X-T3 and Sigma 18-50 f2.8 DC DN aperture issues

David Tanner · Oct 13, 2025

I’m having a problem with this lens since I swapped from an XT2 to XT3. The lens worked perfectly on the XT2 but on the XT3 the aperture keeps changing without me doing anything. ISO is auto, SS Auto. I’m really at a loss to what’s going wrong and would appreciate any suggestions.

Morris0 · Oct 13, 2025

Hi David,

I suggest you talk to Sigma. They may not have tested with the X-T3. A lens firmware fix may be needed.

Morris

Antone · Oct 13, 2025

David Tanner said:
I’m having a problem with this lens since I swapped from an XT2 to XT3. The lens worked perfectly on the XT2 but on the XT3 the aperture keeps changing without me doing anything. ISO is auto, SS Auto. I’m really at a loss to what’s going wrong and would appreciate any suggestions.

This happened to me with my X-M5 until I disabled the front command dial. It turned out, I was inadvertently touching it and changing the aperture without knowing it. Which camera dial controls the aperture?

dccberry · Oct 13, 2025

Morris0 said:
Hi David,

I suggest you talk to Sigma. They may not have tested with the X-T3. A lens firmware fix may be needed.

Morris

We use that lens on an X-T3 with no issues- not a firmware problem...

Feugi · Oct 13, 2025

Are you saying the aperture value changes in your viewfinder or do you hear the aperture change or see a brightness change in your EVF or LCD? Depending on the shooting situation, the camera will open up or close down the aperture to maintain a "proper" exposure in the EVF/LCD. When pressing the shutter button, the aperture will open to the specified value.

io_bg · Oct 14, 2025

David Tanner said:
I’m having a problem with this lens since I swapped from an XT2 to XT3. The lens worked perfectly on the XT2 but on the XT3 the aperture keeps changing without me doing anything. ISO is auto, SS Auto. I’m really at a loss to what’s going wrong and would appreciate any suggestions.

Have you set your aperture manually (and are either in aperture priority or manual mode)? When a lens without an aperture ring is mounted on the camera, it will often change to program mode where the camera controls the aperture. If the front command dial is set to control aperture, rotate it left to exit the auto aperture mode and select an aperture value.

David Tanner · Oct 14, 2025

Thank you all. It was placing the camera in P mode as mentioned above. I cleaned the contacts on the lens and that seems to have sorted the issue. The camera is now correctly in A mode and the Aperture is not changing.

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X-T3 and Sigma 18-50 f2.8 DC DN aperture issues

David Tanner

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Antone

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