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Canon XH Series HDV Camcorders
Canon XH G1S / G1 (with SDI), Canon XH A1S / A1 (without SDI).


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Old February 25th, 2009, 03:28 AM   #1
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xh-a1 aperture values

The xh-a1 Aperture settings range between F/1.6 and F/9.5 but when filming outside in "tvmode" the aperture setting goes up to f.i. F16
Now I allways check this value by pressing the exp lock and switch on a nd filter to get the iris to a value between f/1.6 and f/9.5.
What I don't understand is why the canon is displaying a value that it's not capable of? Is it only a fictive value to help you decide when to turn on the nd filter?
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Old February 25th, 2009, 06:43 AM   #2
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Hi Noa. I think if you put the cam into M mode, you can adjust the aperture smaller. But personally I wouldn't go beyond f8 and even that is a bit uncomfortable. I try to keep it around f4 if possible, to get the sharpest image.

Richard
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Old February 25th, 2009, 07:26 AM   #3
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I do keep the exp. locked in tv mode to adjust the aperture manually if necessary and try to keep it around F4 ike you state. The only thing I don"t understand is why the camera is displaying aperture values that are not possible?
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Old February 25th, 2009, 10:19 AM   #4
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Originally Posted by Noa Put View Post
...in "tv" mode the aperture setting goes up to F16
Wow, I just tried it, and you're right. I even got F21.
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Old February 28th, 2009, 04:43 AM   #5
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Hi Noa. I believe that the aperture readings do reflect the actual aperture. My question would be, why are these settings not available all the time?

Richard
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Old February 28th, 2009, 05:17 AM   #6
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Just did some tests on this. Switching on in Tv mode with bright lighting conditions, the shutter was set by the camera to a fast value like 250 or 500. If I adjusted the shutter to 50 and then pressed Exposure Lock, the aperture value displayed was F22.

Taking note of how much zebra was visible, I then tweaked the aperture ring slightly open until it displayed F9.5. The amount of zebra increased (quite a lot), telling me that the aperture had in fact been smaller than F9.5.

If I tried to make the aperture smaller again, I could not get any reading between F9.5 and "CLOSE". The only way to see the F22 value was to release Exposure Lock and then set it again.

If I varied the brightness of the lighting before pressing Exposure Lock, I could get the aperture to display F14, F16, F17, F21 and F22 (and probably other values if I had tried).

And what I said earlier about M mode was wrong. I could not get the camera to display larger numbers than F9.5 in M mode.

The only reason I can think of for this behaviour is to allow the AE compensation to work even when the camera is stopped down. For example, if the Tv exposure wanted to set F9.5 and the AE Compensation was set to -1, it would still be able to darken the image further by using these small iris settings. I hope I am never in this position though! :)

Richard
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Old February 28th, 2009, 08:32 AM   #7
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Well spotted Richard. The VX/PD Sony range would also do this, and although the iris display finished at f/11, I could film at f/22 and f/45 (two stops smaller) before the iris blades closed fully.

You'd have to do this in the auto exposure mode - in full manual the iris would close completely if you tried to select an aperture smaller than f/11.

The camera had been engineered like this so that should you ignore the silent scream for ND to be applied, you'd still get correctly exposed pictures for a further two stops. The only down side was the fact that diffraction losses made the image noticeably soft after about f/8.

Moral - keep well away from small apertures with camcorders that use tiny chips.

tom.
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Old March 31st, 2009, 10:12 PM   #8
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...why are these settings not available all the time?
Just came across this thread from searching for diffraction. As a self-defense measure against diffraction, the Canon XH and XL H cameras will never go smaller than f/9.5 on their own (that is, in any of the automatic modes), nor in the "M" full manual mode.

If for whatever reason you really do want a tiny aperture, you can certainly force it, as you've found out. For more information in greater detail, see my post at http://www.dvinfo.net/conf/623697-post131.html
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Old March 31st, 2009, 11:24 PM   #9
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.... But personally I wouldn't go beyond f8 and even that is a bit uncomfortable. I try to keep it around f4 if possible, to get the sharpest image.

Richard
Me too. In the very bright OZ summer light I found I need an additional ND filter to keep within that range, use the B+W ND 502 for that.

Cheers.
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Old April 1st, 2009, 02:24 AM   #10
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For more information in greater detail, see my post at http://www.dvinfo.net/conf/623697-post131.html
Thanks all for the answers so far and Thank's Chris for this link, that for sure answers my question.
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Old April 1st, 2009, 06:47 AM   #11
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Just came across this thread from searching for diffraction. As a self-defense measure against diffraction, the Canon XH and XL H cameras will never go smaller than f/9.5 on their own (that is, in any of the automatic modes), nor in the "M" full manual mode.
Canon obviously never tried to shoot a rocket launch at night!

It's one thing to keep it from going past 9.5 but the fact that it lets you close it ruined my 1st attempt at a delta rocket launch video 16 seconds into the launch.
YouTube - Shot in HD. Delta 2 Rocket Night Launch with Kepler Payload - March 6 2009

In this case, I would have welcomed the defraction in M mode as an appropriate special effect and a less blown out exhaust plume. It was operator error and not being able to tilt the camera enough was the bigger shooter error.

I looked in all the custom settings but could not find a way to keep from closing the shutter. I'm interested to know if there is one.
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