? A shorter exposure gives exactly the same result. I can pre expose 24 sheets in a couple of minutes. Try the approach I gave in an earlier post and match it with a long exposure. There will be no difference. Guaranteed. Reciprocity only needs to be taken into account when generating an image at very low light levels.

 

[Claire Senft]

How nice Dear Richard. Have you pre-exposed the issuance of the words from my mouth? Is there any benefit in hearing my answer prior to disagreeing with it? Am I of two minds one in California and one in Wisconsin with both minds competing with each other to produce enough milk to become the cheesehead capitol of the world and also complementing each other by producing wine from Napa to drink with the morning paper produced from the cellulose being packed upon trucks in Greenbay? Maybe so. I begin anew.

This answer will be in segments to avoid what happened last night fron continuing.

 

[Claire Senft]

I have never used Efke 25. I doubt that I ever will. I claim not that there is anything wrong with it or that it is defficient. I am only capable of using a smaller variety of films to effect the photographic work I wish to do without being like an ancient thresher who would not choke herself as grain is being beaten and the chaff is thickens the air. I would prefer to maximize the amount of kernels and the usefulness of the straw and from the grain. I do not doubt that Efke 25 is more than satisfactory. All film makers are producing decent films would be my guess and have survived as they competed to produce their products in a worldwide competetion.

Generally latentisfication by low level light can be counted upon to give 1 stop of film speed increase beyond the nominal speed prescribed by the manufacturer....perhaps a bit more. I therefore am going to conclude that 50 is a good film speed to expect from Efke 25. However, it does no good to specify a number without specifying how and underwhat condition and method it will be used.

 

[Claire Senft]

To use Efke 25 at a speed of 50 I am assuming...actually suggesting...the use of THE INCIDENT SYSTEM as developed by Mr Phillip Davis...who is recently deceased. Mr Davis was a humble man that tried spent his life helping the photographic community be promoting a reasonable basis for understanding photography. He believed that this was a good place for the use of basic sensitometry and a worthwhile investment in a basic densitometer. He was a believer in doing some testing as a reasonable way of most economically using time and money to achieve a basis for making a photo with reasonable methods. (I AM NOT TRYING TO REFIGHT THE BATTLE OF DIFFERENT APPROACHS I AM ONLY TRYING TO BE SPECIFIC.) A portion of what he had to say about this is to be found in his Beyond The Zone System methods that he wrote and had published. The acquisition of one of the books is very warmly and strongly encouraged. A portion of what he had to say in the BTZS books dealt with the use of an "INCIDENT METER" to complement the use of narrow angle reflected meters most normally called A "SPOT METER" for the measurement and placements of tones in the final photograph. I do not believe that it makes all that much difference whether thEse photo were anticipated to the gallery wall or the scientific archive. Equally applicable to both would be my statement.

 

[Jim Fitzgerald]

Claire, thanks for taking the time to give me some insight on this process. I read the article that you referred to by Mr. Stiener and it gave me some ideas. I personally like the look of Efke-25 and figured that the only way to find out how this process would work is by testing it. If I get a stop or two or whatever I get then that will be great. Just another tool in the bag.

I mainly shoot large and ultra large format. 8x10,11x14 and 8x20 negs that I develop by inspection in Pyrocat-HD. I shoot at small stops and I am usually always in reciprocity conditions. If my memory serves me from the article you take and hang the negative on a board across the room in complete darkness and use a green light to give the negative more exposure. From 15 minutes to an hour? The longer the better? If my understanding is not correct then please let me know. I'm just trying to learn and cheese and wine are for another time and place as far as I'm concerned. Thanks for the great information in this post so far.


Jim

 

[Claire Senft]

To have a reasonable Idea whether a specific incident meter is of reasonable accuracy in areas such as the continental United States of America for outdoor landscape use on decently lit conditions do as follows:

Use a summer day.
Use noon time
use a day the allows the sun to be seen without being obscured by clouds or anything else
select a spot that does not have a very strong influence of reflections.
Using the middle of a normal suburban backyard that has mostly grass on the ground and allows it to be used having 25 feet of clearance in all directions, except downward, would, I expect, work well.

set the meter to a film speed of 125.
point the dome directly at the sun.
take your reading.

You should get answer that is the equivalent of 125th of a second at f16. If it is quite different then your meter and a repair person should have a thoughtful discussion. In fact go no further in reading what follows until it does.

 

[Claire Senft]

Jim this is intended for anyone who sticks their nose into the thread.

 

[Jim Fitzgerald]

Claire, thank you. I will do that.

Jim

 

[Claire Senft]

To take a meter reading for general testing after having satisfied the above conditions.

Select a scene that allows you to stand in sunlight with shadows in the background... front lighting. Read your body's shadow with the meter dome completely in shadowed from sunlight. Do so in a manner that prevents your body's shadow from being causing the shadowed meter cell to obscured from skylight.

Set your meter to twice the film speed. In this case 100....we are expecting to achieve a speed of 50.

But why use a film speed twice what we expect to achieve. BECAUSE WE ARE COMPENSATING FOR WORKING WITH AN INCIDENT METER READING A SHADOW.

 

[Claire Senft]

Why would this make any damned sense at all?
If one ignores the bright scintillations coming from the sun off of water or polished chrome or a mirrored surface. If one ignores the stingent blackness to be found 2000 feet below the ground at midnight, with no light available. Then one is working with what I would expect and WANT to print other than pure white or pure black.

If one would take the brightest titanium white paint

or the blackest black paint

a paint test samples upon, say, fiber board

I woulds expect a difference from carefully made REFLECTED readings to encompass a range of 4 1/2 to 5 stops with both receiving the same amount of radiant energy from the sun.

That is why the meter has had it anticipated film speed doubled.

 

[Claire Senft]

Take your reading. Set your camera to what the meter is telling you. Expose your film. Latensify it ....EFKE 25... with the film being latentisfied by using the following device.


More to come.

 

[Jim Fitzgerald]

I appreciate the eduction and interest. I'll let you know how I do and look forward to more.

Jim

 

[Claire Senft]

Obtain a 7 watt nightlight...I mean the entire unit socket, switch and bulb...which should cost<$3.00. Obtain an empty cigar box...or a full one and have some smokes until it is empty. At a cigarette/cigar store it should cost you no more than $4.00 and I would expect that they would have one on the premisies that could be sold or given to you. Obtain a green safelight filter. Iinstall the filter in one side of the box allowing the radiant energy from the 7 watt nightlight which is in the box's interior to go thru the filter. This device, which can, be made much more sophisticated by adding bulb dimming capability, but for Efke 25, should do the trick. I am assuming a room that can be put in to and kept in complete darkness is available. If such a condition can not be created during the day then perhaps it can be done after nightfall. My own dark space was obtained by painting the basement window glass black. I realize that many localities or residences will not have a basements. To do my latensifying, I work after dark in a seperate room which is a portion of the basement and which has its own doors. (the basement has a separate door) Latensifying should have no other light or glowing or luminous objects emitting energy while doing this process. Particularly harmful is the afterglow of flouresent bulbs within 1/2 hour of being turned off. Put the latensifying device so that the area emitting light can be placed 9 feet from the Efke 25 and which will give even coverage to the film receiving the treatment. The film emulsion must face the light. Turn the latensifying light on and leave her rip for an hour. DO NOT ALLOW OTHER LIGHT STRIKE THE FILM. That is correct I said NONE AT ALL. What and how you amuse yourself during this hour is your affair but you might be too twitchy and squirmish to sit still for a hour. So plan ahead. At the hour's end place the film unto a reel and put it where it will not be struck by light.

 

[Claire Senft]

Prepare a latensifying bath. This bath will be a perborate bath with concentration of 1%. You will not need great quantities so I recommend that you make your own. To prepare it obtain some hydrogen peroxide which is commonly available in a 3% contration. This is the stuff you use to treat your ouchies whenst you have broken your skin and you are declaring pre-emptive germ warfare on the local microbes. A pint is more than sufficient. Ready a clean waterproof non reactive container that has a volume of 1 liter. Pour into container 325 ml of the Hydrogen Peroxide. Add to this 675 ml of tap water. Weigh out 10 grams of Sodium Metoborate and add it to this bath. (This is also referred to as Kodalk or Balanced alkali. It can be made from other material that I am not going to mention here. You may have to actually buy some. I bet that more than 30% of the subscribers to Apug have access to a computer that is hooked up to the internet and can buy Sodium Metoborate on line.) You now have, after a bit of stirring, a liquid latensifying chemical.

 

[Claire Senft]

Film developing: This is only an starting trial for Efke 25 but I wish to make it quite usable to you. Set up to do your normal developing of the Efke 25. If you nomally use a prebath of water only use the perborate in its place. Bathe your film with constant agitation for 1 minute in the perborate bath then follow the remainder of your processthru to its completion. The perborate requires no seperate rinse before a developer is used. It would probably be a good idea to add 5% to the developing time but I doubt that it will be very harmful if you use your regular method that has been proven to be highly satifactory to you. If on is using roll film then on could use a portion of a test roll. Class dimissed.

 

[Claire Senft]

If you have with care conducted tests and concluded that pre-exposure, post-exposure and latensification are all the same thing that yield the same results then lets us each peacefully go without animosty our own way.

For myself, I find latensification quite useful. This proccess can also be used with films of many different film speeds after taking that into consideration. The process will respond to the inverse square law very nicely as well as a lower or high level of the latensifying light.

 

[Jim Fitzgerald]

Claire, thank you for the education! I will follow your instructions to the letter. I live in an apartment and it is my darkroom! My bedroom is completely darkened. I will make sure I do the test at night just to be sure I have no stray light to deal with. I can take a nap for an hour! The rest of the "equipment" I have. My testing will be with 4x5 Efke 25. Not that it matters much but is the latensifying bath dumped after use or do you keep it? I expect this process to be fully useful to me and I appreciate your interest in helping me "learn". I love to learn about my craft and realize that being self taught I am willing to learn from those more knowledgeable than myself. Thanks again and I will let you know how I do. Please be patient as I have to earn a living and my passion has to wait sometimes.

Jim

 

[Claire Senft]

What should an latensified negative look like? Well it should have adequate shadow detail. The unexposed film edges should show very little increase in fog compared to a negative that has not been latensified but otherwise given the same development. The negative should look very much as if it was exposed at a lower film speed...say two thirds of the nominal speed on the box...and given a development that is capable of producing a high quality negative.

If you have a good deal more fog on the unexposed film edge, then the negative has not been latensified in the best way possible...it has received more light than is helpful. If the fog is uneven then there may be influences that were not desired or the orientation or distance to the light has been uneven.

 

[lensmagic]

Test of Pre- v. Post-Flash

You are of course correct, and I knew that when I made the initial posting. I just thought to myself, rather than do the work you have just described, maybe the answer is simple and obvious to everyone but me; but now I learn it is not! So yes, it's into the darkroom I go.

I have devised and conducted an experiment to test the difference, if any, produced by pre-flashing and post-flashing film. In effect, I converted the darkroom into a camera, using the enlarger lamp (a cold light head) as a subject, with light from the subject passing through an enlarging lens onto a sheet of film.

I. I covered one-half of the film (creating Side A and Side B), and exposed Side A to a pre-flash of 1.2 times the film's threshhold. Next, I placed a step wedge atop Side A and gave the film a "main exposure," i.e., an second exposure for twice the duration of the pre-flash.

II. I picked up the step wedge and uncovered Side B, then covered Side A.

III. I placed the step wedge atop Side B, and gave Side B the main exposure. I then picked up the step wedge and gave Side B a post-flash equal to the pre-flash that had been given to Side A.

IV. I processed the film.

V. After the film was dry, I compared the densities of the Side A and Side B step wedge negatives, and found those densities equal.

I conclude that flashing film before the main exposure produces the same effect as flashing film after the main exposure. Or stated differently, the effect of flashing film is the same, regardless of whether the flashing occurs before or after the main exposure.

Notes:
1. All exposures were made in total darkness.
2. The exposures were controlled by a Zone VI compensating darkroom timer.

 

[Joe VanCleave]

I have read this thread with interest, as I have worked a lot with preflashing paper negatives for use in pinhole cameras over the last few years as my primary photographic work.

First, I wanted to thank Claire for her thorough descriptiveness of her process, which I'm sure many film users will find useful. My comment is not intended to add or subtract from what anyone has previously posted, as my process involves paper negatives rather than film; but perhaps this may be of some use to someone else.

My preflashing setup uses a type "S11" lightbulb, which is a 120v, standard base, frosted white, mini-globe, 7.5watt lamp, found in the specialty lamp section of the major hardware vendors. I've mounted this in a metallic cylindrical housing (your tomato sauce or soup can of choice; thoroughly washed, of course), with the light projecting through a ~3mm diameter aperture in the housing. This light source is mounted 30" above the darkroom work surface, and is timed using my enlarger timer. I've found that for Freestyle's Arista brand grade 2 paper (my usual choice for paper negatives) a typical preflash time, using this setup, is 8-10 seconds; this delivers a slight density change below paper white on an otherwise unexposed but developed sheet of paper.

Why grade 2 paper, and why preflash? Simple. To control excess contrast. Especially with pinhole exposures, where deep shadows in high contrast light may otherwise not register any detail before the highlights are burned out; but this technique also works very well with glass lensed cameras even better. Multigrade paper has a high-contrast emulsion that is activated by the blue/UV portion of the spectrum, which is predominant in daylight scenic photography, rendering such negatives excessively contrasty. Using grade 2 paper helps eliminate this unwanted spectral-dependant contrast effect. The use of preflashing the paper negative also helps to gain additional shadow detail and further control the contrast of such scenes. In fact, I've found that preflashed grade 2 paper works pretty well for most scenes; even indoor ones illuminated just by indirect sunlight from a window will benefit well, especially the shadows.

This last summer I made a trek to Arches N.P. in Utah, exposing ~30 4"x5" paper negatives in a pinhole camera. These negatives I didn't preflash, but instead post-flashed prior to development. Prior to developing these negatives back home, I also exposed several additional ones in similar lighting conditions, but that were preflashed instead. The results show that the post-flashed negatives have a bit more contrast, and less shadow density, than the preflashed negatives. This is not scientific in accuracy or control, but does point out that, for my purposes, additional calibration is needed should I see the need to post-flash rather than pre-flash.

I should also mention that I found in my darkroom's clutter several preflashed but otherwise unexposed paper negatives that had been in a black envelop from a trip the previous summer; I proceeded to expose these in a pinhole camera, along with "fresh" paper negatives that hadn't been pre or post flashed; the results show that the year-old preflash exposure does seem to retain most of its effect, because the control negatives were obviously of higher contrast and lower shadow density, compared to the old preflashed negatives.

This may or may not be of any help to those wishing to do these sorts of experiments with film, but I would suggest that for LF and ULF purposes the use of preflashed grade 2 paper negatives can be of value, and can yield good results.

~Joe