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RF50mm F1.8 STM - attachment to EOS R7 twist/turn not smooth when installing/removing



I am using EOS R7 wich came bundled with RF-S18-150mm F3.5-63 IS STM.  I then acquired RF100-400mm F5.6-8 IS USM.  Attaching/detaching both of these lenses to the R7 body felt identical - twisting/turning the lens into the lock felt smooth and no resistance.

I then got RF50mm F1.8 STM.  I noticed that when twisting this lens into the lock position, there is a notable amount of resistance compared to my other lenses both when installing and removing the lens.  Comparing the 3, it seems the 2 larger units have a black plastic surface whereas the RF50mm has a silver metallic surface at the twist contact point - perhaps that explains the difference?  It doesn't feel like it's forced in the sense something is blocking it, but more so that the contact points are much tighter.

Anyone have the same hardware and can compare?  I just want to be sure I'm not going to damage anything.  This is my first time working with cameras with swappable lenses. 






 I have these for comparison.  Usually 1 of 2 things.  The flange or mount is bent, or the lens is not being aligned properly when twisting to lock. It must be fully seated.  If you are off by 1mm the lens will feel tight when mounting. 

Bay Area - CA

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Rick - Thanks for your response.  Everything I have is "new" from BestBuy just purchased on different dates.  I hate that Canon doesn't put any sort of seal on the boxes, but given BB's hefty 10 or 15% restock fee I think most likey these are never touched (they appear that way when I unboxed them).


So I went back to review and actually only the RF-S18-150mm has the black plastic ring - this one turns the perfectly smoothly into the slot.  The RF100-400mm is silver metallic just like the RF50mm.  It doesn't turn as smoothly as the 18-150 but better than the RF50.  

I took photos of the ring for the RF50 - do you see anything wrong with it?  Then the last photo is of the 18-150 top view where you can see the ring is black plastic (rather than silver metallic).  I might take it to the local camera store to get their opinion.    



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