What's the use of "AF Stop" on 300 f/2.8 IS L ?

[roli_bark]

As subject says.

In what photographic situations is it usefull ?
And how to use it effectively ?

[Ronald S. Jr.]

Sounds to me like a harder alternative to switching AF to the * button. At least on the 20D, that's custom function 4-1.

[roli_bark]

Sounds to me like a harder alternative to switching AF to the * button. At least on the 20D, that's custom function 4-1.

Either way...But why is it there, and for what photographic situation ?

All 4 top tele lenses [300 f/2.8 L, 400 f/2.8 L, 500 f/4 L, 600 f/4 L] have it [AF Stop button] as an added feature.
There MUST be a reason for this addon for the 4 Super Tele family members !

[roli_bark]

Found some reference to this, in Photozone.de :

"...The lens also features an AF stop button to disengage the AF drive in AF mode..."

But still, it is not clear to me what is the application ?


=====

And, in the Mark II series, there the following custom function:
C.Fn-19: Lens AF stop button function
Only applicable for Canon super telephoto lenses with an AF stop button. This Custom Function controls the operation of the AF stop button.

0: AF stop
1: AF start
2: AE lock while metering
3: AF point, holding down button switches from manual to auto, or from auto to center
4: AF mode, button switches from One-Shot to Al Servo AF modes
5: IS Start (Image Stabilizer).

[Ronald S. Jr.]

That quote makes it sound to me like it's to engage manual focusing...? I was under the distinct impression that all of the L supertelephotos would obviously have full time manual focusing.

[roli_bark]

That quote makes it sound to me like it's to engage manual focusing...? I was under the distinct impression that all of the L supertelephotos would obviously have full time manual focusing.

Of course [ (1) FTM feature, and (2) AF/MF switch, that this lens has...]

But, that button[s] [AF Stop] is/are 2 SEPERATE BUTTONs on the outer RING ... !!!

[storeman]

I have no idea but I found this at http://www.shortcourses.com/10D/lenses.htm

A few lenses have an AF stop feature that prevents focus from shifting when something passes between you and the subject you're focused on. You turn this feature on by pressing an AF Stop button on the lens.

[roli_bark]

On "AF Stop" button, from the user manual:

[roli_bark]

I have no idea but I found this at http://www.shortcourses.com/10D/lenses.htm

A few lenses have an AF stop feature that prevents focus from shifting when something passes between you and the subject you're focused on. You turn this feature on by pressing an AF Stop button on the lens.

Yes, that's is true, but that's reaching out to the outer ring [where the "AF Stop" buttons are located]. I'd rather release the shutter button when an obstruction passes accross the viewfinder, and press it again when the obstruction disappears.

[gmen]

Use of the AF stop button is similar to setting CF 4 to 2 - it simply stops the AF, effectively turning AI Servo into One Shot mode for as long as it is held down.

It's just another focusing 'option' - along with using the * button and also using the focus preset option on some of the long lenses.

It's really what you feel comfortable with. Personally my thumb doesn't enjoy CF 4-1 or 4-3, so I generally use CF 4-2, using the * button to stop the AF when I need to. I don't use the AF stop button on the lens as I personally don't find it comfortable to work with.

An example of when you'd stop the AF may well be to lock focus on the goal-line in a football match when a corner is being taken - this avoids another player coming across your field of view and the focus being thrown off. As soon as you're ready you can release the lens stop button/* button and go straight back to AI Servo.

---- Gavin

[fslshooter]

Gavin - Thanks for the insight! I couldn't figure out exactly what that button does nor an applicaton for it. I doubt that I'll be using it anytime soon though -- I'm still trying to get comfortable using the focus preset :confused: .

[gmen]

Gavin - Thanks for the insight! I couldn't figure out exactly what that button does nor an applicaton for it. I doubt that I'll be using it anytime soon though -- I'm still trying to get comfortable using the focus preset :confused: .No problem Jerry...and thanks for the PM... you'll love those additions to your arsenal ;)

---- Gavin

[roli_bark]

No problem Jerry...and thanks for the PM... you'll love those additions to your arsenal ;)

---- Gavin

Gavin, just a quick question about [or guidance to the motions of] Shooting immediately after pressing the "AF Stop", as I understand from the manual:

1. Press "AF Stop"
2. Make sure that while pressing the "AF Stop" button, the shutter release button isn't pressed half-way...
3. When ready to shoot, release "AF Stop" and press Shutter Release button FULL WAY (at once - with pausing at the Half-Way position...???).


That sounds to me (a) Cumbersome, and (b) Weird - because when one presses Shutter Release 'FULL WAY' he/she is going practically going thru the 'Half-Way' position anyways (no matters how quick the FULL release is squized), causing an instantenuous further AF...

[gmen]

1. Press "AF Stop"
2. Make sure that while pressing the "AF Stop" button, the shutter release button isn't pressed half-way...
3. When ready to shoot, release "AF Stop" and press Shutter Release button FULL WAY (at once - with pausing at the Half-Way position...???).
That sounds to me (a) Cumbersome, and (b) Weird - because when one presses Shutter Release 'FULL WAY' he/she is going practically going thru the 'Half-Way' position anyways (no matters how quick the FULL release is squized), causing an instantenuous further AF......yep, it certainly sounds cumbersome... and it doesn't reflect how the AF stop button actually works.

I've just tested it (in case I'm going mad) and for as long you hold the AF stop button, the AF is locked. You can fire the shutter while the AF lock button is held down... it's pretty much the same as CF 4-2, where the * button acts as an AF stop button.

---- Gavin

[roli_bark]

But the manual specifically warns to not press the shutter button half-way while using the AF-Stop....it furtherly warns that this may cause malfunction.

[gmen]

But the manual specifically warns to not press the shutter button half-way while using the AF-Stop....it furtherly warns that this may cause malfunction.:lol: Well... this probably explains why I never use the AF stop button! :lol: If that is the case, then it simply 'pauses' the AF system while depressed. This means it is only designed to keep the point of focus temporarily in the right area if something is likely to come between the lens and the subject matter.

---- Gavin

[roli_bark]

Yep....to me it looks like a superfluous feature.
I just wonder why Canon have invested in its design in all 4 Super L Telephotos lenses.

[gmen]

Yep....to me it looks like a superfluous feature.
I just wonder why Canon have invested in its design in all 4 Super L Telephotos lenses.I suppose it's not completely superfluous as it could still work in the situation I described above... but it's certainly not quite the same as 'locking' the focus.

Also, I've never dabbled with CF 19-4 which claims to allow the lens button to switch the focusing between AI Servo and One Shot modes. I shall have a tinker later and report back.

As I said before, it's just adding another option to the focus possibilities. For some it may be more comfortable to press a button on the lens as you may be resting your hand on the lens or 'cradling' it when shooting. Hmmm.

---- Gavin

[gmen]

But the manual specifically warns to not press the shutter button half-way while using the AF-Stop....it furtherly warns that this may cause malfunction....and just another thought on this. Does the manual mention whether the same malfunction can be caused by holding down the AF stop button on the lens when using the * button to focus via CF 4-1 or 4-3? I can't imagine why anyone would want to do that (you can just release the * button to lock focus rather than choose to press another button at the same time)... but it's a possibility.

I haven't got a manual to hand at the moment... in fact, I'm not even sure I have a manual for the 400mm :lol:

---- Gavin

[roli_bark]

.... For some it may be more comfortable to press a button on the lens as you may be resting your hand on the lens or 'cradling' it when shooting. Hmmm....---- Gavin

Yes, but suppose you hand-hold it. It is VERY difficult to reach out quite far [to the farest Rubber RING], pushing down 1 of the "AF Stop" buttons, while your other hand is....where is it actually ? :)

[gmen]

Yes, but suppose you hand-hold it. It is VERY difficult to reach out quite far [to the farest Rubber RING], pushing down 1 of the "AF Stop" buttons, while your other hand is....where is it actually ? :)Absolutely. When handheld, the stop buttons are pretty much useless.

When used on a monopod, I sometimes find my hand rests naturally on the lens from time to time... therefore they might be useful under those circumstances.

---- Gavin

[roli_bark]

Nevertheless, it is a beatifull man-made masterpiece !

[gmen]

Nevertheless, it is a beatifull man-made masterpiece !Indeed!... and there are going to be togs out there who absolutely swear by this feature! I've yet to meet one... but they might just be keeping it secret ;)

---- Gavin