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

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#### viix

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

#### megaweb

##### Moderator
Staff member
ND16

.. same to ND8 + ND8 .. become ND64

#### denizenx

##### Senior Member
really? then +1 stack +4 == +4?
I thought the stops were powers of 2

#### denizenx

##### Senior Member
heh is there a +1?

#### denizenx

##### Senior Member
heh paiseh didn't know the numbers not in stops but in 2^stops...
;p

#### viix

##### New Member
OK.. I get it! thanx megaweb!

#### Revo

##### New Member
what if u stack say 4 n 2?? = 8? or something else???

#### shawntim

##### New Member
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.

#### Revo

##### New Member
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??

#### shawntim

##### New Member
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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