Focus-Recompose -- WTF
kevingeary
Registered Users Posts: 194 Major grins
Ok, so while testing out different focusing techniques today, I came across a very weird situation.
On the Canon 7D, there's a feature that displays the focal point when reviewing the image after it's taken. It shows you where the focal point was on the image.
I just turned this on for the first time today.
When I did focus-recompose, the focal point indicator was NEVER on the point where I focused. It was always at the spot AFTER I recomposed.
I thought focus-recompose was supposed to lock focus on the initial point. So why is my camera insisting that I focused somewhere that I didn't???
I was fully expecting the focal point indicator to show up where I initially focused before recomposing and it was the opposite. I was baffled by this. Any insight?
On the Canon 7D, there's a feature that displays the focal point when reviewing the image after it's taken. It shows you where the focal point was on the image.
I just turned this on for the first time today.
When I did focus-recompose, the focal point indicator was NEVER on the point where I focused. It was always at the spot AFTER I recomposed.
I thought focus-recompose was supposed to lock focus on the initial point. So why is my camera insisting that I focused somewhere that I didn't???
I was fully expecting the focal point indicator to show up where I initially focused before recomposing and it was the opposite. I was baffled by this. Any insight?
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D3s, D500, D5300, and way more glass than the wife knows about.
The camera holds the focus exactly as it was acquired it before you move it to recompose. So if you focused on eyes and then moved the camera, the focus point-to-subject distance will no longer *actually* be on the eyes (even though that's where you wanted it); the camera isn't reading subject matter, but actual distance to where the AF was acquired. This is why when shooting at shallow DOF it's really important to move the AF points manually so that the camera stays in the same position during and after AF acquisition and thus the focus doesn't get mistakenly go somewhere you don't want it.
ETA: Btw, this becomes even more critical at longer focal lengths - where DOF is shallower at any given aperture - so something to consider as you move to more tele lenses.
WIth the 7d's many AF points, it's extremely easy to frame in camera even at shallow DOF since you just move the AF point around with your thumb to where you need it and thus don't have to recompose (I have the AF points linked to the joystick and the thumbwheel); takes a little time to master it if you're not used to it, but it's very easy and comfortable once you become accustomed to shooting like that. I very seldom focus+recomp; I'll sometimes shoot loose to give myself more cropping/comp options, but that's more a choice than a necessity.
When you lock focus, then recompose, how do you expect the camera to know you've moved anything?
As to focus - recompose:
I fully understand that I'm the oddball here. I have shot thousands and thousands of focus-recompose images, close-up, far off, short lenses to teles, closed down and wide open apertures. I have NEVER had an issue with my images not being sharp where I originally focused!!! (with a good, consistent focusing lens)
When others jump in here and say that's not so, well, it might not be for them, but it has never been an issue for me. I focus-recompose most every shot to some degree, and I'll challenge anyone to find an out-of-focus image of mine.
I traveled half-way across the US to work/learn under a great portrait photographer. He always focus-recomposed
Anyway, just another viewpoint... YMMV
Right, but when I shoot loose, the focus problem we're discussing is even worse.
Do you shoot wide open?
If you are close to your subject with a very thin depth of field the odds of having your original spot still in focus after you move your camera decrease.
People who shoot at f4+ have much less problem with losing focus when recomposing than people shooting at f1.4. Distance from your subject is a major part of the equation.
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IMO, focus & recompose is a legacy of early autofocus camera technology. Most of you are probably too young to remember when there was no such thing as autofocus. I started out with Leica III split-image rangefinders. Focus and recompose was all you had. Early autofocus SLRs were pretty much the same thing. A single focus area in the middle of the viewfinder.
Focus & recompose is (for me) an emergency technique that I only use when I don't have an extra moment to switch to another of my 51 focus points. Sure, it's good to know how to do it, but for me it's not a preferred tactic.
Natural selection is responsible for every living thing that exists.
D3s, D500, D5300, and way more glass than the wife knows about.
I shoot wide open a high percentage of the time, but that's a relative question/statement depending on the lens in use.
Do I shoot f/4 on my f/4 lens = yes
Do I shoot f/2.8 on my f/2.8 lens = yes
Do I shoot f/2 on my f/2 lens = yes
Do I shoot f/1.4 on my f/1.4 lens = yes
Do I shoot f/1.8 on my f/1.8 lens = yes
Do I shoot wide open ALL of the time = no
It just depends on what I'm after.
Also as zoomer pointed out, it's all interlaced between your lens length, subject to camera distance and aperture, full frame or crop.
My point being; for me, focus-recompose does not pose any problems, if it does for others, well, that's out of my control... and I would suggest that they stay away from the technique.
You've got to learn what works for you
As you'd know, when shooting portraits most of the time you'll be focusing somewhere on the subjects face, typically the eyes, then recomposing and keeping the camera close to same focal plane that you focused on. Typically portraits are at a mid-range opening with a reasonabe DOF, so focus-recompose as a technique will work OK in most situations, even more so in a studio setting where the distance bewteen photographer and subject remains pretty much constant between focussing and shooting.
Adding to the conversation in general ...........
You should try focus-recompose using Medium Format gear at a wide aperture - you'll definitely get out of focus shots unless the subject isn't exactly on the same focal plane as the original focus point!
With the larger distance between optics and focal plane, the DOF using MF gear is much smaller than FF or APS-C format DSLRs and with the increase in sharpness and resolution you really notice it when you've missed the focus, even when you're the tiniest bit out.
That's part of the reason Hasselblad H4 series has the True Focus function. The camera has bulit in accelerometers measuring camera movement that allow you to focus, recompose and then the camera will adjust the focus so the the original focal point remains pin-sharp. It's the only system that I know of that has this function.
After first reading about, then trying it out on a hired H4D-40, I was left wondering why others weren't doing the same thing, but the 'Blad "needs" this as it only has centre point focus. Now I reckon things will go more like the smart phones (and some compacts I think) where you compose first, then easily select anywhere on the image as the focus point.
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I think there are actually three different points under discussion here:
1. Understanding how focus and recompose can cause the subject-to-original-focus-point distance to change after focus acquisition; this can render the resulting image soft, especially when shooting at shallow depths of field (whether that shallowness is created by wide aperture, close subject distance, telephoto lens, or any combination of them all).
2. Whether or not kevingeary's soft images are due to a hardware problem or not. Kevin, if you take well-lit shot using the center focus point where you actually want the focus to be and DON'T recompose.... is the image sharp where you expected when you review it?
3. "You've got to learn what works for you
True dat. Randy, I'd say you are in the minority of being able to f+recomp reliably at shallow DOFs, and I'm going to guess that you have extremely good hand-eye coordination/spatial awareness, and thus are successfully able to keep your camera in a close-enough orientation to the original focus point even once you recompose. Speaking for myself, I can't do that reliably enough at shallow depths of field (it's fine if I'm far enough away or stopped down a little bit, of course). I've noticed that the folks who are good at these kinds of tricky handholding techniques (also handholding at low SS) often have steady hands in other areas (eg surgeons, marksmen etc). Is that maybe true of you too?
I'm actually philosophically opposed to focus-recompose on the 7D because all those precise autofocus points are part of the reason I spent the extra cash on that camera versus a Rebel. I would hate to waste that very advanced system by only using the center point and lowering the accuracy through recompose parallax error. Yes, I'll do it when the light is low enough because then I need the extra-precise center point...otherwise I will always pick the closest one.
By the way, if it wasn't posted already, here's a diagram of focus-recompose error:
http://visual-vacations.com/Photography/focus-recompose_sucks.htm
Natural selection is responsible for every living thing that exists.
D3s, D500, D5300, and way more glass than the wife knows about.
Do you still recompose a little bit even though you're manually selecting focus points? I've found that even with 19, I can't always get the composition I want without a little recomposition.
Not always mutually exclusive, although if I need to I will make those kinds of tweaks with cropping rather than risk blowing the focus point at a shallow depth of field (once it's stopped down, it doesn't matter so much since the DOF is greater). In this case, I was balancing a desire for sharp eyes, with trying to keep the slats of the deck compressed (so light didn't peek through) and blurring out the slats behind her. There wasn't enough length of fence in front or behind her to shoot right down it without a lot of BG distractions, so positioning was actually kind of critical; in that context, I decided it was better to have a bit of "excess" that I would trim in post than trying to frame it perfectly in camera and not have the desired area accurately focused.
Uncropped
ZoomBrowser showing AF point:
Here's a link to the X3 of the SOOC shot - you can see her eyes are absolutely sharp. This was the 135L and exif says f2.5-ISO100-1/500. I was probably ~10-12ft away from her so - for a lens of that focal length at that aperture - quite close, meaning shallow depth of field. Note how her eyes are sharp, but her bangs aren't. For the record, there were more than a few shots where the AF missed and caught her bangs by mistake, leaving her eyes out of focus.
One possible version of the final shot (still tweaking it - may have boosted the contrast/colour too much, but the crop/focus point etc is still relevant to this discussion!
Yes, I think a little bit is OK, also depending on the aperture, since if you have it set for more DOF, you'll have more safety margin. I might change my mind when I buy lenses with narrower DOF than I have now.
I'm interested in Divamum's "don't recompose but leave room for cropping" method...might try that!
I like to frame in-camera when I can but found that too often I made a rod for my own back by not leaving enough leeway for 8x10s (which is where performer headshots need to wind up) and so started consciously making myself shoot a little wider. Given the pixel-density of the 7d, I can't see any reason NOT to leave myself a little room for multiple options when I can.
One thing to ensure you do is when you focus and recompose, make sure you recompose while HOLDING the shutter button halfway. When you initially focus, DO NOT let go of the shutter button. The red square in the view finder only shows what focal point the camera used to focus, or which one you asked the camera to use.
Each time you press the shutter button, it will refocus using that focal point. If you do not want the camera to refocus, keep holding the shutter button halfway down as you recompose.
Actually, in practice I find it works the other way around: I have much more trouble with parallax with the 35/1.4 than I with the 135/2. The reason for the difference is the field of view. A 35mm lens (on a full frame body) has a field of view of 54 degrees (wide direction) so if I focus and recompose to put the focus at the edge of the frame I am rotating the camera by 27 degrees. If my subject is 6 feet away that is a change of focus of almost 9 inches. If I do the same with the 135/2 I am only rotating the camera by 7.5 degrees and the resulting change of focus is only 0.62 inches.
When shooting at f/1.4, a 9 inch change if focus distance is really unrecoverable and, in many circumstances, my only option with the 35/1.4 is to focus manually. However with the 135/2, where I typically need 1/2 inch or less of correction, I can finesse the focus just a tad by leaning forward as I turn the camera and end up dead on most of the time.
It is definitely worth going through the geometry on your favorite fast lenses to figure out when parallax will really be an issue. For the way I shoot, I often have to worry about the 35/1.4 and sometimes about the 50/1.4 but only in extreme circumstances is the error with 85/1.8, 135/2 or 200/2.8 worth worrying about. Even then, with just a little technique the tele lenses are manageable across their entire field of view.
Or just do your focusing using the AF-ON button and remove it from the shutter release. Although it took a bit of an adjustment period, once I got used to separating focus and shutter, I quickly learned why people love the method.
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Bingo!
+1 for AF-ON.
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Interesting. Some of the most trouble I ever had with this was when I first got the 200 2.8 - in fact, that's the lens that really *made* me use individual focus points, and I've pretty much stuck with it ever since. YMMV...
This is interesting. On a subject 50 feet away, your DOF @ 1.4 / 35mm is over 70 feet on a FF body. That seems like plenty of wiggle room, but I guess it depends on what you initially focus on.
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When shooting portraits, one is seldom 50ft away! SPeaking for myself, I'm usually 5-15ft away, depending on lens.
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Natural selection is responsible for every living thing that exists.
D3s, D500, D5300, and way more glass than the wife knows about.