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Long exposures

Discussion in 'Beginner's Corner' started by ipbr21054, Aug 12, 2017.

  1. Chester AP

    Chester AP Well-Known Member

    I invested in a decent ND1000 filter, and found that a little mental arithmetic solved the problem.

    Thinking in terms of 'stops' can be confusing. The light reduction factor is the critical figure - 4, 8, 16, 32 , 1000, etc.
    With a digital camera this process is so simple because you can take a picture without the filter first, at your chosen aperture, and note the shutter speed when the image is correctly exposed. So if you used 1/125, with an ND4 filter you will need 4 times the exposure, 1/30.

    Simple mental arithmetic examples, starting from shutter speed without filter:

    1/125, with ND4 = 4/125 = 1/30
    (the only mental arithmetic is dividing 125 by 4 to get 30, which is easier that diving 4 by 125 to get 0.03...)

    1/125, with ND8 = 8/125 = 1/15
    1/125, with ND16 = 16/125 = 1/8
    1/125, with ND1000 = 1000/125 = 8 whole seconds
    1/60, with ND1000 = 1000/60 = 17 whole seconds (see below)

    The 2 attached images were taken a few minutes apart with the same F11 aperture and ISO 200 setting.
    One was taken at 1/60, and one was 17 seconds with my ND1000 filter
    I used a tripod and cable release, being very careful not to move the camera when attaching the filter. Once the filter is in place the viewfinder is useless.

    Check you camera's user manual to find out how to ensure that the camera shutter stays open - which may depend on menu settings and the cable release used. The longer the exposure, the less difference 1 or 2 seconds make to the result.
    I used my wristwatch.

    A warning - the longer the exposure, the greater the risk of something arriving in shot. In this case my first 2 attempts at 17 seconds were ruined by curious ducks.

    With a digital camera experimenting, and making mistakes, won't cost you anything but your time. Imagine the fun and expense I had when I tried this 30 years ago with Kodachrome.

    Calm (2).jpg Calm (3).jpg
  2. ipbr21054

    ipbr21054 Active Member

    I like the view across the water "without rocks" You can look right into the distance.
    I assume you were shooting in Manual,so maybe you can advise why you used ISO200 & not ISO100 ?

    Thanks for the reply
  3. PeteRob

    PeteRob Well-Known Member

    Some camera's base ISO is 200.
  4. ipbr21054

    ipbr21054 Active Member

    Thanks very much.
    Mine will also go down to ISO 100.
  5. Chester AP

    Chester AP Well-Known Member

    The view without the rocks is the long exposure one (softer reflections in the water). On my Pentax K5 the lowest ISO setting is 160, but I usually use 200. The difference in exposure between 160 and 200 is negligible and would only have changed the exposure time by 4 or 5 seconds. Also, after using 200 ASA (ISO) Kodachrome for over 20 years, old habits die hard.

    I always use manual exposure. Until I got digital camera in 2008 (when Kodachrome died in the UK), I had never had any autofocus or automated exposure on a camera, so I never became dependant on them. The autofocus is great on longer lenses, but I prefer manual exposure. I suppose that if I was trying to photograph fast-moving objects I might experiment with the auto-ISO feature on my camera (so that I could still fix the aperture and shutter speed), but this has not happened yet.

    I would have preferred to use a longer exposure (30 seconds plus), but this would only have been possible by changing the aperture from F11 to F16. The old Sigma 10-20 mm lens I was using is likely to have its sharpness reduced by diffraction at F16, whereas F8 or F11 is probably its optimum aperture for sharpness. If you read some AP lens reviews you will see this is quite common, but the apertures will depend on the lens. I managed to be at Buttermere (in the Lake District) on one of the brightest and hottest day of the year (no cloud cover), and had to go early to take pictures like this before it got busy after about 10 am.

    Enjoy your experimenting, and try to use a stable tripod that you can easily carry. The best camera and lens in the world won't be any good if the tripod moves during the long exposure.
  6. ipbr21054

    ipbr21054 Active Member

    Thanks very much for this useful valid information

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