Does a filter compensate for lack of coating?

Discussion in 'Classic Manual Cameras' started by vincent_frazzetta, Apr 15, 2012.

  1. Just curious. Does adding a good coated filter (I use B&W MRC medium yellow) compensate in any way at all for the lack of coating on an older lens?
     
  2. No. It may make the situation worse by adding a reflective surface in front of the first lens element.
    Coated surfaces do reflect light, just not as much as uncoated surfaces.
    - Leigh
     
  3. ... but a lens shade can help quite a lot.
     
  4. It's not the question you asked, but if the older lens is not very good and has a lot of chromatic aberration, a yellow filter can improve its performance. But that has nothing to do with coatings.
     
  5. Back in the days when photography was identical with shooting b/w, yellow filters were used to compensate the lack of contrast caused by uncoated lenses. There were even cameras with built-in (removable) yellow filters.
    Of course yellow filters can be used wit b/w film only.
    I have never heard of improving performance of lenses with chromatic aberration by using filters, do you have any explaniation for this?
     
  6. In B&W photography, a yellow filter helps with (increases) contrast, not CA.
     
  7. Helps with CA too. I can dig up a reference for this if you want it, but I've personally never used a lens bad enough to need it!
    The reason makes sense if you back up and think about it. CA happens because the different wavelengths of white light get magnified to different degrees (lateral CA), or they get focused at different points (longitudinal CA). But the bottom line is that CA only happens because there's different wavelengths of light.
    If you get rid of some of those wavelengths, CA diminishes. So a yellow (minus blue) filter pulls out the short wavelengths. Tighter spectrum limited to longer wavelengths = less CA, sharper image.
    I can think of two examples where I have heard this is useful. The first is with poorly corrected large format lenses. For example, someone, I think Wisner, was selling custom sets of Protar-type lenses about ten years ago. This is an old classic lens design, and I guess they must be good for some purposes, but they don't have the corrections of modern lenses. If you wanted to get the best sharpness from them, the dealer recommended a yellow filter to cut down CA.
    The other situation is box cameras with primitive lenses. Some optics book I've got (Kingslake or Neblette) says you can hugely improve the performance of a simple box camera, if you just slap a yellow filter on the front of it. Of course, most of us don't use box cameras, so for most of us this never comes up.
    Incidentally, one of the guys who knew a lot about this stuff was Clifford Manley, but he hasn't posted here for many months. Does anyone know what happened to him? I messaged him a few months ago, but he didn't reply. I hope he's OK-- I know he had a health scare a while back.
     
  8. Here's the way to think about this. An *absolutely perfect* multi-coated clear filter (which doesn't exist) would transmit 100.0% of visible light striking its front surface and reflect 0.0% of the light. In other words the perfect filter behaves as if there is nothing in front of your lens. So if your imperfect uncoated lens reflects and scatters 5% of the light entering the lens, with the best possible filter available mounted it would still reflect and scatter 5% of the light. Logically, it follows that adding a filter that does not transmit 100.0% of the light can only *increase* the total amount of light reflected and scattered.
    :)
     
  9. What Dave says. Many telescope and microscope objectives, like older camera lenses, are not well corrected for chromatic aberration. A filter helps to remove the (usually violet) fringes and increase apparent resolution. As for the OP's question, what Sarah says. A deep hood can really perk up an older lens.
     
  10. Back in the heyday of vintage cameras (1940's-50's), many films were not really panchromatic.
    They lacked sensitivity at the red end, and exhibited excessive sensitivity at the blue end.
    A yellow filter (= minus blue) was commonly used to even out the spectral response.
    - Leigh
     
  11. Hello all...I did not expect so many answers to what I thought was a simple question. Here's how it came about: I was considering two lenses for black and white work. One was coated, one not; one was expensive, one was not. I thought that lens coating, when used with B&W film, was used primarily to cut down flare and secondarily increased contrast. Since I always use a good, coated yellow filter, I figured the filter coating would pretty much do what the lens coating would do (plus, the typical blue-blocking and contrast results from a yellow filter). Hence I would save a lot of money, and get precisely the same results with the uncoated lens. Not that simple. Thanks for all your thought and informative answers...Vincent
     
  12. An OT response to one of the comments here:
    I'm interested in the comment on how panchro film wasn't really panchromatic. From reading older (1930s) cinematographic and related technical journals, I got the impression that ortho films were often not as ortho as they should have been (much favoring blue over green), but panchro was fairly even to red and it depended on the brand used how far into the red wavelengths the film would go. The brands were noted for which color they favored most. Of course, in the era I'm reading about there was no such thing as Tri-X. SS-Pan and its competitors from Agfa and Dupont were the most popular cine films.
    In the early '30s even, films speed didn't have any sort of consensus, and cinematographers tested new emulsions to get a base film speed.
     
  13. An *absolutely perfect* multi-coated clear filter (which doesn't exist) would transmit 100.0% of visible light striking its front surface and reflect 0.0% of the light. In other words the perfect filter behaves as if there is nothing in front of your lens.
    Not quite, I think. The hypothetical perfect filter has no effect, but the ring holding the filter will act as a small lens shade!
     
  14. And, of course, a "filter" that "behaves as if there is nothing in front of the lens" is quite the opposite of perfect.
    ;-)

    Anyway, Leigh didn't say that "panchro film wasn't really panchromatic", did he? He said that "many films were not really panchromatic".
    But yes: different films behave(d) differently back in the days when they were still finding out what to use to extend the sensibility for longer wavelengths.
     
  15. I have an impression that even an uncoated yellow filter can cut down the flare with old single coated lenses.
    Explanation could be the same as with the cromatic abberration: single coating works well only in a narrow spectral range, and in the case of "blue" coatings, blue is apparently not part of that range.
     

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