Focus->recompose NOT a perfect approach

Not very long ago I finally realized why I need more than 3 focus points, or at least 3 points more separated than today on Olympus dSLRs.

The focal plane is literally a PLANE, not a sphere! When you focus at e.g. 3 meters you have NOT focused on everything that is 3 meters away from the camera. You have put a plane in focus, a plane that has its closest point to the camera at the intersection with the cameras optical axis. All other points in the focal plane are further away from the camera.

When you recompose after focusing, the focal plane will turn and end up behind the subject that focus was locked on.

An example: If you focus on the eyes of a model 3 meters away and recompose by tilting the camera down by 0.5 meter (on the subject), focus will end upp 4.1 cm behind the eyes. This is a lot if you work with short depths of focus.

The solution is of course to use an auto focus point that lets you focus and compose at the same time. That is why I really hope Olympus will deliver more than 3 auto focus points in the E-1 successor.

Andreas

but the Focus and Recompose method has worked, and worked very well, for me for more than 40 years of shooting.

I do understand the desire, for some, of 45 Focus points but, at some time, all of those Focus points become counter productive.

I'm, admittedly, old school, so I learn to use the capabilities of my camera in addition to learning its limitations and have, miraculously, been able to work around all of the limitations.
Thanks for your thoughts.
--
Troll Whisperer

Dead right Bill, at least for me. The only time I'd like more points available is working close on a tripod. But then again I never rely on AF in those situations so it becomes a moot point.

At normal working distances and normal apertures the error introduced by recomposing is completely trivial in any case.

--
John Bean [GMT - is there any other?]

PAW 2007 Week 10:
http://waterfoot.smugmug.com/gallery/2321711/1/134422693/Large



Index page: http://waterfoot.smugmug.com
Latest walkabout (4 April 2006): http://waterfoot.smugmug.com/gallery/1348582

Although I have no xx year experience, focus-recompose worked for me all the time for the last 5 months with my E-500. I shot 2 low light wedding parties so far and I'm completely satisfied with the results.

Recently I got photos from a fashion model shoot out using Canon 30D by a full time pro. Around 60% of the photos were simply out of focus. Likely because 9 point AF system decided for the photographer.

If you're doing a focus-recompose, then you must be shooting a static scene. Observe the image in the LCD and re-shoot if needed.

--
http://www.flickr.com/photos/foxius/

In another life, at another time, I had a Canon A2 and in all respects, it was a great camera. It featured 7 focus ponts yet I defaulted it to the Center point only.

Prior to defaulting it, I had many OOF images and film was a lot more expensive than capturing an image to a CF card.

The A2E, which I didn't own, allegedly, captured the focus point by eye movement. Interestingly, this technology no longer is avaialble.

--
Troll Whisperer

I have a Pentax DS, which has... well more than three AF points, I can't remember. Like the E-1 I have it set to use the centre point only unless I make the effort to change it.

One thing I never do is let the camera pick the AF point itself. How on earth can the camera know better than I do what I want in focus? Madness.

I mostly disregard almost all the bells-and-whistles that some seem to regard as necessities on a camera, I think it's an age thing. The E-1 is a digital dinosaur with few bells and whistles; it fits this user remarkably well

--
John Bean [GMT - is there any other?]

PAW 2007 Week 10:
http://waterfoot.smugmug.com/gallery/2321711/1/134422693/Large



Index page: http://waterfoot.smugmug.com
Latest walkabout (4 April 2006): http://waterfoot.smugmug.com/gallery/1348582

I agree that in most cases focus-recompose works very well. However, I just recently had the chance to borrow and test a ZD 50mm 2.0 Macro which I used for a couple of portraits of a good friend of mine. The shots were in an upright direction, taken from a close distance and I had to recompose quite a bit after the focus-lock on his eyes.

I ended up with shots that were quite often a bit back-focus. Thats why I started to suspect that the focus-recompose method could be a reason.

I'd guess that I'm from the same era as you.

There are "features" on my E-1 that I've never explored. I shoot in raw format, shutter priority and look at the menu only to change the time when necessary.

Additionally, I don't review the images (chimp) and rely on post processing for minor corrections.
--
Troll Whisperer

There are circumstances when manual focus might help. Your situation may have been one of those circumstances.

Your OP indicated, however, that the focus and recompose solution was useless. That supposition is completely incorrect.

There are also variables that you have not addressed. What lens? What was the f/stop? There are many factors to consider.

Using an 11-22 or an 8mm FE, an image at 3m will have an incredible focus area. If shooting with a longer lens, this may make a difference. If so, understand the limitations and adjust. It's really not too difficult.
-
Troll Whisperer

Similar experience here, I had an Ixus 500 with nine focus points and they were just a pain in the neck as you'd have to half-press several times to get it to lock on to the correct subject. It worked far better with just the centre point enabled.

With the Olympus cameras I find three is too much, if I leave it to choose it often chooses the wrong one so I've similarly ended up sticking with the centre point so I know what I'm getting. Apparently more focus points are better for high speed shooting but for me they just introduce a higher chance of mis-focusing.

John

Some lenses are flat field, like most macros, but the great majority of zooms keep the focus point over a nearly spherical surface, so the focus and recompose is an entirely acceptable approach.

On a tripod, multiple focus points can be useful, in order not to move the camera.

Best approach might be live view with 10x or more, where the actual focusing area can be checked.

I have had EOSes with heaps of focusing points, but I have always used the middle one only. Same with E-1. When neccessary I focus on one object, and then keep the focus for another object (that is not there yet) somewhere else at the same distance for the photo.
--
Raymond
http://home.online.no/~rwardena
http://www.volleyball.no/t3.asp?p=57227

Hi,

Olympus may be able to add an extra 5 or 6 focus points to their future SLRs. However, unless these focus points are completely accurate and reliable, they are useless.

I speak from my experience with the 20D, which although has nine points, I would not dare use any of them in any circumstance where I was relying on a proper lock. I have lost too many shots already when I relied on the outer points in single-shot mode, only to return to the PC and see that the shots are so far out of focus that they are for the bin.

In these cases, using the centre point and recomposing would have given a far higher chance of a usable photograph.

The same is somewhat true of the outer focus points on the E1, which in my opinion will regularly hunt on subjects which the centre point can lock onto instantly.

The only real solutions are 1) outer focus points which are as sensitive as the centre point, or 2) manual focus.

Opting for 2) has solved my problem most of the time.

David

Bootstrap said:

Your OP indicated, however, that the focus and recompose solution
was useless. That supposition is completely incorrect.

Click to expand...

The OP indicated/supposed nothing of the kind. The poster wrote that F&R was "not a perfect approach" and gave an example of a kind of situation in which it does not work well (portraiture at close range with wide apertures). What he wrote was essentially correct (as you mentioned in your first post in the thread).

For the original poster- here's a very old tip for getting better focus on the eyes when shooting models as you describe (i.e., using center point AF focusing, focusing on eyes, then tilting camera down a bit): focus on the tip of the nose instead. This way, once you tilt the camera down and consequently shift your focal plane back, your eyes will be sharp(er).

I do agree with the original poster- a much better solution is to have focal points you can use while already correctly framed. Manual focus is always an option, but it is not particularly satisfying using Oly's dSLR viewfinders to try to manually focus eyes in a full or half-body shot. At least the greater DOF available with 4/3rds helps cover up the problem a little. Still, more focus points and better viewfinders would be a welcome improvement for many.
--
Brian



Some monochromes:
http://mywebpages.comcast.net/spiritmist/SundayBoating/index.htm
Some more monochromes:
http://mywebpages.comcast.net/spiritmist/BWWebPage/index.htm
Some older images:
http://mywebpages.comcast.net/spiritmist/Brian_G_Digital_Image_Gallery/index.htm

'To quote out of context is the essence of the photographer's craft.' John Szarkowski, The Photographer's Eye

This is a repost from info I put in the pro forum a while back, it explains why focus recompose does not work. I have not done the calc for macro work, but if you changed all the dimentsions in feet to inches, you would end up with the same ratio of error.

Although I am not knowledgeable as most here, I would suspect that the reason focus and recompose when a subject is close does not work is based on a trigonometric relationship.

The numbers may not be entirely playsible but it will give you the idea

Eg: The subject is 10ft from you and fills a frame

about 6ft by 6ft. The sbject is located say 1ft from the top and right edge, you move the camera to compose (by rotating on the 3 axis, on a tripod for example), and return. Thus the center of the camera is focused using your subject, but recomposed to the center point is 2 ft lower and 2 ft to the left of the subject. The hypotenuse gives you 2.8ft from your subject on its own focal plane (h^2= 2^2+2^2). You can then use this distance, knowing you are 10ft for the subjects focal plane, and then finding the hypotenus again (h^2=2.8^2+10^2) you get a distance of 10.3ft to the subject you focused on but 10ft to the plane. So effectively, you are focused 0.3ft behing where you wanted to be.

At longer distances this would be rather negligible, but when you get as close as 5 ft with the same assumption, you then have a 0.7ft difference in where you focused, you can imagine the havoc this would cause for macro shooters.

If you don't use a shallow depth of field, then this really doesn't matter. Likewise if your lens is not very wide and does not give a huge field of view. But if your depth of field is only a few inches and given a camera auto focus is usually calibrated to provied 1/3 of the focus in front and 2/3 behind (pretty sure I read that somewhere) if you only had 0.9ft of focusing field, with the above example, you would effectively be out of focus.

Please keep in mind that this relationship only hold true if you keep the camera in relatively the same position and rotate it about the 3 axis to find your focus and recompose points. If you were to focus on the subject and then physically move the camera that 2.8ft as first described to recompose instead which would keep the focal planes aligned the whole time, you would not be introducing the 0.3ft error. But lets be honest, you're not going to be jumping about to focus and recompose and take photographs, taking a single shot you will be in one place and moving your amera slightly to compose and focus.

I hope this makes sense, and I may very well be wrong, but I have heard similar explanations before but they didn't seem to understand the underlying math. And most camera processes seem to make more sense when you understand the math.

--
Chris V

That sounds about right.

The SP500 I used would focus on the best bit of the frame to focus on, and that was rarely the bit of the frame I wanted to have in focus.

So after a little bit of trial and error with my E500, I picked the central spot and have stuck with it ever since. Very occasionally I use the left or right focus marks, usually when using a tripod where focus and recompose isn't entirely practical. But 9 times out of 10 I'm using focus and recompose.

It really does become second nature after a while, even if it is impractical for certain applications.
--
Cheers, Neil
http://dodger.photoblog.com/
http://www.flickr.com/photos/dodger421/

Chris Vervaeke said:

This is a repost from info I put in the pro forum a while back, it
explains why focus recompose does not work.

Click to expand...

Chris, I understand the principles you describe but...

You can't say it "explains why focus recompose does not work" because I have thousands of images to prove that it does work - because I know the principles you describe and how to use that knowledge to my advantage.

--
John Bean [GMT - is there any other?]

PAW 2007 Week 10:
http://waterfoot.smugmug.com/gallery/2321711/1/134422693/Large



Index page: http://waterfoot.smugmug.com
Latest walkabout (4 April 2006): http://waterfoot.smugmug.com/gallery/1348582

John Bean (UK) said:

Chris Vervaeke said:

This is a repost from info I put in the pro forum a while back, it
explains why focus recompose does not work.

Click to expand...

Chris, I understand the principles you describe but...

You can't say it "explains why focus recompose does not work"
because I have thousands of images to prove that it does work -
because I know the principles you describe and how to use that
knowledge to my advantage.

Click to expand...

Call it what you like, but the fact is that when you focus and recompose, your actual focal plane no longer contains the intended center of focus, and instead lies behind it. Whether that will matter in a given photo depends on a number of factors, including all of those that affect DoF, as well as how critical a viewer you are.

Using a technique to focus on something that guarantees your intended center of focus will lie in front of you focal plane is simply not the best approach, whether or not the focal plane difference is visible in any particular shot. There is often more than one way to accomplish the same task, but some approaches are just better than others.

I'd rather have critical focus where I want it, and not use DoF to cover up differences.

--
Brian



Some monochromes:
http://mywebpages.comcast.net/spiritmist/SundayBoating/index.htm
Some more monochromes:
http://mywebpages.comcast.net/spiritmist/BWWebPage/index.htm
Some older images:
http://mywebpages.comcast.net/spiritmist/Brian_G_Digital_Image_Gallery/index.htm

'To quote out of context is the essence of the photographer's craft.' John Szarkowski, The Photographer's Eye

everyone know about your special needs/criteria/requirments once again....

Brian G. said:

John Bean (UK) said:

Chris Vervaeke said:

This is a repost from info I put in the pro forum a while back, it
explains why focus recompose does not work.

Click to expand...

Chris, I understand the principles you describe but...

You can't say it "explains why focus recompose does not work"
because I have thousands of images to prove that it does work -
because I know the principles you describe and how to use that
knowledge to my advantage.

Click to expand...

Call it what you like, but the fact is that when you focus and
recompose, your actual focal plane no longer contains the intended
center of focus, and instead lies behind it. Whether that will
matter in a given photo depends on a number of factors, including
all of those that affect DoF, as well as how critical a viewer you
are.

Using a technique to focus on something that guarantees your
intended center of focus will lie in front of you focal plane is
simply not the best approach, whether or not the focal plane
difference is visible in any particular shot. There is often more
than one way to accomplish the same task, but some approaches are
just better than others.

I'd rather have critical focus where I want it, and not use DoF
to cover up differences.

--
Brian



Some monochromes:
http://mywebpages.comcast.net/spiritmist/SundayBoating/index.htm
Some more monochromes:
http://mywebpages.comcast.net/spiritmist/BWWebPage/index.htm
Some older images:
http://mywebpages.comcast.net/spiritmist/Brian_G_Digital_Image_Gallery/index.htm

'To quote out of context is the essence of the photographer's
craft.' John Szarkowski, The Photographer's Eye

Click to expand...

--



'How one responds to failure, not success, could be the better measure of character.'

Brian G. said:

Call it what you like, but the fact is that when you focus and
recompose, your actual focal plane no longer contains the intended
center of focus, and instead lies behind it. Whether that will
matter in a given photo depends on a number of factors, including
all of those that affect DoF, as well as how critical a viewer you
are.

Click to expand...

I guess Leica users with their f/1 Noktons with millimetre DoF and only a tiny RF patch in the centre of the VF to focus with are just not fussy enough to care. Either that or only compose with the point of focus dead centre. Or... ;-)

--
John Bean [GMT - is there any other?]

PAW 2007 Week 10:
http://waterfoot.smugmug.com/gallery/2321711/1/134422693/Large



Index page: http://waterfoot.smugmug.com
Latest walkabout (4 April 2006): http://waterfoot.smugmug.com/gallery/1348582