GND's - What strength

[tgr141291]

Hi,

I have the cokein p system with the following GND's

P 121 L
P 121 M
P 121 S

What are the ND stregth's (number of stops for these filters)

And how to i calculate the number of stops when i stack them? (add or multiply)

thanks,

tom

[troutfisher]

I think from memory when I bought mine, S=1,M=2,L=3 ( thats how I use them) and you add the number of stops when stacking.

[tgr141291]

You'd have thought that;
S=Small
M=Medium
L=Large

But the L is the weakest ND

[troutfisher]

Thinking about it now I have probably got mine mixed up.I just choose the one that looks correct, ie Light, Med or Dark, soory for the confusion its old age

[tgr141291]

Do your figures still apply?

L=1stop
M=2stop
D=3stop

[troutfisher]

Looking on the bottom of mine they say
Cokin Z121L ( ND2)-lightest
Cokin Z121M ( ND4)-Medium
Cokin Z121L ( ND8)-Darkest
so I was wrong before
I have to admit now I assume that the 2,4 and 8 are stops but the cokin web site is no help either. The only other bit I can add is that I have an 8 stop ND filter ( not a grad) and visually the ND8 Grad looks about the same on the darkest portion, and thats how I use them but I am open to being corrected.I have to say I usually stick the one in that looks correct for the lighting and play, no very scientific I,m afraid

[Jon]

2 4 and 8 there aren't stops, they're filter factors corresponding to 1, 2 and 3 stops.

[troutfisher]

2 4 and 8 there aren't stops, they're filter factors corresponding to 1, 2 and 3 stops.


Thanks for that, I get more stupid as I get older, so really I was both right and wrong.
Repeat after me" Troutfisher is a stupid old b****r"!

[Jon]

A lot of people jump to that conclusion - age has nothing to do with it.

1 stop=2x=0.3ND
2 stop=4x=0.6ND
3 stop=8x=0.9ND

Those are the commonest ND descriptors.