Thursday, June 08, 2006

Pentax DSLR Auto Focus Tips

If you're still getting used to auto focus with a Pentax DSLR, you should know that it's much more sophisticated than the AF in a point and shoot and that enabling some of the features in your camera can help you customize an approach to focusing that might work better for you. Many of these sort of features have been around with advanced SLR camreas for a few years, but Pentax D and DA "Quick Shift Lenses" with your Pentax DSLR can give you some new tricks. Here are some of the easiest things to try that can make the AF behave under your control.

1. Enable spot auto focusing.

Above, I used the selective focus points to choose my focal point, focusing on the tip of the banana. Regular wide auto focus would have chosen somewhere in the middle of the frame.

By using AF spot focusing, you can keep the camera from just focusing on the nearest object (better known as 'wide' mode). Spots give you greater creative control moving focus around your frame. Essentially, you use the red focus points distributed in your viewfinder to specifically direct the focal point, so that the focus for the rest of the frame is ignored. This is important when you have limited depth of field. The DS models and the K100D models all have 11 focus points, while the DL and DL2 have 3 and 5 respectively.

In the DS, it's under Menu>Rec. Mode>Switch dst msr pt>choose one of the two spot focusing options, preferably 11 pt., instead of the default 'Auto'.

In the DL, it's under Menu>Rec. Mode>Focusing Area>choose Spot focusing.

Keep in mind that the AF spots can be hidden from showing superimposed on the viewfinder, but they'll still be active. Under Menu>Custom Setting you turn off Superimpose AF area. This is useful if you don't want anything obscuring your view.

2. Use the OK button option to unlock auto focus.

In AF mode, half-pressing the shutter release button is how we typically enable the auto-focus, but when you want to lock it down between shots you'll have to switch to Manual Focus mode. This isn't bad, but if you do it a lot, there's an easier way to get the lock of manual focus while in AF. How? Essentially, you'll tell the camera to only auto focus when you press the OK button. The shutter release pressed half way will now only meter. The rest of the time, your camera will think it's in manual focus mode (but you're really not, you're still in AF). If you have a quick shift focus lens (DA lenses), this means you'll never need to use the AF switch on the front of the camera again!

Go to Menu>Custom Settings>OK Btn When Shooting>Enable AF

Conversely, you could also set the OK button to cancel auto focus, which will lock the focus while you keep it pressed down. This is more limited in use, but also a pretty effective strategy to stop the lens from hunting if you want to interrupt and use a quick shift lens to manual focus more quickly.

3. Use continuous focus.

The default is single mode, which means that once the focus point is fixed in focus the AF calls it a day. But if you're tracking an object or moving around an object, maybe you'd like the camera to keep adjusting. That's continuous focus. Back in the original DS, this meant using Moving Object scene mode, but since firmware 2.0 and the first *ist DL, continuous focusing is now available as a menu option for Program and Manual modes. Menu>Rec. Mode>AF Mode>AF.C. Used in conjunction with the OK button to activate focus, you can keep the camera focusing on an object independently of ever pressing the shutter release.

4. Use the flash or even a flash light to help focus.

Because I didn't fire the flash for this photo in a museum (to preserve the exhibit lighting), I used an LED on my keychain to focus properly in the very dim light.

If the camera is hunting too long, maybe there's not enough light or contrast in front of you. Often the camera will help itself if you let it pop open its flash in an auto mode. In the Program, Av, Tv, and Manual modes, if you've set your camera to manual flash mode in the Fn menu, you'll have to pop up the flash yourself. It will emit a quick burst of flashes to illuminate the scene and find its focus. Similarly, if you have an on-camera flash with focusing assist mounted on the hot shoe, such as an FGZ model, you can get the same treatment from its IR beam or strobe. And though it may sound dopey, a flash light or laser pen is a trick that many pros use in dim light or the dark. Consider it a portable focusing modeling light. As noted above, even a keychain or pen LED light can do the trick.

Any other auto focus tips? Corrections or input? Again, lemme know in an email or the comments and I'll add them here for everyone.


Ian Goldby said...

I noticed that my DS was never locking focus and I now know why: after upgrading to the 2.0 firmware the AF Mode was set to AF.C - continuous focusing. I've moved it back to AF.S and I will select sports mode for those occasions when I do want continuous focussing. Thanks for the tip.

I've never been fully satisfied with the interplay between focus lock and exposure lock. With my old manual focus SLR, I always used to focus, then point the camera so as to get the right exposure (e.g. away from very bright areas that I want over-exposed in order to preserve shadow detail), half-press the shutter, and then with everything locked recompose for the final shot.

This doesn't work with the default settings on the DS, because half-pressing the shutter doesn't lock the exposure.

As an experiment, I am trying AE-L with AF locked, so that when the shutter is half down both the focus and the exposure are locked. I've also set the OK button to cancel autofocus, and the 'Swtch dst mst pt' setting to centre so that it always focuses on the centre of the frame.

For most shots this will be just what I want. I point the camera at the subject, half-press to fix the focus and exposure on the subject, recompose, and then take the picture.

On rare occasions when I want exposure for one area and focus on another, I can either press the AE-L button to lock the exposure while I recompose and then half-press the shutter a second time to set just the focus, or I can press the OK button to prevent the focus changing while I recompose and half-press the shutter to set the exposure.

Michael said...

I'd like to confirm something which I can't seem to find elsewhere, about the use of the OK button for focus: when the custom function is set to make the OK button activate focus, are you sure that the half-pressing the shutter button then doesn't also activate AF?

Pentax's literature is a little vague about this, so I'd like to check with a human who's actually tried it.

Canon bodies can be set to do this, and it's the behavior I'd like. Because then it's easy to take another shot without thinking about focus all over again, just like a manual camera. This is one of the main things I hate about compact digicams.


OK-1K said...

Michael, yes, the OK button will work independently of the shutter button when you have the OK button set to activiate AF. The camera will need to be "active" in the sense that it must still be powered on and be capable of metering, but you don't have to half-press the shutter button. The shutter button will no longer activate AF when it is pressed. This works in the *ist DS, DL and K100D cameras. The *ist D and K10D both already have an AF button. I can't stress enough how great the Pentax "Quick Shift" lenses are with this camera feature. Hope that helps!

Michael said...

Yes, that's perfect. Thanks!

Top Rated Cameras said...

This is such a very helpful and informative post specially for newbies like me. I just bought a new camera and I'm on the process of learning some basic shots particularly with different light settings and a lot of other stuffs. :) I learned a lot from your post and I hope you post some more techniques on photography! :D

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