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  1. #11

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    So does Heliopan, IMHO.

  2. #12

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    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.
    Steve

    "You don't need eyes to see, you need vision" - Maxi Jazz

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  3. #13

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    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.

  4. #14

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    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.

  5. #15

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    Quote Originally Posted by ajuk View Post
    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.
    Last edited by snallan; 07-22-2009 at 11:31 AM. Click to view previous post history.
    Steve

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  6. #16
    Sirius Glass's Avatar
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    Have you considered just keeping the lens cap on?

    Steve
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  7. #17

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    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.
    My website: Light Work

  8. #18
    Lee L's Avatar
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    Quote Originally Posted by snallan View Post
    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

  9. #19

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    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.

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