Geoffrey Crawley Article: Second of two about 400 speed films (October 2000)
The 400 Club
We take a look at the 400 films available
Article by Geoffrey Crawley (October 2000)
The results of tests on the new Ilford Delta 400 Pro compared with its predecessor 400 Delta Pro and the worthy and still popular HP5 were published in BJP recently (20 September). The conclusion was that the new bi-pack emulsion was superior in speed to the previous 400 Delta by 0.5EV, showed marginally finer grain and better pushability. Its gain in speed and pushability over HP5 was marginal but detectable, though the latter showed up as slightly grainier.
The tests of Delta 400 were run in parallel with identical ones on the other ISO400 rated films on the UK market. These are: Agfapan APX400 Pro, Fujifilm Neopan 400 Pro, Kodak Tri-X 400 Pro and T-Max 400 Pro. Ilford's 3200 Delta was included as a wild card. Since all these b&w films have the 'pro' suffix, there could be an agreement to drop it and simplify matters.
So how does one go about comparing the properties of one film with another? Firstly it is essential that they are developed to the same contrast. Manufacturers give times in various developers which should give negatives of normal enlarging quality, as it is known. These are start points for the worker, intended to be adjusted in the light of experience with particular cameras, exposure techniques, and enlarger types.
A practical average contrast, using the Kodak method of assessing the contrast to which a film has been developed, is a Contrast Index (CI) of 0.58. Ilford has a slightly different method, though its G bar indices are close to CIs in value. It is only when films are processed to the same or a very near contrast, that true assessments of relative speed, grain and sharpness can be made.
To ensure such contrast parallelism, identical contact exposures are made on the films using a step wedge. These are processed to a range of times, the densities read on a densitometer, characteristic curves plotted and the contrast indices calculated. This enables the films under test to be developed to the common index necessary for a strict comparison. Step wedges or grey scales could be photographed by loading the films into a camera, but this obviously brings in other variables. As done here, the exposures are best contact printed in a highly accurate instrument (a sensitometer) that is consistent to one- tenth of a stop or better.
As soon as the curves at the standardised contrast are plotted, the relative speeds of the films under test are shown beyond debate, as are their general responses to the imaging light. When the toe of a curve is placed further to the left or right in the graph, this shows higher or lower speed respectively by an amount read off on the horizontal axis – the logarithm of relative exposure – on the graph. Films of the same speed can have different curve shapes, even though their overall contrast is the same. That can be the reason for individual user preference for a film related to the particular equipment used, the kind of work mostly carried out, and personal darkroom techniques. It is what keeps the film makers in business.
The developer used, for convenience, may be one common to the recommendations for the different makes of films. That usually means the Metol/Hydroquinone and Borax medium fine-grain formula proposed by Henn and Capstaff of Kodak in 1926 to ensure accurate processing of motion picture film. Marketed as D-76, the published formula has been adapted by many firms, notably in the UK by Ilford as ID-11, and has become an industry standard.
Reaching the age of 75 next year, D-76/ID-11 survives because it gives a good balance of film speed, grain and sharpness. Processing in another developer may improve one of these image properties, though usually at some expense of the others. But the relative merits revealed by D-76/ID-11 will remain proportionately the same: a sharper film will still be the sharper, a faster one the faster, a grainier one the grainier, and so on. Sharpness is assessed visually subjectively, and objectively by a microphotometer trace of detail edge contrast.
Once the times to give a common contrast have been established, field tests can be carried out and the processed images compared for their qualities. Field exposures are made over at least three stops at 1/3EV intervals. Enlargements are made to various scales and viewed for sharpness, grain, shadow and highlight detail, and so on. How-ever, truly comparative enlargements are not that simple to make.
There are essentially two methods. Strictly, the negative images to be compared should be printed for the same exposure time on the same grade of paper. That is certainly revealing, but in everyday practice a darkroom worker tries for the best possible print from any one negative. So that is the basis on which the writer makes the comparisons shown, whilst matching the mid-tones as far as possible.
Here, each negative has been printed using a range of times, usually five, and the best comparative match prints from the films under test chosen for publication. It is inevitable that differences are compressed in reproduction, though that itself could be said to add a further dimension to testing, at least for images intended for the printed page.
Field test comparisons are complicated by the need for lighting to be identical, so it is usual to employ a pair of matched cameras. This also enables everyday outdoor subjects and those in motion to be photographed on two materials simultaneously. Otherwise, using a single camera, studio shots may be necessary to ensure identical conditions.
In testing the eight films evaluated here, the camera pair method was obviously out. But since this speed of film may be employed for night shots, outdoor scenes with constant illumination were photographed. And such subjects with deep shadows are anyway the most critical for film speed. Happy snaps, out and about, were also taken at random with the films.
With ISO400 materials, pushability is a more important property in everyday work than with slow and medium speed films. Manufacturers give recommended extended development times for pushing, usually to EI800 and EI1600, occasionally to EI3200. Naturally the contrast index goes up – but the shadow, deep tone, or toe of curve densities (which are weak with normal development) increase too and become more printable. That is the basis for the higher EI meter settings.
The greater the toe density in-crease for controlled overall contrast the more valuable the boost becomes. But the higher the overall contrast, the softer the grade of printing paper needed to accommodate it – and this will reduce the value of an increase in the toe. The exception is if the subject is of low contrast or diffusely lit at a low level; then toe densities give full value in the print, as Grade 2 or higher may be used.
These tests included the extension of development for the times recommended by the film makers for EI800 and EI1600. For space reasons the EI800 results are omitted here; EI1600 is the acid test. The times recommended showed some disparity in the contrast indices reached, so a compromise based on averaging the makers' suggestions was adopted. The ISO400 CI, as noted earlier, was taken as 0.58: to this were added 0.70 for EI800 and 0.85 for EI1600. A push to EI3200 would be a bit desperate but CI=1.0 could be used. These values give equal increments.
In this way a true basic speed and pushability assessment comparison could be made across the assortment of films tested. For publication, 'best-off' prints were made from the ISO400 and EI1600 contrast balanced negatives at normal (x10) and high (x28) enlargements. The latter, being more critical, are the ones published here.
In terms of basic ISO400 rating, Ilford's new Delta 400 gave just – but only just – better lit shadows than Kodak Tri-X Pan and, close to it, T-Max 400 and Fujifilm Neopan 400. That result, as with HP5 in the first section of this review, proves that the so-termed 'traditional' emulsions remain strong contenders.
APX400 lagged behind the others and was also grainier. No really major grain differences between the Ilford, Fujifilm and Kodak films showed up at ISO400, even in x28 prints. If obliged to decide, Delta 400 gave perhaps the smoothest image – only just. Detail definition too was just marginally crisper on Delta 400. But if it takes enlargements to the equivalent of a 28x42 inch print from the whole negative to show differences, there is not much to complain about.
The EI1600 results at CI=0.85 sorted the films out. In shadow penetration Delta 400 Pro scored very marginally over the Fujifilm and Kodak. APX 400 again lagged behind. However, the grain image in the Delta 400 prints was now noticeably more evident than in the others: both T-Max 400 and Neopan 400 retained grain control with Tri-X close to. With such extended development there may be bi-pack interference occurring with Delta 400, but it retains its speed edge nevertheless.
So, what conclusions may be drawn from these tests? The writer was a little surprised not to find a wider demarcation between 'traditional' emulsions, such as HP5 and Tri-X, and the advanced halide grain technology types, such as Delta 400 and T-Max 400, in terms of granularity. The latter have the edge but not by much – and since the former retain good push properties, the continued liking for them is understandable.
Some users maintain also that old-style films seem to yield more attractive pictorial images. It is a quality which, when leafing through prints, seemed to give pause at the Neopan 400 samples. But such aesthetic points offer a question for another day.
First published in BJP 18 October 2000