Luxmeter as Lightmeter

[ForenSeil]

I found a cheap luxmeter (~18€) and was curious how precise it might work as photographic lightmeter.
The luxmeter gives you only Lux as measurement unit, so you need a formula for to get ISO/aperture/shutter speed values.

The formula is
[Lux] = 250/[ISO] * [aperture]^2/[time]

Since I'm not good enough in mental arithmetic, I made a little table as mnemonic for my mostly used ISOs and fixed it with tesa on the front first.
(made at ISO 3200, F2.8, 1/60s; NEX said the same as the chart )
After that I made and fixed a full chart on the back of the device:


EDIT: How to use:

For exampe if you have ISO 400 film, you'r aperture was set to F5.6 und your luxmeter shows a value around 8000 lux - than your correct speed is 1/500s
Of course you could also do it the other way round.
If anyone has an idea for an more clearly arranged chart, please share it!

I've tested it on NEX in M-Mode and afterwards on film.
The results are amazingly precise! - far more precise than very most cheap lightmeters and it can easily compete against the build-in NEX lightmeter.
Only drawback is - of course - that you have to look on the table first to find your exposure times - which makes it a little slower than a professional lightmeter - and you can't do spot measuring.
But if your lightmeter doesn't have a calotte for ambient light and you need one for hard conditions were spot or analog TTL often producing bullshit (sun+snow, sun+beach, dark stuff, low key,...) it's an really cheap and good alternative to an professional lightmeter.

[Attila]

Excellent thank you for sharing it!

[Farside]

Very, very useful, thanks.

[LucisPictor]

Thanks a lot. I will definitely try that. I also have one of those luxmeters at home.

[std]

How do you read this table?
i have a masters degree but still can't figure it out

[ForenSeil]

[std]

Nice
It's a good puzzle.

[Attila]