Neutral density filter

Discussion in 'Beyond the Basics' started by Rabieshund, Jul 23, 2006.

  1. Rabieshund

    Rabieshund TPF Noob!

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    I'm thinking of buying one of those. It's kinda annoying that I don't have one!

    I'm just curious, how long exposures can you get without things getting overexposed? Never used one before, so I don't know much about it really. Can I do like a 20 second exposure in daylight when using an ND filter?
     
  2. Philip Weir

    Philip Weir TPF Noob!

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    You could do a 20 second exposure if you could stop your lens down to say F3200 [not F32] Basically a ND filter is the same as if you are shooting in a low light situation, it simply darkens up your scene, so if you wanted to shoot at a longer exposure and the lens doesn't stop down far enough you can reduce the amount of light coming through the lens. Why do you want to shoot a 20 second exposure ?? I have a filter I had made many years ago for shooting eclipses of the sun, which was so dense, you couldn't even see through it. It seems from many posts that ND filters are the flavour of the month. To answer your question, NO unless you ganged up a series of ND filters, an exposure of 20 seconds could not be done. If you imagine a standard exposure in daylight at a ISO setting of say 100, the normal exposure would be about 125th second at f11, then you can figure out that a 20 second exposure, even stopped right down would need a ND filter so dense, you may as well shoot through the lens cap.
     
  3. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    ND filters come in different strengths from blocking 2 or 3 stops to allowing you to photograph the sun. To get an exposure of 20 sec @ f/16 @ ISO 100 in bright sunlight you'd need one (or a stack, although there are issues with stacking filters) that blocks about 11 or 12 stops (a x4096 ND? ).

    Split NDs have always been popular with landscape photographers to lower the exposure of the sky compared to the foreground. The popular example for a regular ND in bright sunlight is to achieve a slow shutter speed to render moving water blurred.

    My main reason for using ND filters is outdoor portraits with fill flash. With a sunlit background my shutter speeds at ISO 100 @ f/2 can be as high as 1/4000. I don't have a camera with anywhere near that flash sync speed, so I use a ND filter to get it down to 1/250th (my flash sync speed). I find that carrying x8 (3 stops) and x16 (4 stops) ND filters for my lenses come in handy. I sub my polarizer for a 2 stop ND.
     
  4. Rabieshund

    Rabieshund TPF Noob!

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    Ok, thanks for the reply. 20 second exposure isn't something I will shoot, just gave an extreme example, haha.
    But then, a 1-2 second exposure would be no problem in daylight, I guess? Because that's something I more likely will use. ;)
     
  5. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    Sunny 16 says that at ISO 100 your exposure at f/16 is approx 1/100th in sunlight. If you go with 1/60th you still need to block 6 stops to get to a 1 sec exposure. Close the aperture to f/22, and you still need to block 5 stops.

    If you are using a digital camera with a sensor smaller than a 35mm neg then you will begin to have diffraction issues (loss of detail) with apertures smaller than f/8 or f/11, so stopping down to f/22 may not really be an option.
     

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