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Old October 18th, 2005, 11:19 PM   #1
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Accessing f1.6 on an XL2

Yesterday I shot some low-light footage on my Canon XL2 using 6db of gain, and f1.6 (at least I'm ALMOST certain it was f1.6). Today when I try and dial in f1.6 the iris won't open more than f2.0.

I've noted on other occasions that I can't dial in settings below f3.4 on my XL2, but I work around that problem by changing the main settings dial from M to Tv or Av, then when I switch back to manual I can open the iris wider.

I've made sure all the presets are turned off, and that nothing is set to Auto. I've tried setting everything to Auto to force the iris to open, but no luck.

Has anyone had a similar problem and found a solution. I'm almost beginning to doubt that I saw f1.6 in the viewfinder yesterday, but I'm CERTAIN the f stop was less than f2.0

My lens is a Canon 20x zoom, XL 5.4-108mm L IS 1:1.6-3.5

-- phil.
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Old October 18th, 2005, 11:24 PM   #2
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How far you're zoomed in affects your aperture. F1.6 can only be achieved when zoomed out all the way (or slightly zoomed in).
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Old October 18th, 2005, 11:30 PM   #3
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Thanks heaps for that instant solution Mark! My confidence has partially returned! -- phil.
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Old October 19th, 2005, 09:35 AM   #4
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The full range of settings (especially shutter speed) is also a function of being in manual mode. But yes, if you zoom in, you won't be able to open the iris that wide.

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Old October 19th, 2005, 10:34 AM   #5
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Actually, the iris still opens that wide, it's just that you are increasing the focal length by zooming in and the effective aperature is now 'smaller'. That's why you will notice the aperature 'jump' as you zoom in, but jump back when you zoom out.
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Old October 20th, 2005, 04:04 PM   #6
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That's it Phil - your lens is only f/1.6 at full wide angle. As soon as you move away from this setting - even a little bit - the lens starts to lose speed. Of course the v'finder readout only makes the jump to the nearest half stop, so it appears (to Mark) that f/1.6 is held for a few mm of zoom, but this is not the case.

By time you've reached full telephoto the lens is nearly 2 stops down, so you can film in a room at 0dB at wide angle, but you'll need +12dB of gain up in the same light at full tele. This is pretty obvious on DVD.

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Old October 20th, 2005, 06:10 PM   #7
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Thanks all...

I really appreciate the way folks on this message board work at solving another's problems. It's most reassuring, and becoming a rarity in the wider community.

Tom, I appreciate the comment on reduced DVD quality with 12DB of gain. I've not had the chance to convert low light images, so I'll beware. Thank you.
-- phil.
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Old October 20th, 2005, 06:31 PM   #8
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Just to add, you should try to avoid being in a position of having to use 1.6 as your only option. If you have the option to increase the ambient light to allow you at least a couple of stops from wide open, do so. The lens doesn't perform well wide open. It also doesn't perform well at its smallest aperature either.
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Old October 21st, 2005, 12:47 AM   #9
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Good points Dave. I'm much happier shooting wide open as that's how I get that beautiful differential focus into my shots, but I appreciate that vignetting is starting to appear with very evenly lit backgrounds.

But this slight failing is nowhere near as obvious as the loss of sharpness due to diffraction caused by letting the camera shoot af f/11 and even smaller. I'd say this: beware of the small apertures much more than the large, especially with cameras that use tiny 1/3" chips.

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