Shutter button: half-press vs. full-press

A friend of mine, unused to digital cameras, was playing with my A510. He says that he doesn't like the two-step processing of (1) half-press of the shutterbutton to let the camera perform auto-focus and auto-exposure, THEN (2) full press. When he does an immediate full-press without pausing at half-press, he says there's too much of a delay and he wants to be more 'spontaneous'.

I said that he's welcome to do an immediate full-press and that in my mind there didn't seem to be that much of a delay when doing so. (Though I think he was noticing this when we were indoors and relying on the flash.)

My question: what are the consequences of doing an immediate full-press rather than a half-press and pausing? How important is it to do the half-press first?

Simply, if you don't want shutter lag, buy a DSLR.

The only other way to avoid shutter lag with P&S cameras is to use manual prefocussing i.e. first focus on a item at the same distance as the subject, press the manual focus button and leave the camera in manual focus for as many pictures you want to take.

Karl R. Josker wrote:

rick7 wrote:

My question: what are the consequences of doing an immediate
full-press rather than a half-press and pausing? How important is
it to do the half-press first?

I believe that the camera won't go until it has achieved metering
and focusing. The downside of the full press is that it may tend
to be hurried, and that hurry creates a moving of the camera, and
your focus point changes, and what you really wanted is then out of
focus, with you thinking that the camera didn't focus. Not to
mention possible blur caused by a moving camera. I would imagine
that with practice, you could become adept with a full press
technique, and there is no harm in that. Personally, I prefer a
more contemplative, deliberate approach.

This tutorial from Canon should help answer your question:

http://bj.canon.co.jp/english/photoshooting/technihsc/camerafunction/camerafunction01.html

I hope you will not be intimidated by your friend's impatience. Check out the various topic links at the left on the above page and you will be off to a good start with your A510.

To increase your early level of success, try to shoot in good light. As you learn your camera, you can learn the features that will let you get good photos in lower light situations.

You may also enjoy using this Canon Japan site to learn to use your cameras features. I have an S1 and use the comparable site to learn my camera's features. It is often more helpful to me than the manual.

http://www.canon.co.jp/Imaging/psa510/202-e.html

Karen in NC
http://www.pbase.com/kfheggen

rick7 wrote:

A friend of mine, unused to digital cameras, was playing with my
A510. He says that he doesn't like the two-step processing of (1)
half-press of the shutterbutton to let the camera perform
auto-focus and auto-exposure, THEN (2) full press. When he does an
immediate full-press without pausing at half-press, he says there's
too much of a delay and he wants to be more 'spontaneous'.

I said that he's welcome to do an immediate full-press and that in
my mind there didn't seem to be that much of a delay when doing so.
(Though I think he was noticing this when we were indoors and
relying on the flash.)

My question: what are the consequences of doing an immediate
full-press rather than a half-press and pausing? How important is
it to do the half-press first?

Fantastic; thank you VERY much -- that tutorial was really helpful. I think I get the message: not pausing at half-press risks focusing on whatever was at the center of your view rather than what you want to be your main subject. I.e., you may not want your primary subject to be at the center of your picture, but the camera does its focusing at the center of your picture. So: center your subject temporarily, do your half-press, then feel free to move the subject off-center if you like ("compose the picture")

But is all this an issue only if the subject is not at the center? If your subject IS centered, will a full-press adequately focus your subject?

Karen H wrote:

This tutorial from Canon should help answer your question:

http://bj.canon.co.jp/english/photoshooting/technihsc/camerafunction/camerafunction01.html

I'm also noticing that the tutorial seems to show the focusing being done with a viewfinder, since you see a crosshair but no AF frames. Not sure why they would do this as the viewfinder gives no indication of auto-focusing, does it?

But this reminds me: can someone help me understand better the green AF frames I see in my A510's LCD when I half-press? (I've never understood what's going on there and always thought those were light-metering frames!) With AiAF ON, I can't figure out what the camera uses to determine (1) how many green AF frames to display and (2) what criteria it uses to place them. As I sit right now and point at a near subject, I can half-press to auto-focus any number of times on the same subject and it seems that, though I'm not moving the camera at all between half-presses, each time I see a different placement and number of AF frames. Can anyone explain? Thanks.

Karen H wrote:

This tutorial from Canon should help answer your question:

http://bj.canon.co.jp/english/photoshooting/technihsc/camerafunction/camerafunction01.html

Hi Rick,

Turn off the AiAF for better results.

Cheers,bg

rick7 wrote:
I'm also noticing that the tutorial seems to show the focusing
being done with a viewfinder, since you see a crosshair but no AF
frames. Not sure why they would do this as the viewfinder gives no
indication of auto-focusing, does it?

But this reminds me: can someone help me understand better the
green AF frames I see in my A510's LCD when I half-press? (I've
never understood what's going on there and always thought those
were light-metering frames!) With AiAF ON, I can't figure out what
the camera uses to determine (1) how many green AF frames to
display and (2) what criteria it uses to place them. As I sit
right now and point at a near subject, I can half-press to
auto-focus any number of times on the same subject and it seems
that, though I'm not moving the camera at all between half-presses,
each time I see a different placement and number of AF frames. Can
anyone explain? Thanks.

Karen H wrote:

This tutorial from Canon should help answer your question:

http://bj.canon.co.jp/english/photoshooting/technihsc/camerafunction/camerafunction01.html

Hi again rick7,

rick7 wrote:

I'm also noticing that the tutorial seems to show the focusing
being done with a viewfinder, since you see a crosshair but no AF
frames. Not sure why they would do this as the viewfinder gives no
indication of auto-focusing, does it?

That tutorial is trying to explain basic photographic principles of focusing but IMO it's misleading. When Aiaf is switched on there is NO guarantee that if ypu put your main subect in the centre, the camera will choose the main frame for focusing. Also, take into account that focusing by the method Canon describes may be affected by the distance of the subject from the lens. You may get unfocused images if you use such a method for close-ups with shallow DOF.

But this reminds me: can someone help me understand better the
green AF frames I see in my A510's LCD when I half-press? (I've
never understood what's going on there and always thought those
were light-metering frames!) With AiAF ON, I can't figure out what
the camera uses to determine (1) how many green AF frames to
display and

If I'm correct Aiaf uses 9 frames for focusing, the central one and 8 peripheral frames around it.

(2) what criteria it uses to place them.

The frames are always positioned at the same places I believe.

As I sit
right now and point at a near subject, I can half-press to
auto-focus any number of times on the same subject and it seems
that, though I'm not moving the camera at all between half-presses,
each time I see a different placement and number of AF frames. Can
anyone explain? Thanks.

Autofocusing is based on contrast differences. When the camera detects a contrast difference at the subject you're focusing on, it tries to realign the lens element so that they produce maximum sharpness. At this point it has achieved focus lock. Now if you use spot focusing the camera will try to achieve adequate sharpness based just on the central frame only. This may or may not be enough for the available lighting conditions and, also, for the contrast differences it detects. Usually, the autofocus mechanism has a better chnace if the subject has vertical lines (this is so because the sensors are aligned to vertical structures). But when you use Aiaf, any of the 9 frames can be used for focusing and it may be that the one that wins is not the one with the main subject. I don't know the exact details of the algorithm Canon uses for selecting a particular frame for focus lock but as a rule of thumb it has a higher probability of getting it wrong when (a) the contrast differences of the main frame are low, (b) in low-light, and (c) when there are not enough vertical lines.

No, it's the difference between camera field of views. Film P&S cameras have massive depth of field so they do not need to focus...everything is always in focus (except for close up objects...minimum focus). That's what makes them cheap (less mechanical and electrical stuff). Cheap digital cameras might be able to do this, but the thinking is probably that if you're spending that much money on a camera, you might want something that will focus and have better optical quality.

As for SLRs...old film SLRs didn't have the half-press...you had to manually focus before taking the picture. I believe they had a seperate button for metering (if it had that function). Auto-focus film SLRs have the half-press as do DSLRs (they are all autofocus-capable).

sueanne wrote:
won't be focused? Did you look to see how his pictures compared to
yours?

Thats the differences between digital cameras and film cameras.
Maybe a DSLR is more like a film camera, no need to half press...

sue anne
gee-six
------------------------------------

rick7 wrote:

A friend of mine, unused to digital cameras, was playing with my
A510. He says that he doesn't like the two-step processing of (1)
half-press of the shutterbutton to let the camera perform
auto-focus and auto-exposure, THEN (2) full press. When he does an
immediate full-press without pausing at half-press, he says there's
too much of a delay and he wants to be more 'spontaneous'.

I said that he's welcome to do an immediate full-press and that in
my mind there didn't seem to be that much of a delay when doing so.
(Though I think he was noticing this when we were indoors and
relying on the flash.)

My question: what are the consequences of doing an immediate
full-press rather than a half-press and pausing? How important is
it to do the half-press first?

Bluegrass wrote:

Hi Rick,

Turn off the AiAF for better results.

Keep in mind that I'm a beginner and have had a digital camera for all of three weeks! In any case, why does turning off AiAF produce better results?