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I recently bought a Yongnuo 50mm for my Canon 5D MkIII. I'm having problems adjusting the aperture, it seems like it always shoots at ƒ/1.8.

I adjust the aperture in the camera up to ƒ/22 but it doesn't seem to take any effect on the lens. In the live view mode the image gets darker, but when I shoot the picture has exactly the same light as if I shoot at ƒ/1.8.

I'm wondering if this is a common issue on the lens or if maybe I'm doing something wrong or something else needs to be done (I'm really just checking with you guys before sending the lens back).

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    What shooting mode are you using? The only time one would expect adjusting the aperture to result in a darker image is if there's no equal and opposite adjustment to either shutter speed or ISO. If you're shooting in auto modes, the camera will be adjusting these for the new aperture value, so the shot itself will have the same exposure. What WILL be different is the depth of field...not overall "brightness". – Hueco Nov 16 '17 at 21:12
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    terminology usage nitpick: you're not setting Depth of Field to 1.8 or 22. You're setting the aperture to ƒ/1.8 or ƒ/22. Setting the aperture certainly is the way to control or affect depth of field, but you're actually setting the aperture. – scottbb Nov 16 '17 at 21:19
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    Seriously, the much better EF 50mm f/1.8 STM isn't that much more than the Yongnuo knockoff of the EF 50mm f/1.8 II. – Michael C Nov 16 '17 at 22:11
  • @corey I'm shooting in manual mode – petekaner Nov 17 '17 at 7:13
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    When you hold the depth of field preview button, can you see if the aperture blades are closing – Crazy Dino Dec 17 '17 at 17:31
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So, because of your live-view test, we know that the diaphragm is functioning. But on other shots, it isn't.

I'm wondering if there's a timing problem. As in, the lens is stopping down - just after the shutter has already exposed the frame. To test this, use bulb mode and take some frames in the range of a few seconds. Look into the front of the lens - do you see the blades coming together at any point? Does it feel delayed?

Whether that answer is yes or no really doesn't change the outcome. It's a throw-away lens that's giving you issues. It's time to throw it away. Or tear it apart to learn what the inside of the lens looks like. Either way - it'll be cheaper to just replace it.

I've never shot a Yongnuo and have only used the Canon 50mm f/1.4 and 50mm f/1.8 STM. So I don't know if this is a Yongnuo QC issue or not. With the Canon 50's - I used to take them rock-climbing, and they survived all manner of weather and chalk infestation. Given the price point on the STM, that's the one I'd recommend.

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Since you are using a third party lens, the cause of the problem is most likely firmware incompatibility. Updating your camera firmware may help. If your lens has firmware that can be updated, you should try that as well.

I had similar problems with a different third-party lens. In my case, a camera firmware update improved lens function, although it did not entirely fix the problem.

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