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-   -   Manual Focus on the K100D (

Corpsy Jun 2, 2007 10:09 PM

As a lot of you have probably noticed, when using manual focus lenses on the K100D (and probably a lot of other Pentax cameras) the AF assist function will light up on subjects that often aren't nearly in focus and can really screw up a shot if you trust it too far.

For the most part I try to just ignore it and eye up the focus. I found that I get the best results by starting focused to infinity, turn the focus ring until the subject goes into focus and then slightly out, and then bring it back up until it's in focus again. I guess that's front focusing, but I tend to get sharper results this way than by just getting it to look in focus in the viewfinder.

Recently, I've been shooting birds with my cheesy 1980s lenses and was getting a bit frustrated with how many out of focus shots I was ending up with, so I experimented with a different focusing technique that seems to work quite well (in the right circumstances). What I do is set the camera to AF. Then, when I want to take a shot of a subject, I set the focus to somewhere between the background and the subject so nothing is in focus. I press the shutter button completely and slowly bring the focus onto the subject. The instant the camera detects focus, it snaps a shot.

The problem with this method is that you have to use center focus for all your shots, and you have to be careful not to get things in focus you don't want to shoot. Other than that, it's actually quite fun to use. It even works very well with continuous shooting, and will keep taking shots while you hold the button as long as it detects focus.

Here are some sample shots I took a couple nights ago at the Buffalo Marina. It was around sunset, overcast and hazy so the light was rather poor. These were all shot as JPGs at ISO 1600 around 1/1600, though they were all underexposed by at least 1 stop so I really should have been using ISO 3200. Noise Ninja was a big help on these. The lens used was the Takumar 135mm f/2.5 (Bayonet) at f/4.

There were several instances where the camera simply wouldn't take a shot, but considering how poor the lighting was I'm pretty impressed at the number of sharp photos I did get. I imagine in direct sunlight this method ought to perform quite well.

mtngal Jun 2, 2007 11:08 PM

I think your second technique is what people refer to as the focus trap, but not totally sure of that. In any case, I've used it on occasion. My biggest problem with using it me - I tend to move the camera a bit too much when I'm turning the focus ring so haven't had that much success. Looking at your pictures, the technique is much more successful for you. I wish I could get as good results, because it's very useful.

I've sometimes found that I'll "see" the focus when first capturing the scene, but then if I go a bit beyond and then come back, I'll sometimes not see it as well as I did the first time (would have got the shot if I had trusted my eye the first time) - I can only look through a viewfinder just so long before my eyes go fuzzy and I have to look away at something else.

snostorm Jun 3, 2007 12:41 AM

mtngal wrote:

I think your second technique is what people refer to as the focus trap, but not totally sure of that.
Actually kind of reverse focus trap (so maybe "trap focusing" for Corpsy's method), but uses the same feature.

For those not familiar with this feature:

For focus trap shots, the usual purpose is to fire the camera remotely when something enters the frame and the camera's AF sensor finds focus. The general setup is with a manual lens, wired remote shutter release, camera in AF mode on a tripod, you set up the camera (for example at a hummingbird feeder) focus (manually, of course) on one of the feeder stations, move the camera so the center focus sensor area is off the feeder where a hummingbird would be when using the station, but not on anything that is in focus, lock the remote shutter button on, and walk away. Every time a hummingbird enters the frame, and the sensor finds focus, the shutter will fire. Not a foolproof method, but one that I've seen great results from.


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