# Thread: Filters: 2x stacked ND4 equals ND8? or ND16

1. ## Filters: 2x stacked ND4 equals ND8? or ND16

Curious. Does stacking 2 ND4 filters add up to ND8 or ND 16??
How about closeup filters? [+4] stacked above another [+4] = +8?

2. ND16

.. same to ND8 + ND8 .. become ND64

3. really? then +1 stack +4 == +4?
I thought the stops were powers of 2

4. heh is there a +1?

5. heh paiseh didn't know the numbers not in stops but in 2^stops...

6. OK.. I get it! thanx megaweb!

7. what if u stack say 4 n 2?? = 8? or something else???

8. ND4 lets in 25% of the light.. ND2 lets in 50% of the light.

so when you stack 2x ND4, you get 25% of 25%, hence something similar to ND16.

9. Originally posted by shawntim
ND4 lets in 25% of the light.. ND2 lets in 50% of the light.

so when you stack 2x ND4, you get 25% of 25%, hence something similar to ND16.
Would that mean that if i were to stack ND4 n ND2

it would mean it would be 25% of 50% ?? assuming the ND2 is the filter on the top of ND4??

10. Originally posted by Revo

Would that mean that if i were to stack ND4 n ND2

it would mean it would be 25% of 50% ?? assuming the ND2 is the filter on the top of ND4??
25% of 50% and 50% of 25% is the same thing right? so you'll let in only 12.5% of light which is the same as ND8 (100/8)

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