Auto Focus

[SGreen]

I own OM SLR cameras and a Konica Minolta A2 and am shopping for a DSLR. I read about the multitude of autofocus points that some brands have, but they don't explain how easy it is to choose. With the A2 you toggle the pointer over where you want it to focus. If you have to choose among many preset points wouldn't it be easier just to manual focus. It's quick and reliable, and if your vision is off, a split prism works, except in low light

[scoundrel1728]

Unfortunately, today's dSLR viewfinders don't have split prisms unless you get them as extra-cost options. Sure wish my canon 350D had one!

[Blinky]

I really miss split rings and micro-prisms.

[jfrancho]

I generally use the center point, and then manual override, if necessary. All but two of my lenses are full time manual while in auto focus mode. On my camera, Canon 20D, changing focus point is as easy as moving a small jorstick like button on the back of the camera. If you're looking for focus screens, try here: http://www.katzeyeoptics.com/.

[cyclohexane]

Split rings and microprisms are vastly superior to current focusing screens, but once you AF sports, it's hard to go back to full-time MF.* A good deal of my lenses have full-time manual focus override, so I can use AF and override it immediately when it misses.* My D2H's autofocus is almost better than my eyes in most cases, so I don't find myself manually-focusing as much with it.* My D70, on the other hand, needs some help, but it's very hard to see well enough to manually focus with the tiny viewfinder.

[SGreen]

Does anyone know if the Canon 5D and the Nikon D200 use the "joystick-type" button for moving the auto focus spot?

[rootrider]

my vision isn't good enough to focus manually, especially with the smaller viewfinder my d70 has. I've tried focusing manually and I don't think I've ever gotten it just right

[cyclohexane]

The Nikon D200 has a gamepad-style 8-direction "multiselector" keypad inherited from the D2-series, which is, in my opinion, easier to use the joystick, which I find a bit small. *When you're done selecting the point, if you want, you can lock the keypad to prevent yourself from accidentally changing the point. *Also, locking/unlocking the keypad is easily accomplished with a switch around the keypad, so you don't have to worry about fumbling with it and losing a shot. *Personally, I keep it unlocked as I don't find myself hitting it by accident, but some have said that their noses hit the keypad when shooting left-eyed.

The 5D is a joystick camera.

Be sure to check out DPreview. Phil outlines how to select AF points in his reviews.

[SGreen]

Thanks.

[rootrider]

Originally Posted by cyclohexane

Personally, I keep it unlocked as I don't find myself hitting it by accident, but some have said that their noses hit the keypad when shooting left-eyed.

I definitely hit my focus point selector with my nose sometimes when shooting. It's quite annoying

[SGreen]

OK, as usual, I'm a little confused. I've seen the AF points pattern on the 5D and the D200. Are these used during normal autofocus or they the only ones that can be selected,i.e., if I toggle the focus pointer to an area where there are no points, what happens? Or is it only possible to toggle between these set points? I guess that 45 focus points is one reason for the price for Canon's 1Ds Mark II.

[cyclohexane]

You can only focus where there are physical sensors.* The D200 has 7 physical sensors, divided as 11 selectable points in the regular mode (there's a wide mode that only lets you choose from the seven).* The selectable points on the focusing screen do not correspond with the physical size or shape of the sensors (the sensors are much bigger than the brackets).* You can't select any places where there are not sensors, but usually the sensors are large enough that even though there isn't a sensor centered at every location, you can still focus on that object as the edge of one of the nearby sensors wil have enough contrast to grab that object. With my D2H, I can focus almost anywhere on the frame, as the sensors cover most of the usable area in the viewfinder.

The 45-points are really overkill for the 1D/1Ds series; many users I've met have it set to something like 11 active points, which is the same number as Nikon's D2H/HS/X/XS using MULTICAM2000 which has a slight edge in lowlight AF (when it's really, really dark, nothing can AF well) compared to the Canons.

Here's an idea.* Go to the store, and try the D200, D2H/HS/X/XS, 5D, 1D Mk.II, and so on.* That'll probably answer some of your questions, and maybe even some new ones that come up.* And if you're still confused, come back here.

[Max@Home]

Originally Posted by jfrancho

On my camera, Canon 20D, changing focus point is as easy as moving a small joystick like button on the back of the camera.

...but on a 20D you can also use the command dial on top, or the big wheel on the back, by setting a Custom Function
(CFn. 13, AF point selection method, mine is on '1', multicontroller direct. )

Originally Posted by SGreen

OK, as usual, I'm a little confused. I've seen the AF points pattern on the 5D and the D200. Are these used during normal autofocus or they the only ones that can be selected,i.e., if I toggle the focus pointer to an area where there are no points, what happens? Or is it only possible to toggle between these set points? I guess that 45 focus points is one reason for the price for Canon's 1Ds Mark II.

Hi SGreen, although the BubbleGirl beat me to it, I still think this is a good read that might help:

OK, to de-confuse a 'quicky' on AF point selection

You can leave the AF point selection to the camera, with a Canon 20D this is done by choosing 'all' (you see all squares 'red' lighted up in selection mode).

This will make the 20D select the nearest AF area with a decent contrast to focus on, where ever (under whatever sensor) that area is.

If/when the camera finds such an area, it will light up the 'nearest square' to inform you, and says 'beep-beep' to confirm AF lock, and shows a large lit dot right-under in your viewfinder - given everything else is in 'default': you *can* choose to turn off the 'beep-beep' or even the squares-overlay... with Canon, you can...

Now, if your subject is not 'the nearest high-contrast area', you have a problem...

So, to give you 'compositional freedom' , Canon also lets you choose your own 'area' with the methods described earlier.

You can 'only' toggle between the 'given points', but note that the area they cover is larger than the 'square' you see

The nine points in the Canon 20D/30D/5D/400D actually represent 10 sensors, a sensor 'senses' in either a vertical or a horizontal pattern, like a radar-sweep, either left-right or up-down. The centerpoint however has two sensors, to form a cross-sensor. This cross-sensor needs a lot of light to function, so it will only work if your lens is faster than f./2.8.

...and then there are sensors not represented by a square on the 5D, to augment and assist AF in tracking mode.

yes, AF has three modes also, to confuse you even more

...on most Canon camera's they are

- SingleShot - as it says, takes AF for each individual shot, and keeps that focus until you click.
- AI Focus - same as above, but this mode detects movement of your subject and will adjust the AF accordingly.
- AI Servo - this will continuously AF on your subject, used to track cars, flying birds, etc...

...note that this is only a 'quicky': each individual mode has more/deeper specific properties, but the question *was* about AF points and selection, so I'll leave it here )

...and you are right, the 45 focus points make for a part of the price of the 1-series, but only for a small amount, as the basic-development was long ago for the EOS 1 film series (not to say that they are not still 'finetuning' the system, sometimes with more luck than other times )

I hope this helps a little more in your understanding of the wonderfull world of AutoFocus ,

...*my* Little contribution, *my* €0.02 worth...

Kindest regards!

Max@Home

[cyclohexane]

Okay, since we're going into AF modes, and we're talking specific cameras (Max hit the 5D, so I'll get the Nikon D200).

First, we have 11 selectable points, from 7 physical sensors which are larger than the little brackets in the viewfinder.* This is under "normal" mode.* There's a "wide" setting, which only lets you choose from the 7 physical sensors; new brackets will appear in the viewfinder that are closer to the physical size of the sensor.* The center sensor is a cross-type sensor, which Max described up above.

...I, however, am not too sure about the whole f/2.8 thing.* My understanding was that the cross-type sensor is a better choice in lowlight, as my plain stick types will fail in lowlight on my D70, while the center cross-type sensor will continue to function.* Max, maybe you mean that it doesn't track motion unless you're using an f/2.8 lens?* Anyhow, my Nikon D2H has three cross-type sensors (four direction tracking), six T-type sensors (three direction tracking) and two regular stick sensors.* The cross-types are the last to go.* My guess is that we're just running into a different company/different terminology issue.* Anyhow, back to the D200...

Now that you've chosen whether you want "normal" AF points or "wide" AF points, we have the focus mode options.* First, do you want AF-C, AF-S, or M?* These are selectable from a switch on the front of the camera under the lens release button, in that order.

AF-C: Continuous (AI Servo on the Canons); camera will continually adjust focus as long as your AF-On button or shutter release (you can disable AF activation from the shutter release) is held down.

AF-S: Single shot (not to be confused with AF-S lenses, also called SWM lenses for silent wave motor); camera will focus on the subject, lock focus, and stay that way until you lift your finger from the shutter release or AF-On button.* On some cameras, i.e. my D70, it states that if the camera detects subject motion, it'll activate tracking, refocus, and then lock again a la AI Focus on the Canons, but I've never seen it attempt to reacquire a moving subject.* I have not tried it with my D2H (sports cam), as I'm always using continous anyhow.

M: manual focus; the AF screwdrive motor is decoupled.* AF-S lenses (not the focusing mode) can manually focus without decoupling, and also have a M/A - M switch (for AF and manual, or manual only) on the lens which is usually much quicker to operate.* Interal focus (IF) lenses usually have their own A-M switch or ring that needs to be set in lieu of the M switch as well.

Now, there's another switch on the back of the camera under the focus point selector.* This has four choices, from the bottom to top: single area, dynamic area, group dynamic, and closest subject.

Single Area: camera uses only information from the one selected point to focus.

Dynamic Area: camera uses the one selected point to focus, but will factor in motion at all eleven points and adjust focus if necessary.

Group Dynamic: camera uses the selected group of focus points to focus.* You can choose "closest subjeect priority" which means all the sensors are factored equally, or "center priority" which uses the center sensors, and the other sensors in the group are used as if you were using dynamic area, but it won't use all eleven points.

Closest Subject: camera chooses focus point for you based on the area of highest contrast.

That should get you started; to find out how this all works in practice, you should talk to Julio (Nikonfreak) in our Nikon forum, as he uses the Nikon D200, while I'm a D2H shooter so I can't comment on many of the D200's aspects in practice.

[Max@Home]

Originally Posted by cyclohexane

Total Tool =)

...smilies don't work there

...you, she, the camera or all three?

...but liked the bubblegirl better...

...and thanks for the 'Nikon-AF-quicky'

Kindest regards!

Max@Home

[SGreen]

Thanks all. This will help me a lot. The last (and only) time I had a 5D or D200 in my hands I didn't know enough to ask the right questions or experiment with everything. My A2 has continuous, single, and manual focus, but doesn't indicate the focus points available. The EVF doesn't work well with manual, but it seems that (see original question) that with a SLR, I would use manual more than with the A2 - just seems quicker. Again, thanks, I plan to print out your replies so I can take them to the camera shop.

[Max@Home]

SGreen,

Another way to 'get into the specific TechnoBabble' and get some beforehand info on Canon EOS cameras is read their respective whitepaper.

If you can cut through the PR department-stuff, there is actually something usefull in them

...just google 'whitepaper eos -any-xxx-d'

...one of the first hits will lead you to a link from Rob Galbraith's site to a downloadable PDF document.

...I searched, but couldn't find similar Nikon documents per-camera, perhaps cyclohexane or NikonFreak can fill us in

...€0.02...

...again, my kindest regards,

Max@Home

[jfrancho]

...but on a 20D you can also use the command dial on top, or the big wheel on the back, by setting a Custom Function

That might actually be the default. The problem with that setup is the same with ISO - it requires hitting a button to select a focus point, and then rolling the top dial. With CF13-1 (I use this, too) you only need the camera to in active metering mode, and you can just flip the quick dial joystick thingy. I will admit that it takes a little bit practice to get used to it. At first it doesn't always pick the one you want it to.

[cyclohexane]

Originally Posted by Max@Home

...smilies don't work there

...you, she, the camera or all three?

...but liked the bubblegirl better...

If you haven't noticed, I don't really use the graphical smilies, so the "=)" face is exactly what I want it to be. =P

I was just referring to me with that comment, but now that you point it out, it fits all three... >=D

[cyclohexane]

Also, with Nikon products, consult Thom Hogan's site (bythom.com) for the some of the best breakdowns of Nikon products. He goes into detail on the D200's AF in his D200 review.