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Shooting video and diffraction

Discussion in 'Filmmaking' started by GFFPhoto, May 27, 2014.

  1. GFFPhoto

    GFFPhoto Mu-43 All-Pro

    Feb 24, 2013
    Hey Guys, I've been playing around with video lately and to get a proper exposure I often have to really stop down the lens, well past the point of diffraction. Does the video on a GX7 have enough resolution to where this is a factor? What about if I buy a GH4? Will I see a decrease in sharpness past f8 or so? Thanks in advance :smile:
     
  2. Lobbamobba

    Lobbamobba Mu-43 Veteran

    388
    May 15, 2013
    Sweden
    My advise is to buy a ND filter, cheaper than a camera ;)
     
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  3. GFFPhoto

    GFFPhoto Mu-43 All-Pro

    Feb 24, 2013
    I do need one. I had no idea how difficult it is to maintain a proper shutter speed and still get a good exposure on bright days. Aside from getting a good exposure with a correct shutter speed, are you saying I will notice diffraction above f8 or so? If I try and stay below f8 on sunny days, I will probably need a 6 stop ND (or maybe 10).
     
  4. kevinparis

    kevinparis Cantankerous Scotsman

    Feb 12, 2010
    Gent, Belgium
    throwing this out there... dont know the definitive answer.... but when you are shooting HD its effectively a 2 megapixel image, and there is all sorts of compression of the image going on...... so perhaps any diffraction issues that might be seen in a 16mega pixel still image are somewhat hidden in the video process.

    K
     
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  5. GFFPhoto

    GFFPhoto Mu-43 All-Pro

    Feb 24, 2013
    Thanks Kevin. I figured as much, but wanted to see if anybody could verify. Do you think it would show up in the effective-9MP 4k video from a GH4?
     
  6. kevinparis

    kevinparis Cantankerous Scotsman

    Feb 12, 2010
    Gent, Belgium
    possibly yes... but I am really the wrong person to ask... I don't pay much attention to things like diffraction and softness in the corner. My attitude is that if my audience are noticing things like that then my photo/video has failed at a much more fundamental level


    K
     
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  7. Scrowley91

    Scrowley91 Mu-43 Regular

    40
    May 26, 2014
    I certainly noticed it at f22, but I'm not 100% sure where exactly it comes into play on video. For photos, I think the rule of thumb is about f8 on m43, so nd filters get their fair share of use.
     
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  8. Bif

    Bif Mu-43 Veteran

    380
    May 28, 2012
    San Angelo TX
    Bruce Foreman
    When the diffraction effect affects your image it manifests itself in a loss of contrast, loss of edge definition, and an overall look of softness. The effect is going to hit regardless of effective MP count, or whether you are shooting stills or motion picture. I would expect it to get worse on the GH4 due to the higher resolution and rendition of detail (I'll have to try it, just got mine).

    I had it hit real bad on a 6.3MP Canon 300D (the original digital rebel) when I forgot to check the ISO, night before I had been using ISO 1600, the highest on that camera. The next morning I began shooting period re-enactors at Ft Concho and was wondering why I was having to use the smallest aperture on the lens (kit 18-55 f3.5 - f5.6) with the highest shutter speeds. Minimum aperture was marked f22 but at full tele was likely really effective f45 or so.

    Fortunately I caught it fairly early and dropped ISO down to 100 but the first dozen shots were almost useless. Worst case of diffraction I've ever seen!

    I would avoid variable ND filters or "faders". They have 2 panes of glass and in addition to causing extra internal reflections have also been sometimes causing loss of definition at the telephoto end of zooms. I carry Tiffen ND 1.2's (4 stops) in my kits and need to acquire a couple of ND 1.5's (5 stops).
     
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  9. speedandstyle

    speedandstyle Mu-43 Hall of Famer

    I agree that the best thing to do is get at least one ND filter if not a set. I have been spoiled since I access to pro camcorders with built in ND filters. Right now it is the AF100 which has a 4 position ND switch{1 position being none then 2 stop then 4 stop then 6 stop}. Pro camcorders also have customizable gain settings too. There are some very useful advantages in using a camcorder over a DSLR/Mirrorless for video work!
     
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  10. Dramaturg

    Dramaturg Mu-43 Top Veteran

    614
    Jun 7, 2013
    Ukraine
    Yevgen
    For my personal use I shoot video with variable ND filters. They do vignette at higher settings and can mess your colors. But this is the only way to shoot wide open in a sunny day. This is my last clip - all was shot wide open with variable ND filters.

    http://youtu.be/q0Gw3OKvHP4


    Sent from my iPhone using Mu-43 mobile app
     
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  11. Livnius

    Livnius Super Moderator

    Jul 7, 2011
    Melbourne. Australia
    Joe

    I think a variable ND filter will be your best bet. As you move from one scene to the next, each potentially with different lighting conditions...changing from one fixed strength filter to another and then back again too maintain that ideal SS is just way too troublesome. Although a decent variable ND or 'fader' filter is commonly twice the price of say a good B+W, if video is something that you plan on experimenting with quite a bit then it would be money well spent IMO. Less time spent fiddling with multiple filters can only be a good thing. It's just way too convenient having the one filter that covers everything from 1.5 to 9 stops of light blocking with a simple turn.
     
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  12. darosk

    darosk Mu-43 Top Veteran

    705
    Apr 17, 2013
    Kota Kinabalu, Malaysia
    Daros
    As has already been said, if you are planning on doing a lot of video, I think a quality vari-ND is a wise investment. As Joe says, it would be money well spent. This is especially true if you are 'running and gunning'. It's been years since I've done anything that can be called 'serious' video work, but a vari-ND would be right there near the top of my list if I was looking to kit myself for videography again.

    Just don't bother with the nasty cheap ones, some terrible color issues, among other IQ problems.
     
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