EI = Exposure index. It's the film speed you've calibrated your whole system to. Everything from the film,camera and processing. The ISO number given by the manufacturer can't take into account your developer choice.
Originally Posted by peter38
I'll try and explain the way I understand it. What you do is take a clear frame that equals fog base. Now take several zone one exposures at zone I. Starting at 1 stop below the ISO and working up by 1/3s of a stop until you hit 1 stop over. I guess that's seven total exposures. Measure the density of those zone I exposures. The one that is about 0.1 higher in density then the clear frame. Well at leasts that's the way I understand it.
Robert's explanation of the film speed test is accurate and to the point.
By way of example, you might read a blank frame or the unexposed margin between frames to have an absolute density of 0.2, say. Then you would read the frames that are exposed in the way Robert describes to find one that reads 0.3, subtract the value you got for the blank frame (film base + fog), and you get 0.1--your Zone I density.
Sorry if "increased film speed" added another distraction. It is a common misconception that if you extend development time to "push" film to a higher EI, you are actually increasing the speed of the film. I had the misimpression that you were trying to adjust the Zone I density by changing the development time, which you can't do beyond a certain threshold.
By "pushing the shadows off the toe," yes, I mean moving them up to the straight line portion of the film's characteristic curve to improve tonal separation in the shadows. If the film's curve has a long enough straight-line area, you can do this without losing the highlights at the other end.
How much to change development time for a one zone increase or decrease?--depends. It's usually on the order of 20-40% The development time test based on Zone VIII will tell you. Once you've established the film speed (EI), then you can test to see which development times give you normal, +X and -X results.
What developer to use?--There is no particular reason to use the same brand of film and developer. Some, such as Kodak D-76 and Ilford ID-11 are virtually identical. Go to the Ilford website and download the technical data file for FP4+, and it will give you recommendations for different developers for different priorities (minimum grain, maximum speed, best acutance, etc.--you can't have them all!). Anchell and Troop's _Film Developing Cookbook_ also has lots of information on different types of developers.
The way to arrive at a zone I density for your camera, light meter etc. Is to meter the grey card you have in evenly lit conditions. Focus your camera lens at infinity. Leaving the lens focused at infinity, move the camera to where the card fills the viewfinder. Be careful to not shade the card while doing so. If your meter on the camera indicates 1/60 sec at F 11 (for instance), manually set your camera for four stops less exposure. Then make one exposure at F11 and 1/60 second, the second exposure would be F16 at 1/60 second, the third exposure at F16 and 1/125 of a second, the fourth exposure at f22 and 1/125 second. Shoot your fifth through 8th exposure with no exposure by leaving the lens cap the lens. The above exposures are examples only. Use your meter recommendation, and give a total of four stops less exposure (incrementally as in the example above)plus the four exposures with the lens cap on the lens.
Rewind the film and remove from the camera. In the darkroom remove the film cannister, open it. Process the film according to your film and developer combination recommendations. The negatives that are clear are your exposures with the lens cap on. That will be your base plus fog. The first frame that will give you a density greater then your base plus fog with a measurable density of .10 above FB + fog will be your actual film speed. That typically will fall on the third exposure but not always. For instance if you were using a 125 ISO film and using the example above the third exposure showed a density of .10 above fb+fog then your actual film speed would be 64.
Once you have done that test then the next step will be developing for a Zone VIII density. But you need to do the film speed test first. Come back to this forum when you have it finished.
Always remember exposure is for shadows and development is for highlights. Film speed is the place to begin to get your exposure properly placed.
No. The meter itself serves one real function: To measure the amount of light it receives. That is independent of any particular film-developer combination.
Originally Posted by peter38
There is, in most meters a "translation" to produce f/stop and shutter speed information, but there are talbes (I've made one myself) to determine exposure from foot-candle illumination and film speed. The calibration of the METER itself would be to determine the departure from indicated light levels as compared to "true" values.
I have horrible thoughts of those who have fallen into the "Sunny 16" trap, where they maesure light on a sunny day with their meter, and if the reading agrees with the "Sunny 16" idea (when set to f/16, the shutter speed will equal the exposure index) they consider their meter to be "calibrated".
There is a great deal more to calibration, including the "lineartiy" of the reading - is it accurate at high light levels AND low light levels-, how it is affected by the COLOR of the light... and a whole bunch more.
When you determine the aount of light necessary to effect "Zone 1" on the film, you are establishing a WORKING exposure index for that particular film, which may or may not coincide with the advertised exposure index of the film. If it does, it does not necessarily mean your meter is correct, a.k.a, "calibrated".
Ed Sukach, FFP.
Thanks to all of you for your time and help in this matter. By some chance I have found a film processing company that will do a transmission densitometer test on my negatives.
Here is what I’ve done and I am posting this before processing my film. I set up a gray card in deep shade, I set my 50mm lens to infinity and made sure that the card filled the view finder.
My reading was a hair under 125 at f 2.8. I set my shutter speed at a hair under 125 and since this “f” stop would give me a z5 I cranked my aperture down to f 16 (one under z1). Estimated ½ stops between marked f stops coming all the way back up to 125 at f 2.8 or 11 exposures all together. Then I did it again but only going from one ‘click’ f stop to the other for 7 exposures. I also put the lens cap on for four exposures to give me clear film base. Now I will process my film if that all sounds right to you folks and then I will have my film checked tomorrow morning and see what’s what.
After the densitometer reading I will adjust the ASA on my camera to reflect as close as possible the true film speed.
I will then tomorrow shoot a roll at z 8 and process my film for different times (checking with a densitometer or through contact prints?) and finally arrive at an optimum development time for FP4.
Whew! Could I have all this right? I’ll have to admit that pretty shortly into this exchange I was feeling in very deep water.
Ed, thank you and of course you’re right about calibration. I miss spoke in that I was not under the impression that my meter was “calibrated” any further than in a gross way. But at the present that’s all I want.
I have The Film Developing Cookbook by Anchell and Troop but what is disconcerting is that it seems what ever book I read or knowledgeable person I speak with I am given a different way to do things e.g. times, type and amount of agitation. For now I only want the simplest way to give me a ‘normal’ negative most of the time.
If I can get my meter, film and development somewhat synchronized then I feel I will have a firm base to work from for quite a while making modifications from a position of some understanding rather than a series of guesses.
Thanks again and how does that film exposure series that I described above sound as far as my going ahead and processing the film and taking it in to be analyzed?
Hmm, it appears at this point that I'm not posting my replys correctly am I?
Sponsored Ad. (Subscribers to APUG have the option to remove this ad.)
Sounds like you have the exposure test finished. Process the film according to the recommendations for the film and developer combination. Everything that you will do insofar as the development test will be dependent on getting your film speed established. When you shoot your roll at Zone VIII, I would recommend developing to a lower contrast then what I would recommend for sheet film. I would target my Zone VIII densities so that the negative will print on grade three paper. The reasoning behind this is that this reduces developing time somewhat and this will help control excessive film grain. The smaller film format will benefit from all of the help that you can give it. You will still have grade four paper if you need it and you will have grades two and one if you need those as well. Good luck.
Sounds like you're on the right track.
For now it's probably best to use a densitometer to test for zone VIII. For a condenser enlarger targeted for printing on grade 2, you'll want a zone VIII density of about 1.2 over base+fog. A little more if you are using a diffusion enlarger or a longer scale paper. A little less if you take the above suggestion and target your negatives for grade 3. And even then, once you set aside the testing and start taking pictures, you may decide that you generally want more or less contrast than you're getting, and you can adjust your development times accordingly.
If you want to experiment a bit, shoot your test rolls with a few shots at Zone VIII at the beginning to be sure you've got your Zone VIII test, then shoot the rest of the roll in sequence from zone 0 to zone X or more, and then you can read each frame with a densitometer and plot the characteristic curve for the film for each development time you try and see how development time changes contrast throughout the curve.
This morning I wrote this long article on just how I would proceed with the test and what to expect and that sort of thing. When I went to preview it and then send it the site told me I was illegal. It would not post it. Fortunately for you and me the information I wrote about is also being written about by David and Don. Both men know what they are talking about. Follow their instructions. Your photography will thank you for it.
Thank you for the thought on that anyway Lee.
Well, many a slip between cup and… I made all my exposures, wrote down the info and went to mix my developer only to find I had just half as much as I needed!!!!!!!!! I left the film in the developer can, hoping that doesn’t ruin anything and early tomorrow I will buy new developer and have the film tested.
We have condenser enlargers. My amateurish preference would be to print on grade 2 paper but am very curious as to the advantages of printing on grade 3. Grade three it would seem to my ‘newbie’ thinking would print fewer tones than 2 if I am making myself clear.
<<If you want to experiment a bit, shoot your test rolls with a few shots at Zone VIII at the beginning to be sure you've got your Zone VIII test, then shoot the rest of the roll in sequence from zone 0 to zone X or more, and then you can read each frame with a densitometer and plot the characteristic curve for the film for each development time you try and see how development time changes contrast throughout the curve.>>
<Grin> you know these posts have been a whole education in and of themselves! I think that a zone 0 to X test would be a good idea and I can see that each frame can be read with a densitometer but upon what would I plot the test result numbers? And are you suggesting that when I change development times that I run the test again each time? Wouldn’t my ‘eye’ evaluating a finished print be a better judge of what I want than a graph?
You would plot the values on a graph with densities on the Y-axis and the zones on the X-axis. Yes, you could do this test for each development time tested and you could plot each curve in a different color on the same graph. This is called the "characteristic curve" of the film. The flat part on the left near Zone I is the "toe," and the flat part on the right is the "shoulder," and the middle is the straight line portion. Tones that fall in the straight line portion will have good separation, while tones that fall on the toe will be muddy (with respect to each other), and tones that fall on the shoulder will be "blown out."
In the process of plotting these curves, you might discover that one development time gives you a normal contrast range, and another gives you N+1, and maybe another is N-0.5, etc.
Say for example that you've targeted Zone VIII density at 1.2, and you get that density at Zone VIII with your developer of choice at 10 min. Now what if you also did a test at 12 min., and discover that Zone VII has a density of 1.2 at that development time? That would be a one-zone expansion (N+1), and you could use that increased development time to get more contrast in a flat scene. You could also compare the 12 min. curve to the 10 min. curve and discover how much of a change you get at Zone V when you get a one zone increase at Zone VII, which is one of the questions we started out with. Maybe then you might try a test at 15 min. to see if you can get an expansion of N+2 (Zone VI with a density of 1.2), or you might discover that the film doesn't have enough density for an expansion of N+2.
Ultimately, of course the print will tell you all you need to know, but the process of plotting the graphs will teach you a lot about how film works, how to make it do what you want, and what it can't do easily.