Introduction - The Problem
Everyone working in the darkroom is familiar with the difficulty to assess the tonal values and their distribution by simply looking at the negative on the light table. Even when making a contact print with a rather modest gradation (e.g. 2), it can be difficult to judge.
With the following method, you can judge and compare the negatives tonal range and contrast to make decisions for analogue printing and compare different types of development and exposure. It is also a perfect for people using "sunny 16" or doing street photography (which does not allow precise metering) and are therefore unable to work with the zone system to evaluate the perfect exposure beforehand.
Scanning & Analysis - The Solution
If you are not familiar with the method of scanning negatives with a digital camera, please read my article on that topic first as it is a necessary prerequisite.
Once you scanned the images (RAW) with a digital camera, you need to import them to a RAW - converter like RawTherapee , which does not apply any changes to the RAW file if you set it up correctly - so make sure that all auto-functions are turned off.
The image on the left shows the settings I used for the analysis of the following three example images. I clipped the light and dark parts of the RAW - files without information to get more pronounced histograms to judge the exposure and tonal values. Make sure to apply the exact same settings to all the negatives you compare otherwise the results will be distorted.
As you are working with a negative, the light parts will be the dark parts on the final print. You can also apply RawTherapees "negative" HaldCLUT, if you prefer (which I did not in this example).
The following images were shot with a Pentax 6x7 and a 300mm f/4 on a tripod. Two out of three were subject to deliberate incorrect exposure. I recorded the pictures on ISO400 ILFORD XP2 chromogenic black and white film.
The images were scanned with an Olympus OM-D M5 and an Olympus M.Zuiko Digital ED 60mm f/2.8 Macro Lens.
Sample 1 - Overexposure
The overexposed negative shows a harsh contrast between the highlights and the midtones but also a lot of information across the whole tonal range.
Sample 2 - Correct Exposure
The correct exposed negative shows a very well balanced histogram and an even distribution of tonal values across the whole range.
Sample 3 - Underexposure
The underexposed negative shows a relatively small histogram compared to the two previous images. A lack of contrast and / or a loss of detail compared to the two previous images is highly likely.
The final images show the amazing characteristics of analogue film and the exposure tolerance, as all images retain a very good amount of detail.
Nonetheless, the overexposed image yields a picture with significantly richer contrast and more details compared to its underexposed counterpart. Only grossly overexposed images start loosing details in the highlight areas. As a rule of thumb two stops is fine with almost any type of negative film.
If you want to compare different developers and their effects on the range of tonal values of the film and want to ensure very accurate comparisons without wasting a whole roll of film on test shots, just take a picture of a grey scale under studio lights with each roll of film. After using the different developers on the different rolls, you can compare the test images shot on each roll.
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