Amateur Photographer & Cinematographer (1936)

November 4th, 1936 ih( amateur photographer p 6 CINEMATOGRAPHER o irritating feeling of opportunities presented by unusual subject-matter being missed, were first-rate. Some were natural history subjects, no¬ tably a colour f Im by Mr. and ]\Irs. Ridley, who with infinite patience and skill, at Wicken Fen in Cam¬ bridgeshire, had traced the lifehistor^'of the swallow-tailed butterfly. The pretty caterpillar, the curious chrysalis, the gorgeous butterfly emerging for its ten-day life, made a really dramatic picture. It is evident that workers using colour films are paying very great attention to the question of exposure, and the films please not only the eye of the man interested in the several sub¬ jects, but the more critical eye of the photographer interested in a faithful rendering of nature. Photographic Reversal Processes A very scientific communication from the Department of Physical Chemistry at Cambridge was made to the last meeting of the Royal Photographic Society. It concerned the border effects associated with photographic reversal processes. If a plate is exposed and partially developed, and is then exposed again to diffused light and redeveloped, a partial or complete re'V'ersal of the image takes place. This is the well-known Sabattier reversal. The second image which develops up has been shown to be a positive, and the final appearance of the plate depends on the relative strengths of the positive and negative images in the same film. Thus,, if the first expo¬ sure and development are fairly full only the image of the shadows will be reversed. The authors of this communication, Mr. G. W. W. Stev'ens and Mr. R. G. W. Norrish, said that the borders formed in these partial reversal processes were pro¬ duced by the spread of the Sabattier or other reversal beyond the limits of the image. The mechanism of this spreading was primarily the process of scattering of light in the films — what they called diffusion halation. Secondary effects, due to restraining of the second develop¬ ment by products of the first, may reinforce the border effect in some cases. They concluded that the }>roduction of the Sabattier effect itself is primarily independent of the formation of potassium bromide or oxidation products in the film. The A mateur Photographer” EXPOSURE ABLE — November EVERY MONTH a brief exposure table will be provided for the assistance of our readers in their practical work. A glance at the current approximate exposures as here given will serve as a reliable guide for most purposes. The subjects will be varied to suit the time of year. The following exposures will serve as a working guide for any fine day during the month, between the hours of 10 in the morning and 2 in the afternoon, with the sun shining, but not necessarily on the subject. Stop used, f/8. The exposure should be doubled if the sun is obscured, or if stop f/ii is used. For f/i6 give four times the exposure. For f/5.6 give half. From 8 to 10 a.m. or from 2 to"4 p.m. double these exposures. From 7 to 8 a.m. or from 4 to 5 p.m., treble them. Subject. Ordinary. Medium. Rapid. E-xtra Rapid. Ultra Rapid. Open seascapes and cloud studies . . 1/20 sec. 1/39 sec. 1 /60 sec. 1/80 sec. 1/100 sec. Open landscapes with no v'ery heavy shadows in forep;round, shipping studies or seascapes with rocks, beach scenes . . 1/10 1/15 y y 1/30 „ 1/40 yy 1/50 yf Ordinary landscapes with not too much foliage, open river scenery, figure studies in the open, light buildings, wet street scenes 1/4 y y 1/6 y y 1/12 „ 1/15 y y 1/20 yy Landscapes in fog or mist, or with strong foreground, well lighted street scenes . . 1/3 y y 14 y y 1/10 „ 1/12 y y 1/15 yy Buildings or trees occupying greater portion of pictures . . 3/4 y y 1/2 y y 1/4 „ 1/5 yy 1/6 y y Portraits or groups taken out of doors, not too much shut in by buildings . . 2 secs. n y ♦ 1. 1/2 yy 1/3 yy Portraits in well lighted room, light sur¬ roundings. big window, white reflector . . 6 y y 5 secs. 3 secs. 2 secs. n yy yJs a further ^uiile we appetui a list of some of the best-known mokes of plates and films on the market. They have been divided into groups, which approximately indicate the speeds referred to above. The hypersensitive panchromatic plates and films require less exposure than the ultra-rapid. Ultra Rapid. Agfa, Special Portrait. ,, Isf)pan ISS Film. „ Super-speed F'ilm. ,, Isochrom Film. ,, L Itra Special. Barnet, Press and Super Press. „ XL Super-speed Ortho. „ Soft I'anchromatic. ,, Studio F'ast. ,, UPra Rapid. East.man, Par Speed Cut Film. ,, S.S. Cut Film. ,, S.S. Pan. Film. Ensign, rilrat hrome Film. GEVA^ RT, Super Sensima. „ Sensima Fast. ,, Sensima Ortho. „ Super Chromosa. ,, Roll Films and Packs. Ilford, Golden Iso-Zenith. Ilford, Iso-Zenith. Kodak, Verichrorae Film. Agfa, Iso Rapid Chromo. „ Hypersensitive Pan. „ Super Sensitive Pan. „ Roll F'ilm. Plates and Films. Film. Barnet, S.R. Pan. „ Portrait Film (Ortho ,, Panatomic. Marion, Record. ^ „ Studio Ortho. Fast). Ensign, Roll F'ilm. „ Monarch. „ Iso Record. Gevaert, Filtered Ortho. ,, Press. Nuro Film. ,, Chromosa. „ S.S. Ex. Sens. Selo, Selochrome Roll Film and „ S.R. ,, Zenith Ex. Sens: Film Pack. „ Regular Cut Film. „ S.G. Pan. ,, Selo. Pan. Roll Film. X’oigtlander, Illustra Film. Ilford, Auto. Filter. „ S.R. Pan. Illingworth, Fleet. Wellington, Anti-screen. ,, Pan. Film. „ Super Fleet. ,, X Press. ,, Rapid Chromatic. ,, Super Fleet Ortho. Zeiss Ikon, Pemox Roll Film Imperial, Non-filter (new series). „ Pan. Fleet. and Packs. „ Eclipse Pan. B. Imperial, S.S.S. Press Ortho. Extra Rapid. „ S.S. Ortho. „ Eclipse. Agfa, Chromo. Kodak, Roll Film and Film Pack. ,, Eclipse Ortho. Soft. ,, ,, Isolar. ,, Extra Rapid. Pathe, Roll Film. ,, Eclipse Soft. Selo, Roll Film. „ Eclipse Ortho. „ Isolar. Zeiss Ikon, Roll Film and Film ,, Eclipse Pan. Soft. ,, Iso Rapid. 448 Pack. Rapid. Barnet, S.R. ,, Self-screen Ortho. Ilford, Screen Chromatic. „ S.R. „ Comihercial Ortho Film. Imperial, Non-iilter. s’r. Ortho. Kodak, Cut Film. Medium. Ilford, Empress. „ Chromatic. Ordinary. Barnet, Ordinary. Gevaert, Ordinary. Ilford, Ordinary. ,, Rapid Process Pan. Imperial, Ordinary. „ Pan. 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