Look at the RRP price tags extracted from CS Canon Price List. If no IQ differences why pay more.............
EF 50mm f1.2L USM RRP $2899
EF 50mm f1.4 USM RRP $699
EF 50mm f1.8 II RRP $159
Hi, I like to add to the knowledge base here if it has not been done before.It's easy to say there's is a qualitative difference because of the
price difference but it leaves the person asking the question just as ignorant or "blur" in local parlance.This is not to show I know better.
Let's start with the cheapest 50mm F1.8 - this is the mass market made mostly of plastic for the lens barrel and standard multi coated glass
elements.Not to say it's a lousy lens but given it is made at the cheapest cost in great quantities,the materials cost comes down hence it's
cheap price.
50mm F1.4 - If you study the history of this design at F1.4 ( since the 1800s when photography became wide spread ) it had it's technical
challenges when lens design software or computers were non existent then.Still it is not easy to make a good F1.4 because a poorly designed
one will show vignetting at it's widest aperture at F1.4 and sharpness also.Lens grinding and polishing is even more precise because of the diameter and
thickness of the lens curvature.Just google the recent revival of an old design by Cosina/Voigtlander 58 mm F1.4 Nokton for it's illustrious origin that
Nikon and Canon could not do at that time period.
50mm F1.2 - At F1.2 needless to say this is a very challenging design but with the L version which is meant for professional use and FLOURITE
lens element in between the glass elements for colour refractive correction properties make this lens superior in performance.
Do you know that flourite can desolve in water like sugar? Then again you are not likely to soak it in water for cleaning.That's all I have to add.