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Thread: Center filter question - usage on different formats

  1. #21
    Drew Wiley
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    Re: Center filter question - usage on different formats

    Has nothing to do with color per se, Alan. It's entirely contrast-related. Because color chrome films have higher contrast than color neg films or the usable range of black and white films, the falloff issue is statistically more obvious in that case, but can also transpire in the other cases. Even in black and white images, some people enjoy a falloff or darkening toward the corners, some do not. In architectural photography, what is acceptable in a personal creative exercise might not be under contract to the designer, who might want a more objective rendering better suited for publication or his own portfolio.

    Then you've got technical issues especially in color, like when falloff leads to color crossover shifts. I've even employed that error deliberately a few times for creative effect. But most of the time, I don't want it. But in black and white itself, some people reach a point on the characteristic curve where the film ceases to respond in a linear fashion, for better or worse, esthetically. The point in having tools like center filters is to understand what they're for, and when you need to use them. People who go around saying they're unnecessary for this or that genre, or this and that kind of film don't speak for everyone.

  2. #22

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    Re: Center filter question - usage on different formats

    Anyone ever use a CND filter with a pinhole?

  3. #23
    Alan Klein's Avatar
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    Re: Center filter question - usage on different formats

    Quote Originally Posted by Drew Wiley View Post
    Has nothing to do with color per se, Alan. It's entirely contrast-related. Because color chrome films have higher contrast than color neg films or the usable range of black and white films, the falloff issue is statistically more obvious in that case, but can also transpire in the other cases. Even in black and white images, some people enjoy a falloff or darkening toward the corners, some do not. In architectural photography, what is acceptable in a personal creative exercise might not be under contract to the designer, who might want a more objective rendering better suited for publication or his own portfolio.

    Then you've got technical issues especially in color, like when falloff leads to color crossover shifts. I've even employed that error deliberately a few times for creative effect. But most of the time, I don't want it. But in black and white itself, some people reach a point on the characteristic curve where the film ceases to respond in a linear fashion, for better or worse, esthetically. The point in having tools like center filters is to understand what they're for, and when you need to use them. People who go around saying they're unnecessary for this or that genre, or this and that kind of film don't speak for everyone.
    What I've noticed with a 90mm and Velvia 50, if there's a blue sky, the falloff makes the edges darker blue. That's less acceptable than if it was a BW picture. With color it just makes the sky's color look uneven. With BW you get a vignetting effect which is more acceptable.

    Here's an example with a 75mm:
    https://www.flickr.com/photos/alankl...7715763486212/

  4. #24
    Alan Klein's Avatar
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    Re: Center filter question - usage on different formats

    Quote Originally Posted by rawitz View Post
    Oh, YES I see this in my LF color-negs, with are more sensible in densities than slides. What I found is not only radial light-falloff, but also radial color-shift what in BW is not an issue. I found ways to correct it in post, but have no theoretical explanation for this. Maybe anyone here has ...
    How?

  5. #25
    Do or do not. There is no try.
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    Re: Center filter question - usage on different formats

    Quote Originally Posted by xkaes View Post
    Anyone ever use a CND filter with a pinhole?
    That’s an interesting idea! I guess you’d need to experiment with how far in front of the pinhole to place the CND.

  6. #26

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    Re: Center filter question - usage on different formats

    That shade of "blue" is not only darker, it is a different shade of blue with graduated shade of blue and density changes... Typical of ALL color transparency films.

    Previously posted example of 155mm Rodenstock Grandagon @f22_zero camera movement and on center, no center filter, 8x10 Agfachrome RS100 (closer to netrual color, not Velvia fantasy color) , Sinar 8x10 clear sunny day. Note the density AND color shift.
    Click image for larger version. 

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    B&W example, image previously posted on LFF..
    Berlebach woodiee tripod & Gitzo head, Linhof Technikardan 23s with baggie bellows, 58mm Super Angulon XL @f16, 6x9 Super Rollex, 120 Ilford FP4, HC110...

    58mm SAXL image circle is pushed to near it's limits of 40mm rise (mm scales on the TK23s aids in accessing how much image circle is being used or used up) coupled with front tilt of a few degrees and rear swing of a few degrees to bring the base/lower area of the image into what needs to be in focus and why a monorail with precision/accuracy is a GOOD thing as applying 1-2 degrees of camera movement is not that difficult, camera MUST stay put once set while the roll film back is swapped in place of the GG frame.

    Note the light falloff of the 58mm SAXL which now acts as a graduated ND filter... or how a fixed given aspect of LF wide angle lens behavior can aid in image making..
    Click image for larger version. 

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    Need for a center filter can be greater for color transparency film due to the innate lower contrast range of color transparency film.. AND know the color layers can and will produce color shifts if their individual densities vary due to a long list of possible conditions and problems. As to fixing this post production via software.. What are the reference colors and how does the software alter color balance and density as a system?

    Color negative film is lesser sensitive to this due to increased contrast range, yet color negative film remains subject to color shifts due to shifts in color layer density.

    B&W film is strict density.. no color which is much a different can-O-worms..
    Bernice


    Quote Originally Posted by Alan Klein View Post
    What I've noticed with a 90mm and Velvia 50, if there's a blue sky, the falloff makes the edges darker blue. That's less acceptable than if it was a BW picture. With color it just makes the sky's color look uneven. With BW you get a vignetting effect which is more acceptable.

    Here's an example with a 75mm:
    https://www.flickr.com/photos/alankl...7715763486212/

  7. #27

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    Re: Center filter question - usage on different formats

    Quote Originally Posted by Steve Goldstein View Post
    That’s an interesting idea! I guess you’d need to experiment with how far in front of the pinhole to place the CND.
    That would be limited by the diameter of the CND filter (a wider filter could be placed farther out), and the size of the film/paper (smaller paper would allow for CND filter farther out). Maybe there is some sort of way to estimate it mathematically.

  8. #28

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    Re: Center filter question - usage on different formats

    Quote Originally Posted by xkaes View Post
    Anyone ever use a CND filter with a pinhole?
    Thats easy to answer. Provided you have a perfect flat pinhole, the lightfalloff is proportional to the cosinus-falloff by mathlaw. Thats much more than the modern WA-lenses, which by construction correct/minimize this falloff. CND will help you a bit, but less than with those lenses.

  9. #29

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    Re: Center filter question - usage on different formats

    Quote Originally Posted by Alan Klein View Post
    How?
    You have to make a linear-radial soft mask from image center to the edges and then use gradation tool (in Photoshop) for color correction.

  10. #30

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    Re: Center filter question - usage on different formats

    Quote Originally Posted by xkaes View Post
    Anyone ever use a CND filter with a pinhole?
    Did so a number of years ago on my 11x14 very wide angle pinhole camera (with an effective focal length of 5 inches). CND was a Schneider IVa 3x. Ended up shooting three times with the filter mounted at three different distances behind the pinhole. Determining the exposure for the center of the negative was easy. Using a plain pinhole and the light falloff is consistently even from the center to the edges of the film. Adding the CND and the light falloff was not consistent, producing a "doughnut" like effect that I really couldn't see on the negatives, but was readily apparent on the contact prints. After shooting three sheets of HP5 plus and making contact prints, well experimenting by shooting 11x14 film gets expensive very quickly. I think it is very possible to do, but I would use paper negatives.

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