Film Calculator

Pushing and pulling are techniques used when film is exposed at a different ISO than its box speed:

• Pushing: Exposing film at a higher ISO than rated (underexposing) and compensating with extended development time. Each stop of pushing (doubling the ISO) typically requires 15-30% more development time. Pushing increases contrast and grain while extending usable ISO range in low light.
• Pulling: Exposing film at a lower ISO than rated (overexposing) and reducing development time. Each stop of pulling (halving the ISO) typically requires 10-20% less development time. Pulling reduces contrast and grain, and can help preserve highlight detail in high-contrast scenes.

Our calculator automatically adjusts development times based on the relationship between box speed and rated ISO, using industry-standard compensation factors for different film and developer combinations.

Temperature significantly impacts chemical reactions in film development. Higher temperatures accelerate development, requiring shorter times, while lower temperatures slow development, requiring longer times. The standard temperature for most black and white development is 20°C (68°F). Each 1°C increase typically reduces development time by about 10%, while each 1°C decrease extends it by about 10%. Temperature control is crucial—variations of even 1-2°C can noticeably affect results. Our calculator applies temperature compensation factors to provide adjusted development times. For color film, temperature control is even more critical, with much narrower acceptable ranges (typically ±0.5°C).

The three main film formats differ in size, handling, and typical usage:

• 35mm (135) film: The most common format, comes in cassettes with 24 or 36 exposures. Frame size is 24×36mm. Advantages include convenience, availability, and compact cameras. Best for everyday photography, travel, and situations requiring multiple shots.
• 120 (medium format) film: Larger film on a spool without a cassette, typically yielding 8-16 exposures depending on the camera format (6×4.5cm, 6×6cm, 6×7cm, etc.). Provides higher image quality than 35mm due to larger negative size. Ideal for portraits, landscapes, and commercial work where image quality is paramount.
• Sheet film (4×5, 8×10): Individual sheets of film loaded one at a time in specialized holders. Provides the highest image quality and maximum control with camera movements for perspective correction. Typically used for architectural photography, fine art, and other specialized applications where ultimate quality trumps convenience.

The calculator accounts for these differences when estimating how much film you'll need for a project.

Proper film storage significantly extends shelf life and preserves image quality:

Unexposed film:

• Refrigeration: Store at 4-10°C (39-50°F) for medium-term storage (6-18 months)
• Freezing: Store at -18°C (0°F) for long-term storage (several years)
• Humidity control: Keep relative humidity between 40-60%
• Original packaging: Keep film in sealed containers and original packaging
• Thawing: Allow refrigerated film to reach room temperature before opening (2-3 hours) to prevent condensation

Exposed but undeveloped film:

• Develop as soon as possible for best results
• If immediate development isn't possible, store in a cool, dry place
• Refrigerate for longer delays, but never freeze exposed film
• Keep away from X-rays, heat, and humidity
• Mark exposed film clearly to avoid confusion

Remember that expired film can still be usable but typically requires overexposure (1 stop per decade past expiration) and may show reduced contrast, increased grain, and color shifts.

Different developers produce distinct characteristics in the final image:

• Rodinal (Adox Adonal): One of the oldest developers still in use. Produces exceptional sharpness and accentuated grain. Economical with extremely long shelf life. Ideal for creating a classic, gritty look. Works well with Tri-X, HP5+, and Fomapan films.
• Kodak D-76/Ilford ID-11: The industry standard all-purpose developer. Offers an excellent balance of fine grain, sharpness, and full tonal range. Good for almost any black and white film. A great starting point for beginners.
• Ilford DD-X: Professional developer that delivers fine grain and excellent shadow detail. Particularly good for pushed processing and higher-speed films. Ideal for Delta and T-Max films.
• Kodak HC-110: Versatile, long-lasting concentrate. Produces good sharpness with moderate grain. Very convenient with its syrup-like concentrate that allows for one-shot development with small amounts.
• Pyro developers (PMK, Pyrocat-HD): Create a subtle mask that enhances printing contrast. Excellent for traditional darkroom printing. Produces exceptional sharpness and local contrast.

Our calculator provides adjusted development times for common film and developer combinations based on manufacturer recommendations and community experience.

Developer dilution affects development time, contrast, grain, and economy. Higher dilutions (more water) generally require longer development times, produce lower contrast, slightly increased grain, and more economical use of chemicals. For example, Rodinal can be used at 1+25 for standard development with moderate contrast and grain, or at 1+50 or 1+100 for lower contrast and more pronounced grain structure. D-76 can be used at stock strength for maximum sharpness and minimal grain, or diluted 1+1 for slightly more grain but better edge effects. The calculator accounts for common dilutions, but you should consult manufacturer recommendations for your specific developer and film combination. As a general rule, beginners should start with standard dilutions (often 1+1 for powder-based developers or 1+50 for concentrates like Rodinal) before experimenting with other ratios.

The amount of film to bring for a trip depends on several factors:

• Your shooting style: Documentary photographers might shoot 3-5 rolls daily, while deliberate landscape photographers might shoot 1 roll per day
• Destination uniqueness: Once-in-a-lifetime locations warrant bringing more film
• Availability at destination: If you can't buy film where you're going, bring extra
• Film format: 35mm shooters need more rolls than medium format users for the same number of frames
• Subject matter: Events, street photography, and action scenes typically require more frames than landscapes or architecture

As a general guideline, for a week-long trip, a moderate shooter might need 7-10 rolls of 36-exposure 35mm film, 10-15 rolls of 24-exposure 35mm, or 15-20 rolls of 120 film. The calculator provides a more precise estimate based on your specific shooting rate and trip duration. Always bring 25-50% more film than you think you'll need to account for unexpected opportunities or errors.

Modern airport security X-ray machines can damage unprocessed film, particularly with multiple exposures or higher-speed films (ISO 800+). To protect your film: (1) Keep film in a clear plastic bag and request hand inspection at security checkpoints (TSA in the US is required to accommodate these requests, though policies vary internationally). (2) If hand inspection is refused, ask for the film to go through the carry-on scanner, not checked baggage scanners which use stronger radiation. (3) Lead-lined bags are generally not recommended as they may trigger additional scrutiny. (4) Consider buying film at your destination for longer trips. (5) Always keep exposed film with you, never in checked luggage. (6) Remember that developed film (negatives and slides) is not affected by X-rays. The calculator's film usage estimates can help you determine exactly how much film to bring, minimizing what you need to carry through security.