Focus with Shutter or * [AF ON] button? -READ ME-

[HJMinard]

**EDIT AGAIN***

This thread dates back to 2004, BEFORE Canon installed the now ubiquitous "AF ON" button.
In those days, we used the * button.
Modern EOS starting with the 1D MkIII and 40D use the AF ON button instead with a lot of additional options.


** EDIT **
This thread is a "Split" from the FAQ topic re: favorite custom functions;
http://photography-on-the.net/forum/...amp;highlight=

The Custom Functions Thread went a little bit O.T. with the subsequent discussion on the benifits and dislikes of using a particular Custom Function.

The debate over CF # 4 is certainly worth its own thread

** End EDIT **
CDS

Originally Posted by CyberDyneSystems

CF # 4 Get that focus control onto the * button ASAP

CDS, I've seen that mentioned quite a few times. What is the advantage of that feature?

[scottbergerphoto]

Separating focus and exposure on the 10D and 1D Mark II has made a significant change in the way I take pictures. Focusing using the * or X button on the back allows you to choose instantly between all AF points and a manually selected one. In addition you can focus, release the * or X button and recompose, then depress the shutter button for exposure. In addition on the 10D, by not pressing the * or X button, the camera is in Manual focus and this forces the flash metering to average all the sensor input instead of biasing an active focus point resulting in more consistent flash. This is not the case though for the 20D which uses ETTL2. ETTL2 is independent of AF points.
Try it, you'll like it!
Scott

[JLS Photo]

Originally Posted by HJMinard

CDS, I've seen that mentioned quite a few times. What is the advantage of that feature?

It also allows you to track a moving subject continuously, BUT the exposure is only locked in when you press the shutter button. In other words, the standard method is to half press the shutter button--this will lock in AF (or servo mode) AND lock in exposure. However, if you subject moves from light to dark with the shutter button half pressed, your exposure will be off at the time of firing.

Using the * allows you to keep focus, but delay setting the exposure until the picture is actually taken.

[HJMinard]

That makes so much sense it is almost difficult to understand why that is not the default setup ... thanks for the info !!

[scottbergerphoto]

Here is the expert on using the * and X buttons to focus:
http://visual-vacations.com/Photogra...focus_tips.htm
Scott

[CyberDyneSystems]

Originally Posted by HJMinard

That makes so much sense it is almost difficult to understand why that is not the default setup ... thanks for the info !!

Yep...

An article on the subject by famed Bird Photographer Arthur Morris
http://www.birdsasart.com/

Teaching on Old Dog New tricks
Text Copyright and Photography Copyright Arthur Morris©


On a crisp fall afternoon, dozens of Sanderlings scurried frenetically in search of sand fleas and other tasty invertebrates that live in the wet sand along the deserted beach at the very edge of the Atlantic Ocean at Stone Harbor Point, New Jersey. Occasionally, they would stop for a few seconds to preen or simply to stare at the crashing waves.

I was seated (with a wet butt) behind my Gitzo 1548 Carbon Fiber tripod, working with the Canon EF 600mm f/4.0L super-telephoto lens and a Canon EOS 3 camera body. The EF 1.4X teleconverter yielded the 840mm-f/5.6 combination that is my everyday bird photography rig. Before I came to realize the many benefits of Custom Function 4 (CF4), available on all mid-range and high-end Canon EOS camera bodies, I would have faced the following dilemma: Should I work in AI Servo mode so that I could easily track the moving birds, or switch to One-Shot mode so that I could focus on a momentarily still Sanderling, recompose, and make the image?

By opting to utilize Custom Function 4, I had the best of both worlds. When activated, CF 4 transfers autofocus operation from the shutter button to the exposure lock button, the left of the two small buttons on the top right of the camera back. With autofocus set to AI Servo mode (for moving subjects), I simply activated autofocus with my right thumb to track a running or a foraging bird, or tapped the button once to focus on the eye of a stationary bird. In the latter instance, I would quickly recompose and make the image by fully depressing the shutter button. I was able to enjoy the benefits of both AI Servo AF and One-Shot AF without having to toggle back and forth (by pressing the AF button and turning the main dial). In addition, when photographing static subjects, I did not have to keep the shutter button depressed halfway as is customary when working in One-Shot AF mode.

When a Royal Tern flew by, it was a simple matter to frame the shot and activate AI Servo autofocus with my right thumb. To boot, I was able to pre-focus manually before engaging AF. This allows the photographer to drastically reduce the time of initial focus acquisition, and is especially helpful when attempting to do flight photography with the 600mm-lens/2X teleconverter combination. (Focus manually until the bird is relatively sharp, then engage AF by depressing the exposure lock button; thus, the system does not have to struggle to "see" the subject.)

Referring to the use of Custom Function 4 in "The Art of Bird Photography; The Complete Guide to Professional Field Techniques," I wrote, " Many photographers rave about this function, but I do not." And in public lectures and seminars I expressed disdain for CF 4 by stating that those attempting to use it would surely wind up on a psychiatrist’s couch. (I felt that they would become extremely confused when attempting to activate AF--is it the shutter button, or is it the exposure lock button? Is it the index finger, or is it the thumb?) But oh, how wrong I was. Today, when photographing perched birds or those on the ground, I activate CF-4 so that I am always ready to make either static portraits or images of the birds in motion.

For in-flight only photography situations, such as those that often arise at Bosque Del Apache NWR, Socorro, NM, or at the Venice Rookery, South Venice, FL, I find it easiest to set CF 4 to the default setting (0) so that autofocus is activated in the traditional manner, by depressing the shutter button halfway. Additionally, I am often afield with a big telephoto lens and one of Canon’s lightweight, hand-holdable flight lenses, either the EF 300mm f/4 L IS, the EF 100-400mm f/4.5-5.6L IS, or the "toy lens,� the EF 400mm f/5.6L. (FYI, the latter is still the world’s best for photographing birds in flight.) When I carry one of these lenses on a shoulder strap, mounted on a lightweight EOS A2 camera body, I always set CF 4 to the default setting, as these lenses are used almost exclusively to photograph birds in flight or in action. Thus, I simply depress the shutter button to activate AF. The body on my big tripod mounted super-telephoto is, however, set with CF-4 activated, as this lens is used primarily to make portraits of birds at rest. In reality, I do not have any problem switching between shutter button AF activation and exposure lock button AF activation as the shooting situation demands. And, I have not, as I once predicted--needed to undergo psychotherapy.

Though the owners of the newest Canon Super Telephoto Image Stabilizer Lenses have full time manual focus available, (hey--the folks at Canon Japan sometimes do read my product critiques!), they will still benefit from activating CF 4 when photographing perched or standing birds. They will then--as described previously--have the option of working in either AI Servo AF, or, effectively, in One-Shot AF, without having to keep the shutter button depressed halfway. To attain One-shot AF while utilizing CF 4, simply tap the exposure lock button to focus on the bird’s eye, then release the button, recompose, and shoot. As I said, the best of both worlds.

With EOS A2, Elan II, and 1N bodies, activate Custom Function 4 by toggling from CF 4-0 to CF 4-1. EOS 3 users may wish to note that there are two ways to activate CF-4, either by choosing CF 4-1, or CF 4-3. The former locks the exposure when the shutter button is depressed halfway after focus has been set, the latter yields real time exposure. I almost always choose the latter so that I need not keep the shutter button depressed to hold the exposure when photographing static subjects.

To Chuck Westfall, Canon technical representative, who has suggested for years that I give CF 4 a try, I say, "You were right. I was wrong, big time wrong. I wish I that I had listened to you sooner." I guess that you can teach an old dog new tricks.

[drisley]

Originally Posted by scottbergerphoto

In addition on the 10D, by not pressing the * or X button, the camera is in Manual focus and this forces the flash metering to average all the sensor input instead of biasing an active focus point resulting in more consistent flash. This is not the case though for the 20D which uses ETTL2. ETTL2 is independent of AF points.
Try it, you'll like it!
Scott

Excellent!
How does this affect non-flash metering? I know that the 10D biases exposure metering on the focus points too. So would this help?
Does anybody know if the 20D biases to the autofocus point for exposure metering?

[CyberDyneSystems]

Correct me if I'm wrong...

I don't have the reference material on hand.. but this is not how I understand it.

For the 10D and 20D I understand that all metering is biased towards the center "Partial" circle regardless of active focus point.

On the "1" series the ONLY time you get metering biased towards the focus point is when you use "Spot metering"

As the 20D and 10D do not have Spot metering.. they are neccesarily incpabable of this ability.

Correct me if I have misunderstood this.... but with the 10D in partial metering I know it uses the center circle no matter what AF point I use.

Are you suggesting that if I used "evaluative" that the 10D would have "centered" on the active focus point?

[scottbergerphoto]

Originally Posted by CyberDyneSystems

Correct me if I'm wrong...

I don't have the reference material on hand.. but this is not how I understand it.

For the 10D and 20D I understand that all metering is biased towards the center "Partial" circle regardless of active focus point.

On the "1" series the ONLY time you get metering biased towards the focus point is when you use "Spot metering"

As the 20D and 10D do not have Spot metering.. they are neccesarily incpabable of this ability.

Correct me if I have misunderstood this.... but with the 10D in partial metering I know it uses the center circle no matter what AF point I use.

Are you suggesting that if I used "evaluative" that the 10D would have "centered" on the active focus point?

Let's be clear about which metering we are talking about. In ambient light metering, in Evaluative Metering, the metering system gives emphasis to the active AF point(s) while also utilizing data from the other sensors. It clearly states that in the 10D Manual. This has nothing to do with spot metering in which data from other sensors are ignored. It is a function of Evaluative Metering. You can't control how the camera balances the information it gets as you can in spot metering. If you switch to Manual Focusing in Evaluative Metering, it will bias the Center AF Point.(Page 75)

In flash metering, it is my understanding that in ETTL the flash metering is biased to the active AF points and that you can avoid that by switching to MF on the lens or using the Cfn's to put focus on * and X and releasing the button before depressing the shutter button. In ETTLII there is no such bias to AF points.

Here is an additional reference: http://www.camera.canon.com.my/archi...rt/art14/2.htm
Regards,
Scott

[CyberDyneSystems]

Thanks Scott,

in my case I confused the issue beuase I use "Partial" so often... which allways "weights" the center circle for metering regardless of active focus point.

Seems I need to use evalauative more often... particularly when using an off center focus point.

Thanks.

[kawter2]

Originally Posted by CyberDyneSystems

CF # 4 Get that focus control onto the * button ASAP

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[Deckyon]

Originally Posted by CyberDyneSystems

CF # 4 Get that focus control onto the * button ASAP

Would that mean setting it to 1, 2 or 3

[CyberDyneSystems]

Definately 1... and also 3 the difference being how the AE/lock functions on the half shutter press.

I usually use CF#4 @ 1

When you do this.. bursts can be an issue.. as each following shot will use the same mettering.. if the scene or more specifically lighting is changing as you track a moving subject.. then avoid using a "burst" whcih will lock the exposure on the first shot.. instead trip the shutter for each individual shot making sure to let up on it enough to maintain a "half press" exposure lock.

By switching to 3 you can do away with AE lock all together.. but I don't like this as it won't allow the recomposure trick.

[MarkH]

Originally Posted by CyberDyneSystems

CF # 4 Get that focus control onto the * button ASAP

Tried that, absolutely HATED it!

It's so much easier to use the shutter button to focus and then fully press it to activate the shutter. For me it seems that focusing with the * button fixes a problem that I don't have. The only times that I have an exposure problem, the metering would be fooled no matter what and I switch to M to correct the problem.

[elbirth]

Originally Posted by MarkH

Tried that, absolutely HATED it!

It's so much easier to use the shutter button to focus and then fully press it to activate the shutter. For me it seems that focusing with the * button fixes a problem that I don't have. The only times that I have an exposure problem, the metering would be fooled no matter what and I switch to M to correct the problem.

I should be getting my 20D later today, so I haven't had the chance to try it yet... but I agree with Mark, in that I think I won't like the function. The only time I really see that as being helpful is if you're doing a photo shoot with a model that's walking around somewhat, but stays roughly the same distance from you.