Mttran, I can agree from my own observations with my 50L lens with your comments above describing the shift in AF. In 95% of cases I am using my MFA-adjusted center AF point on my 5D II camera and the 50L, so I never have issues there. Recently I used one of the outer AF points with the 50L lens mounted on the camera, and the focus had a hard time to be locked on the target. I was wondering what happened, but I forgot until I read your explanations. It now makes sense to me - it is a camera AF thing, not a lens issue!
retrofocus wrote:
Mttran, I can agree from my own observations with my 50L lens with your comments above describing the shift in AF. In 95% of cases I am using my MFA-adjusted center AF point on my 5D II camera and the 50L, so I never have issues there. Recently I used one of the outer AF points with the 50L lens mounted on the camera, and the focus had a hard time to be locked on the target. I was wondering what happened, but I forgot until I read your explanations. It now makes sense to me - it is a camera AF thing, not a lens issue!...Show more →
+1, there is no reason to pick the 50L from an unstable AF system which can be improved to compensate most optical design constraints. Some just can't see the real issue here.
I think the only real confusion here is that the phrase "focus shift" was used to describe a different effect than what is commonly referred to in photography discussions and technical papers as focus shift. That is all.
dwweiche wrote:
I think the only real confusion here is that the phrase "focus shift" was used to describe a different effect than what is commonly referred to in photography discussions and technical papers as focus shift. That is all.
Maybe "lemon" is not a right word...maybe "not well calibrated at wideopen"
That is the only reason the center point is being shifted. Yes, i do understand this optical phenomenon very well.
That is not the reason for Focus shift (not well callibrated wide open) You are wrong
I don't think you really know what you are talking about here. Please follow the thread from the beginning then we can discuss about it again whenever you are ready.
Whenever you have a chance, go to the lake and look down to the fish in different angles then asking yourself where is the fish position from where you at then you will be snapped out of whatever you are in right now.
You can do the same thing by wearing a pair of near/far glasses then move your glasses back and forth while observing everything infront of you. Thing sometime works simple than your thinking
dwweiche wrote:
I think the only real confusion here is that the phrase "focus shift" was used to describe a different effect than what is commonly referred to in photography discussions and technical papers as focus shift. That is all.
It is more than that...some people does mis-use the term for everything that OOFed. Look at the title of this thread ...it is a result of many misconception that relates only to the 50L but not other fast lenses.
Imo, 50L is a beautiful lens and nothing wrong with its design. It shares the same optical phenomenon like any other fast and short lenses that i have discussed in earlier posts. Mine works just fine and tack sharp just like other lenses i have.
Again when using camera center AF sensor with light & confirmation beep for AF & VFMF processes, i have found no focus shift problem so whatever (at any aperture setting and any subject distance) that people talking about.
When using off center sensor for a focusing point then i have had some expected minor focus shift due to fast lens optical phenomenon (light bending effects when aperture is stopping down) and an unchanged AF focal plane. The focus shifting in this case is too small compared to subject dof from the range of (f1.4 - f2.8) so it is very hard to notice in my image anyway.
Yes, my 50L works the same way just like many other fast lenses i have had. Here are the full size and 100% crop samples that fits in the focus shift constrainst that people is talking about:
1Ds2 & [email protected], off center AF and about 2 to 3 meters away.
As you can see...all of these images fit in the cases of focus shift constraints and none of them has no shift/oof issue at all. Some 50L user does not understand camera AF system so they blame most their OOF on "focus shift" of the 50L. Don't read too much the mis-information on internet. Just calibrate your camera and lens to get the default sharpness like my last image at wideopen then "focus shift" or whatever term you have in your minds shall be soon fading away before you know it.
I like to put down something here that already posted in another 50L thread so you can see how the fast lenses really work:
Fast lens projects almost an "U" oval sharpe focal plane at large aperture so anything behind or in front of the curvy plane will be in OOF; However, anything belongs to final "U" oval curvy focal plane then it will be pin sharp just like the center one. Here are some [email protected] border & center shapness samples:
The 2D MTF graphic from most internet review sites does not reflect the way how fast lenses work in real world. Just by looking at these f1.2 images you can see how the AF focal plan can be easily screwed up when the lens is stopping down. If you still had an OOF image when using center AF sensor after all cam & lens calibration, VFMF & LVMF verification then blame the oof/shift on your body unstable AF system, not the lens.
Don't forget our image sensor is always a flat one and our AF focal plane at open wide lens is a curvy one. Bottom line, any focus shift phenomenon in DSLR system then it is caused by your body AF which can't keep up with your lens just like your brain can't keep up with the movement of your eyes.
Focus shift today is the same as it was with film. I don't know what you talk about in all your posts. But it's not Focus shift