[ColdEye]

I see, Thanks, now I gotta try this.

[mattt]

I'm confused about numbering on ND filters. I asked for a three stop filter, and I was sold a filter marked ND8, and on the back of the packaging is a table with different lighting conditions: daylight/morning&evening/cloudy/ clear flash etc etc. How do I read that information? Cheers and thanks for the tips - good stuff.

[twitch]

I'm confused about numbering on ND filters. I asked for a three stop filter, and I was sold a filter marked ND8, and on the back of the packaging is a table with different lighting conditions: daylight/morning&evening/cloudy/ clear flash etc etc. How do I read that information? Cheers and thanks for the tips - good stuff.

2 ^ 3(stops) = 8, so you were sold the right one. There's three ways the ND's are refered to, number of stops ("3 stop"), power of 2 (3 stops is ND8), or as a log (3 stops is ND 0.9). Confusing I know.

[tuco]

ND filters are usually given by their filter factor or density. It's nice when they advertise the stops too. So you may see ND.3, ND.6 or ND.9, for example, for the density of the filter. And 1-stop ≈ 0.3 density. So a ND.6 would be 2-stops.

They are also given by filter factor. Usually like NDX400 or ND400-X where 400 is the filter factor. And finding the stops from the filter factor you can use either the natural log, ln, or log base 10 ( or look it up on wikipedia)

stops = ln(filter factor)/ln(2)

Examples:

ln(400)/ln(2) ≈ 8.64 = say 9 stops
ln(1000)/ln(2) = 10 stops

And then you see advertisement that simply says ND8. Here you'd assume they mean filter factor since a 3-stop is very common. But an advertisement like the following looks like a mix of density and filter factor:

Multi-Coated Variable Range (ND3, ND6, ND9, ND16, ND32, ND400) Neutral Density (ND) Fader Filter

---

Last edited by tuco; 07-13-2011 at 05:29 PM.

[titrisol]

I remember Hedgecoe saying that 10s was sufficient if people are moving...


I guess 1 minute is more like it.

[Francis]

That looks a bit too "Ghost Hunters International" since there's not enough traffic. Nevertheless it is a nice photo!

[titrisol]

The ghosts of the museum!!! LOL
My thoughts exaclty!!!

Thus ,longer expo would have helped but after 10s it overexposed too much in the DSLR (even at ISO100) and I didi not carry a ND filter with me.

That looks a bit too "Ghost Hunters International" since there's not enough traffic. Nevertheless it is a nice photo!

[gofour3]

Try one of the slower Adox/Efke CHS 25 ISO films or the Adox CMS 20 ISO.
You will be able to get slower shutter speeds just using a b&w contrast filter or polarizer. No need for a ND filter.

Phil.

[tuco]

Try one of the slower Adox/Efke CHS 25 ISO films or the Adox CMS 20 ISO.
You will be able to get slower shutter speeds just using a b&w contrast filter or polarizer. No need for a ND filter.

Phil.

With ISO 25 film and wanting, say, a 60 second exposure, your middle gray exposure would need a light level to be EV4 (@f11) assuming at least doubling your time for film reciprocity. That is a pretty low light level. ND is good when you want to avoid the loss of shadow detail an orange or red will give you if that is a goal.

[titrisol]

Yes, EFKE25 was what I needed... but I only had a DSLR with me

Try one of the slower Adox/Efke CHS 25 ISO films or the Adox CMS 20 ISO.
You will be able to get slower shutter speeds just using a b&w contrast filter or polarizer. No need for a ND filter.

Phil.

[gofour3]

Yes, EFKE25 was what I needed... but I only had a DSLR with me

Yep I guess you were out of luck!

I've only used the Efke 50 & 100 ISO, will have to try the 25 sometime.

Phil.

[titrisol]

The Adox/Efke 25 is great.
One of the few films that develops best in Rodinal 1+100
Incredibly sharp and nice tonality.

On another note, that picture awsa in Prague last week, it as very sad to find that the Foma-Store was closed. Mail order only now ;(
I was travelling with my family so I minimized my camera gear to 1 camera 2 lenses (small bag) to be able to carry the backpack with jackets, snacks, water, etc etc etc

Yep I guess you were out of luck!

I've only used the Efke 50 & 100 ISO, will have to try the 25 sometime.

Phil.

[ColdEye]

Instead of an ND filter, Can I use a red filter and a yellow filter? That's 4 stops reduction I think.

[gofour3]

Instead of an ND filter, Can I use a red filter and a yellow filter? That's 4 stops reduction I think.

I use a red and polarizer at the same time once and awhile and the effects are dramatic.
This combo is great for architectural and scenic shots and may work for you. This combo will knock a few stops off.

Phil

[tuco]

Instead of an ND filter, Can I use a red filter and a yellow filter? That's 4 stops reduction I think.

I don't think I'd mix colored filters. I'm having a hard time visualizing what the results on your BW film would look like. Maybe a polarizer and colored filter would be a better choice.

Another thing to consider when after a long exposure is the film's reciprocity characteristics. Some BW films are pretty resistant while others need a lot of correction.

For example, Kodak Plus-X needs a 50 second exposure for a metered 10 second shot and 200 seconds for a metered 30 seconded shot. On the other hand, 100 Acros does not need any correction up to 120 seconds and after that only 1/2 stop of additional exposure is needed. T-Max films are pretty resistant too.

I tried to find the reciprocity characteristics of that Adox/Efke film but these small companies are short on technical data.