Cinematography-Theory-And-Practice

N = f/numberm = magnificationWhere magnification is calculated by the formula:image sizemagnification =object sizeLens Displacement When Focused Closer Than InfinityWhen focused closer than infinity, front elements of the lens (or allthe elements) are moved away from the focal plane. This is importantin calculating exposure loss in extreme close-up work.d =f2a - fd = lens displacement from infinity positionf = focal length of lens in inchesa = distance focus in inchesCLOSE-UP TOOLSExtreme close-up photography can be accomplished with a varietyof tools; as with all optics, the basics are the same whether you areshooting film, digital, regular video, or High Def.DioptersDiopters are simple meniscus lenses that are placed in front of thecamera lens and reduce the minimum focusing distance of the lens.The lenses are measured in diopters, which is the reciprocal of thefocal length as measured in meters. A plus 1 diopter has a focallength of 1 meter, a plus 2 is 1/2 meter, and so on. Minimum focusingdistance with the lens set at infinity is determined by dividingthe diopter number into 100 cm. For example, a +2 diopter is 100/2= 50 cm. This equals 19.68 inches. You will actually be able to focusa bit closer by changing the focus of the lens itself.A diopter is defined as the reciprocal of the focus of this accessorylens in meters — that is, one divided by the focal length. Thus, a plusone is a magnifying lens of one meter’s focus; a plus 1/2 is a mildermagnifier that focuses at two meters. A plus two focuses at one-halfmeter, 500 millimeters. A plus three at 333 millimeters.This spec shows you the farthest working distance you can work;put a plus one-half on your normal camera lens, set it on infinity, thefarthest, and objects two meters away are in focus. Nothing farthercould be shot sharp. Put on a plus one and the max working distanceis one meter. Put on a plus two and stuff has to be 500 millimeters, orhalf a meter, or about 19 inches away (from the front of the diopter,not the film plane) to achieve sharpness. All those cases are with themain lens (prime or zoom) “set at infinity.”A split diopter is one of these magnifiers split in half, like a halfmoon.It covers half your field, and the stuff seen through the glassis focused closer, and the other half, which is missing ( just air), willbe focused where the main lens is set. Put a plus one-half split onyour camera. Focus the main lens at infinity. One-half of the field,through the diopter, is sharp at 2 meters. The rest of the field isfocused at infinity. If you set the lens at 15 feet, the clear half isfocused at 15 feet and the diopter half might focus at 1 1/3 meters.The point is to fake extreme deep-focus effects. There’s a fuzzy lineat the edge of the split diopter in the middle of your picture, andthis has to be hidden artfully in the composition, which is often donewith a telephone pole, a shrub or some other object that is indistinct.Diopter - Focus Conversion Chart(can be used with any focal length - any format)Diopter power+1/2+1+2+3Focusdistanceof lensInfinity25'15'10'6'4'Infinity25'15'10'6'4'Infinity25'15'10'6'4'Infinity25'15'10'6'4'Actual distancefrom diopterto subject78-3/4"62-1/2"54-3/4"47-1/2"37-3/4"29-3/4"39-1/2"34-3/4"32-1/2"29-3/4"25-1/4"21-3/4"19-3/4"18-1/2"17-3/4"16-3/4"15-1/2"14"13-1/4"12-1/2"12-1/4"11-3/4"11-1/4"10-1/2"Table 14.1. Focus with diopters.optics & focus283