ND400 Filter. Why is it so called?? And what's with the 0.3, 0.9 etc?

Started Dec 22, 2010 | Discussions thread
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plevyadophy
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ND400 Filter. Why is it so called?? And what's with the 0.3, 0.9 etc?
Dec 22, 2010

I have two questions about ND filter, with which I hope someone can help

( 1 )

Hoya do a 9 stop ND filter which they call the ND400, but to my mind (based on the table below) it ought more logically to be called an ND512 flter. So why is it called ND400?

Stops...........Filter Designation................Remaining Light

1..................ND2.................................half
2..................ND4.................................quarter
3..................ND8.................................1/8th
4..................ND16...............................1/16th
.
.
.
9..................ND512..............................1/512th

10................ND1024.............................1/1024th (actually rounded down to 1/1000)

( 2 )

Now the likes of B+W, Helopian, and Lee Filters use a rather (to my mind) ridiculous desingation system, whereby they use designations such as 0.3, 0.6 etc.
Why do they use that designation? Where does it come from?

Stops...........Filter Designation................Remaining Light

1..................ND 0.3.................................half
2..................ND 0.6..............................quarter
3..................ND 0.9..............................1/8th
4..................ND 1.2.............................1/16th
.
.
.

10................ND 3.0.............................1/1024th (actually rounded down to 1/1000)

Thanks in advance.

Regards,

plevyadophy

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