[DM41X] Sunny F16 rule

Contributed programs for the DM41 go here.
Post Reply
jthole
Posts: 82
Joined: Mon Nov 27, 2017 7:46 pm
Location: Netherlands

[DM41X] Sunny F16 rule

Post by jthole » Mon Feb 03, 2020 9:28 am

This program was tested on the DM41X, but should run on the DM41 as well (no additional modules required)

A rough way to estimate exposure is the "Sunny F16" rule, which determines that the following works for a sunny day with a clear sky:

ISO = 100
1/t = 100
F = 16

The following program computes the aperture value (F-stop) given the following inputs:

Z-register = ISO value
Y-register = 1/t (taking 125 as base, because digital sensors like slight underexposure)
X-register = EV adjustment (0 = clear sky, 1 = slightly cloudy, 2 = overcast, 3 = heavy overcast, 4 = rain or sunset)

The output produced is the desired F-stop value. The user is expected to press R/S to end the program.

N.B. currently the program assumes that FIX 6 must be set as the last step (that is what I use, because of date and time display).

Examples:

Z=100 (ISO value)
Y=125 (shutter time)
X=0 (EV adjustment, clear sky on a sunny day)

XEQ FSUN

F= 16.0

Z=200 (base ISO for several sensors)
Y=500 (shutter time = 1/500)
X=2 (overcast sky)

XEQ FSUN

F= 5.7 (the closest F-stop will be 5.6).

Code: Select all

LBL "FSUN"
FIX 01
2
X<>Y
Y^X
*
X<>Y
/
SQRT
17.8885
X<>Y
/
"F= "
RND
ARCL X
AVIEW
STOP
FIX 06
END
Edit:I just realise that the STOP instruction is not really needed; AVIEW already pauses the display until a key is pressed.
Attachments
fsun.raw
(84 Bytes) Downloaded 73 times

Post Reply