Is having a fast lens unimportant if I want to use 100 ISO film?

Question

Concerning fully auto cameras here. Please explain your answer.

Answer 1

ISO 100 is a common speed for a "daylight" film. Exposure comes from a combination of two things, the f-stop (aperature) and time the shutter is open. For 100 speed, a typical exposure would be about f5.6 at 1/100sec on a sunlit day scene. the shutter and aperature settings act in concert. Note the speeds you can set, they double from click to click. Same goes for aperature, eaach setting is double of half depending on which way you go. Open the aperature one click, reduce the shutter by one click. Focus distance has no effect in this. A fast lens is simply one capable of a wide aperature, the wider, the faster. A typical 50mm lens will open to f2.8 (maybe a little slower at f3.5) and is considered fast. I have a f1.2 lens which I can use at night since that is about as fast a lens money can buy. The problem with a fast lens is depth of field. The wider the lens is open the shorter the depth of field. Most automatic cameras try to keep the aperature constant (keep the depth of field constant) and adjust the shutter speed. Some, like my Nikon, adjust aperature over shutter speed. I have another, an Olympus, which adjusts shutter over aperature. The Olympus is better for snapshots, the Nikon better for planned shots. Now, for depth of field, the distance from the lens in which the scene is in focus. A lens at f1.2 focused for 10 feet may have a depth of field of 2 feet (10+/-1foot) which the same lens stopped down to f8 may have a depth of field of 8 feet (10+/-4). So, on a bright sunny day, the kind this speed film is ideal for, a fast lens is not really required. When you look at the aperature ring, you may see marks on either side with colors which correspond to the colors on the aperature ring. For example, if the aperature ring has the f stop number in red, the depth of field is indicated on the focus ring by a red mark on either side of the setting. Match the color of the aperature setting to the colors on the focus ring, and you can estimate the depth of field. now for the problem, which another mentioned, moving objects. At the typical 1/100th sec exposure time a car traveling at 60mph is moving at 88 feet per second. In the 1/100th sec the shutter is open, the car moves 0.88 feet. If the car is only 30 feet away, it may be enough to have a significant blur on the film. So, to take pictures of moving things, shorten the shutter time and open the aperature accordingly, but that also reduces the depth of field, so I think you can see how the tradeoff works. For stationary things, close down the aperature and increase the shutter time so more is in focus because of the larger depth of field.You have to decide which feature is important for each individual picture. Now for a tidbit about film speeds in general. The slower speeds, ISO 100 and below are "fine grain" films. In general, the slower the film speed the smaller the grain size in the negative. The smaller the grain size, the larger you can make an enlargement. Two properly exposed frames, one at ISO 100 and the other at ISO 400 will both look very good at 5x7, but at 8x10, you will see the 400 speed will be a little fuzzier than the 100 speed, becase of the difference in grain size. Faster films enlarged greatly tend to look more like newspaper photos where you can see a lot of closely spaced colored dots (grains). So, the key here is, how big do you want to enlarge an image? The larger the end result print is going to be, the slower film you should use. this is why professionals have varying film speeds on hand as well as interchangable lenses so they can adjust the equipment to fit the shooting situation to achiece the desired result. By the way, my first photo was made with a pinhole camera when I was 10 years old. My father helped me take a shoebox pinhole camera. We cut a hole in one end and covered it with aluminium foil We used a sharp pin to make the tiniest of holes, and then covered the hole with a piece of black tape. Then in total darkenss, by feel, we taped a piece of sheet film on the side opposite the foil and taped the top in place so it was light tight. Not so easy as it sounds when doone in a totally dark closet. We put it outside on the front porch railing, taped in place so it could not move and in the morning, pulled the tape off the pinhole in the foil. We left it to expose the film for 8 hours (very slow film, ASA 32, with a very small aperature). We closed the pinhole and then removed the film in darkness and put it into a light tight developing tank and process ed the sheet film into a negative. Then, we printed the picture. WHat we had was a perfectly focused, perfectly exposed picture of the front yard. Not a car was seen though many passed by during the day. No cars showed up because they were not in frame long enough to be caught in the exposure, the opposite of the picture of a moving object problem I discussed above. Even people walking by, like the postman, didn't show on the film, or the people walking their dogs. Anything moving simply did not show. A big thanks goes out to my dad for getting me introduced into photography at an early age. I still process and print my own black and white, but I leave color to a processing lab.

Answer 2

Well, ISO 100 isn't considered fast, so a fast lens MIGHT be important, it depends upon the lighting conditions you're trying to shoot in. If you're shooting in birght daylight, then the fast lens isn't likely to matter, since a very low aperture would just result in overexposure (even using a high shutter speed to stop action, you probably wouldn't go any wider than F4)

Now if you're trying to shoot at dusk or low light, a fast lens is very important, since shooting wide open at F1.8 or 1.4, you can still obtain proper exposure without having to leave the shutter open for 2-4 seconds and recording a lovely blur.

If you were dealing with a ISO 800 or 1600 film, then having a fast lens becomes less important. The film is dramatically more sensitive to light.

Answer 3

With a low iso, you will probably want the fast lens. This is because the low iso film requires more light for exposure. The fast lens allows more light. Fast lens, if memory serves, are around 50mm 1.5 - 1.8.

Answer 4

100 speed film is not that fast. If you are shooting action or bright light, you will need a faster shutter speed.