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Thread: Center filter question - usage on different formats

  1. #41
    Drew Wiley
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    Re: Center filter question - usage on different formats

    Any kind of wide angle photography is a pain in the butt facing the sun without an adjustable shade.

  2. #42
    Alan Klein's Avatar
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    Re: Center filter question - usage on different formats

    Quote Originally Posted by Bernice Loui View Post
    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.
    Attachment 232209


    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..
    Attachment 232210

    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
    Don't movements affect where the vignetting winds up? So for example, if you shift, you might have more darkening on one side than the other which would look weird. Even with BW?

  3. #43
    Alan Klein's Avatar
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    Re: Center filter question - usage on different formats

    Quote Originally Posted by rawitz View Post
    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.
    Egads. Has anyone done that? With color you have to deal with color shifts as well. Might be easier with BW, but then wouldn't movements shift the falloff areas forcing you to somehow move around a gradation template? Seems like a center filter is the way to go.

  4. #44

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    Re: Center filter question - usage on different formats

    Yes indediee, knowing how the lens behaves coupled with camera movements as needed/as used is then figuring this into how the image could benefit can be a plus to the overall image.

    If wide angle lens is a must with lowered light fall off, using a proper ND center filter is a non-option. This is why ND center filters are made, why they are used and why they remain a needed and in demand optical accessory.

    IMO, the idea/belief post fix up via software is a maybe at best. What is done today, a good number of modern digital cameras apply lens aberration fix-up in camera post image capture.. This is a better way as the software fix-up is lens and image sensor system specific.. The designers here would know more about how get the best out of the overall lens/imager/post capture system than post process software fixiee..

    For film, get the proper ND center filter for the specific wide angle lens, use it as needed is the proper solution.


    Bernice




    Quote Originally Posted by Alan Klein View Post
    Don't movements affect where the vignetting winds up? So for example, if you shift, you might have more darkening on one side than the other which would look weird. Even with BW?

  5. #45

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    Re: Center filter question - usage on different formats

    Quote Originally Posted by Alan Klein View Post
    Don't movements affect where the vignetting winds up? So for example, if you shift, you might have more darkening on one side than the other which would look weird. Even with BW?
    Vignetting is really the wrong term here. Fall-off is better.

    If you've got a center filter on your lens, shifting/raising/lowering the front or the back standards will make no real difference in densities at the edges/corners, since the fall-off is attenuated over the entire projected image circle by the filter. Without the filter, yes, you will end up with more fall-off on the side that you shifted toward. With black-and-white, one can deal with this by judicious burning (I'll start a thread about "center burning" someday). With prints from color negatives, similar adjustments can be made. For color transparency materials, you need the center filter if you don't want the fall-off.

    Note that if you're planning on not using a center filter and correcting fall-off with burning at the printing stage, you still need to add enough exposure from what your meter tells you to get adequate shadow exposure in the parts of the image affected by the fall off (i.e., overexpose a stop or whatever the center-filter factor would normally be).

    Vignetting caused by running out of image circle or by mechanical blocking (e.g., stacking too many filters) is a different issue and not really related to center filters.

    Best,

    Doremus

  6. #46

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    Re: Center filter question - usage on different formats

    Quote Originally Posted by Alan Klein View Post
    Egads. Has anyone done that? With color you have to deal with color shifts as well. Might be easier with BW, but then wouldn't movements shift the falloff areas forcing you to somehow move around a gradation template? Seems like a center filter is the way to go.
    You're right Alan, shifting (or raising/lowering) moves the optical center of the image on the film to an off-center position. However, if you can identify that point in the image, then you can do your burning or masking or whatever you do in Photoshop around that point.

    I print analog with enlargers and do "off-center" graduated radial burns all the time. Either the point around which I should center my burn is obvious, or I've made a note of where it lies at the time of exposure.

    If you've got the center filter, by all means, use it. It is the easier method and indispensable with transparency materials. However, many of us B&W only practitioners dispense with the filter and the extra bulk it requires (along with the need for larger filters to attach to it, if desired), and just deal with the fall-off in the darkroom.

    Best,

    Doremus

  7. #47

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    Re: Center filter question - usage on different formats

    You often end up making adjustments anyway. Center filters don’t fully correct for falloff.

  8. #48
    Drew Wiley
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    Re: Center filter question - usage on different formats

    With the specified combination of specific lens and matching recommended CF, at specified recommended working aperture, a CF can indeed perfectly correct falloff. I've densitometer tested for that. That doesn't mean your enlarger mixing box and its lens is itself perfectly even. But if one just routinely shot a particular WA lens, then its own falloff could be correctly by a matching amount of falloff in the enlarging system, that is, when printing negatives. Lots of old timers knew that. The mixing box diffuser could even be ground convex and fine-tuned for that. But it still wouldn't retrieve shadow detail in the corners of your image if it was so underexposed to begin with, due to falloff, that it's not even there.

    Note my "fine print". We can't always use the ideal recommended working aperture, etc etc. Same when enlarging.

  9. #49

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    Re: Center filter question - usage on different formats

    Absolutely, and this is a method to deal with light fall-off even without a CND filter. If you take a picture of a scene with a lens showing light fall-off, the corners of the negative will be less dense. A normal print will produce dark corners. But if you use the enlarging lens wide open, the corners of the print will be lightened due to the light fall-off in the enlarging lens. This will not, of course, create any more detail in the corners -- because there wasn't that much in the negative, but it can make the print appear more normal.

    And if you use a CND filter that isn't quite strong enough in the corners, you can use the same approach to improve things a bit.

  10. #50
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    Re: Center filter question - usage on different formats

    Quote Originally Posted by xkaes View Post
    Absolutely, and this is a method to deal with light fall-off even without a CND filter. If you take a picture of a scene with a lens showing light fall-off, the corners of the negative will be less dense. A normal print will produce dark corners. But if you use the enlarging lens wide open, the corners of the print will be lightened due to the light fall-off in the enlarging lens. This will not, of course, create any more detail in the corners -- because there wasn't that much in the negative, but it can make the print appear more normal.

    And if you use a CND filter that isn't quite strong enough in the corners, you can use the same approach to improve things a bit.
    I don't print but rather scan. So I either accept the fall-off or use a CF.

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