Spending some time with Google shows that there are numerous comparisons between Kodak Tri-X (400TX) and Ilford’s HP5+ film. Are they the same? Are they different? Is one better than the other? On and On and On. Let’s take as objective look as possible between the two emulsions and see what the deal is here.
Cut to the chase
If you don’t want to read any further, and just want a fast answer, then here it is: Kodak Tri-X and Ilford HP5+ are so close to each other that I can say that they are totally, completely, one hundred percent interchangeable. This means that you can shoot and process them exactly the same way in the same chemicals for the same development time. The end result will be close enough that you can’t tell the difference.
We are going to evaluate the two emulsions on two criteria: Tonal range, and granularity.
To evaluate the tonal range, we’ll shoot an 18% grey card on each emulsion, and shoot it from 7 stops under to 11 stops over normal exposure in full stop increments with a studio strobe. The exposure will be set via a Sekonic light meter incident reading and shot through a T-Stop rated lens, with the light meter reading within 0.1 stops of the actual amount of light hitting the grey card. To evaluate the density values for each stop of light, the emulsion will then be digitized with a DSLR using a studio strobe through the same T-Stop rated lens.
From there, the raw captures are evaluated and the average sample value from a 256×256 square in the middle of the scanned frame is calculated. This is done for each emulsion. This will give us a good idea of the density level of the emulsion for a given exposure value.
This is done exactly the same way for each emulsion. The camera position relative to the gray card does not change between each emulsion, and the focal point does not change between each emulsion.
For granularity, this is actually pretty straight forward. Look at the scan of the correctly exposed 18% grey card for each emulsion in Adobe Lightroom at 1:1. The scans are just over 4200 dots per inch, which is more than enough resolution to actually digitize individual grains.
To ensure that we’re as close as possible for each emulsion, they’re both developed in Kodak D76 1:1 at 20 degrees Celsius +-0.1 degree in the same daylight tank at the same time for 13:00 with 1 fast inversion every 15 seconds. There was a several minute pre-soak at 20 degrees of the tank/emulsions to get everything up to temperature. A 1:4 vinegar/water stop bath was used to stop development. Both emulsions were fixed in Kodak Fixer for 10:00 with constant agitation.
Obviously, this is not up to scientific standards, however, it is within the tolerances that I can bring to bear with the equipment available to me, and I feel that my tolerances are tight enough to use with a reasonable amount of certainty in the results.
Below are the results for each item being evaluated.
Here is the chart of the two emulsions.
When looking at this, there’s a couple of things to remember: It’s not the actual values of each density step that matter because those will vary a bit due to variations in the the power of the strobe firing during the exposures, variations of power of the strobe firing during the scanning, and how many specks of dust and fibers there are on the emulsion in the scanned sample area, which will affect the average calculated sample value. In fact, I’ve repeated this test twice exactly the same way and have even done multiple scanning passes of each emulsion for each test and gotten different but similar results for every single density step. This is the nature of the medium. There’s a lot of moving parts and things that can affect the outcome.
The key takeaway here is the shape of the curve for each emulsion. I’ve included a combined curve that is the average of all the scanning passes of both tests for both emulsions with each end slightly extended beyond sampled values.
In short, both emulsions have the same tone curve and tonal range if developed in the same developer at the same temperature, for the same amount of time and same agitation.
OK, what about the grain? I’ll let the image below speak for itself. You can right click on it and download the full image to look at it at full size if you want to look at it really close.
So, what are we looking at? A comparison of each emulsion scanned in at 4200+ dpi side by side at 1:1 in Adobe Lightroom. The grain structure is readily evident, and frankly, to me, the two emulsions are close enough in their granularity that at sane enlargement levels, they’re nearly if not completely indistinguishable.
With black and white film, the tonal range and granularity are really only the two things that matter, and as I said in the cut to the chase section, if Tri-X and HP5+ are shot and developed the same way, they’re interchangeable in terms of tonal range and granularity.