## Converting between Gain and f-Stops

So cameras work in Stops and composite packages use Gain. To convert between the two we need to do a bit of log maths. Heres how.

To convert from Stops (f) to Gain

Gain = 2f

To convert from Gain to stops (f)

f = logGain

This is equivalent to:

f = ( log10 Gain ) / ( log10 2 )

If you want to see why then we’ll need to look a little deeper at log maths

# Introduction

This tutorial will shows the relationship between Filmback, Aperture, Field of View, and Lens size.

Understanding the 3dsMax camera filmback is useful if you want to replicate real world cameras or accurately extend the frame size and crop it later in a composite package.

The setup for the 3dsMax camera is slightly buried. To replicate real world cameras we’ll look in two areas: the render dialog and the camera dialog.

To simplify the process I have developed this MaxScript which is free to download here.

Like it or not spreadsheets are just too useful. Having the right formula to hand can really make things easier. Plus for me writing a bit of code serves to alleviate the tedium of data entry.

This expression will calculate the difference between two timecodes and spit out the answer in frames. Each cell must written using 11 characters in the standard timecode format. e.g.    10:23:07:24

This version works at 25 FPS and will subtract the IN point cell ‘G4’ from the OUT point cell ‘H4’.

`((MID(H4;1;2)*3600+MID(H4;4;2)*60+MID(H4;7;2))*25+MID(H4;10;2))-((MID(G4;1;2)*3600+MID(G4;4;2)*60+MID(G4;7;2))*25+MID(G4;10;2))`

You can change the frame-rate by swapping the 25 for a different number.

## How it works

The MID function simply grabs individual characters from a cell.

`MID(H4;7;2)`

Will grab 2 characters from cell H4 starting with the 7th character in the string.
E.g. It will grab 07 from 10:23:07:24

`MID(H4;7;2))*25`

07 seconds * 25 fps = 175 frames

## Its simple really.

Now with latest version of eyeon Fusion working camera LUT’s couldn’t be easier. The profiles are all included. The my new workflow is very simple.