zoom lens changes exposure at tele end

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    • #96905
      Avatarhivideo
      Member

      Many camcorders (let's say under $5000) have a lower f number at the wide end than at the tele end. Let's say f1.8 to f4.0

      If I'm shooting in manual exposure mode and want to use the max aperture (shooting in low light and minimizing gain), I can only set it to f4.0, because setting it to f1.8 would cause the exposure to change as I zoom in and out. So the f1.8 capability is wasted.

      It should be possible to make a camcorder that compensate for this exposure change by automatically adding more gain at the tele end. Noise would increase, but not as obvious as underexposure.

      Does such feature exist? If so, which camcorder has it?

    • #278361
      Avatarpaulears
      Participant

      Sadly, if you need to work wide open, you're stuck. I've never seen any proper camera with this facility. It's actually quite a good one, but I'm not sure how they'd do it, because it's an optical function – the actually iris doesn't change on most, but the aperture difference is an effective one, rather than a mechanical one – so there's no feeedback for the camera to base the gain on, if it just gets dim, auto could kick in at the wrong moment – when something bright crossed the frame. I like the idea, but have never seen it implemented as a feature.

    • #278373
      AvatarJackWolcott
      Participant

      Welcome to the club. Unfortunately Paul is absolutely correct: you're stuck. We have Sony NX5Us and one X70 and they behave in the manner you describe. Where I disagree with him is in the suggestion that no "proper" cameras have the feature you're asking for. I have two Sony PD150s that have total iris control, from f18 through f11. These cameras, and their cousin the PD170 provide zooming at will through any iris setting, up and down the range, without affecting the the iris at all. In manual mode the gain is locked in to whatever setting you have chosen and is unaffected by the iris.

      For my money the PD150/170  has long been one of the best cameras below the $5000 price point for shooting theatrical events as they allow the operator to match the light levels provided by the theatre's lighting designer. Regrettably they only shoot in DV.

    • #278388
      Avatarpaulears
      Participant

      I don;t know the 150s and 170s had gain compensation Jack?  Very handy – is it swtichable. None of my current cameras have it, and I usually run in manual iris, so try to never set wider then f4, or when I go right in the brightness drops – this applies to my JVC 100/200/700 series, the older 500 and 5000, and of course my ancioent Betacam Sony 300 series I still have.  So if you set dsay f2, or 2.8 on the 150/170, as the brightness ramps down at the end of the zoom range, the camera brings it back up? Is it reliable doing this?

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