Center filters - WTF? $$$$$$$$$$$$

Discussion in 'Large Format Cameras and Accessories' started by michael_r, Jan 24, 2012.

  1. michael_r

    michael_r Subscriber

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    I'm in the process of re-outfitting my 4x5 gear for wider angle work. I'm looking at a current 90mm Schneider 5.6 XL, and also a 72mm Schneider 5.6 XL (or possibly a Rodenstock 75mm 4.5 Grandagon N).

    Some questions regarding these ridiculously expensive center filters:

    1) If I'm realistically going to be shooting at f16 or smaller, do I really need these? Even on a 90mm?? Is there that much falloff at working apertures??

    2) In the Rodenstock litterature it says the center filters are optimized for the working aperture (say f16). Ok, what happens if I'm at f22 or smaller? Do you need to remove the filter at smaller apertures than the aperture for which they are "optimized"? Seems to me if falloff decreases as you stop down, at some point falloff is reduced to the point where a center filter would be detrimental, causing the center of the image to be darker than the edges. ?

    3) Are these filters always necessary or only when movements are involved (eg significant front rise typically required in architectural work)?

    Experiences and thoughts welcome.

    Thanks
    Michael
     
  2. Bob Carnie

    Bob Carnie Subscriber

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    I will ask some of these questions to Dr Mark , he uses very wide angle lenses on his Linhof and I do not think he uses filters.
    If he does not use filters then I would say you are ok not to use them as I have no falloff issues when printing his work at larger magnification.
    I won't be seeing him until the weekend.


     
  3. keithwms

    keithwms Member

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    Haha reminds me of when I thought I needed one for an ultrawide. The darn thing was almost as expensive as the lens! Then I bought it and wound up selling it shortly thereafter. And just for comparison, the lenses you mention aren't nearly as wide as the one I was using at the time (a 55).

    Unless you are shooting colour slide, you can usually get by without a center filter. What you do is expose and develop to make sure that you will have the latitude in your curve, and don't terribly underexpose the edges. And you simply make yourself a circular dodge/burn tool for use at the enlarger. Or if you are working on a screen, there are other methods. With the wide latitude of b&w film and the ease of d&b and contrast control on modern papers, there is seldom a real need for a center filter... though it can be convenient. With slide, you have much less latitude and you have to worry about not being able to d&b as effectively. I mean, some slide films change colour balance as a function of exposure, then it's a mess.
     
  4. michael_r

    michael_r Subscriber

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    Thanks for the help Bob. Much appreciated. I've also posed the question to John Sexton, who has done work with these lenses that is similar to the projects I'm working on. Falloff might be less of an issue in the house calls pictures since they are more like portraits rather than landscape/architecture. Not sure. Anyhow its a troubling prospect because these things are damn fortune. I can understand the necessity with ultra-wides like 58mm or even shorter, but a 90 is nothing crazy.
     
  5. Dan Fromm

    Dan Fromm Member

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    As has been pointed out, falloff is a worse problem with narrow latitude films, i.e., reversal films. Whether you need a center filter depends on how far you move the lens off center and on how exacting you are.

    Just for curiosity I looked at Schneider's illumination curves for the current 90/6.8 SA. It is down two stops edge of the 216 mm circle covered at f/22. Its down 1 stop at ~ 75mm off-axis, i.e., in the corner of 4x5 when shot straight ahead.

    FWIW, patience in shopping helps. A while back I bought a 35/4.5 Apo Grandagon. With it shooting straight ahead, the corners of a 6x9 tranny are too dark. So I wanted a CF. As you remarked, $$$. So I waited and watched. I eventually lucked into the right CF for that lens for $225 delivered. Used, flawless. And it helps ...
     
  6. wildbill

    wildbill Member

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    Pm sent.
     
  7. michael_r

    michael_r Subscriber

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    Thanks for the replies everyone. I'm really struggling with this given how steep the cost is. The problem is - I am VERY exacting. I guess it might come down to good old fasioned testing. It's frustrating though.
     
  8. DREW WILEY

    DREW WILEY Member

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    Just part of the investment in any especially wide angle of view. I can't imagine any high quality color work without one, either chrome or color neg (latitude is only part of the problem). Some black
    and white work might look nice with a degree of symmetrical falloff, or will partially correct itself with
    a matched falloff in the enlarger lens - but you will have potential issues with shift and swing, or with
    pushing the low values onto a different part of the film curve. Experiment awhile to see what can be
    done without one. And if you do buy one, consider the specific quality distinctions between the
    available brands. Anything really good in this category is inherently expensive to make.
     
  9. michael_r

    michael_r Subscriber

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    I guess what I'm most troubled by is the fact I'll pretty much always be working at apertures smaller than f16. So I'm wondering if a center filter is really necessary in that case, particularly with the 90mm.
     
  10. DREW WILEY

    DREW WILEY Member

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    Center filters work poorly at wide apertures. f/16 on down should OK, but I like them better at f/22.
    Make sure you get the proper one for your exact lens. It's important to have the right amount of
    neutral density at the correct distribution. Most of the fast 90's need a stop and a half correction.
    There's an extensive recent thread over on the Large Format Forum about the newest center filter
    designs.
     
  11. michael_r

    michael_r Subscriber

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    Thanks Drew. Yes I would buy the specifc match for the lens.
     
  12. ic-racer

    ic-racer Member

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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.
     
  13. michael_r

    michael_r Subscriber

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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.
     
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  15. keithwms

    keithwms Member

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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.
     
  16. michael_r

    michael_r Subscriber

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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.
     
  17. DREW WILEY

    DREW WILEY Member

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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!
     
  18. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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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.
     
  19. L Gebhardt

    L Gebhardt Subscriber

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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.
     
  20. michael_r

    michael_r Subscriber

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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.
     
  21. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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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.
     
  22. DREW WILEY

    DREW WILEY Member

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    My own test for center filter eveness involves a bit of overkill. I'll expose a completely even mid gray
    suface like a gray card, give the sheet of film significant plus development, then contact it on hard
    grade 4 paper or max density VC. One thing I discovered this way is that the 82mm center filter I
    bought long ago for my 120 Super Angulon has virtually perfect density distribution on my Nikon
    90/4.5. But once in awhile I deliberately want a non-spec CF for a little different creative usage.
    For commercial architectural shots I always always had the correct CF on hand.
     
  23. Bob Carnie

    Bob Carnie Subscriber

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    I talked to Dr Mark about the filter and he never uses one. Not all his imagery is portraits and as such he will plant a 4x5 in the center of a room and use natural light and long exposure. I have printed a lot of these negatives and never felt there was an issue on the edges due to fall off.
    I would vote not to spend $700 on the filter but buy $700 of Ilford Warmtone Paper.
     
  24. jnanian

    jnanian Advertiser Advertiser

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    i'd not use any camera movements and shoot straight on for a while to see if i could get away without the filter
    and as a last resort buy it. 700$ is a lot of money ...
     
  25. Hikari

    Hikari Member

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    There are two kinds of vignetting, mechanical, which is a problem of the lens barrel cutting off the off-axis light at large apertures, and natural vignetting, which is a product of the angle the light strikes the film. Center filters deal with natural vignetting and so whether you shoot at f/11, f/16, or f/22 etc., it does not matter, the center filter would be needed.

    I have never used a center filter with a 90mm as I did not find the fall off objectionable nor uncontrollable. A center filter really helps a 72mm lens.

    BTW, correcting for fall off in the darkroom is not always idea--the fall off is underexposure and there is so far you can push underexposure in printing.

    I would avoid Heliopan center filters as they are really not well made--mine had air bubbles in the glass and the warranty replacement process was a nightmare. I have been very impressed with Schneider center filters.
     
  26. Martin Aislabie

    Martin Aislabie Subscriber

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    Centre Filters are things of beauty

    To give perfect correction you would need one tailor made to each focal length and as has been noted here, that gets very, very expensive.

    Even on B&W Negs using a 90mm you can see the difference – more so as you push towards the edge of the image circle.

    The wider the lens, the greater the need for a centre filter.

    My experience has shown near enough is good enough and it is worth buying lenses that can use just the one common filter.

    Personally, I would buy the lenses that could use just the one Centre Filter and then try them without buying a Centre Filter. If, when you look at the results and you decide you need a CF, then buy one for the lens you consider most needs it (probably the shortest) and then try again, on both lenses.

    If, in the end you decide you need an exactly matched Centre Filter to each lens, at least you know you have made the decision yourself and have not be suckered into it by the weasel words of the advertising men.

    Martin