Hi Leo,
Yes, those lenses are the same (sort of.. they came from the same design department it seems) but not quite in terms of manufacturing..
I investigated this lens quite a lot and found out on
Radojuva website that DG and DX are Chinese and Korean product (respectively).
Also, after checking Astrobin, it became obvious for me that there are good and really bad specimens.
That is why I decided to try this one.. and it seems it is better. I will take some longer exposures over next couple of nights and I 'll post the results here.