text: ## Formula to Calculate ideal subject height
  
  https://www.scantips.com/lights/subjectdistance.html
  
  Real Object height * = Distance to Object * × Object height on sensor (mm)/Focal Length (mm)
  
  • feet or meters (but both are same units)
  d = 10 # feet
  FFsensorHeightmm = 23.9 # mm
  f = 200 # mm
  
  Assume you want to fill 70% of sensor height.
  
  Real target object height =
  
  rh<- d*0.7*FFsensorHeightmm/f
  rh * 12  # convert feet to inches
  ## [1] 10.038
  
  Any real target less than 10 inches will fill less than 70% of sensor height at 10’ distance.
  
  ## DOF
  
  https://en.wikipedia.org/wiki/Depth_of_field
  
  https://en.wikipedia.org/wiki/Zeiss_formula
  
  DOF approx = 2d^2 * fNum * c/f^2
  
  c = ((FFsensorHeightmm^2 + FFsensorWidthmm2)0.5)/1500
  
  FFsensorWidthmm = 35.9 # mm
  c = ((FFsensorHeightmm^2 + FFsensorWidthmm^2)^0.5)/1500
  c
  ## [1] 0.02875197
  # Using above example with fNum = 5.6
  fNum= 5.6
  DOF = (2*(d*304.8)^2 * fNum * c)/f^2
  DOF * 0.0393701
  ## [1] 2.944571
  
  Result roughly agrees with result from https://dofsimulator.net/en/ 2.9" vs 2.8" correct answer.
  
  ## Tables
  
  For a given real object (e.g., warbler), you can rearrange formulas to calculate zoom for a given distance and a desired fill of the vertical sensor height. Assuming a reasonable DOF for that target, you can calculate the fNumber as well (which is constant for a specific target and sensor fill).
  
  ### Warbler 3" bird height, 1" DOF
  
  ans # fill 70% of sensor height
  ##      dist   zoom     fNum
  ## [1,]    5  334.6 21.29208
  ## [2,]   10  669.2 21.29208
  ## [3,]   20 1338.4 21.29208
  ## [4,]   50 3346.0 21.29208
  ans # fill 50% of sensor height
  ##      dist zoom     fNum
  ## [1,]    5  239 10.86331
  ## [2,]   10  478 10.86331
  ## [3,]   20  956 10.86331
  ## [4,]   50 2390 10.86331
  ans # fill 33% of sensor height
  ##      dist    zoom     fNum
  ## [1,]    5  157.74 4.732056
  ## [2,]   10  315.48 4.732056
  ## [3,]   20  630.96 4.732056
  ## [4,]   50 1577.40 4.732056
  
  ### Blue Jay 6" bird height, 3" DOF
  
  ans # fill 70% of sensor height
  ##      dist   zoom     fNum
  ## [1,]    5  167.3 15.96906
  ## [2,]   10  334.6 15.96906
  ## [3,]   20  669.2 15.96906
  ## [4,]   50 1673.0 15.96906
  ans # fill 50% of sensor height
  ##      dist   zoom    fNum
  ## [1,]    5  119.5 8.14748
  ## [2,]   10  239.0 8.14748
  ## [3,]   20  478.0 8.14748
  ## [4,]   50 1195.0 8.14748
  ans # fill 33% of sensor height
  ##      dist   zoom     fNum
  ## [1,]    5  78.87 3.549042
  ## [2,]   10 157.74 3.549042
  ## [3,]   20 315.48 3.549042
  ## [4,]   50 788.70 3.549042
  
  ### Duck? 12" bird height, 6" DOF
  
  ans # fill 70% of sensor height
  ##      dist   zoom    fNum
  ## [1,]    5  83.65 7.98453
  ## [2,]   10 167.30 7.98453
  ## [3,]   20 334.60 7.98453
  ## [4,]   50 836.50 7.98453
  ans # fill 50% of sensor height
  ##      dist   zoom    fNum
  ## [1,]    5  59.75 4.07374
  ## [2,]   10 119.50 4.07374
  ## [3,]   20 239.00 4.07374
  ## [4,]   50 597.50 4.07374
  ans # fill 33% of sensor height
  ##      dist    zoom     fNum
  ## [1,]    5  39.435 1.774521
  ## [2,]   10  78.870 1.774521
  ## [3,]   20 157.740 1.774521
  ## [4,]   50 394.350 1.774521
  
  ### Penguin 25" bird height, 7" DOF
  
  ans # fill 70% of sensor height
  ##      dist    zoom     fNum
  ## [1,]    5  40.152 2.146242
  ## [2,]   10  80.304 2.146242
  ## [3,]   20 160.608 2.146242
  ## [4,]   50 401.520 2.146242
  ans # fill 50% of sensor height
  ##      dist   zoom     fNum
  ## [1,]    5  28.68 1.095021
  ## [2,]   10  57.36 1.095021
  ## [3,]   20 114.72 1.095021
  ## [4,]   50 286.80 1.095021
  ans # fill 33% of sensor height
  ##      dist     zoom      fNum
  ## [1,]    5  18.9288 0.4769913
  ## [2,]   10  37.8576 0.4769913
  ## [3,]   20  75.7152 0.4769913
  ## [4,]   50 189.2880 0.4769913
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