Multipoint AF tricks?

[GeoffB]

I was excited to get a camera with more focus options with my P150 since the AF on my 707 was sometimes frustrating. The biggest problem was the 707 focusing between people or objects to the background. I thought multipoint would help me out here.

Now that I have it, I don't use it. I find that I lose control of knowing what the camera is focusing on and wind up not perfectly focused where I want. I have many "tricks" to make sure center focus locks on at the correct distance and understand very well how it works.

So the question is: are there tricks to make multipoint focus work or is it always unpredictable? Should I give up and just live with the ocasional miss with center focus?

Thanks,

Geoff

--
http://www.pbase.com/geoffb

 

[Mike Fitzgerald]

Hi Geoff,

Multipoint AF is something I largely regard as a gimmick. Even though many cameras feature it these days, in its simple form it results in exactly the sort of lottery you're describing.

Some cameras seem to insist on using it to locate the nearest part of the framed subject areas that intersects a focus zone, and focus on that; and its rarely the item that the photographer has in mind to be in critical focus.

Multi-zone focus systems can sometimes help in very low light situations by finding a zone that's bright enough for AF to work at all. But that still doesn't help much if your own point of interest doesn't happen to fall within the available depth of field. With this in mind, however, you may be able to use it to your advantage by then moving the correct estimated distance needed to compensate. At least you'll be getting focus lock as a starting point

Best to forget about multipoint and do exactly what you've been doing to exploit the centre focus area which is, as you rightly suggest, a known quantity. With the possible rider, above, for low light, the rest is snake oil.

Selectable single focus zones however, including the Flexible Spot AF found in the F828 (and first seen in the Minolta DiMAGE 7 for this class of camera), can be very useful at times, particularly for tripod work.

I was excited to get a camera with more focus options with my P150
since the AF on my 707 was sometimes frustrating. The biggest
problem was the 707 focusing between people or objects to the
background. I thought multipoint would help me out here.

Now that I have it, I don't use it. I find that I lose control of
knowing what the camera is focusing on and wind up not perfectly
focused where I want. I have many "tricks" to make sure center
focus locks on at the correct distance and understand very well how
it works.

So the question is: are there tricks to make multipoint focus work
or is it always unpredictable? Should I give up and just live with
the ocasional miss with center focus?

Thanks,

Geoff

--
http://www.pbase.com/geoffb

--
Mike
Melbourne

 

[GeoffB]

Thanks for the info.

Some cameras seem to insist on using it to locate the nearest
part of the framed subject

I'll need to check some pics and see if this is what it is doing. At least if I understood how it made the focus decision between the multiple points I might be able to work with it.

Nearest can be a good thing. If I had a nearest focus button for center zone it would solve 90% of my issues. Unfortunately the multi-zone seems to look at too much of the frame.

Geoff

Multi-zone focus systems can sometimes help in very low light
situations by finding a zone that's bright enough for AF to work at
all. But that still doesn't help much if your own point of interest
doesn't happen to fall within the available depth of field. With
this in mind, however, you may be able to use it to your advantage
by then moving the correct estimated distance needed to compensate.
At least you'll be getting focus lock as a starting point

Best to forget about multipoint and do exactly what you've been
doing to exploit the centre focus area which is, as you rightly
suggest, a known quantity. With the possible rider, above, for low
light, the rest is snake oil.

Selectable single focus zones however, including the Flexible
Spot AF found in the F828 (and first seen in the Minolta DiMAGE 7
for this class of camera), can be very useful at times,
particularly for tripod work.

I was excited to get a camera with more focus options with my P150
since the AF on my 707 was sometimes frustrating. The biggest
problem was the 707 focusing between people or objects to the
background. I thought multipoint would help me out here.

Now that I have it, I don't use it. I find that I lose control of
knowing what the camera is focusing on and wind up not perfectly
focused where I want. I have many "tricks" to make sure center
focus locks on at the correct distance and understand very well how
it works.

So the question is: are there tricks to make multipoint focus work
or is it always unpredictable? Should I give up and just live with
the ocasional miss with center focus?

Thanks,

Geoff

--
http://www.pbase.com/geoffb

--
Mike
Melbourne

--
http://www.pbase.com/geoffb

 

[Yehuda Katz]

the Flexible Spot AF found in the F828

What do you mean by Spot AF? Do you relate to the smaller rectangle?

Thank you, Yehuda

 

[Lynn Towns]

the Flexible Spot AF found in the F828

What do you mean by Spot AF? Do you relate to the smaller rectangle?

Hi Yehuda,

Pages 65, 66, and 67 in the English manual explain the AF options. Flexible Spot AF refers to the small rectangle (AF range finder frame) that can be moved around with the joystick (multi-selector) within the field of view to focus on almost anything. The rectangle changes from white to green when AF lock is achieved. The Flexible Spot AF rectangle is smaller than the Center AF rectangle, so besides the capability to move it around, it also provides focusing on a smaller subject area for more precise focusing.

I almost never use Multipoint AF (no control over focus point), and seldom use Center AF. I use Flexible Spot AF with Monitoring AF mode nearly all of the time.

Lynn

 

[Yehuda Katz]

I almost never use Multipoint AF (no control over focus point), and
seldom use Center AF. I use Flexible Spot AF with Monitoring AF
mode nearly all of the time.

That's xactly what I'm doing too.

Thank you for the explanations.
Have an excellent day,

Yehuda

 

[steelheader]

Your applications are for the 828, right? On the 717 the CenterAF is moved around via the jog dial to allow proper framing and yet focus on a specific area other than center as I understand. I have never used the jog dial, rather I lock the focus on the specific target, hold and reframe the image assuming this does the same thing. On the 717 I am satisfied using the Multi Point AF on landscapes, noting if there is any significant difference in various points of interest for exposure with the f stop I have chosen. Since the Flexible Spot AF with Monitoring AF is not available on the 717, I have to be sastisfied with the foregoing. If there are better suggestions, I would be interested. Gale

I almost never use Multipoint AF (no control over focus point), and
seldom use Center AF. I use Flexible Spot AF with Monitoring AF
mode nearly all of the time.

That's xactly what I'm doing too.

Thank you for the explanations.
Have an excellent day,

Yehuda

 

[Lynn Towns]

Your applications are for the 828, right? On the 717 the CenterAF
is moved around via the jog dial to allow proper framing and yet
focus on a specific area other than center as I understand. I
have never used the jog dial, rather I lock the focus on the
specific target, hold and reframe the image assuming this does the
same thing. On the 717 I am satisfied using the Multi Point AF on
landscapes, noting if there is any significant difference in
various points of interest for exposure with the f stop I have
chosen. Since the Flexible Spot AF with Monitoring AF is not
available on the 717, I have to be sastisfied with the foregoing.
If there are better suggestions, I would be interested. Gale

Hi Gale,

Yes, I was referring to an F828. I had an F707, but I've never used an F717. I didn't know the Center AF of the F717 could be moved around...are you sure? Focusing and re-framing is necessary with the F828 when using Center AF. This works fine, but it is tedious when the camera is mounted on a tripod. I use my tripod a lot, and the Flexible Spot AF makes it much easier.

Lynn

 

[steelheader]

Lynn: On the 717 with CF selected, the jog dial will move it to 4 other locations other than center. Gale

Your applications are for the 828, right? On the 717 the CenterAF
is moved around via the jog dial to allow proper framing and yet
focus on a specific area other than center as I understand. I
have never used the jog dial, rather I lock the focus on the
specific target, hold and reframe the image assuming this does the
same thing. On the 717 I am satisfied using the Multi Point AF on
landscapes, noting if there is any significant difference in
various points of interest for exposure with the f stop I have
chosen. Since the Flexible Spot AF with Monitoring AF is not
available on the 717, I have to be sastisfied with the foregoing.
If there are better suggestions, I would be interested. Gale

Hi Gale,

Yes, I was referring to an F828. I had an F707, but I've never used
an F717. I didn't know the Center AF of the F717 could be moved
around...are you sure? Focusing and re-framing is necessary with
the F828 when using Center AF. This works fine, but it is tedious
when the camera is mounted on a tripod. I use my tripod a lot, and
the Flexible Spot AF makes it much easier.

Lynn

 

[Anson MacLauchlan]

thought that I would add this note for beginners...as I was one this past year..

andas a manual photography newby, one of the areas that took the longest for me to grasp, was just this subject

... regarding the working realtionship (difference), between

-Choosing a focus range finder (AF range finder frame)... pg 65

-Choosing a focus operation (AF mode)...pg 66

&

-Selecting a metering mode pg 58

I was so confused for so long, before I Finally figured all three areas out (looking back I just did not internalize the definitions correctly) allowing spot this, center that, multi this, to get tangled-up in my mind.

Boy I was confused on this subject for the longest time ( a major mindblock!)..

Focus http://www.photoxels.com/tutorial_area_focus.html
Metering http://www.photozone.de/4Technique/metering.htm

 

[Lynn Towns]

Lynn: On the 717 with CF selected, the jog dial will move it to 4
other locations other than center. Gale

Gale,

I read the specifications for the F717 a long time ago, and I decided at the time the improvements were not enough to upgrade from my F707. I don't remember being aware of that feature.

Lynn

 

[Lynn Towns]

Boy I was confused on this subject for the longest time ( a major
mindblock!)..

Anson,

These things are even more confusing because of the similar terms that are used in the Sony manual. The manuals always seem to be poorly written, making things more confusing. Sometimes I think I could have made a career of writing manuals for products. I did a lot of technical writing as an engineer.

Lynn

 

[Anson MacLauchlan]

Ha-ha!
...nothing like a good Japlish instruction manual, for bed time reading

re: writing manuals

...my wife has stated the same many times, as she too, is quite adept with the English language..

and thanks for ..
http://forums.dpreview.com/forums/read.asp?forum=1009&message=11898062
...in cleering up confusionssss

all photo newbies (and not so newbie) should follow your posts, as you are one of STF's valuable information resource guru's

 

[GeoffB]

Thanks for the description. I don't think this is available on P150 (need to check for sure) but since I'm still in the market for a 707 upgrade I'll look for this as a focus mode.

And thanks to all for the inputs and links. It sounds like there are no tricks to make multipoint give sharp subject focus. Maybe it's better if you don't understand autofocus but not predictable.

Geoff

the Flexible Spot AF found in the F828

What do you mean by Spot AF? Do you relate to the smaller rectangle?

Hi Yehuda,

Pages 65, 66, and 67 in the English manual explain the AF options.
Flexible Spot AF refers to the small rectangle (AF range finder
frame) that can be moved around with the joystick (multi-selector)
within the field of view to focus on almost anything. The rectangle
changes from white to green when AF lock is achieved. The Flexible
Spot AF rectangle is smaller than the Center AF rectangle, so
besides the capability to move it around, it also provides focusing
on a smaller subject area for more precise focusing.

I almost never use Multipoint AF (no control over focus point), and
seldom use Center AF. I use Flexible Spot AF with Monitoring AF
mode nearly all of the time.

Lynn

--
http://www.pbase.com/geoffb

 

[Mike Fitzgerald]

Nearest can be a good thing.

Oh, often it can; but just as often it will be some extraneous foreground object that has to be in frame for other reasons, and a multi-zone AF system that finds it in one of its zones may not want to let go of it.

If I had a nearest focus button for
center zone it would solve 90% of my issues.

Geoff I'm not quite sure what you mean by that. It's not possible under current methodology to "tune" any given single focus zone to work at a specific distance (or within a nominal range). It simply boils down to what parts of the framed scene fall within an active zone. If we're talking about the centre zone, for example, then focus will attempt to lock on what largely fills that zone. It's the questioin of just how much of that zone needs to be spilling over on to the background, in order for the background to then determine focus, that is best addressed by experiment.

The selectivity of an AF zone that is partially off-target is vey hard to predict in practice and has been the subject of much discussion in dSLR circles. It doesn't appear to be even a hard and fast area or linear percentage either, and a small piece of high contrast background intruding into a low contrast intended target area may end up dominating.

If, OTOH, you're referring to a system that allows you to momentarily switch from multi-zone to centre zone, then yes, that can be quite useful and Canon (at least) includes such a feature in its dSLRs.

Unfortunately the
multi-zone seems to look at too much of the frame.

Yes, and by definition it needs to do that. In its simplest form, that's what makes it more of a PITA than a blessing. In more sophisticated implementations it underpins focus tracking schemes for laterally moving subjects, but that's getting into a realm beyond the capabilities of the P150.

--
Mike
Melbourne

 

[Lynn Towns]

all photo newbies (and not so newbie) should follow your posts, as
you are one of STF's valuable information resource guru's

 

[Mike Fitzgerald]

Thanks for the description. I don't think this is available on
P150 (need to check for sure) but since I'm still in the market for
a 707 upgrade I'll look for this as a focus mode.

The methodology Lynn describes gives you the best of both worlds in the case of the F828. Letting it remain in Flexible Spot AF mode means that if you customarily leave the movable rectangle in the middle then you have a tighter (= generally better) centre zone, and it's always ready to be steered elsewhere the moment you find you need that.

And thanks to all for the inputs and links. It sounds like there
are no tricks to make multipoint give sharp subject focus.

Well it should always give sharp focus somewhere or other; it's not knowing just which zone is going to win that's the problem.

Manufacturers are surely trying to add "intelligence" to these systems, but in the end it is -- and surely must be in what is, after all, an art form -- the phographer's decision to choose what will be in critical focus.

--
Mike
Melbourne

 

[GeoffB]

If I had a nearest focus button for
center zone it would solve 90% of my issues.

Geoff I'm not quite sure what you mean by that. It's not possible
under current methodology to "tune" any given single focus zone to
work at a specific distance (or within a nominal range). It simply
boils down to what parts of the framed scene fall within an active
zone. If we're talking about the centre zone, for example, then
focus will attempt to lock on what largely fills that zone. It's
the questioin of just how much of that zone needs to be spilling
over on to the background, in order for the background to then
determine focus, that is best addressed by experiment.

My understanding of the contrast based AF is that the camera tries to maximize contrast in the area of interest. At maximum contrast there should be focus. I believe some cameras limit the focus range in different modes, for example a portrait mode may limit focus from 2 to 10 feet to avoid locking on to the background.

I imagine if the camera looked at all focus distances for contrast, there would be a maximum for each object when it came into focus. For example if you had an object at 5 feet and one at 30 feet there would be a bump up in contrast at both distances. If the camera had all this information it could choose the 5feet object as nearest. With the current system it chooses the brighter contrast between the two objects.

This is my issue with the 707. The camera locks onto a bright background even if it only covers 5% of the focus area. I usually avoid this by zooming in and out or choosing a large target but when I miss, I might not see the issue until I upload to a large computer screen. Zooming in and out also takes time and requires independant steps for focus and exposure metering.

Geoff

--
http://www.pbase.com/geoffb

 

[GeoffB]

Manufacturers are surely trying to add "intelligence" to these
systems, but in the end it is -- and surely must be in what is,
after all, an art form -- the phographer's decision to choose what
will be in critical focus.

True. When I'm doing photography of relatively still objects I rarely have problems. Even moving objects are OK as long as I have time to set up.

It's when I'm snapshooting the family that I have issues. Now that we view all shapshots on a relatively huge monitor (compared to 4x6 prints) focus is very sensitive. I think anyone who took their old film shots and blew them all up to 11x14 or larger would realise most have focus or DOF problems.

Geoff

--
Mike
Melbourne

--
http://www.pbase.com/geoffb

 

[Mike Fitzgerald]

And my favourite corollary:

"Those who can't write, write manuals." ;-)

Sony seems on a never ending mission to prove that. One of life's great mysteries -- to me at any rate -- will always remain how these $multi-billion corporations, supplying a global consumer market, refuse to employ technical writers truly fluent in each of the major regional languages. Surely there are enough eager and able souls, waiting under enough rocks in Japan, for supply to be a non-issue.

The salaries of the largest imaginable basketload of competent translators would pale into insignificance against the paid time that is surely being wasted, around the globe, in dealing with (notice I didn't say "answering";-) needless consumer queries.

But that's the problem with stand-alone regional operations accountable only to themselves for waste in this regard. If the costs of unnecessary customer interaction were to be passed back to the manufacturing principal then I reckon things would smarten up overnight!

The other silly thing is, at the worst extreme, the needless damage that can be done to a good product's name by a user who fails to properly understand how to drive it, and consequently maligns it to others on account of assumed design limitations or flaws.

Speaking of Sony nomenclature, one of my pet annoyances is the way they keep coining and changing terms. One of the all time greats here has to be "Illumination Snap", the quaintest name yet for what everyone else is content to call "slow sync." and which was used with at least the U10. Thankfully, that one appears to have now gone underground, where it belongs.

These things are even more confusing because of the similar terms
that are used in the Sony manual. The manuals always seem to be
poorly written, making things more confusing. Sometimes I think I
could have made a career of writing manuals for products. I did a
lot of technical writing as an engineer.

Lynn

--
Mike
Melbourne