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Old Oct 15, 2011, 12:55 PM   #1
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Default Need help understanding focus points

Ok, I've had my K5 now for about 3 weeks, and just love this DSLR. Can't think of anything to add to it except 16:9 aspect ratio when shooting stills using liveview. My big question is why do many people beg for more focus points? I always leave my focus on spot, and just point to what I want in focus. I find this method works great. Seems like moving the focus point all around the screen takes a lot of time. Is there something I'm not understanding here?
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Old Oct 15, 2011, 3:32 PM   #2
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I'd also like to see that question answered by someone who finds multiple focus points useful.
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Old Oct 15, 2011, 3:42 PM   #3
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G'day fellas

While I agree with both of you re- usefullness of 'centre/spot' focussing depending upon your requirements ...
It is my understanding that the many & varied focus options are an attempt to cover all eventualities for all users [bit like bill gates & the 1001 ways of doing the same task]

I have a newspaper 'tog mate who likes the focus set to 'full-screen-multi' for crowd shots vs 'centre-weighted' for action shots and so on. For me it seems too much like mucking around

I have another 'tog mate who lives for macro work with insects, she has focus set as slightly off-centre as the head of the insect is nearly always on one of the 'thirds'

So I guess it's 'horses for courses'...
Regards, Phil
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Old Oct 15, 2011, 3:57 PM   #4
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Selecting focus point can also be used for portrait work, where you want to focus on the subject's eyes, for example, without moving the camera between shots. Manual focus can work also, but with shallow DOF, slight movement of the person's head can make for problems.
Sometimes, when shooting action such as auto racing, you don't want the camera to try to focus on the moving vehicle, but on a fixed feature towards the outside of the frame.
For most of my use, I use the center point, but on occasion, it is nice to have the option.

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Old Oct 15, 2011, 5:17 PM   #5
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I agree that it's nice to have the option to set the focus point to something other than center focus, even though I use center focus mostly.

Some reasons for using something other than center - when you know that the subject is going to always to be off-center, just leave the point set to that point. I hadn't thought of Brian's use, but it makes a huge amount of sense to me, especially if you are pre-focusing and don't want the camera to accidentally change the focus when you actually push the button.

While focus/recompose is normally fine, under some situations, changing the angle of the camera will change the distance of the subject to the camera, and if the dof is small enough it might cause focus problems. Changing the focus point can correct this.
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Old Oct 15, 2011, 7:17 PM   #6
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Hi Tony,

Personally, I don't think you're missing too much. The 11 point AF system works fine, as long as you make sure to confirm focus visually.

I'd probably like more focusing points, but not because I want to move the active point around, but because each individual focus area would have be smaller to cover the frame without large dead spots. Smaller would make them more discreet. The central focus "point" in the Pentax SAFOX system is about the size of the central ( ) etchings on the stock focusing screen in the VF and can. The surrounding points are a bit smaller and more oval shaped, and the two farthest side points are even thinner ovals.

The problem with this large a focusing area is that it can pick up on anything within its area, and if there are contrast borders outside your subject that are either more contrasty or more perpendicular to the vertical or horizontal sensor "lines" of the sensor, then the sensor could "choose" these and cause a misfocus.

The thing is, even though this may be a handicap, it's not that difficult to work around it, and in the process, you can make yourself a better photographer technically by forcing you to be more aware of fine focus in your VF, and learning more about how AF sensors actually work.

The K-7 and K-5 both have VF screens that are more optimized to allow you to see fine focus better than with most APS-C focus screens.

Here's a translation of a quote from a 2009 interview in dc.watch.impress.co.jp

"Looking through the K-7 finder, it seems slightly darker in comparison to other Pentax's up until now. This reduction in light transmission was done in order to attain ease of manual focus and see boke. Generally when you increase the transmission of a camera's focusing screen diffusion decreases making it harder to grasp the exact point of focus. In other words, brightness of the finder and ease of focus are inversely proportional. A lot of cheap, popular cameras are sold with slow zooms, and ease of manual focus is not seen as important. So there is a strong trend to pursue brightness. In terms of the screen, you could say that the K-7 is aimed at experts. Particularly when using large aperture, fixed focal length lenses, and select the optical preview, you can shoot while confirming subtle changes in the flavor of the boke through the finder."

Fumio Nakamura

That being said, moving the focus point can be very useful when you're working with very thin DOF as has already been mentioned, as focus and recompose can throw the focus plane off enough to ruin a shot when a difference of a couple of inches or less is critical in terms of focus.


The thing is, the 11 focus points that Pentax now uses in all of it's DSLR models is more than enough to accomplish this, and smaller points would make this more difficult as you'd have to move through more points to get where you want. With 11 points, you only have a maximum of 2 moves to get anywhere starting from the center.

I use center point all the time, and have used any of the other points in selective point mode only on very rare occasions (but was glad they were there when I needed this ) I am, however, not much of a purist when it comes to photography, and usually have enough to deal with with keeping everything I want in the frame, dealing with exposure, trying to get the best background, and confirming focus on living subjects that aren't cooperative. I expect to crop for final composition for just about any shot I take.

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Old Oct 15, 2011, 7:36 PM   #7
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if you look at where the af points are located ( http://www.imaging-resource.com/PRODS/K5/K5A.HTM ), the central 9 cross-points are good for tracking moving objects. the outer two would be useless for anything i do. and there's nothing at the rule of thirds points if you like that way of composing. i haven't looked into this intensively, but what i understand is most if not all dslrs are set up like this. beats me why.
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Old Oct 15, 2011, 10:00 PM   #8
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Thanks all for all the input. It makes a bit more sense now. Some examples I would have never thought of.
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