I downloaded an app for my iPhone (free) called "Light Meter"
It will expose like a point meter where you tap the screen, and then give camera settings it would use to meet that exposure.
Using the following calculation which makes some rough assumptions, you can calculate Lux from the values given.
lux = 50 x f.squared / shutter time (s) * ISO
The great thing about this application is that you can lock the ISO, shutter speed and f stop to anything you like.
Another great thing is that if you lock f stop and shutter speed, then the ISO will scale to any value, unlike the f stop and shutter speeds which are locked to the conventional camera scales.
I thus locked the camera settings at F5 and 1/2000th, giving
lux = 2,500,000 / ISO
This allows us to use a rough table as follows:
ISO >> lux
10 >> 250,000
20 >> 125,000
25 >> 100,000
33 >> 75,000
50 >> 50,000
100 >> 25,000
125 >> 20,000
250 >> 10,000
500 >> 5,000
1000 >> 2,500
1250 >> 2,000
2000 >> 1,250
4000 >> 625
5000 >> 500
10,000 >> 250
I've just used it here at work on as white objects as I can find.
The dark ish overcast sky outside is ISO 430 ~ 5,800 lux
My desk with a white piece of paper on it is ISO 2750 ~ 900 lux (a little bright, they are new lights and we often turn them off as they are too bright!)
So far it seems fairly accurate, and as a free app on the iPhone, with an ISO that scales to any integer right up to silly big numbers, it seems really good as a rough gauge for people wanting to collect real intensity values on the move!
Also great because once you have grabbed the ISO/lux, you can then take an image of the same scene too, great for skies or sunsets or whatever you are capturing!
Feel free to post values you have found, or other techniques on here, to make it a useful resource for anyone wanting easy ways to get realistic values for their environments.
Dave
It will expose like a point meter where you tap the screen, and then give camera settings it would use to meet that exposure.
Using the following calculation which makes some rough assumptions, you can calculate Lux from the values given.
lux = 50 x f.squared / shutter time (s) * ISO
The great thing about this application is that you can lock the ISO, shutter speed and f stop to anything you like.
Another great thing is that if you lock f stop and shutter speed, then the ISO will scale to any value, unlike the f stop and shutter speeds which are locked to the conventional camera scales.
I thus locked the camera settings at F5 and 1/2000th, giving
lux = 2,500,000 / ISO
This allows us to use a rough table as follows:
ISO >> lux
10 >> 250,000
20 >> 125,000
25 >> 100,000
33 >> 75,000
50 >> 50,000
100 >> 25,000
125 >> 20,000
250 >> 10,000
500 >> 5,000
1000 >> 2,500
1250 >> 2,000
2000 >> 1,250
4000 >> 625
5000 >> 500
10,000 >> 250
I've just used it here at work on as white objects as I can find.
The dark ish overcast sky outside is ISO 430 ~ 5,800 lux
My desk with a white piece of paper on it is ISO 2750 ~ 900 lux (a little bright, they are new lights and we often turn them off as they are too bright!)
So far it seems fairly accurate, and as a free app on the iPhone, with an ISO that scales to any integer right up to silly big numbers, it seems really good as a rough gauge for people wanting to collect real intensity values on the move!
Also great because once you have grabbed the ISO/lux, you can then take an image of the same scene too, great for skies or sunsets or whatever you are capturing!
Feel free to post values you have found, or other techniques on here, to make it a useful resource for anyone wanting easy ways to get realistic values for their environments.
Dave