Bought this from eBay at a good price but the condition of one internal element is not mint. I used it on 5D and gave very nice image.

I found a small secret...but maybe somebody already knew and said so...anyway, this is already regarded as king of the lens, but there are a couple of simple ways to further improve the image quality...

It was designed in 1994 and maybe at that time E77 size Leica/Leitz UV filter was not available or some other reason, APO280/4 has a UV filter inbuilt in front of the lens. It also has another changeable UV filter at the rear of the lens. My idea is that if these 2 filters have been taken out, there could be further enhancement on image quality.

I have then tried to take out the rear filter as it is easy. On 5D, under 100% view, it does not have observable impact on sharpness, but it gave slightly more delicate colors. However, the focal plan will shift and the focus ring markings will no longer be accurate. But I guess taking away the front UV filter will not give focus shift. Not sure if Leica could offer such service...

Cheers