EOS Rebel SL3 & Tamron 18-270mm Automatic Settings don't work beyond 100mm

[Eric_Dunn]

I'm new to still photography so please bear with me.

I bought a Rebel SL3 a few weeks ago and have been enjoying it. This past week I picked up a Tamron 18-270mm f/3.5-6.3 Aspherical Di II VC IF LD APS-C Lens for Canon EF-S Mount and spent a good chunk of yesterday taking pictures with it.

When I got home I found that 95% of them were seriously under-exposed. Today I went out to test things and what I found is that any time I zoom past 100mm the automatic settings on the camera no longer work.

In Av mode, (and zoomed past 100) the shutter speed is ALWAYS set to 1/4000. In Tv mode, the aperture is ALWAYS set to F/40 (which the lens doesn't even do). Even the AUTO-ISO does not work, it is ALWAYS set to 100.

I even tried the A+ fully automatic mode ... same problem.

Manual everything seems to be the only option when zooming beyond 100mm, but everything works fine when not zoomed beyond 100mm.

I don't know if this is normal, or if it's something wrong with the camera, or something wrong with the lens. This is the only lens a have that zooms in that far, so I don't know what is normal.

I played around with the metering modes and had the same issue with all four modes.

I appreciate any thoughts anyone might have on this.

Thanks, Eric

[jrhoffman75 · Accepted solution]

If I read correctly you are saying that the parameters you set below 100mm setting suddenly change to the values you posted when you zoom past 100mm?

If so, sounds like a lens communication problem. Maybe a fault in the ribbon cable in the lens. 

[Eric_Dunn]

Thank you, John.

[normadel]

Do you know someone with a (different) Canon crop-sensor camera to try your lens on?

[Eric_Dunn]

I do not, but I just bought the lens so I'm having it replaced. If the new lens does the same thing ... well, I guess I'll know it's not the lens.

I did get the same response from two different people on two different forums. Both suggested that it might be an issue with the ribbon cable. Fingers crossed it's that and not an issue with the camera.