Really powerful ND filter

[ajuk]

I'm looking to get a really powerful ND filter ie one darker than ND8, for taking several second exposures during the day, I haven't much money can anybody give me any recommendations, 49mm or Cokin A will do.

 

[richard ide]

The darkest Kodak Wratten ND96 filter is an ND4 which transmits: .01% , filter factor is 10,000 , or a 13 1/3 increase in stops. Some other manufacturers use an ND rating which is not the same. Try a welding supply firm. They have glass filters and may also have plastic which you could cut.

 

[GeorgeDexter]

I've heard that by using 2 Polarizers stacked (not sure if linear or circular are needed) you can align them so that virtually all light is blocked. That should be a pretty cheap solution, especially if you can use linear polarizers. I've never tried it, so good luck.

Hope this helps.

 

[Drifter]

Hoya make an ND 400 filter which reduces exposure by 9 stops (around 1/500th of the original intensity). I believe they have a 49 mm size.

 

[JBrunner]

ND can also be stacked. Because stops work the way they do, you can get pretty dense, pretty fast.

 

[Robert Hall]

Interesting note on the stacked polarizers. While they block visible light they may very well pass Infrared Light.

 

[bwakel]

If you're skint and you've already got got a red, yellow or orange filter, ND filter and polariser you can stack them to get a pretty good descrease in transmission, so long as you don't mind the effects caused by the colour/polarising filters. I use this technique pretty often.

 

[Solarize]

In the UK Dead Link Removed would be a good bet. Although I am not sure where they will ship to or the costs involved.

 

[Mike Wilde]

Rosco (theatrical and cinematography filter gel vendor) sells a deigner swatch book for about $25 that has every concievable gel theater you can think of. In there are ND's - 1 stop, 2 stop, and I think 3 stop in the swatch book. b&h lists it in thier catalog, and I beileve Rosco also sells them directly.

The full gel sheets are about 20x30" and sell for under $10. Optically not always perfect, but usually close enough to confirm if you want to sink more money into a glass filter, and have loys left over to think up other uses for.

Glass welding filters are frequently green in tint as well as ND. They may be falling out of favour now, because active LCD filters have come onto the market, and if you are a welder, oh, it is so worth the money.

 

[snallan]

B&W do 10 stop ND filters.

 

[Philippe Grunchec]

So does Heliopan, IMHO.

 

[snallan]

Had a little poking around. Heliopan do filters up to ND 4 that's a 13 stop correction (Heliopan filter brochure - pdf), B&W actually do up to a 20 stop correction (B&W filter brochure - pdf).

Suffice to say, any of these extremes will probably be special order.

 

[Peter De Smidt]

I know this isn't exactly what the OP was after, but my Hoya RM72 infrared filter reduces the light by 16 stops with Acros.

 

[ajuk]

I'm looking for something cheap, I thought I would be able to find a cheap plastic A filter from the likes of Kood, but they don't seem to make one, stacking isn't the best option for me at 28mm it might cause vignetting.

 

[snallan]

I'm looking for something cheap, I thought I would be able to find a cheap plastic A filter from the likes of Kood, but they don't seem to make one, stacking isn't the best option for me at 28mm it might cause vignetting.

Problem is, high factor ND filters are pretty specialist items, so the likes of Kood, Cokin, even Lee, don't produce the more extreme examples. If you are shooting monochrome then I have found replacement filters for welding helmets that fit the Cokin 'A' filter holders.

BTW, is ND 8 the Cokin designation? This is one area where manufacturers product designations are all over the place. From the Cokin literature it looks like the value 8 is the filter factor (a 3 stop correction), which would be a Heliopan ND 0.9; the Heliopan ND 4 requires a 13 stop correction.

 

[Sirius Glass]

Have you considered just keeping the lens cap on?

Steve

 

[bwakel]

If you're trying to capture movement in clouds, sea, etc then the other approach is to take a number of short exposures on the one frame. I used this approach recently and it produced a nice effect - the effectiveness will vary with subject and the delay between shots. So, if you've got a 1/30 sec exposure for a particular scene simply break it down into a number of smaller exposures, such as 6 1/1000 sec exposures. Obviously the more you can extend the base exposure the more exposures you can get on the one frame.

 

[Lee L]

BTW, is ND 8 the Cokin designation? This is one area where manufacturers product designations are all over the place. From the Cokin literature it looks like the value 8 is the filter factor (a 3 stop correction), which would be a Heliopan ND 0.9; the Heliopan ND 4 requires a 13 stop correction.

Exposure factors for filters are generally one of three sets of numbers.

The first is an exposure factor like 2x, 4x, 8x, and an ND filter with a stated exposure factor of 8 is most likely to be three stops. In this numbering scheme one stop additional exposure is 2, two stops is 4 (or 2^2), three stops is 8 (or 2^3), four stops is 16 (or 2^4). So the given filter factor is two raised to the number of stops of extra exposure needed.

Some state the number of stops needed, and B+W numbers their ND filters with 100 + number of stops extra exposure needed. So a B+W 101 ND filter needs one extra stop of exposure, a 106 needs 6 extra stops, a 110 needs 10 extra stops, etc.

Some filters are designated with log density numbers. In this system, 0.15 is a half stop, 0.30 is one stop, 0.60 is two stops, etc. So each 0.30 is one stop and the numbers add easily. 0.90 is three stops, and 1.20 is four stops.

Not sure about the Heliopan designations, but log density 4.0 in stops works out to 4.0/0.3 = 13.33 stops.

Lee

 

[ajuk]

I didn't think it was that specialist, I seem to see quite a lot of cloud trail pictures on Flickr, anyway I wanted to capture car movement during the day, hopefully combining it with an UWA 18mm lens when I get one.