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Archive 2013 · 5D3 Back Button Focusing Question
  
 
brad_s
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p.2 #1 · 5D3 Back Button Focusing Question


I've been watching this thread waiting for someone to give the details. ....finally here it is if you haven't already got it figured out. This is the way my camera is set up.

This is pretty much what you are looking for. Go to:
1: C.Fn2isp/Operation
2: AF-On button - select Metering and AF Start. Yes this will also meter and it will continuous meter once the camera is turned on.
3: Shutter butt. half-press button - select AE lock (while button pressed). This will be redundant with the AE lock on the standard * button.

With this setting the half shutter button will act like "metering with the shutter release". Personally, I think this is a very good way to set up the camera.

gel685 wrote:
How do you back button focus while metering with the shutter release? The "AF-ON" button will focus and meter but I want it to just focus with metering with the shutter release. I'm sure I could do this with my 1D2n. Thanks,--Eric.



Feb 23, 2013 at 07:39 AM
cgardner
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p.2 #2 · 5D3 Back Button Focusing Question


Back button AF lock / Half-Press AE lock prevents "focus - recompose" >>>> EXPOSURE <<<<< errors in Av/Tv mode when also using ETTL-II flash with Evaluative (zone) flash metering in Single-Shot AF mode.

Canon ETTL-II flash metering makes a second "baseline" ambient reading, separate from the one used to set shutter / aperture in Av/Tv mode, immediately after FULL shutter press. It is subtracted from the preflash+ambient "zone maps" for each group's pre-flash which allows the metering to logically deduce what each flash group is hitting and which are overlapping for setting ratios.

When AF/AE lock are both on the shutter (half-press) if the shutter is half pressed, then the viewfinder is recomposed, when the shutter is fully pressed the flash metering will be performed on a different scene. That can lead to incorrect exposure if there's a difference between the before / after content in the viewfinder, particularly in the center metering zones.

With AF lock moved to a back button via CF.n it is possible to lock AF with the back button, recompose, half-press to lock AE, then fully press to initiate the flash metering and make the exposure. AE metering is also done when the AF button is pressed, but not locked until after recomposing with the half-press of shutter. Since AE lock and flash metering are done on the same scene results are more predicable.

AF lock + metering with back button (Programmed via CF.n)
Recompose
AE lock with half press of shutter
Full press of shutter
-- second ambient baseline exposure reading is made for flash calculation
-- preflash group A
-- preflash group B
-- preflash group C
-- Flash calculation
-- Coded command signal to flashes to set % power level sent
Shutter opens- First Curtain Clears Sensor (normal flash mode)*
-- Coded signal to fire slaves sent
Flashes Fire
Shutter closes

* It takes about 1/300th sec. for first curtain of shutter to move across and fully expose the sensor so flash can be fired in normal single burst mode. in HSS mode the signal to start pulsing the flashes is sent just before the first curtain opens.

Edited on Feb 23, 2013 at 10:42 PM · View previous versions



Feb 23, 2013 at 11:57 AM
Monito
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p.2 #3 · 5D3 Back Button Focusing Question


Terminology: "Focus / Recompose" errors are geometric errors from a single act of focusing. They are not errors caused by a second unwanted focus action.

http://visual-vacations.com/Photography/focus-recompose_sucks.htm

Thus the back-button-focus, which I recommend, does not prevent focus-recompose errors.

The rest of cgardner's post is excellent information (as is customary).



Feb 23, 2013 at 01:50 PM
BrianO
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p.2 #4 · 5D3 Back Button Focusing Question


gel685 wrote:
...The "AF-ON" button will focus and meter but I want it to just focus...


Back button focus is a good thing for many uses, but it's NOT, by itself, what the OP was looking for.

As I've said several times, to the best of my knowledge you can't seperate focusing and metering, which was the OP's question and which everyone who's posted "how to do it" seems to be ignoring.





Feb 23, 2013 at 02:40 PM
Cometsoft
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p.2 #5 · 5D3 Back Button Focusing Question


BrianO wrote:
Back button focus is a good thing for many uses, but it's NOT, by itself, what the OP was looking for.

As I've said several times, to the best of my knowledge you can't seperate focusing and metering, which was the OP's question and which everyone who's posted "how to do it" seems to be ignoring.



Simple.

Custom Controls Menu - set Shutter button to meter, "*" to focus on. Works for me. Are you talking about the 5D3? When you press the "*" there is no metering going on, just focus.



Feb 23, 2013 at 02:49 PM
BrianO
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p.2 #6 · 5D3 Back Button Focusing Question


Cometsoft wrote:
...Are you talking about the 5D3? When you press the "*" there is no metering going on, just focus.


Canon disagrees with you:









Feb 23, 2013 at 03:21 PM
Cometsoft
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p.2 #7 · 5D3 Back Button Focusing Question


BrianO wrote:
Canon disagrees with you:


Sorry, you're right. Can't be decoupled. Got up to early last night, too much crack...

So the only way I can see doing it is to program the AF-On button as AE-Lock.

I apologize, or maybe there's a way my crack-addled brain can't grasp.



Feb 23, 2013 at 04:12 PM
schlotz
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p.2 #8 · 5D3 Back Button Focusing Question


sounds like first solution is to stop doing crack


Feb 23, 2013 at 06:04 PM
 

Search in Used Dept. 



BrianO
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p.2 #9 · 5D3 Back Button Focusing Question


Cometsoft wrote:
Sorry, you're right. Can't be decoupled. ...So the only way I can see doing it is to program the AF-On button as AE-Lock.


The AF activation would still activate metering, but that's no big deal in my opinion; one could re-meter after achieving focus by using a half-press on the shutter release (when set for metering only), using AE Lock, etc.

That's how I do it on my 7D: shutter button set to Metering Start, AF-On button set to AF, and * button set to AEL and FEL.



Feb 23, 2013 at 06:52 PM
Cometsoft
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p.2 #10 · 5D3 Back Button Focusing Question


schlotz wrote:
sounds like first solution is to stop doing crack


Good idea! The reason it confused me was because I just set up the camera this way and my fingers are always hitting the wrong button. Was hitting the AF-On button, which was programmed to AE Lock, before hitting the "*" button and the exposure would lock so I had the idea that it stopped metering.

Excuses, excuses...



Feb 23, 2013 at 10:18 PM
cgardner
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p.2 #11 · 5D3 Back Button Focusing Question


Monito wrote:
Terminology: "Focus / Recompose" errors are geometric errors from a single act of focusing. They are not errors caused by a second unwanted focus action.

http://visual-vacations.com/Photography/focus-recompose_sucks.htm

Thus the back-button-focus, which I recommend, does not prevent focus-recompose errors.

The rest of cgardner's post is excellent information (as is customary).

The method I list prevents focus-recompose induced EXPOSURE errors resulting from the way the camera meters flash separately from the metering setting the shutter / aperture. That should be obvious to anyone reading the entire message but I've edited the original to clarify that.



Feb 23, 2013 at 10:40 PM
brad_s
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p.2 #12 · 5D3 Back Button Focusing Question


Some may think I'm splitting hairs. ...but meter first then focus. Once you get the focus fire that shutter or wait to release - as long as you have the meter locked you can refocus as many times as your ability to hold your concentration with that half-press on the shutter (for AE lock).

BrianO wrote:
The AF activation would still activate metering, but that's no big deal in my opinion; one could re-meter after achieving focus by using a half-press on the shutter release (when set for metering only), using AE Lock, etc.

That's how I do it on my 7D: shutter button set to Metering Start, AF-On button set to AF, and * button set to AEL and FEL.




Feb 25, 2013 at 07:43 AM
brad_s
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p.2 #13 · 5D3 Back Button Focusing Question


Program the shutter half press as AE lock and run both * and half press of the shutter as AE Lock. ...that's what I do. Anyway when you're running AF-On for back button focus it's too difficult work those two buttons so close to each other with the thumb.

Cometsoft wrote:
Sorry, you're right. Can't be decoupled. Got up to early last night, too much crack...

So the only way I can see doing it is to program the AF-On button as AE-Lock.

I apologize, or maybe there's a way my crack-addled brain can't grasp.




Feb 25, 2013 at 07:47 AM
BrianO
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p.2 #14 · 5D3 Back Button Focusing Question


brad_s wrote:
Some may think I'm splitting hairs. ...but meter first then focus.


I'd say it depends: if the subject is moving but under steady light than metering first makes sense; but if it's a stationary subject under changing light then focusing first makes more sense.



Feb 25, 2013 at 08:09 AM
Monito
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p.2 #15 · 5D3 Back Button Focusing Question


brad_s wrote:
Some may think I'm splitting hairs. ...but meter first then focus.


BrianO wrote:
I'd say it depends: if the subject is moving but under steady light than metering first makes sense; but if it's a stationary subject under changing light then focusing first makes more sense.


Typically, I mix metering and focusing, but with a prediliction for metering first, even when lighting conditions vary. But I don't shoot so much action or bird-in-flight as others.

I typically shoot in Manual & Raw & back-button-focus. I will meter a scene, taking note of readings at several directions if there is shade or other static variation in lighting depending on direction. Then I confirm those with the HistoBlinkyMeter and may adjust them upwards or downwards according to EttR principles (Expose to the Right).

Then while I'm shooting, I focus as needed. If the action or the view moves into an area with different lighting, I adjust the exposure on the fly according to my previous metering and the current reading (with mental notes about compensation due to EttR) and continue shooting.

If the metering changes due to clouds moving in or out (instead of shifts into differing static lighting), then I remeter including checking the HistoBlinkyMeter and applying EttR. If the clouds revert back to the original lighting, then I've already got that on board.

This is not done by using Tibetan memory tricks, but rather by having a base idea of the exposure needed and also of what compensation to apply as needed for different lighting. But I do chimp the LCD and consult the HistoBlinkyMeter on various previous shots as I am able.

I learned this kind of approach from match needle metering for film. I'm not fussy about needing +/- 1/3 or 2/3 stop adjustments in Raw conversion or B&W negative printing, and I don't try to lean on the EttR too much if I am shooting loosely. Of course I will take the time for careful metering if I am shooting something very deliberate like a quality landscape, architecture, or portrait session. (I no longer shoot colour film).



Feb 25, 2013 at 10:36 AM
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