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Thread: Schneider Center Filter IIIa & IIIb - difference?

  1. #1
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    Schneider Center Filter IIIa & IIIb - difference?

    I found the two documents that mention these two center filters on
    the Schneider web site. It seems that both IIIa and IIIb are for the
    90/8 Super Angulon (among a few others). The thread sizes seem the
    same, too. Does anyone know why there are apparently two different
    versions of the same thing?

    Steve

  2. #2

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    Re: Schneider Center Filter IIIa & IIIb - difference?

    I don't see the IIIa listed in my brochure but typically Schneider makes two versions of each size filter, a 2 stop one and a 1.5 stop one. For example the two stop version has two stops of difference in intensity between the outside and the center of the filter. For the lenses I have, they say one can use either filter, the 2 or the 1.5 version. The half stop difference seldom matters.
    Cheers,
    Dave B.

  3. #3
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    Re: Schneider Center Filter IIIa & IIIb - difference?

    The IIIa appears in an scanned "Archiv" pdf on Schneider's web site. The original
    appears to have a date code of April 1984. The IIIb appears in a much newer pdf,
    also on their web site. There's no date code I can see, but it does refer to the SSXLs
    and lists an email address so it can't be too terribly old. Both filters have the same
    threads fore and aft, and both are given as 3x. Maybe they slightly changed the
    gradient to make the one filter match better to the superwides...

    Always curious,
    Steve

  4. #4
    Whatever David A. Goldfarb's Avatar
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    Re: Schneider Center Filter IIIa & IIIb - difference?

    I've compared the III to the IIIb and the difference is 1/4 stop. I use the III on my 90/8 Super-Angulon, 75/4.5 Grandagon-N and 55/4.5 Apo-Grandagon. There are times when I'd like a stronger center filter, but it's something of a subjective thing, since even the dedicated filters don't correct 100% for falloff. If they did, they would have to be darker than most people would tolerate.

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    Re: Schneider Center Filter IIIa & IIIb - difference?

    I have been using a III for my 58mm/5.6 XL and even though it is not the Schneider recommended filter the chromes I shoot all look excellent with no apparent light drop off- I would agree with the 1/4 stop difference cited above and IMHO the difference is a non-issue.

  6. #6

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    Re: Schneider Center Filter IIIa & IIIb - difference?

    Quote Originally Posted by David A. Goldfarb View Post
    I've compared the III to the IIIb and the difference is 1/4 stop.
    Do you know what the rating is on the III? I didn't see it listed on teh Schneider web site.

    I just got one last week and have been testing with Polaroid.

    Thanks!

    Michael

  7. #7
    Whatever David A. Goldfarb's Avatar
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    Re: Schneider Center Filter IIIa & IIIb - difference?

    I treat the III as 1-1/4 stop. I think that's the same as the IIIa.

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    Re: Schneider Center Filter IIIa & IIIb - difference?

    testing with my light meter says that its about 1 1/3 stop

  9. #9

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    Re: Schneider Center Filter IIIa & IIIb - difference?

    Thanks! Never thought of the light meter technique - duh!

    Polaroid sucks for fine gradations.

  10. #10

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    Re: Schneider Center Filter IIIa & IIIb - difference?

    Using my Sekonic digital meter I get 1.4 stops. So I changed the ISO by 1 1/3 (+1.33) of a stop to compensate. Less than .1 stop difference between the two, and I am giving +1/3 stop exposure for negative film, so I am safe. ISO for Prtra 160NC is 50

    Thanks!!
    Michael

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