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  1. #41
    MattKing's Avatar
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    Quote Originally Posted by benjiboy View Post
    If you have a Kodak Grey Card it's easy to ascertain your personal filter factor for each of the filters you own by using your hand held meter at the grey card first, then through the filter .
    Well ....

    This depends on your light source, and the spectral sensitivity of your meter.

    If you don't believe me, try it with a fluorescent light, then daylight, then a tungsten source.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  2. #42

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    I have located a link to the spectral response of CdS cells. Now mind you, as many times as I have searched response curves on the internet, I've found not to stop at 1 and consider it gospel. About mid page of this web page is a link to see more detailed info regarding the product. Click that link and you will download a 7 page PDF. I believe the graph is on p2.
    http://www.token.com.tw/resistor/photo-cds.htm

  3. #43

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    Quote Originally Posted by Alan Klein View Post
    Bill: That was me. The problem was the filter manufacturer of my filters (B+W Schnieder) does not use the Wratten numbering system belonging to Kodak. So the Wratten 25 and 29 indicated on the Kodak Tmax 100 film have no relationship to B+W's numbering system. They use 090 and 091 for light red and dark red. So that's why I used their filter factor. As it turns out, I believe the factor of 5 (2 1/3 stops) they gave for their light red filter is too low. (Can they be wrong?!?) I plan on using a factor of 8 or three stops and then bracket +1 and -1 until I get a clear understanding of what the filter really requires. I want to thank you for adding clarity to this issue.
    Hi Alan, I remember, I just didn't want to be putting you on the spot here.

    It sounds like you didn't see the post I clipped this out of, as it linked to the Schneider (B+W) filter handbook, which seems to confirm B+W 090 red = Wratten 25. Here's the link to my earlier post, which itself contains the link to the handbook: http://www.apug.org/forums/viewpost.php?p=1607629


    Quote Originally Posted by Alan Klein View Post
    (Can they [B+W] be wrong?!?)
    Of course they're wrong! That's what I'm trying to show. They (B+W) give a single suggested filter factor, whereas the real authorities - the film manufacturers - give different values for different films and conditions. So how can the filter maker's single factor possibly be "correct" across different films which list different factors?

    Of course, the filter-maker's factor may be close enough for a starting point, and in fact, most photographers may be perfectly happy with it. The fact that many people are happy with their meter-thru-the-filter results supports this, even though their meter has no way to tell the difference between an extended-red sensitivity film like Tech-Pan vs T-max or the like.

  4. #44
    Alan Klein's Avatar
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    No I didn't see that link or the B+W manual. Pg 34/35 shows that their 090 and 091 light red filter and dark red filter are respectively 25 and 29. It's interesting that they call their 25 a factor of 5 and 29 a factor of 8. In their manual unlike their filter web site they hedge and say approximately5. But if it is 8, I wonder what the real value for the dark red 091 (29) would be for Tmax 100?


    They also recommend bracketing 1/2 to 1 stop with TTL cameras when darker filters are used.


    B+W Light Red Filter 090 (25)
    This is the classic filter for architectural photography. White façades glow brightly, the blue sky is darkened dramatically and clouds become more impressive. It is also excellent for spectacular landscape photo -graphs with greatly improved distant views. Its filter factor is approximately 5.


    B+W Red Filter 091 (29) Compared to the lighter red filter described above, this one even darkens the reds near the yellow tones in the spectrum, as its transparency only begins in the orange-red region. It produces dramatic effects and extreme tonal separation for graphic effects. That accounts for the large filter factor of appr. 8.



    Still, with darker filters (very dense colors), exposure bracketing of ±¡/2 to ±¡ aperture stops is recommended, even with TTL exposure metering, because the spectral sensitivity of the metering cell can be significantly different from that of the film.
    Last edited by Alan Klein; 02-13-2014 at 07:26 PM. Click to view previous post history. Reason: get rid of the html

  5. #45

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    Quote Originally Posted by Alan Klein View Post
    But if it [B+W 090 (25) is 8, I wonder what the real value for the dark red 091 (29) would be for Tmax 100?
    Kodak doesn't give data for T-max with a Wratten #29, only for the #25.

    But just for fun, I did some calcs comparing the two. I used a dozen steps of spectral data in the important range, multiplying filter transmission by the film's sensitivity (estimated from the T-max datasheet graph). (I ignored the light source, tungsten vs daylight shouldn't make much difference in this case.)

    I figure the additional filter factor, beyond the #25, to be about 1.8X, or about 7/8 of a stop. That is, if you have a good factor for the #25, swapping in the #29 should require nearly another full stop. This is for T-max 100, if you used an extended-red sensitivity film, the change would be smaller.

  6. #46

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    Quote Originally Posted by pdeeh View Post
    well, I wouldn't dignify it with the epithet 'satire' but, yes, to be clear, it was intended to be humorous.
    Well I 'got it' and thought it funny.

    The point is all the elaborate rules that people are coming up with are entirely dependent on exactly where you point the meter, and the contrast and spectral range of the scene. The Gould method (the common sense approach), of simply compensating for the filter factor via the ISO dial and then use some intuition depending on the scene and contrast, will only go catastrophically wrong if you are devoid of intuition (a bit more, a bit less). It's no good talking about 'the Zone System' or any other precise approach for exposing the individual negative because this is the 35mm section of the Forum. It has been known for me to process an entire roll of 36 based on optimising one exposure/frame I think may be a 'winner', but otherwise an average approach to metering with filters wins on the 'all for one and one for all' basis as part of a chain of interlinking decisions.

    Steve
    Last edited by 250swb; 02-14-2014 at 02:28 AM. Click to view previous post history.
    http://www.flickr.com/photos/steve_barnett/

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  7. #47

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    Quote Originally Posted by Xmas View Post
    An instruction book should tell you any difference in spectral sensitivity of the photo sensor... should...
    I agree, but the manuals that come with meters don't... at least none of the ones I've read.

  8. #48
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    Quote Originally Posted by BrianShaw View Post
    I agree, but the manuals that come with meters don't... at least none of the ones I've read.
    There's a rule in sales about TOO much info, if you make them sound complicated people are less like I to buy them, I'm not talking pro's I mean the average joe, so they probably don't want to add too much detail, and for the most part unless you're increadibly persnickety, the exposure will be just fine following the filter factor.
    ~Stone | "...of course, that's just my opinion. I could be wrong." ~Dennis Miller

  9. #49

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    I totally understand that, Stone, and agree but these are meters/mauals for professionals (two samples for this AM: older = LunaPro; newer = L-558). If the information is indeed important to making images I would expect it to at least be mentioned. What they do is basically fluff the issue off by saying "YMMV" - know what you are doing. (I'm good with that, BTW.)

    p.s. I am the exact opposite of persnickity regarding this... because in 30 years of photography have never had a significant issue directly attributable to these issues. Maybe I've been lucky; maybe I don't know good from bad... it's anyone's guess. My known failures have always been "something else" - and something much mroe obvious than the spectral characteristic of my meter cell. My inner scientist/engineer is struggling to understand the persnickityisms. Photography boils down to lots of error (using the statistical definition of the word; "margin" to most engineers) in most phases which can either be controlled or they cancel out. If one wants to control then they test and standardize their process and materials. But I remain perplexed by the engineering postmorums of decades old equipment that has proven their worthiness, and the postmortums leading to conclusions that the engineers didn't know bumpkuss and the sellers were liars.

  10. #50
    StoneNYC's Avatar
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    Quote Originally Posted by BrianShaw View Post
    I totally understand that, Stone, and agree but these are meters/mauals for professionals (two samples for this AM: older = LunaPro; newer = L-558). If the information is indeed important to making images I would expect it to at least be mentioned. What they do is basically fluff the issue off by saying "YMMV" - know what you are doing. (I'm good with that, BTW.)

    p.s. I am the exact opposite of persnickity regarding this... because in 30 years of photography have never had a significant issue directly attributable to these issues. Maybe I've been lucky; maybe I don't know good from bad... it's anyone's guess. My known failures have always been "something else" - and something much mroe obvious than the spectral characteristic of my meter cell. My inner scientist/engineer is struggling to understand the persnickityisms. Photography boils down to lots of error (using the statistical definition of the word; "margin" to most engineers) in most phases which can either be controlled or they cancel out. If one wants to control then they test and standardize their process and materials. But I remain perplexed by the engineering postmorums of decades old equipment that has proven their worthiness, and the postmortums leading to conclusions that the engineers didn't know bumpkuss and the sellers were liars.
    I apologize, for some reason I thought that it had been mentioned that the question was why they didn't put the spectral sensitivity info in the FILTER information when they sell them. Imagine mom and pop buy a filter and then have to try and understand spectral sensitivity.

    But yes for a professional meter... I agree completely it should be in there, then again, most these days are assuming color only.
    ~Stone | "...of course, that's just my opinion. I could be wrong." ~Dennis Miller

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