Xref: utzoo rec.photo:1976 sci.electronics:2169 Path: utzoo!utgpu!water!watmath!clyde!burl!codas!mtune!whuts!homxb!houxs!beyer From: beyer@houxs.UUCP (J.BEYER) Newsgroups: rec.photo,sci.electronics Subject: Re: Homebuilt transmission densitometer? Summary: Comparison of densitometer and enlarger-photometer combination. Callier effect (fairly long and specialized) Message-ID: <677@houxs.UUCP> Date: 16 Feb 88 14:13:16 GMT References: <2659@dcatla.UUCP> <11237@shemp.UCLA.EDU> <24105@linus.UUCP> <2493@tekig4.TEK.COM> Distribution: na Organization: AT&T Bell Laboratories, Holmdel Lines: 67 While I don't normally measure density with an enlarger and enlarging photometer, I think it is a pretty good way of controlling the process, and even takes into consideration things like enlarger flare, Callier effect, etc. However, the readings should not be equated to those measured on a true densitometer. (They may even be *more* meaningful in some applications, but they are not the same.) To get an idea of what is going on, and to calibrate 3 new boxes of paper I just bought, I ran some tests last weekend. Those results that I thought might interest others are posted here. Relative speeds of the various papers are not, since the box-to-box variations are the important ones that must be measured individually. I normally use a Macbeth TD901 transmission densitometer, a Beseler 45MCRX enlarger with Aristo cold light head, or Beseler condenser head, and sometimes use a Beseler PM2a color analyzer. As a test, stimulated by recent postings here on netnews, I measured a Kodak T-14 control scale four ways. With the densitometer, over the color analyzer, and projected through a Schneider Componon S 180mm f/5.6 lens. When projecting, the scale was 'pretty well' surrounded with an opaque (litho-film) mask. When using the densitometer, I placed the emulsion side up (toward the diffuser and detector). In all other cases, the emulsion side was down (toward the detector -- where the paper would be). The "white" filter was used. Step D D D D Number TD901 Scale on Scale Scale 3mm aperture Analyzer Projected Projected ColdLite ColdLite Condenser ------------------------------------------------------------------------- 1 0.056 0.06 0.07 0.1 2 0.184 0.2 0.2 0.27 3 0.313 0.34 0.35 0.46 4 0.463 0.5 0.52 0.69 5 0.612 0.66 0.69 0.89 6 0.764 0.82 0.85 1.08 7 0.916 0.98 1.0 1.29 8 1.08 * 1.16 1.48 9 1.22 * 1.32 1.68 10 1.39 * 1.51 1.90 11 1.55 * 1.7 >2.0 12 1.71 * 1.88 13 1.86 * >2.0 14 2.02 >2.0 * indicates too difficult to read (can't see where the steps are). Assuming the TD901 to be the most accurate (I believe this assumption), this seems to show that the PM-2A is pretty accurate, tracking the TD901 quite closely and linearly. Projecting with the cold-light head is also quite close: I believe the slight upward curvature is due to light falloff at the edge of the image where the higher densities on the control scale were. A separate measurement seems to confirm this. The Callier effect is quite pronounced with the Condenser head, but it seems to have more even light distribution than the cold light head. Makers of home-made densitometers can expect similar differences if they are not careful about illumination and collection angles of their instruments. Such makers are urged to plot the graphs, either from my data, or (preferably) their own to see how much this difference is. For speedy printing, I don't bother with the color analyzer (in B+W, that is), I just set the enlarger for an 8x10" print, put the 4x5" negative in, and print 10 seconds at f/11. Sometimes this comes out right. Other times it is close enough so the next print is correct. This is only true for "average" scenes. I do use the analyzer when changing sizes, but one does have to calibrate each box of paper.