Take a look at my images here.
I normally have all my cameras set up so the autofocus function is not coupled to the shutter button. This preference goes way back to the time before autofocus was invented and readily available on camera bodies and lenses. Here is how I worked with manual focus lenses and how I translated that over to autofocus lenses.
When I photographed with a manual focus camera and lens, I would I would focus on my main subject (of course, by hand), then I reframed the subject and pushed the shutter button. As long as nothing in my image changed, I didn't have to touch the focus ring again.
If something about the subject changed, I would again, quickly focus on the main subject, then reframe to make the image. This is the technique users of rangefinder cameras use. The focusing had nothing to do with pressing the shutter. It was a separate and distinct action.
Now, when autofocus cameras and lenses arrived, the manufacturers coupled the autofocusing function with the shutter button, usually a half-press. That works well if a) the main subject falls under an autofocusing point in the viewfinder, and b) you only needed to make one exposure. But if your main subject was off to one side or high or low and is not covered by an autofocusing point in your final composition, then you run into so problems which will slow you down and possibly contribute to a misfocused image. One would have to aim the camera at the subject, press the shutter half-way down to lock focus, reframe the image in the viewfinder then fully press the shutter just like I did for the old manual focus cameras and lenses. Okay. Sounds good so far.
Two things happened. First, many camera manufacturers also lock the auto exposure to that same half press, and in our example, which makes your overall exposure tied to where you point the camera for the main subject, then press and hold the shutter half-way. In many instances, the images are made with the wrong exposure values.
Second, if you wanted to make another exposure, you had to go through the same routine. And go through it again and again, for each subsequent exposure. Not fast and not accurate, exposure wise, but nails the focus each time. If you forget and just press your shutter button again, the camera will focus on wherever the autofocus point is, not necessarily where you want it to focus. You have to consciously remember.
By de-coupling your auto focus function from the shutter button, you emulate the old method of focusing once, then leaving it alone unless your subject moves. Now, however, instead of focusing with your left hand, the camera and lens do it automatically. The upshot is this.
I place my single, center, most efficient and most accurate focusing point on my subject, press the "AF ON" button (Nikon) or function button on my Olympus and release the button when the subject is properly focused. Then I reframe and make the exposure. What that does is allow the light meter to meter the whole scene as I have composed it, which is generally more accurate with the complex, matrix metering. Only if my subject moves, do I go through the quick process again. Otherwise, I can make as many exposures as I need without having to go back and focus and recompose each time as I would if the shutter was coupled with the auto focus.
Think about how this would work well when your camera is mounted on a tripod. You compose your image, swing your camera to a position to find your desired focusing point (could be the hyperfocal distance, a piece in the foreground, etc.), then recompose your image and lock it down. Now you can make as many images, HDR or otherwise, without having to worry about the camera/lens combination refocusing. The alternative would be to put your camera on manual focus and hope you don't forget to put it back on autofocus later.
To accomplish this on the E-M5, I set my camera's AF settings to S-AF Mode 3, which de-couples the auto focus function from the half-press of the shutter. Then I assigned this function to function button #1. But, it didn't work very well for me so I had to come up with a couple of fixes to make it work better.
The Fn1 button is really small (for my thumb), didn't stick out from the camera body very far and was very difficult for me to push comfortably. I didn't want to assign it to another function button as the other function buttons are in the wrong places for this procedure to work seamlessly, so I needed to find a way to increase the size of the Fn 1 button and make it stick out farther so it is very easy to push. The key is to have it comfortably sit under where your thumb would rest.
First, I have taken some black gaffer's tape (which has strong adhesion and doesn't leave a residue) and cut a piece about an inch long. Then I cut a strip a bit wider than the function button on the back upper right of the camera body (Fn 1). I then rolled that onto itself, sticky side out, and gently stuck it on the Fn 1 button. With another strip, about 1/4" wide, I placed a piece over the rolled tape and stuck it to the top edge of the boy and also below the Fn 1 button. See the images below.
Now, when I frame the image, a quick press on the tape pressed the Fn 1 button underneath it and the camera focuses immediately. Great. Will it last or lose its stickiness and fall off? I have been using it this way for a few weeks now and the tape method works well. If it comes off, I can quickly replicate it with fresh tape.
If it becomes unworkable, as an alternative that I might try is this. I have cut a mechanical pencil eraser, which is just the right diameter to fit over the function button, in half horizontally. The full eraser would make the button too tall. I think rubber cement, placed on both the button and the eraser, would be strong enough to withstand a lot of use. If I find the tape method doesn't work, then I will go to the eraser method and see how that works.
I have used the de-coupling method for years now. I don't even have to think about pushing the "AF-ON" button when making images, even in fast moving situations. It is second nature. At first, it felt a bit foreign, but after a week or two, I never had to think about focusing this way as my thumb automatically pushed the button when my brain sent the unconscious signal that I needed to focus.
You should try it with your SLR if it has a back-focus button that is programmable to do this. One caveat, however, don't change it then go out and make images at an important event if you have not practiced and this has gotten to be second nature. You may forget to push the button. Practice this method a few weeks before photographing something important.
Thanks for looking. Enjoy!
Dennis Mook
All words and images are © Dennis A. Mook. All Rights Reserved. Feel free to link to this website from yours with full attribution. Permission may be granted for use. Please contact Mr. Mook to discuss permission to reproduce the blog posts and/or images.
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