The ring itself doesn't slip. The slip is when the - lets call it the foot - that's used for mounting the lens to a tripod.
The lens foot - technically the tripod socket (Sigma calls that) slips against an arca mount.

The MC11 is a Canon / Sony E mount adaptor - that part works really well and the lens works quite well on A7r4.

I just purchased the Sigma 150-600 Contemporary lens with an MC-11 adapter to use on Sony A7R4. I sometimes use a gimble / tripod with an ARCA mount.
The Sigma has a single mounting screw socket. No matter how tight try to tight the D Ring mounting screw, it isn't long before the camera and lens start to slide - the lens foot against the ARCA plate.

I'm thinking perhaps a good epoxy would hold the mount plate to the lens, but haven't tried it yet. I'd rather have a less permanent solution.

And, did I mention, the little mounting plate and ring is just too small to carry the camera.

Any other suggestions?
Thanks.

The Naval Air Station closed 24 years ago, in 1997 - back when we though we were done with wars. About the only thing left are a few sheds and a whole bunch of that concrete they poured. Check it out on Google Earth.

Four seconds until the hawks were vanquished.

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I've had both lenses replaced using the special lenses for astigmatism. Very good success and an improvement in my ability to spot birds and see more detail around me. I'm 20/20 for distance, and use drug store readers for the newspaper and small print. Most things, no glasses at all.
Good luc

Yes, when birding I'm always in silent mode. These are pretty rare.

Chickadees are fast, but something happened in this photo I can't explain, can you?

Sony 7AR4, Sonly 200-600 @600mm F5.6 1/2000 ISO 1000

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Uninstall everything Topaz.(use the control panel-programs and files) If you can, that step alone would show your machine is OK. Shut down, restart. Go to Topaz and download all new.
Still not working? Search windows 10 iso, install the install tool and install windows 10 latest. Try try again

Some very nice corrections. Thanks everyone.

In Topaz Denoise I used the latest version - 2.3.2 and you are right, the image was perfect when I used your settings - however on my copy the preview didn't show the correction. Once I saved the image the corrections were made.
I just installed the update today . . . I think a call to Topaz is in order.

Thanks.

Jon

Thanks everyone.
I tried your solutions and found - Affinity worked the easiest. The Luminance slider on the denoise filter smoothed the background easily.
Lightroom also had a luminance slider - odd though I couldn't find the equivalent in PS although despeckle in PS worked though not as well as LR.
Topaz Denoise - my go to software for noise, just didn't help this image.

As for opinion that noise or grain is part of the photo - I agree, but I may enter this our camera club competitions and untreated noise always gets a ding by judges.

A dark overcast day. Sony 7AR4 set to 1/2000, 200mm F5.6 (Sony 200-600) auto iso @ 12800.

Timing is everything and timing was just about perfect for this confrontation between a downy and sparrow.

The noise unavoidable but can it be corrected. I’ve tried Photoshop and Topaz denoise with almost no effect. This OOC image just won’t correct. Any ideas how I can smooth out that background? BTW, shot was through a glass door.

Image, uncorrected, resized, jpg from raw file.

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Red Tail morning bath.

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Strap is always on the lens bracket. I shoot at least 2000 photos a month, mostly over trails. It's the same mounting plate used on a small 50mm prime. Someone didn't test it like I use it. My s/n is 670, one first made. If it was defective, the problem would have shown up last October when it was new. It just wasn't build for wear and tear.

You seem to be one of those blame the user people. Bad manors.

There are a lot of YouTube videos on real estate photography - I'd start there just to get a feel for the different kinds of real estate photography.