semrich
Well-known
Summarit LTM, wide open, fomapan 200 @ 200, early evening light.

Just two days ago I got my Summarit back from a CLA. After three years of looking around, I found a place that wasn't scared of taking it in without quoting an outrageous sum (the diaphragm blades were stuck, and one of them was out of place).
The condition of my Summarit is out of the ordinary (never mind that it's the less-common M-mount version): zero scratches, zero fogging or haze, incredibly smooth, and on-spot focusing. It does not exhibit the softness most Summarits are known for except when wide-open and shot against a strong source of light.
The same day I got it back, I decided to test it to a test shooting I was invited to participate. The only two shots taken wide-open that I've posted online are:
Leica M8 + 50mm f/1.5 Summarit @ f/1.5
Notice how there's no overdue softness with a straight light coming in. My point is: get your lens cleaned! These fog easily --mine, for some reason, doesn't. The first one I had had lots of front-element scratches, and exhibited the flare you're exhibiting, even stopped down to about f/5.6
The shots stopped down at f/4 or f/5.6 blew me away: nice rendition and contrast, yet has that unique Summarit "creamy" signature.
Always loved the 50mm Summarit, and still do. This may make my recent contemplation of selling my tabbed (yes, tabbed) 50mm Summilux pre-asph E46 (finances are a bit tight) less painful.
Low contrast, low resolution and prone to flare is the character of the lens. So don't waste your time to looking for a really mint copy and expect something different (as I ever did).