Canon 50mm MkI loses optical sharpness at F1.8 than at F2-F4?

Hi there, i just got my hands on a 50mm MkI F1.8 lens mint condition. I noticed that when i take pictures of computer fonts on a document paper, i played around with the aperture sizes... i noticed that at F1.8, the optical sharpness( not caused by shake), is not as good as... say F2 or F4... is that a normal thing with this lens? I made sure the camera didnt shake by puttng it on a tripod and using the timer function

thanks in advance

All (well, almost all) lenses become softer wide open, it's pretty normal. Your 50mm behavior is perfectly normal.

Take a look at this comparison here:
http://www.photo.net/e​quipment/canon/ef50/

You will notice that the 1.4/50 is a little sharper at f/2.0 than the 1.8/50.

This is mainly because the 1.4/50 will be stopped down a bit if you use it at 2.0.

Best regards,
Andy

Take a look at this thread I posted yesterday. I'll update it on the weekend to have more shots at the lower end of the scale for both lenses, and also to include the Tamron 28-75 and the kit lens.

Most lenses are a little soft wide open. Don't worry about it.

I have this lens as well and I have noticed that the best sharpness is obtained by using the F2.8 setting. I hardly use any other, except when I need shallow DOF or to photograph in dark without flash.