This lens is a rather old version of the standard 50mm SLR lens by Canon. The “FL” shows that it is the predecessor of the “FD” series. You can find excellent information about those lenses here.
The FL 1.8/50 is a beautiful lens with its slivery rings and black barrels. Here you can see some images of different FL lenses. The problem with those FL (and FD) lenses is that due to the shorter register distance, they cannot be easily adapted to EOS cams. If you want to use an FL lens on a digital cam, you have four choices:
1. Use a 4/3 or an EVIL cam.
2. Adapt the lens with an adapter that has an optical corrective lens inside. That’s the way I go.
3. Use the lens only for close-up work.
4. Rebuilt the lens mount. Here you can read how you can do that.
As said, I use a corrective adapter which influences the optical performance a little, not too bad in normal circumstances but it generates flare and thus reduces contrast quite often. I’m going to show some examples soon.
Built and handling are very nice, somewhat typical for manual Canon gear.
For the rest I’d like to quote a paragraph by Erwin Puts who knows much more about lenses than I do:
“Canon 1.8/50mm FL and FD. Both are classical 6 element Double Gauss designs. Both show strong curvature of field, as can be seen from the figures. If you focus on the center of the image, the outer zones are quite soft and if you focus on the outer zones the center becomes soft. This is a classical dilemma for camera designers. Most lenses exhibit this form of aberration. A lens does project a curved image on a flat receiver (the film). So the designer can select a back focus distance where the tip of the curve intersects the front of the film plane: we have excellent center sharpness. Or the designer can select a distance where the outer parts of the curve intersect the film plane, giving a high quality in the outer zones with a weaker center part. You can count on film curvature to correct the center part, but in any case the designer has a choice here. For a normal standard lens it is important to have even coverage, so the second solution would be wise. for a high speed reportage lens, the first option may be advisable. The official approach in lens testing is to focus on the center part and use this position as an analyis base. Here it comes:
At 1.8 and on axis both lenses have a central disk of about 6mm radius (12mm diameter) of high resolution and low contrast. These lenses resolve easily 125 linepairs/mm but the contrast is very low and some flare can be seen on axis.
In the outer zones the resolution drops to about 20 lp/mm with a higher contrast, but now we see soft edges at the black/white borders. The lvel of astigmatism is very low, which is a major feat. There is low vignetting and some very small pincushion distortion.
Stopping down to f/2 and f/2.8 brings a slight improvement in contrast and it is at f/4 that the lenses start to show a punchy performance. At f8 we have excellent performance with high contrast, and good edge contrast (micro contrast) over the whole image field. The FD version shows a slight improvement in the outer zones, but overall both versions perform identical.There is no decentring: always a good sign of outstanding workmanship in manufacturing and quality control.
As the FL version is steel and glass, where the FD version already uses plastics, my preference would be for the FL version, but generally both are fine performers. There is some tendency to flare and overall contrast is low, giving the pictures a flat and dull appearance when uses wide open. Stopped down the perfomance is very commendable.“