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  1. #11

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    Thanks Drew. Yes I would buy the specifc match for the lens.

  2. #12
    ic-racer's Avatar
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    If you are shooting B&W negative film, you don't need a center filter. You may get some noticeable falloff when using that 90 XL with a lot of front rise, but this is easily taken care of when printing. Just be sure to give enough exposure to that part of the image. Unless you are using some narrow latitude 'classic' film or something, you should not have any problem getting the entire scene's values on the negative. I think these center filters were marketed toward those shooting reversal film. Ansel Adams does not even mention center filters in the book The Camera.

  3. #13

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    At least it seems like if I had both a Schneider 72 XL and 90 XL, the Schneider literature indicates I could get away with one center filter (IVa) that will work on both of them, although I guess that means the falloff on the 72 would not be fully corrected. Still, half a stop of falloff is probably worth living with given these things are $700 each. Wow. $700 for a filter.

  4. #14
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    Well if you become really desperate you can inkjet a pretty decent approximation onto transparency and go that way. It'll be so far out of focus that it'll work surprisingly well. It won't be perfectly neutral... so probably won't cut it for high-end slide, but... works well enough if you don't mind experimenting.
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  5. #15

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    I think I'll do some testing with the lenses before I get the filters. If it turns out I really need one, I think I'll just bite the bullet and invest in the right one from Schneider. It's a little depressing spending so much on a filter, but I'd feel more comfortable doing that than trying to make one myself.

  6. #16

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    If you had different center filters side by side on a lightbox, you would see that not only the thread
    diameter and maxiumum density differ, but also the concentration of the density center to edge.
    Sometimes center filters can be successfully interchanged between different lenses, sometimes they
    cannot. A half stop error might be neglible with many film, but hopeless with others. Chromes of course are very fussy. But don't buy that nonsense that just anything can be corrected in Fauxtoshop. It's also nice to have the creative option to use or not use a center filter. They're
    certainly worth it, but I'd hate to drop one of those puppies!

  7. #17
    David A. Goldfarb's Avatar
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    Center filters are not precisely matched to the correct 100% of the falloff on the lens that the manufacturer recommends. If they were, they would be impractical, and no one would by them, because they would be about 2-3 stops at the center, and it's just too much, when you're shooting at f:16-22 ideally and then dealing with reciprocity, and with color transparency that could mean additional filters for color correction. Bob Salomon once posted on the LF Forum that manufacturers tried producing such filters at one time, and they just didn't sell.

    Correction of falloff of illumination is a combination of taste and practicality, so they tend to be 1.25-1.75 stops, as well matched to the lens as they can be allowing for a tasteful amount of falloff. I'd say get the one for the lens you plan to use the most, and it will probably be fine for other wide lenses of the same diameter.

    The reason center filters are so expensive is that they are manufactured like lenses. They are a plano-convex ND filter and a plano-concave clear filter of glass with the same refractive index, ground to fit together precisely and cemented together, such that their planar surfaces are perfectly parallel. They may be coated, and the German ones are made with high-end Schott glass and set in brass mounts, so all around, they aren't cheap. I have two, both purchased used.

    Compare square resin ND grads which are simply dipped in a dye and sorted for density and having a hard or soft transitional edge.

    I like center filters usually with ultrawide lenses when I can use them, even with BW neg. I don't often find a center filter necessary with a 90mm lens on 4x5" unless I'm using a lot of movement, like the maximum front rise on a vertical shot where I might really have the center and the edge of the image circle in the frame.
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  8. #18
    L Gebhardt's Avatar
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    I find I would like a center filter on my 90mm f/6.8 when I use it for 6x17, or use lot's of rise on 4x5. The edges/corners do get dark, especially with reversal films. If you shoot negatives you can just give the film an extra stop and a half of exposure and fix it when printing (which is a pain). I don't have one yet, but I'll probably buy one soon, since I just learned the same one should work on both my 75mm and 90mm lenses.

  9. #19

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    According to the Schneider literature, you can use the IVa filter on both a 90mm 5.6 XL ("full correction") and a 72mm 5.6 XL ("partial correction"). For "full correction" on the 72, I'd need the IVb. Unless the manufacturer clearly states a given filter will work on more than one lens, I would not assume you can use a single filter on both your 75 and 90. As Drew indicated it is not just the diameter and difference in density between the center and edges, but also how that transition is made.

    David, thanks for the clarification on how they are made. I simplistically assumed it was just a regular clear filter with some kind of precision ND deposit on it.

  10. #20
    David A. Goldfarb's Avatar
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    I've had occasion to swap center filters in the field with other photographers, and I haven't found them to be matched with such precision that they aren't interchangeable with differences of maybe 1/4-1/2 stop density in the center. Perhaps there are such, but I have my doubts. Heliopan even makes generic center filters that I suspect should work fairly well. I've read speculation about banding that could occur with the wrong center filter, but I have yet to see an example.

    In any case, my point is that it's best to buy one and test it out on your other lenses before buying a separate dedicated center filter for each lens. You might find it perfectly satisfactory.

    I would also take Schneider's description of "full correction" with a grain of salt. There will still be some falloff of illumination with such "full correction" of less than 2 stops, but it should keep the tonal range of the image within the range of transparency film.
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