10-08-2020 06:01 PM
I'm having an issue with inconsistant focusing at 2.8 to 4.5.
I'm doing tight portrait at 200mm, not at the closest focusing distance though and focus point from shot to shot is shifting from dead on to half an inch back or front focused at random. When I look at the focus points in DPP they're just where they should be, but around 30% of the time the focus is just slightly off.
I've just started try to shoot with this shallow a depth of field. I always tried to shoot with this lens in the past around ƒ8 - ƒ11 as that's where it's sharpest, but I'm working on a new shallow depth porfolio.
I'm shooting in single shot, half press shutter button, and picking the closest focus point and setting it on the inner corner of the closer eye.
Would either of the AI modes help? Does tracking help if the subject is moving very slightly back and forth and than across the frame?
Would shooting bursts help?
I've tried back button AF, but all the buttons I could use to start and stop it are awkwarding placed on the camera for my hands.
10-08-2020 06:24 PM
When you are shooting at very shallow depth of field, the AF calibration has to be spot on for the lens and most newer/better Canon cameras make it easy to do that calibration. Here is a link to the Canon microfocus adjustment guide: https://cdn.static-bl.com/images/manual/Canon-AF-Micro-Adjust-Guide.pdf
The forum strips some links and Canon's USA website probably has their guide on it but searching that site is an exercise in frustration so if the link gets stripped just google Canon micro focus PDF and several links to their guide will show up.
10-08-2020 07:20 PM - edited 10-08-2020 07:23 PM
"When I look at the focus points in DPP they're just where they should be, but around 30% of the time the focus is just slightly off."
You might need a focus adjustment. I'm curious as to what camera body are you using, though. Not every camera offers AFMA. An old and weak battery can cause focus to be inconsistent, too. I just had to order a pair for my 7D2.
Using back button focus does not improve focusing. It can only improve your, meaning you not the camera, ability to acquire a subject for focuing under certain shooting conditions.
[EDIT] How many focus points do you have active? Try using just the center AF as the only active AF point.
10-09-2020 10:11 AM
What I would do is use just the center focus point. Turn all the others off. You are just missing focus plain and simple. No, do not use Ai-servo. It will only make things worse. I seriously doubt you need focus adjustment. I don't know way folks jump to that conclusion so quickly. Most "L" lens do not need it.
Your question implies something in the photo is sharp. The first place to look is mis-focus not it's the lens fault.
10-09-2020 06:25 PM
10-10-2020 08:20 AM - edited 10-10-2020 10:47 AM
Canon 5D Mark III
Actually 2 of them and the lens exhibits the same behavior with both bodies.
Back button focus allows for taking multiple shots without the camera trying to refocus every time.
I'd use the center point, but I'm trying to capture very fleeting expressions and constantly recomposing doesn't work.
I know [how] BFF works, and why people use it. I it is good that you checked focus and discovered that it did not improve your results because the problem is not with the lens. The problem really appears to be user error.
It has been suggested to you that you at least try using just a single AF point, but you have rejected that idea. I believe your issues are a result of you not fully understanding how the [very complex] AF system works, and the behaviors to expect in different AF modes.
If you are not willing to try what has been suggested, then that leaves only [one] solution for you. I sugggest that you download a free copy of the full User Guide from Canon. Please do not reject that advice. Good luck.
10-10-2020 10:16 AM
" The problem really appears to be user error. ... because the problem is not with the lens."
I respectively agree, please heed this.
10-10-2020 08:04 PM
10-10-2020 08:23 PM - edited 10-10-2020 08:25 PM
So, it's "user error" to expect that a lens focuses consistently while using one of the 61 focus points built into the camera body with an L lens?
I really don't appreciate the condescending attitude.
There is a reason why I don't want to use the center point and recompose every single frame. I'm trying catch very subtle, fleeting expressions in the eyes of the actor as I'm shooting. If I was constantly moving the camera, I'd be missing as many chances to get what I'm looking for as I'm losing to focus issues.
I thought this was about the lens, not AF points. It was suggested to you to try a test, in order to check the lens. You asked for help and categoricailly rejected the idea to test the lens.
I suggest that you contact Canon Support, and do follow their suggestions and troubleshooting. Good luck.