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The gelatin silver print, champion of definition

In the studio, two Edmund Optics USAF targets are placed on one of the devices, horizontally and diagonally, to compare the definition of silver and inkjet prints.

The resolution of a gelatin silver print is limited only by that of the film and the magnification factor of the image. It does better than digital printing, especially inkjet.

In the film Gruppo di famiglia in un interno, by Luchino Visconti, Burt Lancaster plays the role of a retired teacher keen on painting. In the first scene of the film, we see him inspecting a painting, a magnifying glass in hand, marvelling at the subtleties of the work. A photographic print can also be appreciated in close observation, because nothing beats its precision. Becoming a professional photographer also means appreciating these delicate subtleties.


To verify this, we take several film and digital shots in the studio. The scene includes an USAF 1951 resolution target. Three cameras of different film formats are loaded with Ilford Delta 100 black and white film (100 ISO): a Nikon F100 for 24×36, a Pentax 67 for medium format and a 4×5 view camera Ebony SV45U2. For digital shooting, a Nikon D850 (45.7 MP) is set at 100 ISO.

Resolution of an inkjet printer

An inkjet printer uses a specific resolution for printing. The highest resolution that can be achieved is obtained with Epson printers, in particular the SC-P800 or SC-P900: it is 720 ppi. This resolution corresponds to 14 LP/mm (pair of lines per mm, resolution unit commonly used to define the resolution of an optical or printing system).
A Nikon D850 delivers files of 5504 x 8256 pixels. If you want to print at the highest resolution that the printer is capable of, i.e. 720 ppi, the image measures 19.42 x 29.13 cm.

Film and gelatin silver paper resolution

Let’s see what happens with film in the field of resolution. According to Kodak and Fujifilm, the resolving power of 100 ISO black and white film reaches 200 pl/mm with a high contrast target (1000:1). With low contrast targets (1.6:1), it is 60 LP/mm.
The resolving power of an image on a film depends on the resolution of the latter and that of the lens. The resolving power of an optical system (film + lens) is always less than the weakest of its constituent elements. A 100 LP/mm film and a 50 LP/mm lens (in the case of a good camera lens) will best render between 33 and 45 LP/mm.
The resolving power of photographic paper easily reaches 100 LP/mm, especially in black and white. A contact print delivers the highest resolution attainable. Hence the persistent interest in large format film photography and contact printing, especially in 8 x 10 inches (20 x 25 cm) format. With contact printing we obtain a resolution at least twice as high as what we get with inkjet printing.
If you enlarge a negative, the resolving power of the printed image drops. The larger the negative, the less you enlarge and the better the definition of the image. The resolving power of the enlarging lens also comes into play, reducing the resolving power of the final image. By enlarging 5 times a 24×36 negative of an ISO 100 film, we reach around 15 LP/mm, knowing that a human eye is not able to perceive more than 6 to 7 LP/mm at a viewing distance of 30 cm .

Droplets versus silver halides

An inkjet printer delivers ink droplets of variable size, the smallest of which are around ten micrometres. The highest resolution of an Epson SC-P800 or SC-P900 pigment printer is 2880 dots per inch (or dpi), or about a hundred dots per mm. In the lightest areas of an inkjet print, the drops are more spaced out than on a dark portion. They are visible with a good magnifying glass. The silver halide crystals (bromide, chloride and silver iodide) which form the image on a silver print are a hundred times smaller than pigment ink dots and only a very high magnification microscope is capable of distinguishing them. The transitions are more continuous, unlike those of ink droplets.
Mathematical conclusion: the nuances and the high resolution of a print remain the prerogative of film photography… provided you do not enlarge your films too much.

Discover the Spéos training courses

To obtain prints with maximum detail, it is important to be familiar with the settings of the printing systems. For this, no secret: the main thing is to train! However, starting photography without help can be frustrating. Undertaking a training course or a workshop to learn the basics can therefore be a good way to learn the photographic technique before getting started.

Spéos photography school offers professional photography programs in 1 year2 years or 3 years, short programs, as well as photography workshops. The long courses to become professional photographers allow you not only to master all the photographic techniques and its vocabulary (blurs, hyperfocus, sharpness zone, depth of field, backlighting, focal length, shutter release, autofocus, wide-angle, rule of thirds, etc.), but also all the stages of shooting and image processing.

The Edmund Optics USAF pocket model. It measures 50 x 89 mm and reproduces a USAF target with 4 groups of 6 elements and a Ronchi target of 1 line/mm. It is used to assess the resolution of imaging systems.
The shot is taken with a Nikon D850 (45.7 MP) and an AF-S Nikkor 50 mm f/1.4G lens open at f/5.6 (ISO 100, 1/45 s). A close-up of the chart shows a loss of resolution from element 1 of group 2. It means that the system has a resolution of 60 LP/mm.
The highest resolution you can get with an Epson printer is 720 ppi. This resolution means a print size of 19.4 x 29.1 cm with the 45.7 MP of the D850. The aspect of the inkjet print is pointillist. Only element 5 of group 1 is distinguished.
From a 24×36 format (Nikon F100, AF-S Nikkor 50 mm f/1.4G, 1/30 sec at f/5.6), the 29.1 cm long gelatin silver print has lower resolution than inkjet , but without a pointillist effect. In terms of resolution, the digital camera is superior.
With a 6×7 format (Pentax 67 and SMC PENTAX 67 90 mm f/2.8 at f/8, 1/15 sec Element 6 of Group 1 is clearly visible due to the larger size of the negative. Slight advantage to the silver gelatin print.
With 4×5 format (Ilford Delta 100, Ebony SV45U2 and Nikkor-W 150 mm f/5.6 opened at f/16, 1/4 s), we distinguish element 2 from group 2. The print delivers a higher resolution than the combination of a 45.7MP 24×36 sensor with an inkjet printer.

Text and photos: Philippe Bachelier, teacher of Printing techniques at Spéos

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