Film speed test – use just 2 sheets of film – no densitometers
Film speed test for Ilford FP4. How to establish your personal film exposure index and normal development time without the need for expensive densitometers. This is a visual check using a graphic arts step-wedge tablet.
Below is a quick overview of the method for how to conduct a film speed and development test to obtain a normal development time. It is particularly handy for 4×5 users. You can
Time needed: 2 hours.
How to test film speed without a densitometer
- Load step tablet and unexposed 4×5 sheet into a film holder
I use a Stouffer step wedge as my calibration tool, avoiding the need for a densitometer.
- Expose the film with step tablet with a Zone 10 exposure
Use a white card for exposure.
- Develop your test film in the developer of your choice
- Make a contact print from your test film.
Visually read off the contact print your film speed index and confirm normal development.
Step 1 Load step tablet and unexposed 4×5 sheet into a film holder
This film speed test uses a Stouffer step wedge as your calibration tool. Modify your step tablet by placing an opaque paper dot sticker above step 21 on the tablet. The film under the dot will not receive any light. The resulting clear film base becomes a reference point later.
The 21 step tablet or step wedge is a calibration device traditionally used in graphic arts applications. It has been carefully processed under laboratory conditions to give 21 steps of grey in 0.5 stop densities. Using a step tablet is one way to avoid the need for densitometers.
In a darkroom or film changing bag load an unexposed sheet of film overlayed with the Stouffer step tablet. The two are sandwiched together and carefully pushed into place within the sheet film holder. Due to the combined thickness of two sheets, this can be a little difficult. Using some care and practice it can be achieved. Treat the test tablet with the same care as film and avoid fingerprints and
Step 2 Expose the film with step tablet with a Zone 10 exposure
A Zone 10 exposure is 5 stops more exposure than what your meter is indicating. Observe the following points:
- Use a white card as your exposure subject and fill the viewfinder completely. If you use a darker object the exposure time required will be longer, hence use white.
- Choose a normal focal length lens. Wide angled lenses suffer from light fall-off at the picture edges and can affect the test
- Have your lens focused at infinity. The test object will not be in focus and focus is not desirable for this test.
- Choose a day with consistent light, cloudless, south-facing is best if in the southern hemisphere.
Step 3 Develop your test film in the developer of your choice
My current developer is Ilford LC-29. Conduct your tests with the developer that you prefer to use with your film. Prepare it as you would normally. So that you have repeatable results, be consistent with your film processing procedures.
For my processing set up, Ilford HP5 takes about 11 minutes to develop normally. Looking at the Iford tables for FP4 suggests that it develops in slightly less time that HP5. So I cut my time from 11minutes down to 10 minutes. Why? 10 is an easy number to work with. If I need to reduce or increase my development times further I will usually adjust by at least 10%. In this
Step 4 Analyse your results to get your personal film speed index
The first piece of information in a film speed test is at what ISO speed should I be exposing the film for with my camera gear and development procedure.
This is where placing the opaque sticky dot near the 21st step is so helpful, circled in red. Here there is no exposure so it gives you a clear film base reference. Step 21 on the wedge is also Zone 0. If it is the same density as the red circled clear film base then the film is not overexposed. If step 21 is equal to the circled area and there is
If steps 21, 20, 19 had been clear with no tonal separation between them, then I know the film was underexposed. I would need to reduce my ISO number by about half a stop and try the test again.
Conversely, if steps 21, 20 and 19 had definite grey tones I would need to decrease my exposure by increasing my ISO rating for the film.
Step 5 Proper proof time
From the previous step I am confident that an ISO of 64 is close enough for my camera and developer combination. Now I need to find out what is the normal development time.
A second sheet of FP4 which remained unexposed was also developed at the same time as the step wedge test for 10 minutes.
For all contact
What I am looking for is the first almost black tone which shows very little discernible tonal difference to the next strip after it. This is in the region of the minimum print exposure required to print through the unexposed film to yield a black print value.
In my case above, I could see clear differences between the dark greys at exposures of 8.6 and 10.4 seconds. At 12.4 seconds I could see no appreciable change in blacks between 12.4 and 15.0 seconds. So I choose the 12.4 seconds as the minimum time to achieve close to maximum black.
A note of caution, this is a visual test and it is easy to be overly enthusiastic about achieving maximum black thereby overexposing when establishing your minimum time for close to maximum black.
Here we are working at an extreme end of the paper sensitivity where small changes in exposure can give large changes in density, so take care not to overdo it.
Remember that you want the exposure time just before there is no real appreciable difference in the black with next exposure time which follows.
Step 6 Establishing normal development – printing the step wedge.
This is the final stage, establishing what is a normal development time for your film, camera and developer combination. We need to make a contact print of the actual Zone 10 film exposed with the image of test tablet. Using the exposure determined above for the minimum time for maximum black (in my case 12.4 seconds) I contact print the negative onto the photographic paper. See the results below.
In the image above I have shown in red letters the various print value zones and their respective step tablet numbers. Remember each step is 0.5 of a stop. Step 1 on the tablet is equivalent to a Zone 10 print value, Step 2 is half a stop lower at Zone 9.5 and Step 3 is Zone 9.0 respectively.
I like to have a good separation of tones from Zone 2 print value (Step 17) through to about Zone 8 print value (Step 5). After Step 5 – Zone print values 8.5 to 10, the scale remains paper base white. This is a normal contrast range. If the light grey scale ended earlier at say Step 7, this would indicate the film has been developed with higher contrast than normal of about one stop. This is referred
In this case above 10 minutes development has produced results which show normal negative contrast.
Film speed test Ilford FP4 in LC-29 developer conclusion
Using just 2 sheets of Ilford FP4 film I was able to determine that my personal exposure index is 64 ISO. I achieve normal development at 10 minutes. This accounts for my usual dilution and agitation methods consistent with all my film processing procedures
I have only used my results here as an example of the process. Expect your results to be different from mine.
Having conducted my film speed test for my personal exposure index and normal development I can now go about photographing with my new stock of Ilford FP4. This gives me a genuine basis to compare results of my images with other films I have used and to observe characteristics particular to this film and developer combination.
Conclusion: Film speed tests are necessary to understand how to best manipulate your creative materials – your photographic film and paper.
References Calibration and Transmission Step Wedges
Film Speed Test References.
Paul Wainwright has written a nice little pdf which you can download. It goes into greater detail the technical details behind this visual test. Go to “Use Your Eyes, Zone System Testing Without a Densitometer” and download the pdf link.
Visit Stouffer Graphic Arts for details regarding transmission step wedges and photographic scales. I rely on these tools to avoid the need for costly laboratory equipment like densitometers. Handle your calibration scales like negatives, keep them clean and store in neg files. That way these scales will last you for years and be well worth the investment.
If you have any questions feel free to drop me a line.