Hawaii 2023

I've just returned from a trip to Oahu and Molokai, Hawaii, during which I shot the Canon 5DS with the pancake 40mm, 50mm f/1.8 lenses and the Tamron zoom 28-300mm, about which I'm still uncertain of its sharpness as compared with the 24-105mm until I study more photos. The 40mm was nicely sharp in city scenes.. I also used 2 of my Sigma cameras. I've started processing a few in DPP and have started a "Hawaii 2023" album on my flickr page. The first 5DS shot is a bit unusual in its angle on the peninsula with Kalaupapa, the town which served many decades as a leper colony. There is a wider shot of the peninsula as well on flickr, and Sigma shots. MANY more photos will be coming asap.

2O6A1229 Canon 5DS Kalaupapa cliffs Molokai by Sandy Fleischmann, on Flickr

Yes, please report back on your Tamron experiences. It is an interesting lens. Which version do you have?

My results with the Tamron 28-300mm on the Canon 5DS were VERY disappointing. I know it wasn't a camera problem, as the photos I took with either the Canon 40mm pancake or Canon 50mm f/1,8 are fine. Unfortunately the lens I used most of the time on the Canon 5DS was indeed the zoom. I have some 5DS photos online in my flickr photostream and Hawaii 2023 album. But the majority of my photos online at flickr are with my other 2 cameras I had along, the Sigma DP3Quattro and the DP2Merrill. I'm also working to process on a new computer which has made it difficult to judge the lightness/darkness of my processing. So many of my early photos online (DP2Merrill mainly) are really too light. Every photo trip is a learning trip, correct?

I still haven't been able to analyze what was going on with the zoom. Windy conditions at great zoom length above 200mm? Maybe the UV filter contributing to aberrations? How the directional light was hitting the lens, ie north, south, east, west shots? Really puzzling to me as I had used the lens around Virginia before the trip rather extensively, with only a note to self that it wasn't as sharp as my 24-105mm. Much blurriness isn't visible in small versions, it's when I look at 100-200% that I realize, wow this is bad.

No similar problems with my Sigmas.

Here's one okay Canon shot toward the end of our stay on Molokai
More photos on flickr under my name Sandy Fleischmann all at large sizes. Typically 10MB to 20MB JPEGs online
2O6A1252 Canon 5DS Murphy's Beach area Molokai by Sandy Fleischmann, on Flickr

I feel sorry for your negative experience. My experience was similar with EF-S Tamron 18-400 mm and EF-M 18-200mm on EOS-M 6.
You may have an AF issue at the longer focal lengths due the AF-protocol and the slow aperture.

The Tamron may work better on a MLC then DSLR, too.
Again, there are 2 versions of this lens, which one is yours?
Unfortunately I sold the zooms before I could test them with modern M6ii's AF.

Thanks Maxmolly for the comments. I had some decent shots with it earlier in Virginia when doing my form of testing, trying it out in different real-life photo situations. Some examples in the wisteria series and garden greenhouse photos on page 2 of my Canon 5DII & 5DS album.
Wisteria below. Shot also gives specifics of which Tamron 28-300 it is
flic.kr/p/2ow7kH1