Neutral density filter question.

pbromaghin · Apr 15, 2014

I have an odd-ball neutral density filter. It's a Kodak Series VI and it says it is a 2.5. Looking around I see info on 2.4 and 2.6, but no 2.5.

Does that number mean it is a number 2.5 and so about 8 stop, or is it a factor of 2.5 and so a little more than 1 stop?

Dan Fromm · Apr 15, 2014

pbromaghin said:
I have an odd-ball neutral density filter. It's a Kodak Series VI and it says it is a 2.5. Looking around I see info on 2.4 and 2.6, but no 2.5.

Does that number mean it is a number 2.5 and so about 8 stop, or is it a factor of 2.5 and so a little more than 1 stop?

You have it. Why don't you look through it? -1 stop doesn't look at all like -8 stops.

LJH · Apr 15, 2014

Dan Fromm said:
You have it. Why don't you look through it? -1 stop doesn't look at all like -8 stops.

Or just meter through it.

pbromaghin · Apr 15, 2014

You have it. Why don't you look through it? -1 stop doesn't look at all like -8 stops.

Hmm. Good question. It's the only neutral density filter I have. I've never dealt with them before and so have no basis from which to judge.

I plan to be using iso 400 film in an old folder with a fastest shutter of 1/250. In the past a red filter has worked with B&W to get the exposure down to what the shutter can handle. I found this in the drawer and thought it would work for color film.

pbromaghin · Apr 15, 2014

LJH said:
Or just meter through it.

Another good suggestion. It's a Series VI which is quite a bit smaller diameter than any lens I have for a metered camera.

RalphLambrecht · Apr 15, 2014

Yes,81/3 stopsstops go in o.3 density steps0.1 density is a 1/3 stop.

Bill Burk · Apr 15, 2014

Hmm won't fit a camera with a meter...

How about shining a light on a table with a beam that you can cover with the filter... Meter the light before and after.

Ian C · Apr 16, 2014

Depending on the filter makers policy, ND filters can be marked in:

1. Density units

2. Stops of light absorbed

3. Time multiplication factor

I have examples of each type in my possession.

For example, 0.40 ND = 1.5 stop = 2.5X time factor. Each value describes the same filter expressed in different units.

I suspect that your 2.5 filter is time factor 2.5X.

pbromaghin · Apr 16, 2014

From looking at this link, posted by Shootar401, I suspect Ian is right. On page 17 there is a chart with densities, transmission percent and fraction, as well as multiplying factor. Factor 2.5 is listed but the densities go only to 2.0, which is 1% transmission. Factor 2.5 would make this one a ND 0.4.

https://archive.org/stream/WrattenLightFilters/Kodak-WrattenFilters#page/n9/mode/2up/search/neutral

Thank you all for helping

pbromaghin · Apr 17, 2014

Now that I have seen the filter in good light, I feel really stupid for even starting this thread. It says very clearly on the edge of the filter - 2.5x multiplication factor - meaning a little over 1 stop. Thanks to all of you for your help.

Neutral density filter question.

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