What's the point of xx points area AF

[Fota]

Hi,

Coming from a prosumer camera I don't fully see the advantage of an xx point/area AF.

I mean, when focusing uw on e.g. a fish, I probably aim for the eye (or just in front, depending on its position). I would be very upset if the camera would go for another focus point than the one that I was aiming at.
Even when shooting on a coral, I really want to be in control which focus point to go for.

Maybe when I shoot sharks (doesn't happen that often), or something else in a distance, it could be good if the camera did all it could to find just any focus point. But at least to me those are rare situations and something I can live without. But in all D-SLR reviews the number of focus points is always a very big deal.

I do appreciate the possibility to move the focus point (but even my prosumer camera can do that trick).

Or did I get this all wrong!?


/Fota

[Mike Veitch]

selective focus is a great tool. when composing a photo you don't want to always have your strongest point smack dab in the middle. It can often be a pain to focus with the middle point, hold the focus down, and recompose to get the composition you are looking for. This doesn't necessarily work all the time.

By using selective focus points you can get that off centre focus in any number of places. for example, my D70 only has 5, nothing in the 4 corners... often times i want my sharp focus point to be in one of those 4 corners.... so i for one wish i had more selective focus points

[AUTiger]

One other good thing about multiple focus points is that in some designs they better fit the photography "rule of thirds". People often compose the photo so that the subject is located at one of the four intersections created by the four imaginary lines that dive the frame into thirds (in both directions, creating nine smaller squares). Having a focus sensor at or near that point makes it easier to lock focus without having to shift where the camera is pointed.

Some cameras also have additional sensors along the horizontal middle axis at the far left and right. These are to catch moving targets as they enter the frame from the left or right (outside the initial field of view) - such as would occur if you were photographing moving cars at a race or a bicyclist passing in front of you - or perhaps a shark swimming into your field of view from the side.

Additionally, my Nikon has a center autofocus point that can be smaller or larger, depending on how much territory you want it to cover. One might use a larger center autofocus point to better ensure that you catch a moving target such as a hummingbird or fish.

In a good camera, you will easily be able to swith number of focus points or which individual focus point is activated with minimal effort. On my D80, I have set the assignable function button to activate focus selection so that I can use the thumb wheel to shift my selection. I can easily go from all focus points to the center focus point and then use to a particular focus point.

David

[Fota]

selective focus is a great tool. when composing a photo you don't want to always have your strongest point smack dab in the middle. It can often be a pain to focus with the middle point, hold the focus down, and recompose to get the composition you are looking for. This doesn't necessarily work all the time.

By using selective focus points you can get that off centre focus in any number of places. for example, my D70 only has 5, nothing in the 4 corners... often times i want my sharp focus point to be in one of those 4 corners.... so i for one wish i had more selective focus points

OK, but why not simply move the (main) focus frame (AF target)?
I can do that easily even on my prosumer camera (a one button operation and then move around the AF frame with the arrow keys)!


/Fota

[Fota]

One other good thing about multiple focus points is that in some designs they better fit the photography "rule of thirds". People often compose the photo so that the subject is located at one of the four intersections created by the four imaginary lines that dive the frame into thirds (in both directions, creating nine smaller squares). Having a focus sensor at or near that point makes it easier to lock focus without having to shift where the camera is pointed.

Some cameras also have additional sensors along the horizontal middle axis at the far left and right. These are to catch moving targets as they enter the frame from the left or right (outside the initial field of view) - such as would occur if you were photographing moving cars at a race or a bicyclist passing in front of you - or perhaps a shark swimming into your field of view from the side.

Additionally, my Nikon has a center autofocus point that can be smaller or larger, depending on how much territory you want it to cover. One might use a larger center autofocus point to better ensure that you catch a moving target such as a hummingbird or fish.

In a good camera, you will easily be able to swith number of focus points or which individual focus point is activated with minimal effort. On my D80, I have set the assignable function button to activate focus selection so that I can use the thumb wheel to shift my selection. I can easily go from all focus points to the center focus point and then use to a particular focus point.

David

It's nice to be able to set the size of the center AF point.
But, (again ;-)), I can't see the benefit from having 11 (or more!) selectable AF points, compared to having a single movable (as I do in my compact camera). It's a one button operation and then I can move around it as I please with the arrow/menu keys.

I have more or less decided to get a D200, but I still wonder this. ;-)


/Fota

[Mike Veitch]

you are confusing me....

i simply move the push pad to the area of focus i want with the arrow keys to highlight the point that i want.. this is called single focus area

there are several different ways of using the auto focus on slrs, what you need to do is select the one from the menu that you want.

i think you are thinking that dynamic area is the only way. But, that is only one way, closest subject is another, the third (and the one that gives you the most control) is single area- this is the one where you control which point is the selected one by moving the arrow keys

[Fota]

you are confusing me....

I usually do that. ;-)


i simply move the push pad to the area of focus i want with the arrow keys to highlight the point that i want.. this is called single focus area

Yep, I actually have a D200 right in front of me that I've been testing for a couple of days. I have to give it back today though. :-(

When you select focus point I can see that it's good to have as many points as possible to select from. But, why select point at all, if you could instead move the main focus brackets (on my compact I only have one point, but it's movable)?
I don't know if it's at all possible to move the selected focus point (e.g. the main/center focus point) on a D200?
On my compact I have 11x13=143 possible different positions (AF points) to place the AF bracket. I find it hard to believe that an advanced D-SLR as the D200 woudn't be capable of that trick!?
So, lets say it is (perhaps with even more possible positions), then again I don't see why I should not use that function instead of picking a fix focus point when I want to set AF somewhere else but in the center?


there are several different ways of using the auto focus on slrs, what you need to do is select the one from the menu that you want.

Sure, but the main benefit that both you and David gave me with having multiple AF points is that you can use a different one that the one in the center.
So again, why is this better than being able to move the focus point to "any" position (not just a few)?

I'm sure there is a reason but I just can't see it!



i think you are thinking that dynamic area is the only way. But, that is only one way, closest subject is another, the third (and the one that gives you the most control) is single area- this is the one where you control which point is the selected one by moving the arrow keys

Well I know there are a few other AF modes and they are interesting too (I'm not sure what the Dynamic Area means though). In clear water "closest subject" could be very interesting. Especially when shooting corals and such from a little distance, as my compact AF often goes for a spot inside the coral making the top unsharp. In Sweden this will probably set the AF to the particles in the water ;-), well perhaps when shooting anemones in super macro it would work nicely.

So, I fully understand the value of lots of focus points when working in "closest subject" mode but not in the other modes.


/Fota

[Mike Veitch]

hmmm...


interesting. I have not seen a compact that allows you to move the center focus point to different areas. but that sounds like an interesting way of doing things, you can set it to the exact area you want.

But, that is not the way slrs work, slrs work by giving you a large selection of focus points that you can choose from instead.

thats just the way it is...

i always use single point as opposed to the other choices in AF

[Fota]

hmmm...
interesting. I have not seen a compact that allows you to move the center focus point to different areas. but that sounds like an interesting way of doing things, you can set it to the exact area you want.

Yep, and like I said, we are not talking about 3-11 points, but 143 even on my crappy camera! It's an Oly 7070 btw.


But, that is not the way slrs work, slrs work by giving you a large selection of focus points that you can choose from instead.
thats just the way it is...

Well then it makes lots alot of sense of having as many AF points as possible.

I really wonder why D-SLRs went for this truly less good solution...? Hey, here I was expecting the D200 to be sooooo much better than my 7070 and instantly I find limitations. ;) On the other hand, if I would go for a D-SLR with only 3 points (like the E-330) I would have felt really limited.


i always use single point as opposed to the other choices in AF

The problem with too many choices is that you keep forgetting about them. Not until you "develop" your photos you realise that "on no why didn't I think of using this or that feature". Well, at least that's how it is for me. ;)


/Fota

[AUTiger]

Fota,

It seems that most of your focusing method is based on a single moveable focus point. The 7070 does seem more flexible in that you have many more places to put that one point. Thats only an advantage if you are using a single focus point.

With the eleven point system, you can use all eleven points and your subject will probably be located at one of those points. With eleven points, you don't have to put your focus point in the upper left quadrant and then frame the fish at that spot, you're ready if the fish appears in the upper left, uppper right, lower right, center, etc. With the far left and right sensors, the camera will start focusing as soon as an object enters from the side, but with the right setting, it will continue to adjust focus on that moving object as it crosses the three middle horizontal regular sensors and then to the far right sensor. This is useful when the path of the object you are focusing on results in the focusing distance changing across the viewfinder. The object will be in focus no matter what point you press the shutter button. With the single point, you are unlikely to be focused on the target unless it is exactly under your single focus point and remains there long enough for the camera to focus.

In short, your 7070 might have an advantage in the one situation where you want to put a focus point in a specific location, but it probably looses in every other situation (I say this having moved up from a 5060), particulary on land.

Additionally, my d80 locks on and focuses much more quickly than my 5060 ever did, particularly in macro mode.

David

[Fota]

Fota,

It seems that most of your focusing method is based on a single moveable focus point. The 7070 does seem more flexible in that you have many more places to put that one point. Thats only an advantage if you are using a single focus point.

Well me and Mike did (above) discuss other focusing methods. His idea was that he seldom used anything else than single focus point. I was trying to imagine situations when for instance "closest subject" multi focus point mode would come in handy.


With the eleven point system, you can use all eleven points and your subject will probably be located at one of those points. With eleven points, you don't have to put your focus point in the upper left quadrant and then frame the fish at that spot, you're ready if the fish appears in the upper left, uppper right, lower right, center, etc. With the far left and right sensors, the camera will start focusing as soon as an object enters from the side, but with the right setting, it will continue to adjust focus on that moving object as it crosses the three middle horizontal regular sensors and then to the far right sensor. This is useful when the path of the object you are focusing on results in the focusing distance changing across the viewfinder. The object will be in focus no matter what point you press the shutter button. With the single point, you are unlikely to be focused on the target unless it is exactly under your single focus point and remains there long enough for the camera to focus.

Good point! ;)

But, is this must be the "closest subject" AF mode? If not, why wouldn't it just as well focus on something behind the fish (well unless you are shooting out in the blue).


In short, your 7070 might have an advantage in the one situation where you want to put a focus point in a specific location, but it probably looses in every other situation (I say this having moved up from a 5060), particulary on land.David

Yeah, but if I would go for a 3 point focus D-SLR (like the Oly E-330) I might not have agreed with you. I still wonder why you can't have both on an advanced D-SLR...


Additionally, my d80 locks on and focuses much more quickly than my 5060 ever did, particularly in macro mode.David

You bet!
Well this is the main reason for me to upgrade. I've just tested a D200 with Nikon 28-120 VR for two days, and compared the speed of the AF indoor with my 7070 alot.
The D200 really shined! Super fast and handled almost any situation. When no contrast was to be found, the D200 did fail though.

I have no idea if the 28-120 VR is considered a fast or a slow lens, but to me it was super fast. I hear Canon people claim that their AF is always soo much better. Well, maybe, maybe not, but what I got with the D200 (indoor, no window, only a bulb and tricky objects, both close and far away, max zoom etc) was nothing but truly fantastic.

Even though I am not 100% positive about the D200 (I have this idea that I will really miss the liveview but then again nothing beats a good viewfinder... and the D200 is a little heavy), I am just a few days away from placing my order of a D200 with 18-200 VRII (topside) and 60mm macro (uw and topside) and Ikelite housing (I'll order the housing after x-mas, hey diving season is over here anyway). :)


Thanks for your comments,
Fota

[Jamdiver]

hmmm...


interesting. I have not seen a compact that allows you to move the center focus point to different areas. but that sounds like an interesting way of doing things, you can set it to the exact area you want.

But, that is not the way slrs work, slrs work by giving you a large selection of focus points that you can choose from instead.

thats just the way it is...

i always use single point as opposed to the other choices in AF

Mike, the Canon Powershot compacts have the selective focus feature.
Activate the option and you can move the focus square all over the screen.

Great for creating unique compositions and Depth of field...

[RonFrank]

If we limit this discussion to pure UW shooting, than the AF features of todays SLR's are generally not as useful as they are in topside situations, especially action.

However tools like Group dynamic AF, and subject tracking can be useful UW if the photographer is comfortable with them.

The D200 has 11 AF points (seven in wide mode). A couple of people have indicated they think that being able to set the center AF area wider is useful. Others think moving around the AF points is cool. DSLR's don't work like that (or none that I'm aware of) mainly because they don't need to. Having more points creates better control, accuracy, and results with less manual overhead on the user. IOW's why move an AF point when the camera can track the subject from one to another? Why make it wider when the points cover most of the viewing area?

Here are some things one can do with Nikon's Focus system:

One can select a group of sensors to use and the camera will find the subject in that group, and track focus.

One can select and use all sensors, and the camera will focus on the closed subject in the frame, and track the subject movement from shot to shot.

One can select ONE sensor, and the camera will track subject movement to the next.

You can tell the camera to wrap, and the camera will track focus out of one side of the frame, and into the other side if you allow the subject to leave the frame, and them move the camera so the are reentering the view.

This is only a few of the options, and with four mode settings (SA, DA, GDA, DAA), three focus settings (M, S, C) the drive settings (S, CL, CH), and additional custom menu settings this quickly becomes an advanced subject to discuss.

All these options, how well they work, and when they are best used are something I've been working on since I've had the D200. I just purchased Thom's Ebook on the D200 (actually an XMAS gift), and the main reason I did so was because of how complex, but also how flexible, and capable these settings are.

I think it's outside the scope of UW photography, or at least this thread to go into a lengthy discussion on this subject. But leave it like this, the AF in today's DSLR's compared to most PnS's is like comparing a glider to a jet. Why would anyone what to have to move a focus point if the camera can just lock on the subject, and then follow it? Nikon and Canon both have been refining their focus tracking technology for over two decades, it it works rather well even if it has become a bit complex.

However no worries, if you don't want to learn to use these features, they are easy enough to ignore.

In any event, after reading this you may decide that for UW shooting all those AF settings are more than needed. OTOH, some of these tools, especially for shooting moving subjects like sharks, Rays, Whales, Turtles, etc., are very useful. I will likely switch modes more often next time I'm UW as I think I missed some shots (or got soft shots) using my single area mode only way of shooting. I definately think there are times when Dynamic AF would have focuses better than my OOF attempt using Single area lock mode.