Alan Marcus

<p>Studies show that people tend to view image at a distance about equal to the diagonal measure of the display be it print or monitor. </p>

<p> Hi Kenneth,<br> Film consists of a coat of highly purified gelatin on a flexible base. The light sensitive goodies are imbedded in the gelatin which acts as a glue to hold everything to the base. Gelatin is used because it swells when wet allowing the fluids of the process to percolate freely within the structure. The last major step is the fixer. This solution contains sulfur and if not washed out, the sulfur attacks the silver based image and tarnishes it. We wash for 20 to 30 minutes to ensure all the fixer is rinsed out completely. An alternate is to use a hypo (nickname for fixer) clearing agent. These are special salts that help flush out fixer. A hypo clearing bath followed by 5 minute wash in running water is ample.<br> <br> The key drying technique is to use a final rinse fluid free of foreign particles. Highly filtered water is OK many use distilled or deionized bottled water. Now water tends to bead on the surface of the film will be in the form of localized water droplets that dot the film’s surface. As film dries the swelled gelatin shrinks. If water droplets are present, they retard shrinkage in a localized way. The film dries with uneven shrinkage and the result is water-marks that are likely irreversible. The counter measure is a wetting agent rinse bath. 30 seconds soak in PhotoFlow or equivalent does the trick. This is a sequestrate that breaks the surface tension of water. The water now sheets instead of beads. Many now sponge the film or squeeze to ensure water drops are absent. I run the film through two fingers wet with the rinse. </p>

<p>Alan Klein,</p> <p >Diffraction is a big problem regardless of format, it an optical phenomenon that plagues all lens and we can’t improve as per the well-studied works of Nobel laureate Lord Ryleigh, England Astronomer and Physicist published as the Rayleigh Criterion and it still stands today.</p> <p >Resolving power decreases with aperture: Resolving power = 1392 ÷ f/#</p> <p >f/1 = 1392 lines/mm</p> <p >f/2 = 696 lines/mm</p> <p >f/2.8 = 497 lines/mm</p> <p >f/4 = 348 lines/mm</p> <p >f/5.6 = 249 lines/mm</p> <p >f/8 = 174 lines/mm</p> <p >f/11 = 127 lines/mm</p> <p >f/22 = 63 lines/mm</p> <p >f/32 = 44 lines/mm</p> <p > </p> <p >Note: The resolving power at apertures larger that f/8 is higher than that of pictorially useful film emulsions. </p>

<p>To Andrew <br> The size of the circle of confusion is the key to this discussion. It must be perceived as a point without dimension or the image appears unsharp. This stuff is all based on the fact that a coin viewed from 1/3000 of its diameter is perceived as a point without dimension to a person with 20/20 vision. For photographic purposes the industry adopts 1/1000 of the viewing distance which is equivalent 1/100 of an inch in diameter viewed from 10 inches or 2/100 of an inch viewed from 20 inches (standard reading distance). This is the criterion: 2/100 of an inch disk size is 1/50 of an inch = 0.02 of an inch x 25.4 = 0.5mm. This lower standard of 3.4 minutes of an ark is adapted because of the contrast of photographic image and uncorrected aberrations and the presence of flare. Elongate the viewing distance and the larger disk diameter is acceptable. </p> <p>Because of all the different format sizes it has become customary to use 1/1000 of the focal length for the size of the disk at the focal plane. This assumes the image will be enlarged for viewing. As an example, a 35mm full frame image is enlarged 10X. A 50mm is mounted. Using the 1/1000 rule of thumb, the permissible size of the disk at the focal plane is 50 ÷ 1000 = 0.05mm. Now if we enlarge 10X making a print 9 ½ x 14 inches, the disk on the final image is 0.05 x 10 = 0.5mm. Thus the disk size meets the criterion.</p> <p>The 1/1000 of the focal length is crude and assumed to take into account the fact that longer lenses will be mounted if the format size is large, and shorter lenses will be mounted if the format size is smaller. One guideline fits all. Again precision work requires 1/1500 or 1/1750, however most tables charts and online calculators use 1/1000.</p>

<p>Your question gyrates around “hyperfocal distance”:<br> Setting your camera to a specific distance called the hyperfocal point delivers the maximum span of depth of field that just kisses off infinity ∞. Fixed focus “Brownie” cameras are set to this value and landscape photographers routinely set focus to this value. This is because the span of acceptable focus starts at ½ the hyperfocal distance and stretches to infinity ∞. Let me add that it is a special case of depth of field calculations. You will find it listed on line with all the depth of field calculators. You can make your own calculations; it’s easy!<br> First we must agree on the criteria that constitutes optical sharp. We are talking about the size of the circles of confusion. These are super tiny disks of light projected by the lens onto film or digital sensor. They must remain super tiny so they are perceived as points of light and not disks by the observer. That means they must be tiny enough to withstand enlargement. Generally charts and tables are based on making a final print or display that measures 8x10 inches. Most will be based on a circle size that is 1/1000 of the focal length. For scientific and serious work Leica uses 1/1750 and Kodak 1/1500. It is customary to use 1/1000. The basis is: the circles remain just below the appearance of a disk at a viewing distance of 20 inches (500mm). This dictates the final circle size shall be no greater than 1/50 inch or 0.5mm. <br> Now for the math:<br> f = focal length<br> a = aperture (f/#)<br> d = diameter of aperture<br> c = circle of confusion diameter<br> <br> Say you mount an 80mm lens set to f/8<br> The aperture diameter is 80 ÷ 8 = 10mm thus d=10<br> c = 80 ÷ 1000 = 0.08mm<br> <br> Formula = fd/c<br> 80 x 10 ÷ 0.08 = 10,000 (this is the hyperfocal distance in millimeters <br> 10,000 ÷ 2.5 = 394 inches<br> 394 ÷ 12 = 33 feet.<br> Set your camera to 33 feet and everything will be in focus from ½ the hyperfocal distance to infinity ∞.<br> Thus the range of acceptable focus is 16 ½ feet to infinity ∞.<br> <br> Once more for a 100mm lens set to f/11<br> <br> The aperture diameter is 100 ÷ 11 = 9mm thus d=9<br> c = 100 ÷ 1000 = 0.10mm<br> <br> Formula = fd/c<br> 100x9÷0.10=9,000mm<br> 9,000 ÷ 25.4 = 354 inches<br> 354 ÷ 12 = 29 ½ feet<br> <br> Set to this distance, everything will be in acceptable focus 15 feet to infinity ∞.</p>

<p>What focal length we choose is based on need. To understand we must know what focal length delivers a normal view. By unanimous agreement, if we mount a lens with a focal length that about equals the diagonal measure of the film or digital chip format, it delivers a “normal” view. This will be an angle of view of about 45⁰ with the camera held in the landscape position. Longer and the angle of view becomes narrower and the image is magnified. Shorter and the angle of view increases and the image is minimized. <br> <br> For the full frame, the format measures 24mm height by 36mm length. The diagonal measure is 43mm. This is an odd value so by mutual agreement a 50mm lens is considered “normal”. If we mount a 300mm the image will be highly magnified. The math is 300 ÷ 50 = 6. This tells us that the view is about the same as a view with 6X (six power) binoculars. If we mount a 400mm the view is 400 ÷ 50 = 8 ---- the equivalent view of 8X binoculars. <br> <br> Now high magnification demands a sturdy support. To hand-hold you are advised to us a minimum of 1/300 of a second with a 300mm and 1/400 of a second with a 400mm. My thinking is the 300mm will be a better choice as it will be easier to hand-hold. <br> <br> Let me add that a compact digital measures 16mm height by 24mm length. The diagonal measure and thus the “normal” lens for this format is 30mm. Mount a 300mm and the magnification is 300 ÷ 30 = 10X. Mount a 400mm and the magnification is 400 ÷ 30 = 13X.<br> <br> Likely the temptation is to choose the higher power. Practicality dictates that the lower power is more practical. </p>

<p>Macro in photo jargon translates to a lens capable of imaging at life-size. This is magnification 1 (one) often called “unity” or expressed by the ratio 1:1 (one-to-one). Often a lens will be advertised as a “macro” however it may fall short of “unity”.</p> <p>To understand you need to know that a typical camera lens is optimized to image objects at a far distance (infinity symbol ∞ meaning as far as the eye can see). When ordinary camera lenses are tasked to image at near distances they are slightly compromised. The degradation is minuscule so you may not notice.</p> <p> Worse, at distances closer than 1 meter (1 yard), the f-numbers engraved on the standard lens barrel become invalid as you close focus. Should the ordinary camera lens be tasked to image at “unity”, the f-number error is 2 stops (4x less light transversing the lens). As to the standard lens being optimized for distance, it is figured to image a curved world and project that image on flat film or the surface of a digital imaging chip.</p> <p>To close-focus, the camera lens must be moved forward increasing lens-to-film or digital chip distance. At ‘unity”, the lens extension will be one complete focal length. Since many cameras will not allow close-focusing, a workaround is to dismount the lens and use a spacer called a ring to increase lens to film or chip distance. Ring sets are sold with various size spacers to allow several close-focus magnifications. Often the standard lens is reversed. This points the back of the lens at the subject. The idea is, the back of the lens is optimized to focus on a flat surface and most close-up subjects are nearly flat.</p> <p>Still the photographer must compensate for the f/# error. This problem is moot in a modern camera that meters exposure through the lens.</p> <p>Macro lens to the rescue: The macro is optimized to image flat subjects at “unity”. The macro is slightly compromised when tasked to image distant subjects. This compromise is likely too small to be noticed. Most important, the macro design solves the problem of the f/# error (called bellows factor). The macro design uses a strong front lens element that magnifies the size of the lens aperture as seen from the front. This element moves as you focus -- thus the apparent size of the aperture is made adaptable; it compensates for light loss as the lens is close-focused. The modern macro is a marvel of technology. </p> <p>The distance lens to subject at any given magnification is a matter of geometry. At unity, the subject is 4 focal lengths from the film or digital chip. The lens is extended and rests in the center. Thus a 100mm lens focused to unity, the subject to image plane is 400mm in separation, the lens is 200mm forward of the image plane and 200mm from the subject. Measurements are taken from a point within the lens barrel called the rear nodal.</p> <p>Nobody said this stuff is easy. Hats off the modern opticians who now use computer software to design. Not too long ago it took years to do the math by pencil and paper using a slide rule and math tables</p>

<p> <br> Before you jump to the conclusion that your processing in D-76 failed, look at the film. Tell us about the edge printing. I am taking about the emulsion numbers, the words “Kodak” and perhaps “Safety Film” etc. Edge printing is applied during manufacturing by exposure to light. Thus the edge printing developers up just like a latent image. Also, is there any fog on the strip? If the edge printing developed up and is readable, then likely the developing is OK. Also, D-76 is a great all-purpose developer that should work with most any black & white film. </p>

<p >Salt (solid particles) adhering to the emulsion side is likely one of the ingredients of the fixer. Also remotely possible it is residue from the developer. When mixing chemistry, best you allow some time between mix and use to allow stubborn ingredients to completely dissolve. Filtering the fluids can’t hurt. This stuff might be from the wash water. </p> <p >I suggest re-washing in running water for an extended time like 30 minutes. Then place in a bath of wetting agent for 30 seconds and squeegee with your wet fingers. That way you can feel if any particulate matter is on the film. </p>

<p>Film is under-fixed or film is fogged due to age, exposure to light - heat - radiant energy - over development etc.<br> I suggest under -fixed -- no harm to re-fix in normal room light. This time immerse a piece of film along with the sheet film. Place all in a tray of fixer solution. Time how long it takes for the test film to change from opaque to clear. Keep the sheet film in the fix for double this time. Then wash in running water for 30 minutes then wetting agent then dry. This likely will improve the base fog you are complaining about. </p>

<p>Why would lens design effect image contrast? The job of the lens is to gather light rays from the outside world and project them as an image on the flat surface of film or digital sensor. This is accomplished by altering the path of light rays. We call this action refraction. This is accomplished by the shape, material of construction, and spacing of the individual lens elements that make up the camera lens. <br> <br> All camera lenses suffer from natural defects called aberrations. The lens maker attempts to mitigate but none have been eliminated. To minimize, different densities of glass, each with different figures are packed into the lens barrel. Each element of the array takes a toll reducing the light energy that should make up the projected image. Only about 92% of the light will transverse each element. What happens to the light that reflects off each polished surface? <br> <br> Reflected light from each lens surface bounces about. Some will strike the walls of the lens barrel and the hollow of camera body. Some will strike the lens ahead or behind. In other words, the image forming rays are comingled with stray light rays. It is these misdirected light rays that will eventually bath the film or digital sensor with non-image forming rays during the exposure. To migrate the inside walls are painted flat black. To further migrate, each lens is “boomed”. <br> <br> It was discovered that older lenses passed more light then new ones of the same design. Investigating, Harold Dennis Taylor (English 1862-1942) discovered that old lenses had a thin film of “bloom” deposited by air pollution. He experimented and artificially aged lenses (patent 29,561/1904). The thin film of “bloom” now applied, drives the transmission percentage up to 98%. <br> <br> Optical coating on lens elements and filters is the major mender of stray light in the image forming rays. It is these rays that induce flare. Flare is devastating as it slashes contrast. A singe thin coat mitigates best only one color. The coat thickness must be ¼ wavelength. Complex lenses can have as many as 12 coats. All this adds costs. You get what you pay for. Hats off to Harold Taylor! </p>

<p>Prime lenses are fixed as to focal length. These lenses are optimized to image distant objects. A true macro lens is optimized to image at unity (1:1 magnification 1 life-size). At unity there is very little depth-of-field; thus most subjects are flat. Prime lenses are designed to image a curved world and project an image on the flat surface of film or a digital imaging chip. That translates to the fact that the rear of the lens is optimized to image a flat plane. For this reason, primes when tasked to image at unity often perform best when inverted. Thus the prime is often mounted on extension tubes with a reversing ring. Now the rear of the lens faces the subject. This configuration yields a higher resolution. To obtain unity, the prime is extended forward one focal length. Extension tubes and the reversing ring de-couple the lens electronically from the camera body. Now you are on your own to manually adjust the taking aperture. The distance subject to focal plane at unity is 4 focal lengths. In this configuration the f/#’s engraved on the barrel are invalid. This error is called “bellows factor”. The error requires the lens aperture be opened two f/stops. <br> <br> A true macro is optimized to image at unity. It is optimized to image a flat subject. The macro design counters “bellows factor” thus the f/#’s remain accurate. Magnificent images are obtained both with a macro and a prime with extension tubes. The macro design, by its very nature, takes the pain and drudgery away. </p>

<p>This camera sports a guide number of 12 for those folks using the metric system. For folks living in Liberia and the USA, (only countries still using the old English measure system). The conversion factor is 3.28 making the guide number for feet =40 of ISO 100. If we choose to use 200 ISO we multiply the guide number by 1.4 thus for 200 ISO the guide number is 56. For 400 ISO the guide number is 80. OK to round values for convenience. <br> <br> We use this guide number by estimating the subject to camera distance and dividing this value into the guide number. Say we set our camera to 100 ISO and the subject is 7 feet from the camera. We divide 40 by 7 = 5.6). This tells us to set our camera aperture to f/5.6. Set the camera to 400 ISO the guide number is 80, subject at 7 feet, the aperture setting is f/11.<br> <br> Sorry to report that the flash produced by the built-in flash is quite feeble. To get more power, heavy duty batteries and a component called a capacitor must also be heavy duty. We get powerful flash units when they are permitted to get. This built-in flash is typical in power for this camera type. <br> </p>

<p>Likely a camera light leak. Procure one of those tiny key-chain LED flashlights. You need the kind that stays on. Insert flashlight into camera and close. In a darkened room, sit with the camera for 20 minutes. It takes that long to fully dark adapt. Now examine the camera from all different angles. If the camera’s seals are faulty, light will leak out. </p>

<p>If an astronomical telescope is setup for eyeball observing, you can image what you see with your camera. This is called afocal photography. Afocal translates to no focus meaning the light emitted from the eyepiece of the telescope is exiting as parallel rays (no focus) as opposed to converging rays that will focus at some distance further downstream. Anyway, place your camera close to the eyepiece and snap away. If the camera is in manual mode, set focus to infinity (symbol ∞). <br> <br> You can practice using binoculars. Set the binoculars on a suitable support and focus it to magnify a distant tree etc. Bring your camera up to the eyepiece and snap away. You might practice on the moon. Note that most astronomical objects viewed by telescope are quite dim and most likely will require at time exposure of several minutes. Such subject will be impossible to photograph using the afocal method unless the camera is clamped to the eyepiece. It is unlikely that Mt. Wilson staff will allow such carry-ons. </p>