Exposure issues with 5D MK IV and Tamron 150-600

[SSipple]

I seem to be experiencing e posture issues with my 5D MK IV when using my Tamron 150-600.    I did send the Tamron for the latest firmware update.   I took the camera and lens on a trip and was shooting with auto ISO and shutter priority.   All of a sudden, the exposures were dark.    I switched to my Canon 24-105, and then everything was dark.  Called Canon and they had me reset the camera settings.  Appears to have corrected the 24-105 issues.    For the most part, the 150-600 is working, but at the 150 range appears to randomly underexposed.   I looked and the auto ISO is being set to a very low ISO.    I was using evaluative metering.

called Canon and they basically told me I was using an inferior lens and that was the problem.   This has been working fine until now.  Not sure whether to send the camera to Canon, he lens to Tamron.   I used partial spot metering and the exposures seemed better.

[ebiggs1]

"It seems that you should respect that I have been very pleased with Tamron and the quality of my shots."

Don't hold you breath on that guy.  He is always like that.  You are on the right path and I am sure the issue will be resolved.

It seems Canon can upgrade their lenses but Tamron can't!  Right?  I would love to be able to give you the answer but I don't have that problem with my Tamron(s).  I owned the first 100-400mm and sold it after I got the first Tamron 150-600mm.  I tried the second version of the 100-400mm and was not sufficiently impressed with it either. Some folks like it and more power to'em.  Beside that fact it isn't 500mm or 600mm long.  Who wants to mess with a tele converter at all.  Let alone spending two grand on the lens and another $450 on the converter.

If were are not careful there is probably an MTF chart in our future.  

[kvbarkley]

Dumb question, but I don't think I saw it addressed.

Could you have accidently dialed in exposure compensation with the QCD? I just did that with my Rebel.

[TTMartin]

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@kvbarkley wrote:

Dumb question, but I don't think I saw it addressed.

Could you have accidentally dialed in exposure compensation with the QCD? I just did that with my Rebel.

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I think that was half the problem. The half that affected their Canon lens and was corrected by resetting the camera.

The other half with the occasional under exposure at the wide end of the Tamron 150-600 is most likely a lens issue. 

[SSipple]

I had the Canon 100-400L and prefer the Tamron. I really do need the extra reach of the Tamron

[TTMartin]

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@SSipple wrote:
I had the Canon 100-400L and prefer the Tamron. I really do need the extra reach of the Tamron

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Did you have the original 100-400 or the 100-400 II? There is a night and day difference. Like I said the Canon 100-400 L IS II with the 1.4X TC III (140-560) is sharper than the Tamron 150-600. And being a Canon EF lens it is going to work properly with your EOS camera.

[ebiggs1]

"The camera is already on the way to Canon to look at. Tamron will also be getting a call."

This is what I would do if you did the reset and test in good light with auto ISO off.  Some other info you are getting here is bogus. Surprise!  It sounds like you are on the correct path now, though.