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"Print So Fine" paper developer
"Digitaltruth" wrote in message oups.com... Nicholas Lindan has written to me and will be posting the response I sent him, but the claim we make is supported by subjective analysis of the print. We strive to post accurate information on our web site and all product descriptions are designed to help people find what they are looking for. Unlike a lot of other companies in the market, Digitaltruth Photo is run by photographers. Personally, I have used a lot of print developers and based on my own experience if I was looking for a warm-tone image with excellent gradation, then Print-So-Fine would be my choice. Its not a fast developer - typically taking a minute more than a standard developer - so its not for everyone, but I would recommend it to anyone who wants better contrast control. The image appears slowly so it is easier to pull the paper out of the developer before the highlights lose their sparkle. I agree with Richard Knoppow's post, and given that sensitometry is complex I prefer to judge things with my own eye. A print is usually judged by people who look at it and not by scientific analysis; however, we do have people making sensitometric tests and will publish the data as soon as it can be properly assessed. I can assure you that there is no apparent visible loss of density reported by the various people who have made subjective analyses of the prints, so even if the sensitometry shows a technical reduction in density this does not invalidate the experience of actual users. I'd love to publish jpegs on our web site, but there is no way to show the subtlety of the effect on a monitor. --Jon Mided Digitaltruth Photo http://www.digitaltruth.com I did not mean to give the impression that sensitometry is complex. The principles are fairly simple. Controlling the variables so that the measurement is valid requires some care but not beyond what a careful darkroom worker can do. For serious work it is necessary to have a real densitometer. They are rather expensive new but used ones are available at rather low prices because they have been displaced by the shift to digital imaging. The densitometer, as its name implies, measures the density of the image after development. There are two types of densitometer, one for transmission, another type for reflection. Some densitometers are equipped to make both kinds of measurement. To make the test exposures one needs some method of controlling the relative exposures accurately. Simply photogaphing a flat surface with a camera is usually not good enough because neither shutters or f/stops are sufficiently accurate. However, step wedges and reflection step tablets are readily available. These are offered in both calibrated and un-calibrated versions. The only difference is that the calibrated ones are individually measured with a NIST certified densitometer and correction factors are supplied. These are necessary for very accurate work but ane not required for simple experimental measurements to find the curves of film or paper or measuring approximate exposure index or the effect of different developers or development time. Such wedges are avaialable from Stouffer at http://www.stouffer.net/Stoufferhome1.htm where they are fully described. The wedges can be used by contact printing or enlarging. A reflection step wedge is useful for calibrating a reflection densitometer but it can also be used for direct visual comparison. The eye is very good at matching relative brightness of adjacent areas. So, one can get a pretty good measurement of print density by laying the step tablet on the print and matching the visual density of the area of interest. In serious scientific sensitometery its necessary to controll a lot of factors that are not so significant where one simply wants to compare printing papers or developers or films. "Real" sensitometery must take into account: The color temperature of the exposing source The diffusion of the source compared to the method of illumination to be used for the actual results, that is, it must take into account the Callier factor. It must take into account the effect of reciprocity failure. That is, there is a difference between step exposures made by holding the time of exposure constant and varying the intensity, and those made by constant intensity and variable time of exposure. Development methods must be such as to be highly reproducible. For instance, in making film speed measurements a special insulated tank (like a Thermos bottle) is used and special methods of agitation are used. Again, this degree of control in not necessary for the kind of determination most of us want but one should be aware of all the variables and try to contoll them the best one can. Now, as a minimum for experimentation I would suggest a reflection step tablet. One can photograph this and print the negative and then compare the tablet visually to the print. This simple procedure can tell you a lot about the tone rendition of the system. Beware that in prints the paper surface or texture makes a lot of difference. The highest contrast and widest range of brightness is gotten from glossy paper. Surface textures reduce Dmax and contrast because they scatter light. A highly textured surface will also suppress image detail (sometimes desirable) so textured papers should not be used for overall testing. However, the method described above will also tell you what the losses from the texturing are. -- --- Richard Knoppow Los Angeles, CA, USA |
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