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12882Re: [PPLetterpress] Re: Laser Engraved Photopolymer Plates

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  • Gerald Lange
    Oct 23 6:38 PM
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      Not sure how to respond to this but imagine no relief as possibly cut by
      a laser. The structures would collapse under impression. Letterforms
      greatly differ in their surface structure. Counters, stems, serifs. And
      varying sizes. A relative relief helps provide support. In the
      punchcutting of type faces, varied relief is a characteristic as well.

      I don't know off hand what the slope of a 150 lpi halftone dot would be
      on a photomechanical engraving but I assume it would be much different
      that than of a metal typeface, though I have one of the last thorough
      print studies on this and will look it up and report back.


      On 10/23/11 1:05 PM, Erik Desmyter wrote:
      > Gerald,
      > I understand the variable relief but not such a variable angle. To me it still is a very small round dot created by the UV light going through a very small circle in the black film and hardening the polymer that can be exposed by that UV light bundle. I am still surprised at the 45 degrees on such a small halftone dot and I try to understand technically or optically why this would be so different to a letterform.
      > Best regards,
      > Erik
      >> Eric
      >> These are halftone dots at 150 lpi not letterforms. They would show the
      >> tiniest of surface image at extreme proximation and the shallowest of
      >> relief and the foundation needed to support it. The least of impression
      >> is all that is required to reproduce a halftone with accuracy to detail.
      >> As I mentioned, the photopolymer process produces variable relief.
      >> Gerald
      >> http://BielerPress.blogspot.com
      >> On 10/23/11 12:34 PM, Erik Desmyter wrote:
      >>> Gerald,
      >>> I agree that this is the main problem with lasers. However I am surprised to see here on this film based photopolymer http://www.flickr.com/photos/bielerpress/6272724517 an angle or slope around 45 degrees. That can result during inking with soft rollers and under pressure that the ink goes rather easy over the top surface on to the sides of the mountain what then gives no longer sharp printed edges. With tradition metal type those sides would be around 75 degrees I guess.
      >>> Best regards,
      >>> Erik
      >>>> Scott
      >>>> Maybe a picture or two is worth a thousand words:
      >>>> http://www.flickr.com/photos/bielerpress/6272724517/in/photostream/#/photos/bielerpress/6272724517/in/photostream/lightbox/
      >>>> http://www.flickr.com/photos/bielerpress/6273250924/in/photostream/#/photos/bielerpress/6273250924/in/photostream/lightbox/
      >>>> These are microscopic views of the surface of a halftone image. This is
      >>>> why photopolymer can provide such exquisite detail. The relief depth
      >>>> between imaging of close proximity decreases with exposure and provides
      >>>> structure.
      >>>> Gerald
      >>>> http://BielerPress.blogspot.com
      >>>> On 10/23/11 10:00 AM, Scott Rubel wrote:
      >>>>> Gerald,
      >>>>> Good thinking about all this. I certainly would want it to be a
      >>>>> minimum of 2400, for one thing, but I have not known how to think
      >>>>> about the other disadvantages.
      >>>>> The thing that I hope for when I think about the potential of laser is
      >>>>> straight sides to the raised type. I don't I understand why there
      >>>>> would be a limit to the depth in a counter as opposed to any other
      >>>>> part. My knowledge of lasers is based on mostly half- or 3/4-witted
      >>>>> speculation mixed with fantasy, which is why I do not understand your
      >>>>> last paragraph, but I trust your assessment.
      >>>>> --Scott
      >>>>> On Oct 22, 2011, at 10:57 PM, Gerald Lange wrote:
      >>>>>> Scott
      >>>>>> I suspect that if cut just short of the floor of the plate rather
      >>>>>> than down to the backing there would be no problem with the steel
      >>>>>> reflecting. A more significant concern would be cutting through the
      >>>>>> pre-exposed floor as plate stability would be sacrificed. Actually,
      >>>>>> with this technique, the thinner the plate the better. All that
      >>>>>> I assume the identity of the plates themselves and the correct
      >>>>>> timing for the exposure is a minor problem. 1200 dpi is still not
      >>>>>> good enough, basically high-end laser printer quality. Imagesetter
      >>>>>> quality at a minimum of 2400 dpi would be needed to match current
      >>>>>> film based exposure.
      >>>>>> A major concern would be maintaining relative reverse relief depth,
      >>>>>> which is fairly uniform when exposing photopolymer plates specified
      >>>>>> for letterpress applications, no matter what the thickness of plate.
      >>>>>> For instance, the relief depth of the counter of a small point size
      >>>>>> lowercase e or o is not going to be open to the depth of the floor
      >>>>>> of the plate. It is halted with maximum exposure at a specific
      >>>>>> range, about .30 mm; relief depth is not uniform [which is actually
      >>>>>> the best technical argument refuting the practice of extreme
      >>>>>> impression]. I don't see how this could be controlled with a laser
      >>>>>> cutter.
      >>>>>> Gerald
      >>>>>> http://BielerPress.blogspot.com
      >>>>>> --- In PPLetterpress@yahoogroups.com, Scott Rubel<scott@...> wrote:
      >>>>>>> The website days it goes to 1200 dpi. If the coordinate tracking is
      >>>>>>> accurate as it cuts, that should render pretty good six point type.
      >>>>>>> It is hard to tell the quality of the laser, but I think I will ask
      >>>>>>> them for a sample of steel backed polymer. I wonder how that works
      >>>>>>> without the steel acting like a mirror.
      >>>>>>> These laser beams can be unbelievable thin, if they are high quality.
      >>>>>>> I work at a place where we make giant cameras for giant telescopes,
      >>>>>>> and we order custom "slit masks" which are large sheets of aluminum
      >>>>>>> with thousands of precision placed cuts in them. The cuts aren't much
      >>>>>>> thicker than a hair, and you would think the laser is just moving
      >>>>>>> along a path and cutting the slit, but in reality it cuts out the
      >>>>>>> shape of the slit and almost microscopic blanks fall out of the metal
      >>>>>>> every time a slit is cut. So if this Epilog Legend 36EXT machine is
      >>>>>>> high quality, I would think six point type should work fine.
      >>>>>>> --Scott
      >> ------------------------------------
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