09-11-2014, 08:57 AM

I just wanted to share an couple of equations I wrote(*) long ago to help in my photography classes.

The first one calculates equivalent exposure values. It was quite useful when working with an old mechanical camera and a very simple external lightmeter (that didn't allow exposure shifting or compensation).

EV100=INV(LOG(2))xLOG(AV^2xTV)-INV(LOG(2))xLOG(ISO/100)+COMP

Just enter the values for:

AV (Aperture value in f/ numbers)

TV (Time value in 1/seconds)

ISO

COMP (Exposure compensation in f/ stops)

Then claculate for EV100 (equivalent Exposure value for ISO 100) and now you can just enter new values for AV, TV, ISO or COMP, and calculate the rest for am aquivalent exposure level.

(NOTE) Due to the aproximative condition of TV and AV values in cameras (for example, 1/60 is used as double time of 1/125) the values obtained don't always match the ones available in camera dials.

The second one allows the calculation of the Hyperfocal and Depth of Field:

IF(S(HYP):F^2/(AVxCC)+F-HYPx1000:IF(S(DN):(Sx1000x(HYPx1000-F)/(HYPx1000+Sx1000-2xF))-DNx1000:(Sx1000x(HYPx1000-F)/(HYPx1000-Sx1000))-DFx1000))=0

In this case you have to enter first the focal length of the lens (F) in mm, confusion circle diameter (CC) in mm and aperture (AV) in f/ number, then solve for HYP (hyperfocal distance) that will be shown in meters (originally the equation used it in mm, that is why all those x1000 appear there).

Once we have the hyperfocal distance, enter the subjet distance (S) in meters, and solve for DN (near distance in focus) and DF (far distance in focus).

As the confusion circle diameter is fixed for each camera, I usually replace CC for its actual value, limiting the number of variables to six, so all of them fit in just one menu line.

(*) or, better said, I adapted them to work on HP Solve

Enjoy them!

The first one calculates equivalent exposure values. It was quite useful when working with an old mechanical camera and a very simple external lightmeter (that didn't allow exposure shifting or compensation).

EV100=INV(LOG(2))xLOG(AV^2xTV)-INV(LOG(2))xLOG(ISO/100)+COMP

Just enter the values for:

AV (Aperture value in f/ numbers)

TV (Time value in 1/seconds)

ISO

COMP (Exposure compensation in f/ stops)

Then claculate for EV100 (equivalent Exposure value for ISO 100) and now you can just enter new values for AV, TV, ISO or COMP, and calculate the rest for am aquivalent exposure level.

(NOTE) Due to the aproximative condition of TV and AV values in cameras (for example, 1/60 is used as double time of 1/125) the values obtained don't always match the ones available in camera dials.

The second one allows the calculation of the Hyperfocal and Depth of Field:

IF(S(HYP):F^2/(AVxCC)+F-HYPx1000:IF(S(DN):(Sx1000x(HYPx1000-F)/(HYPx1000+Sx1000-2xF))-DNx1000:(Sx1000x(HYPx1000-F)/(HYPx1000-Sx1000))-DFx1000))=0

In this case you have to enter first the focal length of the lens (F) in mm, confusion circle diameter (CC) in mm and aperture (AV) in f/ number, then solve for HYP (hyperfocal distance) that will be shown in meters (originally the equation used it in mm, that is why all those x1000 appear there).

Once we have the hyperfocal distance, enter the subjet distance (S) in meters, and solve for DN (near distance in focus) and DF (far distance in focus).

As the confusion circle diameter is fixed for each camera, I usually replace CC for its actual value, limiting the number of variables to six, so all of them fit in just one menu line.

(*) or, better said, I adapted them to work on HP Solve

Enjoy them!