40D + Recomposing the shot + displayed focus point: fairy tale?

As the 40D Manual tells us on page 117, when the AF Point Display is set to Enable, the AF Point which achieved focus will be displayed.
That's correct, everybody can verify it.

We also know how to achieve focus lock and how to recompose the shot. And as it says on page 48, the focus will be locked. And locked is locked, is it not?

Seems not to be the case.

I had thought the achieved focus would remain at the same position when keeping the shutter button pressed halfway. But it seems I was wrong: after recomposing and pressing the shutter button now completely, the achieved and displayed focus point had shifted its original position and had put itself to the shifted position.

I don't see the logic of it. What am I missing here?

Are you set for one-shot AF? p. 76

chisquared said:

Are you set for one-shot AF? p. 76

Click to expand...

Yes, I am. And as it says on that page, while you hold down the shutter button halfway, the focus will be locked, and you can recompose the shot if desired.

Which brings us back to the same question - as far as I understand, at least...
But perhaps I am missing something...

Make sure you have focus lock enabled and make sure you have only a single focus point selected.

Going to see if I understand what you are saying:

Let's say I focus lock with the center focus point on a subject's right eye. Now I recompose the shot so that the center focus point is actually on the subjects left shoulder. (Not sure how this picture would look but it's just an example..) LOL

When I take the picture and review the image on the back of the camera I would expect to see that the center focus point shows that it was the one used to achieve focus. (It will be red while the others are black) Even though it is now on the subject's left shoulder...It was the focus point I used to achieve focus...

Is this not what you would expect?

Now take this example one more step and open the image up in Photoshop and the subject's right eye will be sharper and more in focus than the subject's shoulder... because I focused locked on the eye and then recomposed.

The camera knows you focused locked... it just doesn't know what you did after that.... also

The focus points know you focused locked... they just don't know what you did after that.

John
--

Feel free to use any of these additional letters to correct the spelling of words found in the above post: a-e-t-n-d-i-o-s-m-l-u-y-h-c

Anandaji,

Are you stating that after achieving focus lock by half pressing the shutter the camera does not maintain focus on the area originally selected, resulting in that area not being in focus in the captured image? This would be an anomaly. Or are you stating that when you view the image on the LCD with focus point displayed, the displayed focus point is not on the area where it was locked? This of course would be expected since the camera has no way of “knowing” that the field of view has shifted. As long as the focus is locked and maintained on the original area selected your camera is working normally.

John has it 100%.

gL

John, Henry, Guy,

Thanks for shedding some light into my darkness.

Pity, though, this shifting of the displayed focus point can happen without the camera knowing it. For it takes away some of the information 'at first sight' and it sort of fools ZoomBrowser possibility of showing that displayed auto focus point.

Kind regards,

Ananda

Maybe a pity... but maybe not really..

Last night when I responded to your question, I did a test to see if I was giving you accurate information. (Sometimes what you think you know is not always, what is really true). Anyways.... I focused locked and then recomposed and sure enough it worked like I described.

However, the actual subject that was in focus was not covered by ANY focus points when I recomposed.

I would rather the camera tell me which focus point I used to focus lock rather than trying to make a "best guess" of which one is closest to the area that I locked on to after recomposing.

Without the ability for this "shifting of the focus point" to occur.. we could never focus lock and recompose. I guess it is just the nature of the beast.

John

--

Feel free to use any of these additional letters to correct the spelling of words found in the above post: a-e-t-n-d-i-o-s-m-l-u-y-h-c

One way to get around this is to set the custom function so that you can select the focus point on the fly using the multi controller then focus and click without having to recompose. This way the correct focus point will always lighted when the picture is displayed later.

This method will not work 100% because in some extreme cases the focus point will be out of range then you will still need to recompose.

One added suggestion is to set the custome function so that you can focus separately using the AF-ON button then only use the shutter release button for metering and taking the picture. This way you don't have to use the press half way method to lock the focus.

You must remember that the camera focuses in a plane. This means that if you focus and recompose the original focus point may not be in focus, especially if you move quite a bit and/or are close to the subject. This is why Canon says in the manual to not use this technique closer than 15 feet.

The area of focus is essentially a tangent to the point of focus on a circle around the camera at a distance of the focus length. If you move from one point to another on this circle (focus and recompose), you move to a different tangent and they will not intersect.

See subject.

Did not use anything else than what you mentioned.
And how does your chapter continue now?

No idea what Greg is talking about and Peter is off the mark as well (as far as why the focus point that is shown as being the one that was used for focus lock) .

Anandaji,

As we already discussed the issue is that the camera does not know where or how much you have moved the camera when you focus locked & recomposed.

That is why the initial focus point you locked with is the one that is shown in red when you look at the lcd on the back of your camera (or on some photo editing programs that offer this option).

Again I would rather have it this way then have the camera try to guess which focus point is closest to the original spot that I focused locked onto. Because that is all it would be... a guess.

John
--

Feel free to use any of these additional letters to correct the spelling of words found in the above post: a-e-t-n-d-i-o-s-m-l-u-y-h-c

John

Thanks for your input. Wonderful to find someone who wants to make things clear for other people, and does not easily give up.

balloonchasers said:

As we already discussed the issue is that the camera does not know
where or how much you have moved the camera when you focus locked &
recomposed.

Click to expand...

You did explain that, sure, and I think I understood. Perhaps Greg has not read the other messages.

balloonchasers said:

That is why the initial focus point you locked with is the one that
is shown in red when you look at the lcd on the back of your camera
(or on some photo editing programs that offer this option).

Click to expand...

Yes, the initial one - i.d. NOT RECOMPOSED - and which is shown in red on the lcd. But once recomposed, it is no longer the initial one, is it? And so, when you send someone that recomposed photo, and (s)he is eager to see the focus point in her/his ZoomBrowser, (s)he will be misled by that recomposed focus point.

I can understand I am asking something which is difficult to achieve for a camera.

I tried the same thing with my 350D. I know it does not register it on the lcd, but it does in ZB. And here again, we are misled by a recomposed shot.

Now, I won't miss any sleep because of it, but I was just curious to find out what was going on. I was in the opinion that locked meant locked, i.e. it remains where it is once taken. You explained it in a comprehensible way: the camera does not know what happened next.

Or am I walking in a dense fog again? Don't be surprised if I do. Growing old, you know, but still thinking one is young to learn and to enjoy!

Kind regards,

Ananda

Anandaji said:

But once recomposed, it is no longer the initial one, is it?

Click to expand...

Hmm, yes, it is. Recomposing with the shutter button depressed means no refocusing will be performed by the camera. Therefore, by definition the initial focus point used to achieve the focus is still the initial one.

The original poster says that "focus lock is focus lock"

Not so if you focus and recompose because of the plane of focus. I believe (perhaps incorrectly) that the poster assumed the point he originally focused on would still be in focus after focusing and recomposing and as mentioned this is not true.

You say "the subject's right eye will be sharper and more in focus than the subject's shoulder... because I focused locked on the eye and then recomposed."

This may not be correct, if you focus and recompose the right eye is no longer in the plan of focus. This is common when photogrphing couples at weddings - there's a gap between them so you focus and recompose on one of their eyes - they can very easily lead to soft results.

Here is an excellent article that explains more (first link in Google search for "focus and recompose")

http://visual-vacations.com/Photography/focus-recompose_sucks.htm

--Peter

Peter

Thanks for your input. And for your patience. Do you still have some more? For I'm getting the impression some people do not really get what I am trying to ask.
Here goes...

Peter Rowe said:

The original poster says that "focus lock is focus lock".

Click to expand...

Yes, and by that I meant that I had expected that the initially in red displayed focus point would not have shifted after recomposing. If I park my car in the correct way, my car is supposed to remain on one and the same spot.

Peter Rowe said:

I believe (perhaps incorrectly) that the poster assumed the point he
originally focused on would still be in focus after focusing and
recomposing

Click to expand...

Something like that, yes. And as proof of the pudding, I had expected the in red displayed focus point to remain in one and the same area. For how else do I have to understand what is being said in the 350D manual on page 71: "The exposure setting and focus will be locked as long as the shutter button is pressed halfway. You can then recompose the shot while retaining the exposure setting and point of focus." While using the 350D I had always thought I was using one and the same focus point [ I mean: sharpest area ], even when recomposing. But now that I can use the 40D, I notice that after recompsosing the in red displayed focus point is no longer on the same spot. Hence my question.

This evening I tried once again with my 350D and verified the in red displayed focus point in ZoomBrowser. Imagine my total confusion: it was not in the area I had initially focused on. All those months ZB has shown me lies... ???

Peter Rowe said:

You say "the subject's right eye will be sharper and more in focus
than the subject's shoulder... because I focused locked on the eye
and then recomposed."

Click to expand...

Yes, that was what John said, and that is, I think, more or less what the 350D Manual teaches us. But afterwards, the visible shifted red point seems to contradict one thing and another...

Peter Rowe said:

Here is an excellent article that explains more (first link in Google
search for "focus and recompose")

Click to expand...

Interesting article, but I'm sorry and a bit ashamed to say I am confused one more time. After all, I took it for granted that the focus point would be fixed, locked [so, that area would remain the sharpest ], and would still be the same after recomposing [ so not shift to another area ]. Why else would I need to keep the shutter button pressed halfway? Why talk about locking if it does not do what it is supposed to do? That's a logic I fail to see...

Looking forward to your answer tomorrow, for it is nearly midnight over here.

Oh, before I forget, I can understand if you give up removing the darkness in my mind...

Kind regards,

Ananda

One last try....

What Anandaji is asking about is the red light that you see in the LCD that shows which focus point was selected during focus lock which has nothing to do with the focus plane at all.

In my example Anandaji would like to see that as you move the camera it still shows the area that was originaly used for focus lock highlighted by the new focus point that is now closest to that spot... That way you could always look back at your image at a later date and see the place on the subject that the focus locked on to.

As I explained this is not something that the camera can do because it has no idea of how much you moved the camera (it can't say "hey he locked onto the subject's eye so no matter how much he moves the camera I will always show that the eye was where focus lock was implemented). Heck with enough movement the subject's eye might not even be in the frame!

As far as the possible error induced by Focus Lock & Recompose I thought I said something about this being up for debate.. if not I do now... but this has nothing to do with the focus point being highlighted in red on the LCD of the camera.

Clearer than mud now? ;-)

John
--

Feel free to use any of these additional letters to correct the spelling of words found in the above post: a-e-t-n-d-i-o-s-m-l-u-y-h-c

Anandaji,

If what I just wrote does not help or is completly off the mark. Let me end by saying this...

The red highlighted focus point you see in the LCD on the back of your camera when reviewing a shot you took.... only shows you which focus point was used to achieve focus...

If you did not move the camera after getting focus lock this area should be in focus... if you moved the camera (as in recomposing) that area under the red highlighted focus point may not be in focus... (for reasons I described above... )

John

--

Feel free to use any of these additional letters to correct the spelling of words found in the above post: a-e-t-n-d-i-o-s-m-l-u-y-h-c