What is the largest possible size I can enlarge to with 35mm film?

Question

What is the largest possible size I can enlarge to with 35mm film?

Answer

There's an interesting and thorough paper explaining film resolution, granularity and print grain: http://cool.conservation-us.org/coolaic/sg/emg/library/pdf/vitale/2007-04-vitale-filmgrain_resolution.pdf

There is no clear answer to your question as it depends on multiple factors, namely:

• Film's ability to record fine detail or resolution, which in turn consists of:
  • resolving power (function of particle density in the emulsion)
  • granularity (function of particle clumping in the emulsion)
  • sharpness (perceived edge distinction)

The resolution depends on:

• camera quality (lens mount and film plane alignment, etc)
• lens quality (resolution and amount of aberrations)
• film type (different films of same speed have different resolution)
• film speed (granularity increases with speed)
• exposure (overexposure leads to more granularity)
• film processing (handling, developer, conditions, etc)
• film age and archival conditions

One can say that this is all unimportant, unless I suddenly want to make prints from, say, ORWO film shot by my grandfather in the seventies with Smena.

Also different methods of judging resolution lead to different results, magnification under loupe or microscope is different from enlargements which in turn is different from scanning and printing.

Finally, the viewing distance plays very important role in how big you can print. Kodak has published print grain indexes for their Portra line (page 7). It says that the grain of 35mm Portra 160 film is visible already in 4x6'' (10x15cm) prints, but without visual comparison or experience this does not mean a lot.

So the suggestion would be - test yourself, whatever numbers you get from here might not fulfill your expectations in the final print.

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