I will post a detailed article from lensrentals.com.
If you have a digital lens and if you use it at film camera , result will be bad. Why ? Because digital lens is optimized to to send light rays through the glass infrared mirror.
If you attach film lens in to digital camera , glass infrared window will decrease the mtf %20 and increase the spherical aberration.
Thats why , glassless BW Leica M9 is the best for accepting old lenses.
Mustafa Umut Sarac
Here is the article below :