35mm Film Resolution

35mm film has a resolution of approximately 5.6K — equivalent to an image of about  5,600 × 3,620 pixels. The finite resolution of film will fluctuate based on the type of film and the film's processing methods.

All these characteristics influence the film's resolution:

• Black & White or Color film
• "fine grain film" or "low light film" – which is directly linked to the light sensitivity of the film
•  the type of grain T-Grain film, or traditional grain film
• Ektachrome, Kodachrome, and many others
• The film's developing method increases the processing time. Raising the processing solution temperature will increase the silver grain size, thus decrease the film's resolution.

In short, image quality is dependent on film grain – the very small silver particles stuck between color layers in the film's emulsion. To be exact, it is the aggregate effect of these particles holding the light back that form a visual effect, which resembles a grain. The job of these small silver particles is to store the image information.

An Overview on MP (Megapixel), DPI (Dot Per Inch), and Print Size

		Megapixels (more is better)	Image or Frame Size in pixels	Print Size in inches at 300DPI
VHS (NTSC)		0.16MP	480×333 luma 480×40 chroma	1.6 × 1.1
VHS (PAL)		0.19MP	576×335 luma 240×40 chroma	1.9 × 1.1
Full HD	2K	2.1MP	1920 × 1080	6.4 × 3.6
UHD TV Apple iPhone X	4K	8.8MP	4096 × 2160	13.6 × 7.2
35mm Film resolution (1) (2) (3) (about 4,000 DPI)	5.6K	21MP (3)	5600 × 3620	18.7 × 12.1
5,000 DPI Scanner (5)  (8)	7.1K	37MP (9)	7150 × 4767	23.8 × (15.4) (10)
Braun 7000 (10,000 DPI) (9)	Tests have shown that it is not performing at 10,000 DPI (9)  but at approximately 6,500 DPI -- even if the scan mode is set to the extended scan setting. Transfer houses avoid this mode, because it takes too long for a slide scan.
FilmFix 35mm Slide Transfer System (4) (6,800 DPI) Learn More	9.5K	61MP	9504 × 6336	36.6 × 21.1 (10)

Enlargement Limits

The renowned photographer Ansel Adams' rule of thumb for enlarging images was simple: avoid printing film to paper at more than 4 × its original size.

For 35mm negative film (frame size 24mm × 36mm) Adams would print at a maximum of 96mm × 144mm – which converts to only 3.8 × 5.6 inches.

The reason Adams would not enlarge more, is because any further magnification would too clearly reveal the film grain. However, when archiving slides one wants all the grain to be visible.

Transfers at FilmFix are designed for archiving slides.

We transfer beyond what film can store. At 9.5K we out-perform all commercial slide scanners. We deliver an impressive 9,504 × 6,336 pixel file and have the highest optical film transfer system we know of.

If you print at 300DPI (the printing standard), you can expect a quality print from our high resolution scan. This will be true for images printed up to a size of 21.1" x 31.7" (for 35mm film.) However, this voids Adams' rule of thumb technique mentioned above. You will see the grain in the image with more details represented in the grain.

Keep in mind that the quality of the image depends on the original type of film and lens used. Additionally, the outcome will depend upon the skill of the photographer.

---

Foot notes and sources

¹ 35mm film 20MP https://pic.templetons.com/

² 35mm film 21MP https://www.quora.com/

³ 20MP "A 35mm scan with an effective resolution of 3900 contains about 20 million pixels, that's enough in order to take out all image information from a 35mm film in terms of resolution." (source)

⁴ At FilmFix we visually inspect and manually adjust each slide for its optimal exposure. The camera we use is a Sony A7R IV, capturing RAW at 14-bit, with a Dynamic Range of nearly 15 stops (14.77 EV). This degree of resolution shows the film grain in great detail, and stores all the image information a slide is capable of.

⁵ Braun 6000 (16-bit) if scanning at ME MultiExposure "The tool is called ME in the software and serves as a means to increase dynamic range" up to Dynamic Range 3.8 Dmax (but takes longer to scan)

⁸ Pacific Image PowerSlide X Automated 35mm Slide Scanner (48-Bit)

⁹ "Is advertised as 10,000dpi but is 5,000dpi" (source)

¹⁰ It can be argued that printing anything larger than what the film will store will bring a better image, but the only thing it will do is increase the grain size and produce bigger more defined grain.

Author: Nathaniel Courtens
Monday, May 11, 2020