Table showing distance of object upon which to focus with any stop in order to secure the greatest depth (hyper focal distances).

To Find the Hyper Focal Distance the formula is : - Focal length squared, - ratio of stop X circle of confusion. Now when making these tables it is generally assumed that a point represented as a circle of confusion not exceeding 1/100th inch in diameter will be considered satisfactory as regards definition in the negative. Then by the above formula suppose we have a lens of 5-inch focus with stop f/8 the hyper focal distance will be

If we, therefore, withsuch a lens and stop focus on 26 feet we shall have objects from half that distance (13 feet) to Infinity in good focus.

Mr. Welborne Piper, in his useful book on " The Lens," has pointed out the interesting fact that if we divide the hyper focal distance by 1,2, 3, 4, 5, etc., we shall get a set of distances such that, if we focus on any one of them, the next two distances on the scale are the distances of the furthest and nearest objects in focus. Say the hyper focal distance is 30 feet, then 30/1, 30/2, 30/3, 30/4, etc., will represent 30, 15, 10 and 7 1/2 feet, and if we focus, say, on 10 feet then the 15 and 7 1/2 ft. will be the near and far depths, or on 30 ft. then on Infinity and 15 ft.

To Calculate Near Depth when Focussing on near objects.

Formula. - Distance of object in focus X Hyper focal distance. Distance of object in focus + Hyper focal distance.

Example. Hyper focal distance 26 feet object at 8 feet,

For far depth the formula is

Distance of object in focus X hyper focal distance. Distance of object in focus - hyper focal distance.

If the sharp focus is secured at Infinity, then, with the stop indicated, all objects are in focus from the above distances up to Infinity. If, however, the pointer is set to the above distances then, with the stop indicated, all objects are in focus from half the distance focussed up to Infinity. These figures are based on a circle of confusion of 1/100th of an inch, and the distances must be reduced if greater sharpness is desired.

 Focal lengthLens in inches. Apertures marked on Stops. f/4 f/5•6 f/6 f/7 f/8 f/10 f/11 f/15 f/16 f/20 f/22 f/32 f/44 f/64 BEST POINT ON WHICH TO FOCUS IN FEET. 4 33 24 22 19 17 13 12 9 8 7 6 4 3 2 4 1/4 38 27 25 21 19 15 14 10 10 7 7 5 34 2 1/2 4 1/2 42 30 28 24 21 17 15 11 11 8 1/2 7 1/2 54 4 3 4 3/4 47 34 31 27 24 19 17 12 12 9 1/2 8 1/2 6 5 3 5 52 36 35 30 26 21 19 14 13 10 1/2 94 6 1/2 54 34 5 1/4 57 40 38 33 28 23 21 15 14 11 1/2 10 1/2 7 54 34 5 1/2 63 45 43 36 31 25 23 17 15 12 1/2 11 1/2 74 6 4 5 3/4 68 50 46 38 34 27 25 18 17 13 1/2 13 8 1/2 64 4 6 75 54 50 42 38 30 28 20 19 15 14 9 7 44 6 1/4 81 58 54 46 40 32 29 22 20 16 15 10 74 5 6 1/2 87 62 58 50 44 35 32 23 22 17 1/2 16 11 8 54 6 3/4 94 67 63 54 47 38 34 25 24 19 17 12 84 6 7 101 72 68 58 51 40 37 27 25 20 18 12 1/2 9 6 7 1/4 109 78 73 62 54 44 39 29 27 22 20 13 1/2 10 64 74 117 83 78 64 58 47 42 31 29 24 21 14 1/2 10 1/2 7 7i 124 90 83 71 62 50 45 33 31 25 22 15 1/2 11 74 8 132 96 88 76 68 52 48 36 32 28 24 16 12 8 8 1/4 141 102 94 80 71 56 51 37 35 29 25 17 1/2 12 1/2 84 8 1/2 151 107 100 84 76 60 54 40 38 30 27 19 13 1/2 9 8 3/4 156 114 104 89 78 63 57 42 39 32 29 20 14 10 9 168 120 112 96 84 67 61 45 42 34 31 21 15 10 1/2 9 1/4 180 127 116 101 90 71 65 47 45 35 32 22 16 11 9 1/2 190 133 125 107 95 75 68 50 47 37 34 24 17 12 9 3/4 197 141 131 113 99 79 72 52 50 39 36 25 18 12 1/2 10 208 148 140 120 104 83 75 55 52 42 38 26 19 13