Film Reciprocity Failure Adjustment Calculator

Overview

A high-performance, single-file browser utility designed for analog photographers. This tool calculates the required exposure compensation for long-exposure photography, ensuring that the Schwarzschild effect is accounted for to prevent underexposed negatives.

Core Features

• Film Preset Database: A dropdown containing common reciprocity coefficients (Schwarzschild exponents) for popular black and white and color negative film stocks.
• Custom Coefficient Input: Ability for advanced users to input custom exponents if a specific film stock is not listed.
• Real-time Calculation Engine: Instant calculation of the adjusted shutter speed based on the user's metered time.
• In-Browser Timer: A built-in, visual countdown timer that triggers once the "Start Exposure" button is clicked, helping the photographer time their manual "Bulb" mode exposures.
• Light-Mode Aesthetic: A clean, airy design featuring high-contrast typography, soft shadows, and a professional, calm color palette.

UI Layout Specification

• Header: Simple, clean title ("Reciprocity Failure Calculator") with a brief sub-headline explaining the tool's purpose.
• Main Input Section: A centered, card-based layout featuring:
  • An input field for 'Metered Time' (seconds).
  • A searchable dropdown for Film Stock presets.
  • A display area showing the 'Calculated Exposure' time.
• Timer Interface: A prominent, large-text display that activates upon starting the exposure, using a progress circle to visualize time elapsed.
• Results Area: A card showing the final math clearly, with "Copy to Clipboard" functionality.

Technical Constraints & Directives

• Architecture: Must be a single index.html file containing embedded CSS and JavaScript.
• Environment: Must function perfectly inside a sandboxed iframe. NO usage of localStorage, sessionStorage, or cookies.
• Responsive Design: Mobile-first approach. All elements must scale elegantly on phones (320px width) up to desktop resolutions.
• Interactivity: Use CSS transitions for button hover states and card appearances. Avoid browser-default alert() or prompt() calls; use a custom modal overlay if user feedback is required.
• Dependencies: Only reliable CDNs allowed (e.g., Google Fonts for typography, FontAwesome for icons). Do not use build tools like Webpack or Vite.

Visual Styling (Light-Mode Only)

• Background: Off-white (#F8FAFC) to reduce eye strain while remaining vibrant.
• Primary Accent: Professional Blue (#2563EB) for call-to-action buttons and active states.
• Typography: Sans-serif, geometric fonts (e.g., Inter, Montserrat) for a modern, clean look.
• Shadows: Subtle, soft shadows (elevation) on input cards to create depth without dark-mode styling.
• Animations: Ease-in-out transitions for input focus states (0.2s) and smooth opacity fading for the results section.

Implementation Note

The calculation logic must use the formula adjusted_time = base_time ^ coefficient where coefficient represents the Schwarzschild exponent for the chosen film stock. The application should handle input validation to ensure only positive integers/floats are accepted.