OK

I think Feinstraster is expressed as high screen ruling:

DEI Systems - Rip Options - imagesetters, prepress, typesetting ... -
... This screening method allows higher detail with minimized moiré by making it possible
to print at high screen rulings (above 150lpi) without loss of highlight ...
www.printusa.com/deisystems/rip_options.htm

[PDF] Fujifilm Co-Res Screening Fact Sheet
Dateiformat: PDF/Adobe Acrobat - HTML-Version
... Sheet A revolutionary screening software developed by Fujifilm, Co-Res Screening
allows computer-to-plate customers to print high-screen rulings while using ...
www.getitfromtheexperts.com/docs/fujifilm/ Co-ResScreeningFactSheet.pdf

The German term FM-Raster stems from the English frequency modulated. The abbreviation has been kept in German for obvious reasons.

And just for the record, this hasn't anything to do typography.

FM (frequency modulated, also called stochastic) screening is a relatively new screening method. It is not widely spread yet, for several reasons: 1) producing the seps requires more sophisticated RIPs (raster image processors), more computing power, and film with specific characteristics; 2) printing requires special ('hard-dot') printing plates, plus much greater precision in plate production and printing press adjustments (printing FM-screened material on an older press can have disastrous results, even though conventional halftone screens may come out just fine); and 3) you can't print FM-screened material on just any paper (I'm not going into details here).

The difference between FM and conventional halftone screening is as follows:

- The conventional halftone screen is a grid consisting of the so-called halftone dots. These are actually 'cells', each containing a single dot which varies in size to reproduce the different tonal values, from 0 (no colour, white) to 100% (solid colour). If e.g. the dot occupies 50% of the cell area, a screen of such dots is a 50% screen. The dot shape may be different (round, elliptical, rhomboid etc.), and varies a little for the tone value ranges below and above 50%. The four primary inks (cyan, magenta, yellow and black) have screens rotated at different angles (standard values are 105, 75, 90, and 45 deg).

- FM screening uses dots of equal size, which are very small - hence the extremely crisp image. The dots are distributed across the sheet with varying density (tonal value here is reproduced by varying the dots' density, not by varying their size). The distribution is seemingly random - under a magnifying glass, it looks very much like what you get from an inkjet when printing with diffusion dithering. However, 'random' is not at all true, this is why the term 'random screening' is generally frowned upon. In fact, what seems like a random distribution is carefully calculated so, that the dots do not form *any* repeating patterns. This is done by stochastic calculation algorithms (hence, 'stochastic screening'). AFAIR there exist a few proprietary trade names, but the commonly used term is 'FM screening'.

As both sparkie and Klaus quoted, halftone screens (rulings) higher than 60 lpc (150 lpi) are considered high screen rulings. FYI newspapers are normally printed at abt. 80 lpi, low-quality offset - at 120-133 lpi, the majority of offset jobs - at 150 lpi. Standard high ruling values are 175 and 200 lpi (I don't think I've seen anything printed at more than 200 lpi).

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Note added at 4 days (2003-12-21 04:08:35 GMT)
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http://www.druckerei-duennbier.com/_glossar.htm

See \'Autotypische Rasterung\' and \'FM-Rasterung\' (w/ pics)