only the last versions of the 3,5 and 2,8 Elmar had an E 39 thread. The Summitar was an uncoated pre war lens that was continued after the war until in 1953 the collapsible Summiron was presented but with coating and the number of diaphragm segments was reduced from 9 to 6. The front lens was made of a rather soft glass and therefore many Summitars have a scratched front lens. The sharpness is good in the middle but falls down noticeably to the corners. The lens is more susceptible to flare than the Summicron, lens shades are very rare and expensive. The 2,8 Elmar is only hardly better than the 3,5 but due to the use of rare earth glass the speed could be increased by 1/2 stop. The resolution of the collapsible 7 lens-Summicron (it is not identical to the rigid) is better than the Elmar and the Summitar, the best stop is 5,6. With all old collapsible lenses you can have the problem that the mechanical mount is worn and wobbly and the parallelity and the register of the lens is no longer guaranteed. If you forget to pull it out or you don't bolt it correctly, you don't get a sharp picture!