Canon 50mm f1.4 infinity focus

[NovaXeros]

Hi all, first thread, so sorry if I'm posting in the wrong place.

I've just purchased a canon 50mm f1.4 in great condition, glass is immaculate and apart from stiff aperture, everything looks and feels great.

Focus close up on my Leica and my a6300 seems really good and sharp, with some pretty heavy ghosting and flaring at 1.4 when the subject is backlit (from what I've seen online, this is relatively standard for 1.4,so I'm not concerned), but what confuses me is the infinity focus on my a6300 is wrong.

So the lens agrees with my Leica IIIf's RF regarding what's infinity at the lens' infinity lock, but if I take a picture on my a6300 at infinity, the subject at infinity is actually not quite in focus, and is much better in focus if the focus is taken back slightly, as if it's backfocusing beyond infinity.

Targets close up at 1.4 seem accurate enough, though a test shot at 1.5m seemed to show a bit of back focusing of about 2cm or so.

Is this a quirk of using the lens on a digital body, and actually it will be fine on the film Leica, or is this something I should be looking to fix/return before I start throwing film at it? I think there should be a shim in these that can be thickened with other shims etc, which should move the focus closer I believe, but with it seeming accurate at 1m, I'm wondering if that will ruin things or if maybe the back focus is so small at 1m that I'm just not noticing it?

I really hope this is something fixable/workable, I've been pining for one of these lenses for a LONG time, especially after the disappointment that was trying to shim my beloved Jupiter-8.

Many thanks

 

[rcubed]

If its accurate with your RF, its probably your NEX adapter thats off. Most cheaper aftermarket adapters go a little past infinity to account for manufacturing errors.

 

[jonmanjiro]

Suspect no.1 is definitely the NEX adapter. Most likely its a bit too thin.

Check infinity on your IIIf on film before you go messing with the lens.

 

[NovaXeros]

My first thought was the nex adapter too, but I have a few other M39 lenses that all hit infinity on the same adapter, so i have doubts. I think I'll throw half a roll of apx100 at it today and take a few shots at infinity, then I'll develop tonight and update.

Just surprises me that the adapter works fine on other lenses - can an adapter work on some lenses and not others?

 

[Sumarongi]

Just surprises me that the adapter works fine on other lenses - can an adapter work on some lenses and not others?

Yes, this can happen. Even if there is no third-party-make involved!
I know of a quite famous member here who has one Nikkor that fits two of his Fs, but not a third one...

 

[jonmanjiro]

I think I'll throw half a roll of apx100 at it today and take a few shots at infinity, then I'll develop tonight and update.

At infinity with the camera on a tripod, with the lens as close to max aperture as possible! Also take some shots with one or two of your other LTM lenses that do focus to infinity correctly on the NEX adapter. I suggest also doing a series of shots focused on something around 10-15 meters away with objects in the frame closer up and further away (to infinity if possible).

 

[NovaXeros]

Okay, so update time:

Tested out the lens on the leica with some APX100. Thankfully, conditions were bright enough to use fast shutter speeds with f1.4, which was good as I didn't have my tripod to hand.

Sadly, the results appear pretty damning to me. The lock in these images was at infinity focus according to the RF, so all I did between these two images was take one at infinity lock, and the other slightly backwards "in front" of infinity, which according to the RF should have been out of focus.

Not the case though:

(at infinity lock)

(manually adjusted)

Neither pic has been edited or sharpened, but the adjusted one is CLEARLY better focused on the lock and beyond.

I suspect the flare and softness I'm seeing elsewhere is related too, as no other examples of this lens online exhibit nearly as much softness as my copy appears to.

So it's with sadness that I must resign myself to returning this lens to the shop.

Maybe some day I'll have a working, reasonably fast and Leica compatible 50mm lens.

Thanks for the help all.

EDIT:

Decided not to give up so easily and added a 0.5mm copper tape layer to the metal shim in the lens. Results on the digital look very promising, with the lens hitting infinity correctly now at 1.4 and also hitting 1m as well, with maybe a touch of front focus, but not enough to throw focus right out. Will throw a test roll at it tomorrow with some real-world examples such as portraits and see how it plays out.

Also, it was really hard to see the issue on those pics I attached, for sure. :S

Fingers crossed.

 

[NovaXeros]

Okay, so quick update for those interested or facing a similar issue: a 0.05mm copper tape shim worked a treat and the lens now hits infinity focus at f1.4 (though much better at f2), and still focuses correctly close up, resulting in a working reasonably priced fast 50mm that just oozes character.

The shim took about 5 minutes and was so simple to do it was almost a joke, and whilst I intend to post some nicer pics to the "show off your Canon 50mm f1.4" thread that I spotted earlier, here's a couple to show infinity and close up focus, both wide open.




Thanks all for your time and if anyone needs any guidance on getting into this lens feel free to PM me, though there is a very helpful video on YouTube.

Thanks.