Luminous Landscape Forum

Equipment & Techniques => Cameras, Lenses and Shooting gear => Topic started by: Guillermo Luijk on April 10, 2025, 04:13:22 am

Title: Cropping DoF calculator
Post by: Guillermo Luijk on April 10, 2025, 04:13:22 am
Have you ever achived a given focal length cropping a fixed lens? this is what all smartphones do ("digital zoom"), but also serious high resolution cameras like the Leica Q3 or the new Fujifilm GFX 100RF play this game.

To find out how DoF gets modified after the cropping and what native lens would have provided the same DoF as your cropping, enter 4 parameters in the calculator and that's it:

Link to calculator:
https://docs.google.com/spreadsheets/d/1HYkLnIs1ZYKNpN5sSevFrarJF_4aLnUH/edit?usp=sharing&ouid=108439842499958120951&rtpof=true&sd=true

E.g.:
"When in a 35mm lens at f/2 we crop the FOV of a 50mm equivalent lens, we get aprox. the same DoF (27cm in FF) as using a native 50mm lens at f/2,8 (~0,8 stops slower)"

(https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgI4OwNn65s6EYGT7R7c26YLEPlEFKYmuh2KSqrP3V3_KoQtL1nVPA0WCq91nkU4koqImQlHu3CbQ8ikYDJ7cznZlNHjYko0cGZnN6rEjQ6GP3DbNKn7M0mkCjHBavnxHr7_1wJMXL6egBosmoTMZEWzs9L1JCdviECcQu69PD3AoV48JFGJ2uUqNqbOfgn/s1600/pdc_recorte800.png)

There is a tab in English.

Regards
Title: Re: Cropping DoF calculator
Post by: Chris Kern on April 10, 2025, 11:06:34 am
Interesting.  Thanks for making this available.
Title: Re: Cropping DoF calculator
Post by: Guillermo Luijk on April 15, 2025, 03:22:08 pm
When using the simplified version of the DoF equations (valid on non-macro applications where focal length << focus distance), the effect of focus distance cancels in the equations and the equivalent DoF of the crop can be easily calculated multiplying the f-number by the native/cropped focal length ratio:

(https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9MbwjeNkHoQbAIhwZx__Svato_qSk8YRoEv-fzUz0UQLsjIvipOLsCv4Nk4Gp5Lu9SJ5S1f_QDOLx_-WRTIbZmegeeAGqX9uDhQXJY6elDbCs65KqiqRmmxTBoATbEvUIBPM5vNpUueGZkOQAPsxHpAJs3vc4IH33FStG_rTk9pGcuDJDTlA1rc_rJR_p/s16000/cropdofaproxequationbn.png)

By applying this approximation to the Leica Q3 (Summilux 28mm f/1.7) crop modes we get the following equivalent DoF's:

Regards