colin_d Posted March 22, 2011 Share #1 Posted March 22, 2011 Advertisement (gone after registration) I picked up this book at a second hand bookshop last week while on holidays. The first edition was printed in 1955, mine in 1971. It is very technical, I suspect written as an industry reference but it has some interesting statements I never heard of including this one: 1/ The ideal photo would be taken by a lens with a focal length about double the diagonal of the negative. ie. for 35mm = 70mm. This has a relationship with perspective of the print to the eye, making it look real. Also the author states that the closer the shutter plane to the film plane the more accurate the shutter speeds are, which makes sense when you understand the technical reason why. On this point, does anyone know the distance of a Leica M shutter plane from the film plane. Does it differ between models? A challenging but interesting book. Link to post Share on other sites More sharing options...
Advertisement Posted March 22, 2011 Posted March 22, 2011 Hi colin_d, Take a look here W.F. Berg - Exposure, A Focal Manual of Photo Technique. I'm sure you'll find what you were looking for!
jaapv Posted March 22, 2011 Share #2 Posted March 22, 2011 Well, #1 seems more of an opinion than a fact to me. For instance, the diagonal of 35 mm film is not 35 mm. And I doubt that the ideal lens for taking a photograph of a tiger is 50 mm (which is the lens he is referring to). Each subject has its own ideal focal length. And I would say the second is also open for discussion, so I would love to know the technical reason given. Link to post Share on other sites More sharing options...
Michael Hiles Posted March 22, 2011 Share #3 Posted March 22, 2011 Interesting point about perspective matching what the eye sees. I always thought that the 50mm was best matched to the eye (but no research or references). Perhaps that is why I have generally favoured by 50 and 90. Link to post Share on other sites More sharing options...
tobey bilek Posted March 22, 2011 Share #4 Posted March 22, 2011 There is a relation between focal length, print size, and viewing distance to make it all work. For example, at work we have a 4x6 foot picture of the original EMD diesel freight demonstrator unit pulling freight through the mountains. Time frame was late 1930`s and I am sure it was 8x10 format and most likely therefore not tele or wide. One day I noticed where I stood to look made a hugh difference in a 3D effect. At one distance and one only, it just came alive. I believe you will also see this with 8x10 prints taken with a "normal" lens and observed from reading distance. Wide angle needs to be observed closer or larger print size and telephoto shots from further away or printed smaller. It is a very interesting effect, but it takes time to see. Link to post Share on other sites More sharing options...
jaapv Posted March 22, 2011 Share #5 Posted March 22, 2011 That is correct, Tobey, and the reason Barnack chose the 50 mm lens as the standard lens for the 35 mm system. 35 mm being determined by the film he had available. Link to post Share on other sites More sharing options...
pico Posted March 22, 2011 Share #6 Posted March 22, 2011 Interesting point about perspective matching what the eye sees. I always thought that the 50mm was best matched to the eye (but no research or references). Perhaps that is why I have generally favoured by 50 and 90. The standard viewing distance is about ten inches for an ~8x10" print. This according to my old Air Force recon tech manual. It's the distance at which we can take in the whole print and resolve the smallest dot the eye can manage. Note that it is different for contrasty lines. The eye can recognize a black human hair against a white background at 30 feet! (Which is why I date blondes.) Link to post Share on other sites More sharing options...
colin_d Posted March 23, 2011 Author Share #7 Posted March 23, 2011 Advertisement (gone after registration) Tobey and Pico seem to have picked up the thrust of the size of print and viewing it principle. When I get a chance I'll quote directly from the book, but very simply for the print to look more appealing/real at 10 inches it should be at a size that replicates the original perspective when the shot was taken. On the shutter plane issue, for shutter speeds to be 100% accurate they would have to be on the film plane so that the cone of light coming through the lens will hit the film plane exactly as the slit in the curtain passes by. It's splitting hairs, but technically the speeds can be out quite a bit depending on shutter time and the distance between the film and shutter plane. On the issue of the diagonal of 35mm film, I did a measurement of the image frame excluding the perforations at the top and bottom and got 35mm, did I do it incorrectly? When I got 35mm I thought that made sense. Link to post Share on other sites More sharing options...
giordano Posted March 23, 2011 Share #8 Posted March 23, 2011 The "35mm" frame is nominally 36x24mm, but - as you'll understand - the actual size varies with the distance between the gate and the emulsion and the position of the exit pupil of the lens. Non-retrofocus wide-angle lenses produce a larger exposed area than long-focus lenses. 36 x 24 gives a diagonal of about 43.3mm. Link to post Share on other sites More sharing options...
Xmas Posted March 23, 2011 Share #9 Posted March 23, 2011 On the shutter plane issue, for shutter speeds to be 100% accurate they would have to be on the film plane so that the cone of light coming through the lens will hit the film plane exactly as the slit in the curtain passes by. It's splitting hairs, but technically the speeds can be out quite a bit depending on shutter time and the distance between the film and shutter plane. There are two things effective exposure shutter efficiency. Cause the shutter is some way forward of the film the cone shaped 'light beam' from the lens (in the time domain) is like a sausage, sort of. When the 1st blind passes completely but before the 2nd blind is near, the full beam from the lens is used, when either blind is close less of the beam is used. At higher speeds (cause of the narrow slit) with a wide aperture lens the efficiency can be lower. If you are shooting with a f/0.95 and 1/1000 and using slide you might have to compensate... Otherwise I'd not worry. With a typical between the lens camera you get the same effect and I stick a look up table Avery label on the back of camera, used to use slides... Used to use 1/2 to 3/4 of a stop more time when lens wide open... Noel Link to post Share on other sites More sharing options...
colin_d Posted March 23, 2011 Author Share #10 Posted March 23, 2011 Noel, you've hit it bang on the head, as I understand it from reading this book. Another thing I picked up was that there exists image distortion with focal plane shutters when shooting moving objects. Again it depends on shutter speed and speed of the moving object, but by using simple physics it seems correct. It's a fascinating read this book that was written some time ago when only film existed but I assume some of the principles apply to digi. To give you an idea, below is the sections in one of the 19 chapters titled Properties of Photographic Materials: The Characteristic Curve The Logarithmic Scale Differences in Brightness Density Kinds of Density Density Wedge Tone Reproduction The Shape of the Characteristic Curve Overall Gamma The Contrast Index and Printing on Typical Materials Tone Reproduction and Scattered Light The Effect of Development Time Intensity of Exposing Light Gamma and Colour of Light; Latitude I'll keep reading and discovering... chapter 12. Link to post Share on other sites More sharing options...
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