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I have read tips about where one can autofocus by a half-shutter pre-press and then shoot fast by a full shutter press. So that I can avoid the autoexposure and autofocus lags.

What's the right way to do this? On my Powershot SX700 even if I fully press the shutter button quickly it seems to still go through the full motions.

What's the right way to instruct the camera to shoot immediate? I have tried this in Auto mode as well as Program mode

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    When you say you push it fully, do you mean that you finish pushing the button the rest of the way or that you push it fully from unpressed? You have to push it half way, wait for exposure and focus to adjust and lock, then you can push it the rest of the way. You don't let go in-between and you still can't go before it gets a good lock, which can take some time, particularly in low light. – AJ Henderson Dec 5 '14 at 16:31
  • @AJHenderson: Thanks! I was pushing it half way, letting it focus & then letting go during my wait for the right moment. Based on your description I ought to retain the half-press hold? They don't just remember the last exposure / focus value & use that on a direct full press? – curious_cat Dec 5 '14 at 18:21
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    I moved my comment to an answer now that I know it is actually the problem and added some additional explanation of why. – AJ Henderson Dec 5 '14 at 18:51
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    Note about my comment, it may or may not lock both exposure and focus. It depends on the model of camera and the settings selected on the camera. I assumed that what you had read about your camera doing both was to be taken at face value, but it not all cameras do both by default or in all modes. – AJ Henderson Dec 5 '14 at 19:24
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    Related post... photo.stackexchange.com/questions/22885/… – AJ Henderson Dec 5 '14 at 19:27
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You need to keep the button half pressed. The setting is not locked when you push half way. If you let go, the system believes you decided not to take the photo or the lock was no good (maybe it focused on the wrong thing). When you release the button, the settings are also released.

You need to press half way and keep the button half pressed after the lock. Then, when you finish the press, it should take without having to make the adjustments again.

Some cameras have an exposure lock (FE lock) button that you can use to lock exposure until the next photo even if you let go of the button, but that's a different feature. Every camera I know of only keeps the half press lock until you release the button.

It is also worth noting, as Romeo Ninov pointed out, that the exact details of what is locked can vary from camera to camera or even based on settings on the camera.

  • Thanks. So, for arguments sake, if I half-pressed, released & then full-pressed without the usual half-press wait for focusing would it shoot immediate or still go through the pre-focus ritual. If it does shoot immediate which settings for focus & exposure would it use, if not the last ones? i.e. When you say "the settings are released" does it fall back to some default settings? Or.... – curious_cat Dec 5 '14 at 19:51
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    It would go through the same ritual. The camera needs to focus and determine exposure before it can take a meaningful picture. Otherwise you would just have a blurry white or black square. The only other way around it is to fully manually set your exposure and focus. – AJ Henderson Dec 5 '14 at 19:52
  • Gotcha! Thanks. So essentially, the Auto mode is making it close to impossible to get out of focus / mis-exposed pics? Except when things change fast in the interval between the camera's decision making & the actual shutter release? Which seems quite often really. :) – curious_cat Dec 5 '14 at 19:56
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    @curious_cat - yep, that's the goal, and the lag is also one of the reasons avid shooters often prefer DSLRs where the AF can be more responsive and it takes less lag time to take the photo. In general, point and shoots aren't very good at action shots for this exact reason (though there are some exceptions that have shorter lag times). – AJ Henderson Dec 5 '14 at 19:59
  • For my SX700 reviews show an approx. 100 ms lag in good light situations. Not sure if that's good or bad though. Is there anything about the DSLR itself that allows them to be built with low lags? Or just that they are more expensive? The lag ought to depend on the algos & they both (some DSLRs & some point n shoots) share the DIGI-6 processors it looks like. SX700 was very close in pricing to an entry level DSLR but I just chose it because I loved the compact form factor & light weight. – curious_cat Dec 5 '14 at 20:12
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You can do few things: - shoot in manual mode, this will help you avoid metering lag - try (if its possible) to assign AutoExposure Lock to some of the buttons on the camera and premeasure the exposure, lock and shoot - shoot in manual focus mode to avoid lag from focusing - try (if its possible) to assign AutoFocus Lock to some of the buttons on the camera and prefocus and shoot

AJHenderson, halfpress the shutter do not keep exposure constant, when you move the camera metering measure this new situation and recalculate the exposure. AF Lock button lock the exposure, but for some time (which is adjustable) but not forever. So this also is not a solution for OP question

  • Well, Manual mode would force me to decide all three of ISO, shutter speed and aperture. That's not what I wanted. I just want to let the camera auto-focus and decide the exposure by a half-button-press and then let me wait for the right moment at which I just press and it releases the shutter instantly with the parameters it has already decided. – curious_cat Dec 5 '14 at 15:42
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    You can use AutoExxposure lock and AutoFocus lock. But based on my humble knowledge AE Lock usually expire after some time. And shooting in manual is not so complicated, just set to P,As,Ts (depend of what you want to accomplish), check what are the camera suggestions for aperture, ISO, and soeed, switch to manual and set them. Prefocus to some object near to place you expect object and shoot when the act happen :) Of course there is always solution as buy new camera which have less lag... – Romeo Ninov Dec 5 '14 at 16:22
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    Do you know more about this specific model of camera? On my camera it is something that is adjustable, I can have half press lock both exposure and focus, only lock one, or just maintain both without locking either. This question actually covers it pretty well as well. – AJ Henderson Dec 5 '14 at 19:26
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    On my camera, which is also canon, but DSLR halfpress the shutter do not lock anything. I have two additional buttons AF-L and AE-L to lock the focus and exposure. But if I want to use them I should set shutter to only make the photo (w/o measure light or focus). Unfortunately I have experience with mentioned above model – Romeo Ninov Dec 5 '14 at 19:41
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    @RomeoNinov - ok, just to let you know, that is adjustable on many Canon DSLRs. In certain metering modes, my Canon 5D Mark iii will lock exposure on half press as well, though I forget if this was a default or something I configured. It is useful when spot metering prior to composition. – AJ Henderson Dec 5 '14 at 19:57

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