Comparison Between My Two Wide-angle Conversion Lens

Here are some tests between the two wide-angle conversion lens I now own: The Fujiyama 0.45x and Vitacom 0.25x conversion lens.

Taken with Fujiyama 0.42x wide-angle conversion lens on Canon 18-55mm kit lens

Taken with Vitacom 0.25x Ultra super wide-angle conversion lens on Canon 18-55mm kit lens 

Taken with Vitacom 0.25x Ultra super wide-angle conversion lens on Tamron 18-270mm zoom lens

These two pictures were taken from the same spot. The images have been resized down to 800x800. First 2 images were taken with the Canon kit lens, the first was Fujiyama 0.42x conversion lens and the second was Vitacom 0.25x conversion lens. 

I would say that the angle has been increased by quite a bit, judging from how much more of the table can be seen from the bottom right hand side in the image. 

The other thing I notice, is how much the image quality of the Vitacom 0.25x deteriorates at the edges of the image. It is apparent even at 800x800 resolution. The same features in the bookshelf on the top left, like a the binded spine of a book and vertical lines are very obviously blurry. 

I wanted to find out if the image quality would be any different on my new Tamron 18-270mm zoom lens, so I took the third image, the Tamron zoom lens with the Vitacom 0.25x conversion lens. Seems like the Tamron gives a softer image overall, but the test is in no way conclusive due the following: The camera was hand-held, not mounted on a tripod, therefore the framing across the 3 pictures are not exactly the same.

This is the initial test, and I'll try and do more tests under different conditions.

The Vitacom does not have a true 180-degree coverage, but I wonder if it is enough for me to use it as an accurate environment map as well as take images for image-based lighting purposes.