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Luxmeter as Lightmeter
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PostPosted: Sat Oct 06, 2012 12:00 am    Post subject: Luxmeter as Lightmeter Reply with quote

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 Smile)
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! Wink

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.


Last edited by ForenSeil on Sat Oct 20, 2012 5:16 am; edited 12 times in total


PostPosted: Sat Oct 06, 2012 1:12 am    Post subject: Reply with quote

Excellent thank you for sharing it!


PostPosted: Mon Oct 08, 2012 1:40 pm    Post subject: Reply with quote

Very, very useful, thanks.


PostPosted: Mon Oct 08, 2012 2:12 pm    Post subject: Reply with quote

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


PostPosted: Mon Oct 08, 2012 2:24 pm    Post subject: Reply with quote

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


PostPosted: Mon Oct 08, 2012 5:19 pm    Post subject: Reply with quote

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


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 for example

Of course you could also do it the other way round.

If has an idea for an more clearly arranged chart, please share it! Wink


Last edited by ForenSeil on Tue Oct 09, 2012 1:45 pm; edited 3 times in total


PostPosted: Mon Oct 08, 2012 5:41 pm    Post subject: Reply with quote

Nice Smile
It's a good puzzle.


PostPosted: Mon Oct 08, 2012 6:00 pm    Post subject: Reply with quote

std wrote:
Nice Smile
It's a good puzzle.


Don't ashamed Stefan I also couldn't figure out Laughing thank you for explanation.