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I am shooting with a Canon 6D and an f4 24-105 L-series lens. I am pretty certain I set the aperture at f4.

After inspecting my pictures later, I am noticing that the aperture goes to 5.6, 6.3, 7.1, and 8 in some cases.

I have IS (Image-Stabilization) on, but that shouldn't affect the aperture setting, right?

Additionally, the lens should support f4 throughout the range. I have exposure safety shift enabled

I did NOT manually adjust the exposure with the jog dial and accidentally bump the aperture setting, so I must be doing something wrong every time or there is another piece to this puzzle.

Any ideas?

Yaron
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Walter
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    Does your camera have Exposure Safety Shift? Is it enabled? – mattdm Aug 02 '17 at 02:56
  • Yes, it is enabled, let me read up on that. – Walter Aug 02 '17 at 03:01
  • Okay, I remember reading up on these years ago ... This shouldn't be a problem though because if I were to shoot at f4, I'd have more light, so I'd need less exposure. The picture was shot at around 1/200, well within limits. I used a flash, and believe I had high-speed sync on, so again, I would think the camera should be able to handle it, right? – Walter Aug 02 '17 at 03:03
  • Okay, I was wrong, I had it on first-curtain sync, so that would probably limit the shutter speed to 1/250s. – Walter Aug 02 '17 at 03:06

2 Answers2

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I believe the answer to the question is that I needed to change the flash from first curtain sync to high-speed sync.

I thought I changed that setting before I started shooting, so that would limit the shutter speed of the camera and hence why the aperture was locked down more.

Also, I have the setting Exposure Safety Shift enabled, so that is what was used to compensate for an unattainable shutter speed, change the aperture. Thanks for mattdm for the pointer.

Walter
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A Zoom lens (eg. 24-105) has a variable Focal Length.
In 'simple' terms- Aperture (f-numbers) are a ratio of [ Lens Diameter : Focal Length ]
When you change the Focal Length (zoom) and the lens aperture diaphragm (diameter) remains the same, you are then changing the f-number.
So you are seeing the f-number set on the camera but the "effective" f-number (in your photo metadata) shows differently.
Some 'professional' lenses are constructed to maintain a constant "effective" f-number when changing focal length.
eg. If the diaphragm diameter is 12mm-
at 24mm zoom the f-number = 24/12 = f2
at 105mm zoom the f-number = 105/12 = f9

Roberto
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