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Frequent Contributor
Posts: 30
Registered: ‎05-16-2015

DRIVES, AF OPERATIONS (specifically continuous autofocus), and AF POINT SELECTIONS

I have some questions in regard to the correlation between DRIVES, AF OPERATIONS (specifically continuous autofocus), and AF POINT SELECTIONS. Because I realize that AI FOCUS AF will initially focus using the CENTER POINT then track the moving subject much like AUTOMATIC FOCUS POINT does, I imagine that if one is using AI FOCUS AF, an adequate FOCUS POINT SELECTION companion would either be CENTER or AUTOMATIC . Which is better? Also, if one should decide not to use any AF OPERATION at all but instead use CONTINUOUS DRIVE mode in conjunction with MANUAL FOCUS, would that have any bearing on which AF POINT SELECTION option one chooses. For example, a guy I read about had been using AI FOCUS AF during a Formula race. While realizing his camera couldn't keep up with the fast cars closing in, he decided to do just that. He explains he could lock the focal distance, keep it fixed in place and shoot in CONTINUOUS DRIVE to increase his chances of at least one frame being sharp. Since he furthermore says that he selected a FOCUS POINT, it makes me wonder what bearing AUTOMATIC FOCUS POINT SELECTION would have had, and could he have chosen that option for the same scenario?

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Honored Contributor
Posts: 5,528
Registered: ‎06-25-2014

Re: DRIVES, AF OPERATIONS (specifically continuous autofocus), and AF POINT SELECTIONS

That paragraph is a masterpiece of literary craftsmanship. It could easily be mistaken for a coherent sequence of English sentences.

Bob
Philadelphia, Pennsylvania USA
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Esteemed Contributor
Posts: 2,369
Registered: ‎11-14-2012

Re: DRIVES, AF OPERATIONS (specifically continuous autofocus), and AF POINT SELECTIONS

Firstly different bodies have different AF systems & so do the different lenses, SO as a good rule of thumb a more expensive body or lens should AF faster & more accurately.

 

Secondly forget AI Focus & start using AI Servo. The pro bodies don't have AI Focus which should be a clue to the idea AI Servo is better.

 

Thirdly YES you can MF on a place on the track & bang away in continous mode to get at least one decent shot per burst. That's how we did it in the film era when we didn't have AF. The idea was to MF in the center of a corner, wait for a group of cars to enter & hope someone screwed up and as they did you fired away. That worked for me so I know it can be a useful way to get a shot or 2 per burst, BUT the better bodies can do it even better with the  AF on.

"A skill is developed through constant practice with a passion to improve, not bought."
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Frequent Contributor
Posts: 30
Registered: ‎05-16-2015

Re: DRIVES, AF OPERATIONS (specifically continuous autofocus), and AF POINT SELECTIONS

Thank you! I agree, especially because I even matched the capitalization of certain keywords in the the title with iterations of the same inside the paragraph. Smiley Happy

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Frequent Contributor
Posts: 30
Registered: ‎05-16-2015

Re: DRIVES, AF OPERATIONS (specifically continuous autofocus), and AF POINT SELECTIONS

Hmm. That's a very interesting point you make about faster AF systems. I've learned that the speed of CONTINUOUS mode could be slightly slower while using AI SERVO AF. Certainly, as a novice who uses the Rebel SL1, I have to read the manual to get better aquainted with all the different methods of operation. But when I think of delay or lag, I think of the intial focus lock-in on a subject that's affected because I know its sort of a process on its own that needs to happen before the camera can track it. If you had a Rebel SL1 like me and a  EFS 17-55mm f/2.8 IS USM on it, would you still shoot like you did in the film era or go for AI SERVO AF? It seems that with that lens, even with it zoom in all the way, you would have to use MANUAL focus at a Formula race because the cars would be so small in the viewfinder. An AF system would have trouble tracking them. Does it sound like I'm on the right track?

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Esteemed Contributor
Posts: 2,369
Registered: ‎11-14-2012

Re: DRIVES, AF OPERATIONS (specifically continuous autofocus), and AF POINT SELECTIONS

I've never shot an event with that wide a lens other than a parade but the depth of field should really help at the track. I'd start with the AF in AI Servo, using a single point on a specific car & check my results. After that I'd try a slightly expanded zone & check to compare. If you really want good results (assuming you attend more than 1 race a year) you need a longer lens & I recommend it be a zoom for the versatility.

Also if you don't know how to shoot auto racing the plan is to pan with the car, freeze the car but use a slow enough shutter speed to have the wheels & tires PLUS background blurred a bit to imply the car is speeding down the track. Freezing everything "says" it parked there.

"A skill is developed through constant practice with a passion to improve, not bought."
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Frequent Contributor
Posts: 30
Registered: ‎05-16-2015

Re: DRIVES, AF OPERATIONS (specifically continuous autofocus), and AF POINT SELECTIONS

There's no spotting me at the motorsports facility other than driving go-carts, unfortunately outside the placement of merit. Hahaha! My mentioning the guy who did shoot at Formula races was more or less an effort to give context to the problem I was trying to figure out, which really has to do with the FOCUS POINT SELECTIONS one has to consider as they relate to the different AF MODES. The guy says that he selected a SINGLE POINT to lock-in distance to the track and then switch to FT-Manual focus to take CONTINUOUS shots, whereas I'm wondering could he have used AUTOMATIC POINT selection to lock-in beforehand. It seems if the AF system is advanced enough, it would be able to focus well during the burst. Moreover, you mention panning for a more creative effect along with a bigger zoom that what I have, which in that case, I know for sure I would select a SINGLE POINT. I'm mostly uncertain when it comes to the SELECTION POINTS, particularly when I want to focus MANUALLY, and under what circumstances, if any, I would want to use the AUTOMATIC POINT SELECTION?

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Frequent Contributor
Posts: 30
Registered: ‎05-16-2015

Re: DRIVES, AF OPERATIONS (specifically continuous autofocus), and AF POINT SELECTIONS

I just realized that I'm not even sure whether it's the lock button that actually sets the focal distance. Do you need to push the lock button at all or does pushing the af switch to manual actually lock-in the focal distance?
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Frequent Contributor
Posts: 30
Registered: ‎05-16-2015

Re: DRIVES, AF OPERATIONS (specifically continuous autofocus), and AF POINT SELECTIONS

[ Edited ]

Also, I'm confused. Would automatic point selection workat all in manual focus mode or is it tied in with autofocus modes only? It's been suggested that while in AF mode, automatic point selection is only good if the subject is in the middle of the frame and nothing is in the foreground to confuse the AF system.

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