PRE-FLASHING THE POSITIVE PAPER

difference in exposure from centre to edge That difference was too extreme in this case. I tried taking some other pinhole shots using the Walker Titan pinhole 5x4 camera, which has a 35mm-equivalent focal length of 70mm, and got more consistent results The aperture of this camera is f/250. and with Direct Positive paper in the back this gives exposures around 2-3mins in direct sunlight If you wish to try Direct Positive paper in a home-made pinhole camera, make sure you work out what the pinhole aperture f-stop is, otherwise any exposures will be way off the mark. With a commercially made pinhole camera the aperture is laser-drilled so the f-stop is known exactly, but home-made cameras vary wildly in the size of the effective aperture. Combining a known aperture with accurate metering will give consistent results, but even then metering must be done with care because the high contrast of the paper is unforgiving of over or underexposure. The ’ISO also needs to be established, although this is relative, the actual speed of the paper can be worked out for a particular meter with a few simple tests. I found mine to be VS stop slower than recommended by Harman, which makes it ISO 2. Check your own results against my speed, but bear in mind that your meter may be calibrated slightly differently to mine. My next tests were using a 5x4 MPP with a 180mm lens, as I found the control of exposure and narrower angle of view gave more consistent results. As the contrast of this paper is high, even when pre-flashed, the chosen subjects and lighting conditions will have a big impact on the success of an image. I would recommend not shooting into the light and avoiding sunny days unless very graphic black & white shots are desired. PRE-FLASHING THE POSITIVE PAPERPRE-FLASHING is an old technique for improving highlight detail in darkroom prints, or it can be employed with sheet film to increase shadow detail. I tried pre-flashing in the darkroom and found it a little confusing at first I m used to looking at test strips that go from light areas (short exposure) to dark areas (long exposure), but these are the other way round. The dark end of the test is the shortest exposure and ithard to see where the pre-flashing is beginning to take effect. I had already worked out that the speed was approximately the same as Multigrade IV paper, so I tested in the normal way for pre-flashing on that paper. I then transferred the exposure over to the Direct Positive paper. It seemed to work well so that has now become my normal method with this paper To establish the pre-flash time using ordinary Multigrade paper (not Warmtone, because it is a different speed), first put the enlarger up to the top of the column, making sure there is no negative in the carrier Then stop the lens down to the smallest aperture and set the timer to 5secs. There are huge differences in the amount of light output from various types of enlarger, so I m not going to hazard a guess at what your exposure is likely to be. Also, make sure there are no Multigrade filters in the light path and no filtration dialled in. So, to establish the correct time for your set-up, place an object on top of the paper that will span the length of the test piece, such as a pair of scissors, and expose a series of sections. While exposing, count up the exposures as you go. In this way, if the first few exposures are blank, you can work your time out backwards from the dense end of the test When the exposed test is processed, lift it out of the fix and examine it in good light. Look for the exposure that shows the faintest shadow of the object that was on the paper and note what time that exposure was Choose the exposure just before that one, which is lighter and has not produced tone. This is the preflash time. When ready to shoot, expose each sheet of the paper for the chosen time and then load them into dark slides or cameras. It is probably best to pre-flash just before going out shooting as the exposure will deteriorate with time. On the two shots above, the effect of pre-flashing is really obvious. They were both shot at the same exposure, but the lighter one has had the pre-flash. The test shots clearly indicate a big improvement with pre-flash, but if contrast is your thing, then quite strong, graphic results can be achieved right out of the box. With another image I rated the paper at between ISO 1.5 and 3, and took two readings - one off the brightest areas and one off the darkest. I then simply placed the exposure between the two.

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