Re-compose issues..

Hey everyone.. I have had an issue with recomposing in my front room studio. I'm using a 6D and 24-75 f2.8-5.6 typically, in Manual mode, center point focus. I grab the eye with back button then recompose to fill the frame. Some are razor sharp some are just off a little.
I really try to stay the same distance, in fact I'm on a tripod, but in portrait orientation I may focus on the eye but when the shot is recomposed the center point may be on the waist..
Any thoughts to fix this issue?

EightEleven wrote in post #18050264
... but in portrait orientation I may focus on the eye but when the shot is recomposed the center point may be on the waist..

First, I would try to duplicate the problem with a fixed target to eliminate a focus/recompose problem or a subject moving slightly problem. And when "center point may be on the waist", try using the custom functions to choose a focus point that's on the eyes instead of focus/recompose.

Try different f-stops, too, because most lenses are sharpest about 2-3X (f-stops) stopped down from wide open. After that, diffraction will start to degrade the image as you get up toward f/16.
Read this: -=What to do if you suspect a focus problem=-
And use this target: Focus Testing

Sure, there could be movement from the subject.
Because the 6D only has the 1 cross type focus (center) I'm worried that the focus will miss (be less sharp) if using a different focus point.
I have been conscious of shooting with a higher f-stop for a more favorable result. I rarely shoot wide open anymore..
The tripod pivot point may be the main issue, Since it pivots under the body and not at the lens plane.. The geometry involved will actually change the distance, obviously a higher f-stop would fix this. I am using flash so I can get away with that..

One thing you could try, as you're on a tripod, is use Live View and manual focus. With the 5DM3, you go into Live View, move your magnifying frame to the face, magnify to 10x, and focus. Then shoot. While the 6D may be different, it should be similar.

EightEleven wrote in post #18050279
Because the 6D only has the 1 cross type focus (center) I'm worried that the focus will miss (be less sharp) if using a different focus point.

Test that theory.

That, too.

You're shooting portraits, not sport or other action shots. You really shouldn't need to be using the centre point and recomposing. I am pretty sure the outer points should be able to cope with focusing on an eye that isn't moving about.

Focus-recompose is subject to the angular change of center of field. Sometimes, the magnitude might be sufficiently compensated by DOF, but sometimes not. Here is a table, and (assuming 20/20 vision of the viewer) all of the yellow fields (columns C and K) indicate angular change, at the focus distance, is NOT sufficiently compensated by DOF, thereby inducing 'out of focus' results.

Thanks, Wilt!

Oh my.. Thanks for that Wilt!
The live view does the aforementioned process. I will give these points a go!
In other news, I have designed something that will help work thru this.
Thanks for the support

EightEleven wrote in post #18050928
Oh my.. Thanks for that Wilt!
The live view does the aforementioned process. I will give these points a go!
In other news, I have designed something that will help work thru this.
Thanks for the support

One has to keep in mind that DOF assessment is very dependent upon the SIZE of the detail which is being assessed for focus...the standard DOF calculation assumes an 8x10" print being viewed from about 12" distance. So when you look at a LiveView image on a dinky LCD on the back of your camera, you need to really examine the image magnified on the LCD, not full frame but at 10x.

Even then, when I focus my 75mm f/2.8 lens on a test chart at 10' and shift by 1/2 the frame width (16 degrees, half of 32 degree frame) I honestly cannot tell my target fell outside the DOF zone by 1", per the chart! If I fine tune focus on the LCD, I do not notice a net improvement of sharpness on the LCD with my test chart subhect at the very edge of the frame.

I'm no mathematician, but I would think the chances of a non-center cross-type focus point missing focus would be less than using the center cross-type focus point and recomposing.

Mr_ipsum wrote in post #18059528
I'm no mathematician, but I would think the chances of a non-center cross-type focus point missing focus would be less than using the center cross-type focus point and recomposing.

But in action scenarios, having to A. first choose the AF point, then focus and then shoot is slower than B. using center AF point, focus and recompose and shoot. Sometimes there simply is insufficient time to choose the best AF point.

Wilt's chart is cool, and illustrates well the biggest issue with recomposing, which is that the angular change of the camera of course tilts the focal plane. It's possible to focus on the subject's eye with your camera level, then tilt the camera when recomposing such that the plane of focus (which is parallel to the plane of the sensor) now passes through the back of the subject's head and in front of their feet. Recompose is always going to tilt the focal plane, but whether or not it results in a focus miss depends on the severity of the recompose, and the depth of field (as determined by aperture, subject to camera distance, etc.), which is what that chart is putting theoretical (ideal) numbers to.

Dan's advice of not needing to recompose is true for some cameras. When I shoot with the 5DSR, I use the cross-type point nearest my subject's eye and minimize recomposing. However, with the 6D, I get significantly higher keeper rates if I use the center point and recompose, even stopped down to f/5.6-f/11. This is undoubtedly partly due to the 6D's outer points not being as precise or sensitive as the center point. Just how well the outer AF points also depends on things like the lighting, contrast of the subject, and characteristics of the lens. I've found that both the 85L and 50 STM get very high focus miss rates when using the 6D's outer points. I have theorized, but not scientifically tested, the possibility that the results are especially bad with these lenses because they are soft at the edges wide open. The camera focuses with the lens wide open, of course, and the outermost AF sensors are effectively "looking" through a part of the lens where things are not sharply resolved. I can't help but think that this must affect the ability to achieve critical focus with the outer points at least a little bit.

Wilt wrote in post #18059554
But in action scenarios, having to A. first choose the AF point, then focus and then shoot is slower than B. using center AF point, focus and recompose and shoot. Sometimes there simply is insufficient time to choose the best AF point.

But this isn't an action scenario. The OP is shooting portraits in a home studio.

Dan Marchant wrote in post #18060029
But this isn't an action scenario. The OP is shooting portraits in a home studio.

No argument on that point. I was merely stating the reality that all shooting scenarios are not so static as to make Live View focus and/or AF point selection a practical solution to focus-recompose error.