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Thread: Nd filters versus stopping down

  1. #21

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    Re: Nd filters versus stopping down

    Quote Originally Posted by Jim Jones View Post
    Pfsor, star trail photographs often use exposures of many hours. Sky light can then wash out the faintest stars. Either stopping down or using a filter compensates for this. As I recall, a 11 hour polar area star trail on 35mm Kodak Tech Pan film in the Midwest worked best between f/5.6 and f/8 without a filter. I wouldn't have wanted to stop down smaller than f/8 due to diffraction.
    Interesting. You realise that reducing the background light with a ND filter reduces also the star light so their mutual ratio doesn't change, does it?

  2. #22

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    Re: Nd filters versus stopping down

    Let's go far afield -- from the original simple question -- as we often do!!

  3. #23

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    Re: Nd filters versus stopping down

    Quote Originally Posted by Pfsor View Post
    Interesting. You realise that reducing the background light with a ND filter reduces also the star light so their mutual ratio doesn't change, does it?
    But stars are very bright point sources, it's that pesky atmosphere and light pollution that's the problem...

    Where's contrast when 'ya need it!?!!!

    Steve K

  4. #24

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    Re: Nd filters versus stopping down

    Quote Originally Posted by LabRat View Post
    But stars are very bright point sources, it's that pesky atmosphere and light pollution that's the problem...

    Where's contrast when 'ya need it!?!!!

    Steve K
    Like I said, the original question had nothing to do with astro-photography.

  5. #25
    Drew Wiley
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    Re: Nd filters versus stopping down

    It's already been hinted at, but not all are created equal and can potentially affect sharpness or create a bit of flare just like other cheap filters, esp if stacked. The also can mess with color film due to often having a bit of hue bias.

  6. #26
    Drew Wiley
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    Re: Nd filters versus stopping down

    ...I almost always encountered density labeling, which is logarithmic. Every .30 added up equals a full stop or a EV. Pretty darn simple, even for me. For example, .90 means I count three fingers, equating to either three f-stops I need to open up the lens, or three full steps of less speed on the shutter, unless long time exposures are needed.

  7. #27
    Jac@stafford.net's Avatar
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    Re: Nd filters versus stopping down

    You guys are just too much! I shot stars using a 70's Instamatic with a flash cube!
    Yea sure, it burned my forehead, damn near blinded me, but with modern gear...

    Some amateur said I had the camera turned backwards, but I saw stars!
    I STILL see stars.

  8. #28

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    Re: Nd filters versus stopping down

    Quote Originally Posted by LabRat View Post
    But stars are very bright point sources, it's that pesky atmosphere and light pollution that's the problem...
    Where's contrast when 'ya need it!?!!!
    Steve K
    Really? So why are the stars drowned by the ambient light then? And how does the ND filter helps them if it doesn't change the mutual light ratio between the two??

  9. #29
    Huub
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    Re: Nd filters versus stopping down

    For me there are two reason to use a ND filter. First is when i want to shoot (nearly) wide open and the fastest shutter speed of the lens i use is way to slow, for instance when using a 360mm tele-xenar for a portrait. That lens is in a synchro-compur 3 of which i don't trust the fastest speed, so i try to keep it over 1/60 sec. The second reason for using ND-filters is when taking pictures of slow moving rivers, lakes and ponds where i want to create a wash out effect in the water. This calls for speeds of 30 seconds and beyond, which will be hard to reach by stopping down in broad day light.

  10. #30

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    Re: Nd filters versus stopping down

    Thank you all for your views.

    Therefore, my understanding is :-
    1] Given the optimal (recommended/preferred) aperture for large format images seems to be f16 or f22
    2] Given a lens with a large aperture but no diaphragm.
    Then I could use ND filtration on the lens to give an effective f16/f22 setting and use the appropriate speed for that pseudo f16/f22 lens aperture.
    [Again I'm ignoring the effects of the ND filtration on the image due to its manufacturing characteristics, and the difficulties of focusing through high ND filtration]
    Right or wrong???????
    Regards
    Tony

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