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Thread: Determining Shutter speeds and F values

  1. #1
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    Default Determining Shutter speeds and F values

    This question has been bothering me for quite sometime.

    How do you pros determine the shutter speeds and F-values for a shot?

    If you are using a DC, I understand that you can set a guessitmate value, take a sample shot and adjust accordingly.

    But what about a film camera? You do not have the luxury of seeing your results immediately.

    So how do you guys do it? Set a guesstimate value and hope for the best? or is it from experience?


    Oh yah, can someone also tell me what the heck does the F-value do? how is a photo affected by different F-values?

    Thank you!

  2. #2
    Senior Member Kit's Avatar
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    Not a pro but here goes..........

    If you're using an automatic camera, then the camera does the work for you. In aperture priority mode, you set the aperture (f value) and the camera sets the shutter speed for you. Vice versa for shutter speed. However, you can always switch to manual mode and set both the aperture value and shutter speed yourself. Most camera will have an in-built meter to guide you to what it think is the correct exposure. You'll learn to second guess the camera's decision as you gain more experience on the way because the camera's metering system is not foolproof.

    F value refers to the size of opening of the lens diaphram. A higher f value(smaller opening) gives you a deeper DOF(depth of field). This will result in a slower shutter speed.

    A lower f value(bigger opening) does the reverse which gives you a shallower DOF. Faster shutter speed.

    You'll need deeper DOF when say......shooting buildings or skylines where you need sharpness throughout the image.

    Shallower DOF are good for e.g. portraits where you want to isolate your subject by blurring out the background(bokeh).

    Above mentioned are just examples I can think off hand. Hope it helps.

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    Thanks!

    I know have a better understanding!

  4. #4
    Midnight
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    The vast majority of both film and digital cameras have built-in meters (mainly TTL, but some are off the lens axis) that measure the amount and distribution of light reaching the camera from the scene. Based on the metering method and auto-exposure program you set the camera to, it will provide you with a set of exposure values required to obtain a "correct" exposure for the scene. If you wish to vary the exposure values, you can do so while maintaining the same overall exposure by increasing the shutter speed while decreasing the aperture size, or vice versa (using the principle of reciprocity). Generally, this yields good results for most day-to-day situations.

    For more precise metering or in tricky lighting conditions, one can calculate exposure settings by taking readings at different parts of the scene, possibly with the aid of incident light meters. You can then input the settings manually into your camera, provided that the camera and lens are capable of the aperture size / shutter speed you specify, of course.

    When in doubt, bracket your shots. This means taking multiple exposures of the same scene at slightly different exposure values, and then subsequently comparing the resultant image/negative/print to see which one works best.

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    Won't that mean alot of wasted film when you are bracketing?

  6. #6

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    Originally posted by Evilmerlin
    Won't that mean alot of wasted film when you are bracketing?
    But at least, the tendency of one of these shots turn out well is higher.

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    I see.......

  8. #8
    Midnight
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    Originally posted by Evilmerlin
    Won't that mean alot of wasted film when you are bracketing?
    Yup, you're right. Just consider it an investment as part of the process of learning photography. A point&shoot casual photographer doesn't need to bother too much about getting individual shots right, but a more serious enthusiast will want to learn how to master the different types of exposure settings to use under various conditions, so this will almost invariably involve taking the same shot several times with different settings and recording the exposure settings used, then looking at the final print and analysing which settings worked better (and why) in achieving your intent.

    I'm still working on learning this too, and nowadays I find that I normally discard about three out of every four shots I take (and even more if I do a lot of bracketing), which ironically is an even higher rate than when I first started, possibly because over time I've become much more critical of my own shots (or maybe I just haven't been learning fast enough! . Then again, since my medium is digital, I must admit that the cost-per-exposure factor isn't exactly very major for me.

  9. #9
    Senior Member Kit's Avatar
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    Originally posted by Midnight
    I'm still working on learning this too, and nowadays I find that I normally discard about three out of every four shots I take (and even more if I do a lot of bracketing)
    A hit rate of 1 in 4 is pretty good, about 25%. I'm lucky to find 1 image that I really like in each roll. Assuming a roll of 36, that's 2.78%!!!

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