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Thread: What's going on?!

  1. #1

    Default What's going on?!

    Hello, haven't posted in here for a while!

    Filming tonight with my VX21 (which I've not had long, and not really had the chance to use it much). I was using a Raynox mx3k fisheye, and full manual settings: manny white balance, manny focus, shutter speed at 300, and exposure set to open/12db grain (as well as some cp, and manny audio of course).

    As I'm filming the image starts off nice and exposed, then fades to underexposed, then back to exposed, then under exposed.. etc. It did this all night and I couldn't work out why, it's as if it was on auto exposure, but it wasnt. Had me stumped so I just filmed anyway and my footage is all pretty ruined, haha. Luckily it's just mess around/throw away stuff.

    Here a clip to show you: http://bert.skill.ws/schoft/schoft/M...20Heel%202.mov

    Does anyone know why this is happening?

  2. #2
    Join Date
    May 2004
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    Kansas City, Missouri, USA, Earth, Sol, Milky Way, Local Group, Universe 42
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    Default

    I can't see the video, don't have QT 7 here. But I'll take a SWAG (super wild a**ed guess) anyway... your lighting may be at fault. Many outside nighttime lights are gas discharge types and these emit light in pulses at twice the power line frequency. Your camera's effective shutter rate will be very nearly, but not quite, synchronized with a multiple of this. In the USA, it's 60Hz and we have a camera field rate of 59.94/sec (interlacing) for a frame rate of 29.97/sec. In the UK it's 50Hz and 24.98fps. If this is the case, you'll see a dimming and brightening occuring in slow cycles that I roughly estimate to be about 40 second long. There isn't much you can do about this except provide incandescent lighting which has a much more constant output.
    Fav quote - "Experience is whatcha don't get 'till ya don't need it no more."

    System - Athlon 1.4GHz, Win98, Hauppauge PVR250 receiver and compressor.
    Software -Magix Movie Edit Pro 10, Nero 6 + NeroVision Express, Moho 4.61, PSP 8.1, Bryce, Quicktime 6.52 pro, Goldwave 5, DVD-Lab.
    Cameras - Panasonic GS9, Canon ES8400V, Canon EOS D20 and Canon A70

  3. #3

    Default

    Thanks for the reply. I think I can agree with you on the lighting, it makes sense, but the lights didn't really dim every 40 seconds. It seemed like they just went whenever they wanted, sometimes it was about 40 secs, sometimes every 5 (shown in the clip).

    I put the cam on full auto and it didn't seem like they dimmed at all, I'm not 100% on that though. But if full auto works, then there must be a way around it?

  4. #4
    Join Date
    May 2004
    Location
    Kansas City, Missouri, USA, Earth, Sol, Milky Way, Local Group, Universe 42
    Posts
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    Default

    Try longer shutter speed settings and narrow down the lens aperture to compensate. If it makes a difference, at least you'll know you're on the right track.
    Fav quote - "Experience is whatcha don't get 'till ya don't need it no more."

    System - Athlon 1.4GHz, Win98, Hauppauge PVR250 receiver and compressor.
    Software -Magix Movie Edit Pro 10, Nero 6 + NeroVision Express, Moho 4.61, PSP 8.1, Bryce, Quicktime 6.52 pro, Goldwave 5, DVD-Lab.
    Cameras - Panasonic GS9, Canon ES8400V, Canon EOS D20 and Canon A70

  5. #5
    Join Date
    Aug 2005
    Location
    Western Europe
    Posts
    3,409

    Default

    Hi Dom

    We tend to use slower shutter speeds after dark like one and a quarter and one and a half seconds and even longer. The '300' you talk about can I assume that is 1/300 of a second? Probably the reason why you weren't getting the 'dimming' effect when you were on Auto mode was because the camera was using one of the much slower speeds like I mentioned at the beginning.

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