50mm f1.4 'tests' - thoughts & outcome!

Hi All

I got this lens as Xmas gift (it was on my requested list).

My initial shots made me think it was suffering from front focus but the LCD preview is not the place to judge that.

I have now done some chart image test shots and have come to a conclusion ~ none of which surprises me ~ at f1.4 the DoF @ 1 to 1.5 metres is razor thin and as such even repeat shots of the chart show some small (10mm to 14mm) back / front focus variation I put this mostly down to the AF shifting ever so slightly between shots (NB This tripod mounted and using the countdown timer). Closing down to f2.8 and f4.0 I get a noticable bias to back focus but is this just the DoF 1/3 to 2/3 split showing up.

So, how have you found your 50mm f1.4 of absolute sharpness? Is there much copy to copy variation such that by getting it exchanged I will see an improvement?

I will examine the test shots more critically but would welcome any feedback. But having said that even with razor thin DoF at f1.4 with this lens I should at least expect the point of prime focus to be sharp, shouldn't I?

TIA

My 50/1.4 seems sharp, at least even across the frame. I find it still sharp wide open although I hear some reviewers say it has some mild CA wide open.

I think using the AF to check for sharpness wide open is problematical as you have noted. Canon aparantly accept anything within the DOF as focus OK. For doing proper chart tests at wider than 2 stops down you probably want to have a split image focus screen fitted to ansure the focus is spot on.

I don't do chart tests but my copy seems to be sharp and well focused where I need it to be. No issues yet.

What do you mean by biased to back focusing? I'm assuming the point you focused on is still in focus because you are thinking it's within the DOF... I'm not following you.

Hi Nezmo

Sorry if my description was too loose. What I was trying to say that at f4.0 I can see that more of the background area is in focus than the foreground. It is my understanding that lens/AF systems do an approx 1/3 to 2/3 split front to back for the focus zone.

I have since read a few comments elsewhere that the 350D is not ideally suited to the f1.4 ; its performance with the 20D is better because of the increased number (or accuracy ?) of the central focus point(s).

My prime use for the lens would be low light interior shots i.e. as close to wide open as possible at lower ISO ~ the DoF will obviously depend on the distance to the prime focus subject & (occassional) portrait with and without flash.

So, if there is an issue with this copy of the lens I would like it replaced - Note here that all my other Canon zoom lenses are crisp to exceptionally sharp wide open though benefit from a little stopping down. The 50mm f1.4 is my first prime.

I got you now. Thanks for explaining further.