In may last post titled "Ebony 4x5 view camera", I mentioned an app I use to calculate depth of field called pCAM. Originally created in 1998 for the Palm Pilot by a working Camera Assistant, pCAM is an app for iOS devices "sorry android users" that helps quickly obtain calculations for a multitude of functions related to still photography and cinematography. I highly recommend this app and as I stated I use it all the time for depth of field and hyperfocal distance calculation. The focal length matching function is another handy calculation for determining focal length over several different formats such as 35mm to 4x5. other functions include...

Depth of Field, Hyperfocal Distance & Image Circle
Splits-Aperture Finder
Field of View (Image size) with 8 Preview Illustrations & Angle of View. Works in both Portrait and Landscape camera positions.
Focal Length Matching
Relative Size (compares digital sensors or film apertures)
Triangulate
Exposure (compensating changes in Shutter Angle, FPS Speed, Filters, Film Speeds, Exposure Time & Light foot-candles or lux)
Running Time to Length
Shooting to Screen Time
HMI Flicker-free
Color Correction (filters and mireds)
Diopter
Macro
Time Lapse
Underwater Distance (flat ports)
Scene Illumination
Light Coverage
Mired Shift (with Suggested Color Correction gels)
Light (eye-light, catch-light, miniature softbox, or for tabletop photography.
Light Effects (Animated light effects such as fire, strobe, lightning, police lights, blinking neon, flashbulbs, etc.) Can be used on HDTV screens via AppleTV and AirPlay. Playback Light Effects on HDTV screens!
Conversion Calculator(Length, Distance, Kelvin/Mired/Decamired, Footcandles/Lux)
Siemens focus Star
Insert Slate
Reference (Technical charts, lists and tables: Cine Film Stocks, Cine Lens Manufacturers, False Color/Exposure Change Miniature Shooting, Safe Panning Speeds, Zone System).
Includes all common professional Still Camera, Film & HD Camera Formats
User-definable custom Camera Formats, CoC & Filters