Perfect 50L for longest time, suddenly needs MFD...

So I've owned the 50L for almost a year now, and since day 1 I've always had great results. Tack sharp wide open (for a 1.2 lens) and never had any issues nor ever felt the need to use the micro adjust tool. I feel like out of nowhere, it's missing focus. For no reason. I never dropped the lens, I always am careful, it sit snug in my pelican case when on a job. Did a portrait session for fun last week, tack sharp results as usual (could count hairs on face etc.). I buy a new 6D and decide to test lenses, and now my 50L is wonky. I figured must be new camera, so I popped it on my old 6D and same results. I decide to go extreme and set the micro adjust to -20. Tack sharp perfect results every time. No matter the distance or aperture, perfect in focus shots. I did tripod test, hand held, you name it. I simply don't understand what might have caused this. Ive so far been testing in my room and have fluorescent bulbs, would that affect focus? Any help would be appreciated. I want to do more real world out side testing tomorrow.

Tony_Stark wrote in post #17374986
Ive so far been testing in my room and have fluorescent bulbs, would that affect focus?

This is the problem.

Go outside or use studio light and you'll notice it nails focus again like magic.

Very best,

MalVeauX wrote in post #17374991
This is the problem.

Go outside or use studio light and you'll notice it nails focus again like magic.

Very best,

Maybe Im lacking sleep or something, but when I move my exposure compensation to about a third stop higher, results are wonky. I do the exact opposite and under expose a touch, its clean and sharp. Ive always hated fiddling with MFA. I should get some rest.

Tony_Stark wrote in post #17375007
Maybe Im lacking sleep or something, but when I move my exposure compensation to about a third stop higher, results are wonky. I do the exact opposite and under expose a touch, its clean and sharp. Ive always hated fiddling with MFA. I should get some rest.

Heya,

In fluorescent light, the shutter speed matters. So when you were changing the compensation you were putting the shutter at a point that didn't match the frequency of the fluorescent light. There's a few studio masters that can put it more eloquently than I am here, they should chime in shortly.

Very best,

I have gone through some images I have taken with the 50L, seems to be consisten back focussing in all shots Ive taken, however, Ive only realized this now. Not sure why that is. Ive never had issues and love every image I have taken with this lens. Why am I only noticing it now? Perhaps getting a new body has made me pixel peep more then before for some reason? Weird.

Change the body the camera is mounted on, and you change one half of the tolerances. MFA is ALLOWED to be slightly different between different bodies with the same lens, Just as you can have differences with the same body and different lenses. Variations in tolerances is why they put MFA systems on to the bodies, of course it is also more noticeable with the narrower DoF of wide aperture lenses.

Alan

MFA is supposed to be for your one body only. Different body, different MFA.
I think it's Roger at LensRentals that explains this in much more detail.

Does the 50L (like the 85L) suffer from focus shift as a design compromise that Canon had to make?