# ND4 and ND8

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#### attap seed

##### Senior Member
i am thinking of buying ND filter to create some super long exposure.

ve some doubts to clear.

1. ND4 is 2 stops, ND8 is 4 stops, correct?

2. exposure calculation after puttin on ND8

in aperture priority, scene requires 20 sec at F8 (w/o filter)

so, after puttin on filter, exposure is 20 x 2 x 2 x 2 x 2 = 320 sec, rite?

3. any other advise is much welcome.

#### ExplorerZ

##### Senior Member
1. ND4 is 2 stops, ND8 is 4 stops, correct?
wrong, ND8 is 3 stop... they go buy power of 2 and not multiple

2. exposure calculation after puttin on ND8
in aperture priority, scene requires 20 sec at F8 (w/o filter)
so, after puttin on filter, exposure is 20 x 2 x 2 x 2 x 2 = 320 sec, rite?
:dunno: 3stops down... 160s f8 or 20s f2.8... 320s is correct if ND8 is 4stops(ND16)

3. any other advise is much welcome.

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#### JacePhoto

##### Senior Member
I wish i could help and i too wanted to ask the questions. Thanks for asking first, Attap Seed.

I think this is a place where fellow CSers can help to point out or advice others with their experience rather than asking them to read up. Remember that we were all newbies once. We were not born with a photography implant. Newbies who ask questions can also be experts in other fields.

There are many good patience photographers, one of them is night86mare and YouHong. I have benefitted from their guidnace. I am sure they and others will gladly share when others exhibit less of a patience.

#### attap seed

##### Senior Member
actually can goggle, but i jus lazy.

ok, now i know, ND4 is 2 stop, ND8 is 3 stops.

many thanks!

Staff member
2x = one stop
4x = two stops
8x = three stops
16x = four stops
32x = five stops
64x = six stops

#### giantcanopy

##### Senior Member
There are various nomenclature for stating the density of filters. As defined by Kodak in 1940s, a filter can be represented by its density ( n = 2^f ), f stop, transmission ( percentage ), the opacity

For example -

NDn absorbs f stop, 1/n ( 100/n% ) transmission, ND ( 3f/10 )

ND2 absorbs 1 stop , 1/2 ( 50% ) transmission, ND 0.3

ND4 absorbs 2 stops, 1/4 ( 25% ) transmission, ND 0.6

ND8 absorbs 3 stops, 1/8 ( 12.5% ) transmission, ND 0.9

and so on and so forth

ND400 translates to 8 2/3 stops, 0.25% transmission, ND 120

Makers do not have a standard for labelling their items. Singh Ray refers them by stops to cut confusion across. Lee and Tiffen refers them as 0.3, 0.6 ( for one and two stops ) The use of ND 2 / ND 0.3 can be rather confusing at times, do check out what exactly you are buying before hand

Ryan

#### attap seed

##### Senior Member
ok, thks.

i jus lookin at the basic hoya ND8.

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