Lackluster K100D + 21mm focussing

[arond a.]

Is it normal to expect that 1/4 of shots will be improperly focussed when using

the 21mm DA AF? I realize manual focus is an option, but I would hope by this

late date camera manufacturers could have most of the kinks worked out in this

area. Is it the lens or the camera or me? Would a different lens respond

differently? I don't recall this ever being a problem w/ my previous dslr with

its comparable focal length lens. Specifically, this camera has difficulty

locking onto subjects in the foreground, especially when within a meter of the

lens. What is going on here?

[michael_mermagen1]

How many focus points are you using? What is the subject in the foreground and how close is it? Most AF cameras I've tried cannot lock in on objects that don't have color contrast or texture. For example, if my focus point was on the green open space of a tennis court, it wouldn't lock. If the focus point were at the edge of a white line on the green court, it would lock.

Mike

[william-porter]

Arond,

 

Over on the Pentax Forums site (pentaxforums.com), you should search for this issue. I am pretty sure -- but not 100% sure, so check for yourself -- that early in the summer Ben Kanarek had a backfocusing or some kind of focusing problem with one of these lenses. I've heard others say that this is a fantastic lens, indeed, that seems to be the consensus. But you might have one that has problems.

[hakon_soreide]

Doesn't the camera tell you in some way if it fails to focus on the focus point you are using? I've not used the Pentax myself, but basically every camera I've ever owned has some sort of indication whether it is in focus before you shoot.<p>

And, if the autofocus finds something to focus on, then - no - you should not expect a quarter of your shots to come out unfocussed. Unless you're using long shutter speeds and are experiencing motion blur instead.

[mc2imaging]

I've got a few comments for you, but I'll start of by assuming you are talking about a focus

issue not a motion blur issue...

 

1. You say that it is a particular problem when focusing on subjects close to the camera.

My wife had a similar issue once when she first got her Tamron 28-200mm on her ZX-50.

The problem was that this particular lens has a minimum focus length of 4 feet, so when

she was trying to focus on things that were on the edge of her range, the camera would

have a freakout

session.

 

2. I like to make my intern get detail shots with a 50mm f1.4 to make him practice his

focusing skills. More than once he has come back and said, 'the camera won't focus' or

something to that effect. To this I say, 'MAKE the camera focus.' It can't read your mind,

that's why we don't use P'N'S cameras. Sometimes you have to take control and actually

tell the camera what you want.

 

3. When using AF, the body decides when focus is achived optically. This means that if

the shutter fired, the camera thought SOMETHING was in focus (whether or not the

PROPER something was in focus is between you and the camera). Now, unless something

moved between the time that the camera saw focus and the shutter actually released

(which is always possible), if absoulutely nothing is in focus in 1/4 of your shots, I would

be more worried about the camera than the lens.

 

All of that said, it is really a judgement on the skill of the shooter and the subject being

shot. If I were to go shoot a basketball game with my 50mm f1.4 with the lens wide open,

I would expect at least half of the shots to be out of focus, AF or MF, because of the

shallow DOF and the fast motion. On the other hand, if

I'm in the studio shooting an adult who is sitting still on a stool while using the same lens

at

f11, I would expect 100% of the shots to be in focus.

 

 

Do you have another body to try the lens on? Do you have another lens to try on the

body?

[michael_kuhne]

At such close focus distance, even with a wide angle lens as 21mm, depth of field is significantly reduced. All areas in the frame are not likely to be sharp. Point of focus then becomes a critical issue, especially at wider apertures. Switching camera to center-only focus sensor is advised for selective focussing.