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Confusing Custom Function on 7D

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Thread started 31 Dec 2012 (Monday) 11:02   
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RPCrowe
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I am somewhat confused with the 7D Custom Function III-02 (AI Servo 1st/2nd image priority.

It has to do with how autofocus prioritizes Focus/Shutter release in continuous shooting. It allows the photographer to specify what takes precedence when the shutter release button is pressed all the way down.

The choices are:
0: AF Priority/Tracking Priority
1: AF priority/Drive Speed Priority
2. Release/Drive Speed Priority
3. Release Tracking Priority

I cannot understand what happens in choices 0-3 or under what circumstances I would wish to switch the priorities...

Post #1, Dec 31, 2012 11:02:16


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mainbyte
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Here is a bit of a description of what each setting is for and why you may wish to change it. This is described on page 4 of this technical paper. In fact the whole article is helpful for custom settings.

http://cpn.canon-europe.com ...om_functions_explai​ned.doexternal link

Ron

Post #2, Dec 31, 2012 11:30:37


Canon 6D | Canon 7D | 17-40 f/4L | 24-105 f/4L | 70-300 4/5.6L |100mm f/2.8L macro | 50mm 1.4 | 580exII | 2 - 430exII |

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vorlon1
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Excellent article.

"C.Fn III -2 – AI Servo first/second image priority

For AI Servo shooting, you can adjust the priority for the first shot or the second and subsequent shots. It deals with two issues:

How quickly the camera will fire if you suddenly press the shutter button fully.
If the shutter button is held down for continuous shooting, whether AI Servo AF will always take time to ensure correct focus for each shot (which may result in slowing down the drive speed), or whether the camera will always fire at top fps speed (even if proper focus cannot be ensured for each shot in the sequence).

There are four settings:

0: AF priority/Tracking priority – this will give more time to achieve focus before releasing the shutter and then during continuous shooting, focus tracking will be given time to keep accurate focus.
1: AF Priority/Drive speed priority – like setting 0, the first shot will prioritise focusing. However, after that the camera will try to maintain the maximum shooting speed. This is useful if the subject is large and easy to focus on, or not moving over great distances.
2: Release/Drive speed priority – this will fire the shutter as quickly as possible for the first shot, not giving as much time to finding focus. For subsequent shots, the camera will continue to fire at the maximum frame rate in preference to giving time to focus driving. If you have to capture the moment at all costs, this is a good option to use.
3: Release/Tracking priority – this will work like option 2, in that priority is given to releasing the shutter, but for second and subsequent images, the camera will then pass priority to focus tracking, rather than trying to maintain the maximum frame rate."

Post #3, Dec 31, 2012 11:41:29


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MikeWa
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Pushing the shutter release button half way energizes Auto Focus and Image Stabilization in the lens. But what happens when you push the shutter release button all the way down? You would think the shutter would just release. But actually you have choices on what occurs both for the first photo in a burst and for subsequent photos. Your choices are
First picture / Subsequent pictures
1 Check focus release shutter / track focus release shutter
2 Check focus release shutter / release shutter
3 Release shutter / release shutter
4 Release shutter / track focus release shutter
So what is more important to you? Double checking focus or instantly releasing the shutter?

Mike

Post #4, Jan 01, 2013 09:32:08


Mike...G9; EOS 7D; EF-S 10-22mm; EF-S 18-135mm IS; EF 28-300mm F3.5-5.6L; EF 70-300mm IS USM; EF 70-200mm F2.8L IS-II; EF 100-400mm f4.5-5.6L IS; EXT 1.4-II & 2.0-III; The more I learn the less I know.

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The ­ "Canon ­ 7D" ­ Kid
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I hope this may be of help also
http://www.deepgreenph​otography.com ...ing-up-your-new-canon-7d/external link

Post #5, Jan 01, 2013 09:51:51 as a reply to MikeWa's post 19 minutes earlier.


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convergent
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RPCrowe wrote in post #15427473external link
I cannot understand what happens in choices 0-3 or under what circumstances I would wish to switch the priorities...

The best way to describe, to me, is to give an example. Say you are shooting a basketball game. A lot is happening and you see a fight break out and a player punches another player in the face. You pull the camera up to shoot and hit the button (AI-Servo). Do you want it to take the picture immediately when the button is pressed, or do you want it to delay the shutter release until it is absolutely confirmed in sharp focus. If you go with shutter priority, you may get the peak action of the guy's fist in contact with the face, but it may not be sharply in focus. If you go with focus priority, you may get a sharply focused image of a split second after the guy was hit.

There are various different scenarios with this, but the gist of it is what I described. And you get to choose to have the first shot in a burst be treated differently from the rest. Personally, I have always opted for focus priority because a slightly blurry picture of something is not that interesting to me.

Post #6, Jan 01, 2013 09:55:41


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apersson850
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vorlon1 wrote in post #15427609external link
If the shutter button is held down for continuous shooting, whether AI Servo AF will always take time to ensure correct focus for each shot (which may result in slowing down the drive speed), or whether the camera will always fire at top fps speed (even if proper focus cannot be ensured for each shot in the sequence).

This isn't 100% true.
In release priority, the camera will make one focus measurement, evaluation and lens drive cycle, and that's it. If the subject is an easy target, this will be enough, the image taken will be in focus and the drive speed will be maintained, as there is time allocated for this focusing operation in between the shots.
If the subject is difficult, the camera may drive the lens to the wrong distance setting, or fail to drive the lens at all, if the camera is utterly confused. The image will be out of focus, but it will still be taken, at the claimed frame rate.
This is exactly as described in the quote. However, when set to AF priority, the camera will make one or more attempts at measuring, evaluating and driving the lens to achieve proper focus. Exactly how many Canon does not disclose. But the important thing to understand is that this is a finite number. After a couple of attempts, which will take enough time to slow down the frame rate, the picture will be taken, regardless of if focusing still has not been accomplished successfully.

Thus when using Servo AF, there's no setting which will ensure that every image is properly focused. It's only when using One Shot AF a 7D will refuse to take a picture if it's out of focus. If the picture is taken, the camera is convinced it's focused. It may have focused on something else than what you intended it to, or it may be completely fooled and not focused at all, but at least it thinks the image is in focus.

Post #7, Jan 01, 2013 13:34:57


Anders

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vorlon1
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Well. that's interesting, because I just copied that whole post from the relevant part of the canon article referenced. I should have put quotation marks around the whole thing. Now done.

Post #8, Jan 01, 2013 14:06:45


"We don't see things as they are, we see them as we are." -- Anais Nin
5Dc Gripped, 7D Gripped, T3i, S100, Pentax 50 1.4, 40mm f/2.8 Pancake, 24-105 mm L, 85mm 1.8, 18-200mm 3.5-5.6, Tamron 60mm f/2 Macro, 70-200mm f/4 L, Tokina AT-X 12-24mm etc.
Smugmug: http://paladinphotos.s​mugmug.com/external link

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apersson850
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Seems they didn't go into every detail. The quote is correct to a certain degree, just skips mentioning that the camera will fire even if focus can't be accomplished, even in AF priority.

Post #9, Jan 01, 2013 15:25:20 as a reply to vorlon1's post 1 hour earlier.


Anders

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