Wednesday, December 09, 2009

Pre-focusing

I just learned something practical from a discussion under a tOP article.
The article had mentioned how the author preferred to have the autofocus function separated from the shutter button. Somebody asked why, and somebody else said:

"There are many situations where you want to pre-focus the camera and use the same focus point for several pictures. If the shutter button focuses, then you lose the locked focus after each shot. Worse, you have to wait for the camera to focus every time you hit the button."

So I asked:
I never really thought about separating the autofocus function from the shutter button, but I'd like to try it. Does anybody know if I can do it with the Panasonic G1 or GF1?

And then continued:
(Why do they keep saying "RTFM" to me?) [Note: "Read The Friendly Manual".]
...OK, in the custom menu, if you set AF/AE lock to AF, and the AF/AE LOCK HOLD to On, then the AF lock button will hold the focus through several pictures until you press it again. (Or until the camera is turned off.)

Can also be helpful for faster operation, doing "zone focus", if you have the depth of field for it.

... Come to think of it, this also makes it easier to prefocus on a developing situation, since you no longer have to carefully keep the shutter button half-pressed, trying not to fully press it prematurely.

The more I think about it, the better I like this setting. It is rather accidental if the focus point is exactly in the center of my composition, and if I can set it with a separate button, then the shutter button operates much faster, and I don't have to think about holding while re-composing (or waiting).

One small danger does present itself: you might forget to turn off the focus-lock, and not notice (in a busy situation) that the camera does not focus before exposure. One would have to pay a little attention to that until getting used to it.
... Of course one can set the camera to not lock the focus after one picture, and yet use the AF button. (Hmmm, I'd like a setting where one press locks it for one picture, and two presses (or a long one) locks it until you press it again!)
(Hmm, I should look at the Function button (arrow down), I have never used that for much on most cameras, maybe it can expand the options. Update: sadly no, it only has a short range of pretty useless options, the most interesting to me is setting file quality.)
Note: does anybody know a way to get AE (auto-exposure) lock on the G1/GF1, once you have set the AE/AF button to AF only?
.
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On a different but related subject: if I ran a camera company, I'd make a high quality compact camera with a small sensor, 28mm-e lens, 4.0 aperture, and no autofocus, just fix-focus. Even with a very good lens, it would be cheap, simple, and dead-fast to react. Should be popular.
What they at least should do is make it simple to set the camera to fix-focus for max dept-of-field.

... Please note that the bulk of this post (pre-focusing) applies equally well to situations where you do need accurate focus, but you have either good time to do it (more than three seconds), or almost no time (less than half a second).
... Actually, come to think about it, it's getting harder for me to imagine many situations where focusing being set by the shutter button is really an advantage. When you have to take a series of pictures where the focus point is off-center, it's a bit of a p.i.t.a. to got "fetch" it between each shot. (Other possibilities are manual focus or "follow-focus" or face recognition. But I think this button and lock is an excellent solution which deserves to be better known.)

11 comments:

Aaron said...

Once you get used to it, it's hard to go back to a camera where the AF is tied to shutter button. I've got my d300 and LX3 set up that way; it's really handy.

Eolake Stobblehouse said...

Thanks.

Yes, it's funny that I never thought very much about this.
And that it's so prevalent to tie focus to the shutter button. It really is a little strained to use and hold that half-press.

I guess the reason is that the majority of snap-shooters don't actually think about where focus falls, crazy as that sounds to some.

Eolake Stobblehouse said...

Just checked the Canon S90, you can make the custom button lock focus, but it seems only for one picture.

Anonymous said...

I set up my Canon G9 as a Box Brownie; aperture at f4.5, lens at 35mm (equiv) and focus at eight feet, flash on or off as needed. That's CF2.
DOF provides acceptable sharpness from around three feet on out and exposure takes care of itself.
It isn't extremely-high-quality photography but it's quick-shooting with no concern about focus etc, and with the Canon's viewfinder it's all ballpark anyway. For high quality I use a Rolleiflex like I'm supposed to.

-jbh-

Philocalist said...

THis is akin to a very common technique, in use for many year with all sorts of cameras, but normally takes into account a couple of other variables too ... typically the set-up involves using a wide-angle lens, smallish aperture (and an ISO setting that will allow a suitable shutter speed at that setting.)
The camera was then focussed at a point to allow maximum depth-of field (both functions of a small aperture / wide-angle lens), and then the settings left alone ... just point-and-shoot!

Funnily enough, this principle was used on cheaper compact camera for many years!

With the right combination, you can get virtually limitless DOF, but you need to understand a little photographic theory to accomplish this, rather than just pres-and-hope.
DOF can be reduced of course, intentionally, with longer lenses, larger apertures and different pre-focussing points (all of which make using this set-up less easy)

Philocalist said...

And can we PLEASE have an 'Edit Post' function so I can do the necessary to my mis-spellings etc, afetr a long night with the baby?:-)

Eolake Stobblehouse said...

Pray to the big Blogger god. (I think his name is guggle or something.)

Anonymous said...

Funny thing, the dp2 got trashed because it's slow autofocus.

yet it does have a dedicated focus wheel (with distance marks to allow for quick zone focus even if the monitor is switched off). In addition, it has a dedicated button for focus lock. So it is very well designed for manual focus.

Eolake Stobblehouse said...

And that's definitely a good thing.

I do hope, though, that Panasonic will soon get much stronger competition the compact camera autofocus speed playing field. It's really one of the few weaknesses left in other cameras.

Anonymous said...

I've *always* put the AF function to a separate button when taking picture with an SLR camera. That way the auto-focus system doesn't have to "hunt" every time I want to take a picture.

Pascal [P-04referent] said...

Comment from your average not-too-moronic amateur photographer:

Yeah, that's what I miss about my last film camera (which was also my first own one): fixed focus, just point-and-click, great simplicity, used in the blink of an eye, LITERALLY.

I've missed many candid photos of the kids because by the time the @#$%& camera focused, the expression I wanted to capture was there no more, or they had noticed me and gone into reflex "posing" mode. ):-P
Not to mention those great many times (not great moments at all!) when the dang autofocus inexplicably failed, forcing me to re-aim all over again, "no, wait, it wasn't good".