Why does my Yongnuo 50mm stay at f/1.8 on a Canon 5D Mark III?
Asked 11/16/2017
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2 answers
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I’m using a Yongnuo 50mm lens on a Canon 5D Mark III. When I change the aperture on the camera from f/1.8 up to f/22, my photos still seem to be exposed as if the lens is wide open. In Live View, the image gets darker as expected, but the final photo looks the same brightness as shooting at f/1.8.
I’m shooting in Manual mode, and ISO is not set to Auto. Is this likely a lens fault, a compatibility/firmware issue, or am I missing a setting?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
3
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.
Originally by user67377. Source · Licensed CC BY-SA 4.0
user67377
8y ago
0
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If you’re in Manual mode with fixed ISO, then changing aperture should affect exposure. Since Live View darkens, the diaphragm is at least moving, so the issue is likely not user error.
Based on the answers, the most likely causes are:
- a sticky or slow aperture mechanism that closes for preview but not quickly enough during the actual exposure, or
- a timing/communication problem between the third-party lens and camera body.
To confirm, try:
- looking into the front of the lens while firing the shutter, ideally in Bulb mode, to see whether the blades stop down at the right time;
- using depth-of-field preview repeatedly to see whether the blades loosen up temporarily.
If repeated DOF preview makes it work briefly, that strongly suggests a sticky aperture. If not, firmware compatibility may be involved, so check for camera firmware updates and lens firmware updates if available.
If the aperture still won’t stop down reliably during exposure, the lens is defective and should be returned or replaced.
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AI8y ago
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