Focus-Recompose WTF - DPChallenge Forums

Canon EF 17-40mm f/4.0L USM

04/19/2011 08:47:39 PM · #1

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?

kawesttex

Apple iPhone 11 Pro

04/19/2011 08:50:03 PM · #2

When you recompose the focus point should be locked where you put it. Is it staying on the focus point you started with or moving somewhere else?

eta: Remember that the camera is not smart enough to know where you wanted the focus, only where you told it to focus. If you went back to the old Canon system of eye focus then your problem would apply to your delimma.

Message edited by author 2011-04-19 20:52:03.

cpanaioti

Canon EOS-40D

Canon EF 70-300mm f/4.5-5.6 DO IS USM

04/19/2011 08:57:09 PM · #3

The focus points are at a fixed location within the viewfinder. What you're being shown is the focus point that was chosen. If you recomposed, the position of that point will be different from the position you were at when you locked focus.

Example: if you used the centre point to lock focus but then recomposed so that the subject wasn't central to the composition the chosen focus point is still the centre point, not the one that is now over the subject.

04/19/2011 08:59:21 PM · #4

Originally posted by kawesttex:

It's moving to where the focal point ends up after I recompose. That's why I was baffled.

If it's truly supposed to mark where I focused, then something is horribly wrong. If it's just supposed to indicate where the focal point moved to, I don't see a point in having the feature. I want to know where focus was LOCKED. Not where the point came to be after recomposition.

So I half-press the shutter over the eye, recompose, and the focus indicator indicates focus on the chin in the image review. That's a big WTF to me.

Canon EF-S 18-55mm f/3.5-5.6 IS

04/19/2011 09:00:26 PM · #5

Originally posted by cpanaioti:

Then the feature is useless because it doesn't indicate which point was used. It indicates only where the point was when the shutter was clicked. It doesn't tell you if it was the center point or an outside point. So what's the point (no pun intended)?

EL-ROI

Canon EOS-450D Rebel XSi

04/19/2011 09:00:37 PM · #6

If I am understanding you correctly you chose an AF point, used it to autofocus, locked your focus on the subject, then recomposed the shot keeping the focus locked, then took the shot. When you view the AF point in your file, it reveals which of the AF indicators you used, not the actual spot on the subject you focused.

Make sense??

The point of the feature is to aid full auto users and show them which auto focus point is being selected for them. You are smarter than that and don't really need it.

Message edited by author 2011-04-19 21:03:48.

cpanaioti

Canon EOS-40D

Canon EF 70-300mm f/4.5-5.6 DO IS USM

04/19/2011 09:01:05 PM · #7

There aren't infinite focus points only the ones you can select. What do you expect to happen if the subject you focused on is no longer under any of them after you recompose?

Message edited by author 2011-04-19 21:01:31.

04/19/2011 09:09:40 PM · #8

Originally posted by cpanaioti:

There aren't infinite focus points only the ones you can select. What do you expect to happen if the subject you focused on is no longer under any of them after you recompose?

Yeah, why would I want to know where I locked focus? {/sarcasm]

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

04/19/2011 09:11:50 PM · #9

Originally posted by EL-ROI:

It doesn't really say which focus point was used. It just shows where A focus point landed. It doesn't show you which point out of the grid was used. So I don't see the point.

BrennanOB

Canon EOS-1D Mark II

04/19/2011 09:18:17 PM · #10

Try locking in the focus point manually to see if the are being stored correctly. Pick a target and rotate through the focus points as you select them. I've never heard of such slippage, but given an infinite number of monkeys....

Are you half splat recomposing with a new body? If that the case, it would be the simplest answer. Occam's razor says you aren't riding the splat hard enough as you re-compose.

cpanaioti

Canon EOS-40D

Canon EF 70-300mm f/4.5-5.6 DO IS USM

04/19/2011 09:19:55 PM · #11

The manual says it indicates which focus point achieved focus. pg 163 This would be the one you used to lock focus. If you recompose, all bets are off.

spiritualspatula

Panasonic LUMIX DMC-LX100

Nikon AF-S NIKKOR 24-70mm f/2.8G ED

04/19/2011 09:51:48 PM · #12

Perhaps I'm not understanding the issue... but are you expecting the camera to interpret the scene as it changes when you recompose and display a focus point that moves relative to your framing?
If you're having such frustrations, isn't there some way you can just select your focus point manually within your frame? I'm not familiar with Canon AF but that's how I've always shot- manually selecting one of the 51 individual focus points. It's surprisingly fast and I nail focus much more, plus recomposing always frustrated me...

Canon RF 24-70mm f/2.8 L IS

04/19/2011 11:18:41 PM · #13

I'm wondering why the feature exists relative to what I wanted from it.

If you focus on the eye, what's the feature good for if it doesn't show you that you focused on the eye? That's the question. I get that it's possible I overlooked the limitations of camera technology. Barring that...what use does it have since it didn't perform the function I assumed it would.

kirbic

Canon EOS R5

04/19/2011 11:25:27 PM · #14

Originally posted by kgeary:

Focus/recompose is not a camera feature, it's a user feature. If you set the center focus point, focus on the eye, and with focus locked, recompose and fire the shutter, the camera *should* record that the center point was used to focus, and yes, it will be away from the eye, since you recomposed. The camera cannot know you recomposed, you are effectively fooling it by doing so.
Now, focus/recompose is still a valuable technique, letting you set and use one focus point, recomposing as desired after focusing. It does have drawbacks, one of which is the possibility that you will sway toward or away from the subject during recomposing, introducing focus error.

chromeydome

Nikon D7000

Nikon AF-S NIKKOR 24-70mm f/2.8G ED

04/19/2011 11:31:07 PM · #15

If you focus on the eye by placing a focus point on the eye, lock focus and then move the camera to recompose, the camera has no idea what you are pointing at any longer. It is, as you requested, locking the focus at the distance you focused on with that particular point. You could spin 180 degrees and take a picture and the camera won't know that.

So, yes, the feature is not going to read your mind. If you move the camera after focus locking, that point is not telling you much. The feature works as designed/intended. You are using in a different way. Lock focus means Lock focus. How is the camera supposed to read your recomposition? Even if it could do what you want, it couldn't, for example, highlight the focus point used if you recomposed to where the subjects eye was no longer under a focus point.

The use it has is if you do not recompose after focus lock, or if you are in a mode where it is doing an auto tracking thing, automatically selecting focus points for you--you can see which points were selected. Once you lock focus, the focal distance is, well, locked, right? You point the camera somewhere else while locked, it is not refocusing, because it is locked at the distance you chose. It is no longer locked on the part of the subject you focused on because you moved the camera. Not sure why you think it can keep track of the eye or tree branch or whatever you focused on AFTER you lock the focus distance and move the camera 1, 2, 10, 20, etc, degrees in any direction.....