50L query

Possibly already been done to death, but I'm considering picking up the 50L.

I'm not one to dwell too much about design faults (if indeed they exist) and I appreciate there are multiple causes of the 'focusing issues' whatever they might be.

Reading around, the only two things I see myself needing to be concerned about are 'focus shift' and 'back focusing' - the latter is less important as it can be MFAd, but also reports of it are highly likely down to the extreme shallow DOF. The former is of more concern to me. When people speak about focus shift, I get the impression they're first acquiring focus on their chosen point, then changing aperture which I find an unusual approach. It seems unusual enough to me to think that that's what's causing the focus inaccuracy. Why wouldn't you just set aperture and acquire focus, then shoot.

I'm bothered about focus accuracy when taking shots like those below, taken with a 50/1.8 (is this also missing the floating element?) - can any existing users vouch for accuracy with subjects quite close? I understand if you shoot at 1.2, it's not going to shift because the aperture doesn't move when you release the shutter. It's only when you're stopped down a little.

I can't understand why there'd be a problem if you acquire AF *AFTER* you set aperture.

IMAGE LINK: https://flic.kr/p/KESj​tA

Focus shift occurs in DSLR lenses (not just the 50L btw) because when using phase detect AF the camera has the aperture wide open to give most light to the AF sensor. Once focus has been achieved the aperture is then closed down to the chosen value. Depending on the lens design the "plane of focus" may shift with the change in aperture. Why not just focus with the chosen aperture? As I mentioned earlier it is to get the most light to that little AF sensor but I think it is also so that the sensor has best difference between in focus and out of focus.


Unless you are shooting in live view with appropriate settings to have the aperture close down to the chosen setting or hold down the DOF Preview button it won't matter what your chosen aperture is, the body will acquire focus with the aperture wide open, then close just in time for the shutter to open.

I think I already knew that, needed a refresher obviously!

That's what happens with the 50L then as far as I'm able to gather from existing info on the web.

Any users able to say whether it's easy to achieve the image above? Focus distance is within 1m (3ft).

I had a heck of a time when I bought my 50L and tried using it at 1.2. It was all me. It just takes practice and you have to accept that you will blow a few shots if you are handheld or the subject moves at all, so take a couple if possible. At the distance you mentioned, it's razor thin for reals, but put it on a tripod with a still life and you can quickly rule out the gear being at fault. That was the gist of the advice given to me because I initially thought, no way am I this bad...
Now I am needing to upgrade to a 5D3 or 5D4 for the focus points. The focus/recompose thing with the 6D falls on its face at 1.2 a lot of the time, and I don't view live view as practical outside of landscape work.

battletone wrote in post #18109039
I don't view live view as practical outside of landscape work.

That should change with the 5D4, thanks to quick dual pixel AF, touch screen, and face recognition.
Can't wait to try the camera.

I've always similarly heeded the focus shift alarm, although my understanding is that it's more prevalent at 2.8-4.0, not 1.4-2.5. At any rate, I only do this for fun, so for a shot like that I would likely use the center point (on 6d & 5d3) and recompose in post (from a step or two back, obviously), which also makes the exposure metering simpler.

It works for me.

Treetownie wrote in post #18109179
I've always similarly heeded the focus shift alarm, although my understanding is that it's more prevalent at 2.8-4.0, not 1.4-2.5.

Focus shift will be higher with a higher f-stop number. It will actually be zero wide open.

Thanks for responses, I think I'm going to opt for something else in the short term.

Will keep a close eye on what's rumoured as it's still a favourite FL.

1.8STM has better optics than the 1.8v2 I understand, perhaps that can be a replacement if mine dies.

My copy of 50mm f/1.2L was bad. It was brand new and my camera (5dmk3) was brand new, but I was NOT able to achieve sharp focus at 1.2 even with tripod, so I returned it for a refund, and ordered 85mm f/1.2L II instead.

nate704 wrote in post #18110803
My copy of 50mm f/1.2L was bad. It was brand new and my camera (5dmk3) was brand new, but I was NOT able to achieve sharp focus at 1.2 even with tripod, so I returned it for a refund, and ordered 85mm f/1.2L II instead.

So you wanted a 50/1.2, and because your copy was bad you realized you actually wanted a 85/1.2 ?

UKmitch86 wrote in post #18110210
1.8STM has better optics than the 1.8v2 I understand, perhaps that can be a replacement if mine dies.

If you look at Canon's specifications the optical formula for the two lenses is the same, except for improved lens coatings. Contemporary reviews of the STM lens at places like PhotoZone indicate that the main improvements are the mechanical portions: the focusing helicoid, aperture assembly and motor. And looking at the test results, there seem to be few differences between them optically.

The 50/1.8 has a bad rap due to focusing accuracy (it can front-focus somewhat unpredictably at wide apertures), and this seems to be due to spherical aberration giving an insufficiently defined image on the AF sensor, rather than any kind of defect in the focusing system of the lens. That's a potential concern, and I haven't seen any confirmation that it's been fixed on the STM version.

All that being said, it's a killer lens for the price, and the STM does focus more quietly, with the option of manual override that the mk II does not have.

I had the 1.8 v2 for many years and upgraded to the 50L. Color and contrast are much better on the L lens. Focus shift hasn't been an issue once you know about it. But, since it has a curved focus field, you can MFA at one focus point, wide open. In my case I adjusted for the center focus point. But you have to crop for portraits unless you like the center composition look.

GregDunn wrote in post #18112449
The 50/1.8 has a bad rap due to focusing accuracy (it can front-focus somewhat unpredictably at wide apertures), and this seems to be due to spherical aberration giving an insufficiently defined image on the AF sensor, rather than any kind of defect in the focusing system of the lens.

Can't be spherical aberration, because multiple AF attempts on the exact same point result in different focus errors.
I don't know about the STM version, but as far as the 50/1.8 II is concerned, I blame the crappy motor.
You get what you pay for.

Never had a problem with the 50L. Admittedly, I am self-taught, and perhaps, do not know how to view/perceive focus and sharpness, but most of the shots I took with it were fine. When they weren't, I attribute it to my own mistakes. I consider the examples below to be fine. Perhaps others will see them as mis-focused.

IMAGE LINK: https://flic.kr/p/yJcM​eb

IMAGE LINK: https://flic.kr/p/pSgR​G7