Why is my picture so much darker when I zoom in at DVinfo.net

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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 26th, 2008, 03:03 PM   #1
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Why is my picture so much darker when I zoom in

I notice that my A1 produces a much darker picture when I zoom in. Is that normal or is that because of a faulty setting?
Ofcourse I can turn up the gain but than my picture is to bright when I zoom out. Is there a solution for that problem?
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Old February 26th, 2008, 03:09 PM   #2
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It's normal. As stated in the lettering printed around the top front edge of the lens, the maximum aperture at full wide angle is f/1.6 while the maximum aperture at full telephoto is f/3.5.
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Old February 26th, 2008, 03:15 PM   #3
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The A1 has a variable aperture lens. When it is set on the widest focal length it has a maximum aperture of f/1.6. When it is zoomed in all the way it has a maximum aperture of f/3.5 (over 2 stops less light). So, if the aperture is opened more than f/3.5 when you are wide and you zoom it, the lens has to close down as you zoom.

A way to avoid this is to set the aperture no larger (smaller number) than f/3.5 and you will be good throughout the entire zoom range. If the camera is in auto it will just change the shutter speed as you zoom, keeping the overall exposure the same.
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Old February 27th, 2008, 01:57 PM   #4
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Is that really true? I remember I did the testing in the [A] mode and still it is for sure 2 stops darker when I zoom in. But the test was done on a evening, inside, with only a 40W halogeenspot at the ceiling.
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Old February 27th, 2008, 02:01 PM   #5
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Also, when you zoom in, the picture will become darker anyway unless you compensate by opening the aperture wider. This is true of any camera, still or photo.

-gb-
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Old February 27th, 2008, 06:18 PM   #6
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Greg:
Could you explain? Are you speaking in terms of the "lens extension factor" which tends to happen if you are within about 8 focal lengths of the subject, or some other effect?

Kees
Variable aperture zoom lenses are the type commonly found on camcorders and even still cameras. Constant aperture zoom lenses cost a lot more, and are heavier for the same focal length range and wide open aperture.

Also wide open apertures tend to have some vignetting (darkening) at the corners. This is common for all lenses,and is most apparent when shooting a uniform field, such as a white wall.
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Old February 28th, 2008, 05:52 AM   #7
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Quote:
Originally Posted by Greg Boston View Post
Also, when you zoom in, the picture will become darker anyway unless you compensate by opening the aperture wider. This is true of any camera, still or photo.

-gb-
Not so if we use the common f-stop figure to denote the aperture, not the real diameter in mm or fractions of inches. f:4 means actually focal length devided by 4, and all cameras adjust the aperture so that this ratio holds true when you zoom in or out. The actual aperture diameter does vary, but the lens aperture machanism takes care of that automatically when zooming.

Or does, as long as the aperture is available throuhgout the range. The problem with cheap overly long zooms is that their maximum aperture is not constant, but drops at the long end for cost and size reasons. Also on Canon XH-A1.
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Old February 28th, 2008, 07:11 AM   #8
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Just to point out that as others have said your image will only get darker as you zoom towards telephoto if you're using any aperture wider than f/3.5 at full wide-angle.

If you're shooting at f/4 at wideangle, then you can zoom all you want and the exposure on the chips will remain constant.

Greg Boston - with respect that's not right what you say.

tom.
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Old February 29th, 2008, 05:56 AM   #9
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Correct. I tested according to some other answers and when I set the aperture no larger (smaller number) than f/3.5 I can zoom without problems regarding the brightness of the picture. I also noticed that a well lit setting does miracles too. Thanks for the tips.
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