 BetterPhoto Member |
F-stops and Shutter speeds I am a student in a photography class and am having some trouble with my f-stops and shutter speeds. I have a Asahi Pentax, K1000 SE, camera and am using Arsta.edu ultra black and white 400 photographic film. Please send my a chart of f-stops and shutter speeds so I can get a general idea of what I should set them at. Thanks so much, Erin
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Samuel Smith |
that's your job.
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- Dennis Flanagan Contact Dennis Flanagan Dennis Flanagan's Gallery |
Holt, there is no true answer. Since I suspect that model does not have a built in light meter, you may want to purchase an inexpensive one. If you want a good starting point, go with shutter 125 and f11. Then leaving your shutter at f11, take the same photo with your f/stop up one and then down one. This is guessing you have have decent light to work with.
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Samuel Smith |
ah gee. if 1/125th and f8 is close to what you want,a start. now if you need to freeze a little more action set it to 1/250th at f5.6 . if you want more depth of field go the other way and set it to 1/60th at f11. the same but different,sam
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Alan N. Marcus |
Samuel you need to buy a light meter. How about shopping for a used one? Exposure Guide 400 ISO Film Bright sunlight - 1/250 f/22 Alan Marcus
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Christopher A. Vedros |
The K1000 has a built-in light meter. Install a fresh battery, if needed. Set your ISO speed to match your film. You need to do a little research about f-stops and shutter speeds to learn when you would want to use larger apertures vs. smaller ones, and faster shutter speeds vs. slower ones. For any f-stop that you set on your lens, adjust your shutter speed until the needle in your viewfinder points to the middle. If your shutter speed is too fast, the needle will point down (underexposure). If the speed is too slow, it will point higher than middle (overexposure). Good luck,
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Samuel Smith |
all that seems backward to me alan,well except the sports and i'd like 1/250th. i'm probably wrong again. but yet i'm fine,sam
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anonymous A. |
I remember the Asahi Pentax. It had a cadmium sulphide exposure meter you couldn't turn off, so if you lost the lens cap or just left it off too long, the battery used to go flat! Top speed was 1/1000. THe "sunny 16" rule suggests that on a sunny day with the sun over your shoulder and 400 ISO film, the correct exposure will be 1/400 @ f16; open shade 1/400 @f8; shadow areas 1/400 @ f5.6 etc. I think Holt was asking for a chart of equivalent f stop/shutter speeds: there are dozens on the web, but the key to understanding them is that larger f numbers represent smaller "holes" for the light to pass through to your film. Each f stop is double the size of the one below it. It is easy to see thatdoubling the shutter speed means letting in 1/2 the light (the shutter is only open half as long) so bigger numbers mean smaller exposures. The same is true with apertures, because they are fractions, just like shutter speeds (we say 1/500 sex at f22; we should say 1/500 Sec at f1/22). Hope that's not confusing...but your classes will cover all of this.
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Alan N. Marcus |
Hi David, No the f/numbers are not fractions they are a ratio. Sorry to be long winded but I can't help it the teacher in me takes over. Sorry this is so long winded. You guys might not like it. That’s OK, I take criticism well. During exposure the camera lens projects an image of the outside world on the film/chip. This position is known as the image plane. The ability to accurately and consistently control the brightness of the image is a major ingredient for successful photography. The photographer can regulate image plane brightness by somehow changing scene brightness or by varying the camera lens to somehow increase or decrease brightness. It seems the lens operates like a funnel gathering light. The larger the lens diameter, the more light gathered and the brighter the image will be. Thus exercising control over lens diameter is a no-brainer. This adjustment is complicated however by the fact that the projection distance inside the camera (focal length) has a surprisingly big influence. Consider what happens when you move a slide projector further back from the screen. Doubling the projection distance causes the image on the screen to become twice as big (2x larger). Twice as big means the light from the unchanged projector lamp must now cover four (4) times more surface area (height x width). You guessed it, the image brightness at the screen is reduced by a factor of four (4). The same thing happens when double the focal length with your zoom camera lens. The zoom lens mechanics changes lens diameter at the same time as you focal length to compensate. If curious about the effects of distance changes, you can look up the rule in physics know as the law of the inverse square. Now consider that the two most important in-the-camera factors controlling brightness is the working diameter and the focal length of the lens. With thousands or perhaps millions of camera designs that bring into play a hodgepodge of lens dimensional combinations. Each will presents a different brightness at the image plane. You guessed it – disorder results. Without a solution, most pictures you take will would be under or over exposed. Ratio to the rescue: The ratio of two numbers is pure because it is devoid of dimension. In the case of the camera lens we divide the focal length by the working diameter to get a ratio which we call the focal ratio or in other words the f/number. The beauty of the f/number system is, when any lens is set to a specific f/number it delivers the same image brightness at the image plane as any other lens set to the same f/number regardless of different dimensions. Simply stated, the focal ratio or f/number gets rid of the chaos revolving around the setting of the lens aperture. Other systems have been proposed and tried but we still elect to keep the one that has works best. (You’re free to invent a better system). The problem is: The number set used seems illogical. Who would have thunk up this sequence. 1 – 1.4 – 2 – 2.8 – 4 – 5.6 – 8 – 11 – 16 – 22 – 32 – 45 – 64 – 90 Well the span has logic. Any number in the set multiplied by 1.4142 yields the neighbor going right, conversely, dividing by 1.4142 yields the neighbor on the left. 1.4142 is the square root of 2 and its OK to round it to 1.4. So what’s the significance? Say you have a circle (the lens is a circle) and you desire to change the lens diameter in order to alter image brightness. To increase lens surface area by the most logical increment of adjustment which is a doubling (2x), you multiply its diameter by 1.4. The product is a revised diameter that produces twice the light energy at the image plane. Conversely, divide the diameter of the lens by 1.4 yields a revised aperture with half the surface area thereby reducing brightness by half. As to the two engraved f/numbers: It has become customary to label a lens with its maximum f/number. When calculating the f/number of a zoom lens you must take into account that the maximum diameter (aperture) is fixed but the focal length is a variable. Thus the zoom lens will be labeled with two different maximum focal ratios, one for max zoom and a different one when operating at minimum zoom Sorry to report that us poor photographers must forever cherish the lowly focal ratio (f/number) system until you think of something better. Alan Marcus
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Michael Skelton . |
Purely mathimatically speaking "Ratios" and "Fractions" are one in the same. One just has to look both up in the dictionary to see this. All numbers can be expressed in fractions. "An expression that indicates the quotient of two quantities" The point is that it doesnt matter what you call it , I have found that explaining F/ stops in fractions makes it much easier for others to understand , which is really the point.
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Alan N. Marcus |
Dear Michael, As you know: The f-number is an expression of relative aperture derived by dividing the focal length by the effective aperture. We need a universal system to express settings that will produce a predictable brilliance at the film/chip plane. Universal means the brilliance will be the same for lens x or y, when set to a common value. The snag is; lens x and lens y have different dimensions (focal length and aperture). Ratio to the rescue. The ratio is a dimensionless quantity. You are correct; a fraction is a specific application of the ratio as it relates the part (the numerator) to the whole (the denominator). It seems to me that using the ratio expresses an f-number best as apposed to the fraction. Indeed the camera manufacturing segment agrees with me as nearly all lenses are engraved 1:1.4 or 1:1.8 etc. Two values separated by a colon is the universal notation for the ratio. One can win the Pulitzer Prize with a simple non-adjustable camera. The odds of success improve when adjustments are available, these expand the picture taking environment. Over the last umpteen years cameras have evolved with chip logic that greatly reduce the photographers need to know all this technical stuff and I applaud. The perfect camera would have no controls, knobs, or buttons. One would simple think (pre-visualize) the finished picture and the camera would respond telepathically. The real question is; how do we teach people who want to learn these concepts? I applaud you for teaching and helping others to understand. You have my blessing to use whatever works for you. Best regards, Alan Marcus
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Michael Skelton . |
Alan, You are absolutely right with your explanation of ratios and fractions.( : ) is the universal connotation for ratios ,I have commomly seen it substituted and acceptable with the ( / ) also. When I tried to explain F/stops as a ratio in the past ( Maybe due to the way I tried to explain it),It just seem to drive people bananas . I don't know if your profession is teaching , but it should be. Thank you for your input and kind words. Best of light always, Mike
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anonymous A. |
The original correction should stand for the sake of accuracy: a fraction is part of a whole (1/4 means one part in four) while a ratio compares two or more separate groups/objects/quantities (e.g. the ratio of debt to income) Only some ratios are fractions... but people seem to understand fractions easily, and this wasn't meant to be an English or maths lesson: so my apologies to Alan and others for misusing the term, and to Holt for leading this discussion so far off the question.
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BetterPhoto Member |
Erin, It's virtually impossible to set exposures according to various conditions. Yes there is some general rules, such as the Sunny 16 rule (shooting f/16 at the shutter speed of your film speed or ISO, in generally blue sky sunny days), but light changes every second and the art of photography deals quite of bit with exposures you choose. Don't get my wrong, exposure sounds like an easy concept, but is more complicated that most think. As an pro photographer of 20 years and BP instructor, I still deal with exposures on every shoot. A good start is finding a camera manual for your specific camera, and reading it through to understand your camera as best as possible. Then you can begin to learn about exposures. Good luck & Happy Shooting!
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