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12-06-2013, 05:46 AM   #1
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K-3 (SAFOX 11) AF-precision for portraits?

I have read a lot of good reviews of the K-3, but I have yet to find an answer to maybe the most important question for me... AF precision in Single AF mode.

I shoot with the K-5 mk1 today and mostly portraits. My favorite lens is the FA77 but the results are similar with other portrait lenses. I shoot at around f/2.5 mostly and after a photosession of a couple of hundred images the results are usually something like 70-80% keeper rate (focus within acceptable limits) and 40-50% is perfectly focused. These figures might vary a bit depending on color temperature, backlit scenes etc. I use single point AF and choose the point suitable for my composition (wish they where wider sometimes). Single AF-mode. I'm not interested in continuous AF, tracking capabilities or improved AF speed. Just want higher keeper rate. Will the K-3 / SAFOX 11 be an improvement compared to the K-5?

12-06-2013, 05:56 AM   #2
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I cannot comment on the K-5, I went from the K20D to the K-3.

I never found AF accuracy to be lacking with my K20D. When focus was poor on a shot, in good light, it was generally because the subject or me had moved. This can be a problem when shooting wide open with any camera, of course. In low light the K20D struggled a bit sometimes.

The K-3 is a tremendous improvement in low light, and that observation will apply to your K-5 too. It can focus in near darkness. amazing really.

In good conditions, barring user "error", the K-3 will not be more nor less accurate than previous iterations. However, the larger number of AF points means that each point is smaller. So when you are trying to focus on a precise area of an image, it will be much easier to exactly pinpoint that spot and make sure it is sharp. So in this regard the K-3 will be an improvement.

Pentax lenses and cameras are usually quite reliable in their AF. I saw a test a few years back showing that when compared to Canon the AF was slower with Pentax, but the ratio of in-focus shots was higher. Now the AF is faster than before, but I guess it's hard to improve on already reliable accuracy.
12-06-2013, 06:04 AM   #3
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My experience is that the 'keeper rate' goes down mostly in difficult light, which may be mix or odd color temperatures or strong backlight. I never shot portraits in super low light that would require the improved low light focusing capabilities of the K-3 or K-5 II (but in other situations that might be useful of course). I was thinking that the new metering and white balance system would help the AF precision a bit

Interesting about the smaller focusing points though, that might help in placing the focus point just right. I have noticed that the focusing indicator on the K-5 seems to be a bit larger than the actual focusing point that the camera uses, and that they might not be 100% aligned either. Is the focus indicator on the K-3 of similar size compared to older cameras (just that there are more of them) or are they smaller too?
12-06-2013, 06:17 AM   #4
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I always use the center focus point, then focus on the eyes and recompose the scene. At wider apertures, too much difference in the recomposed shot could greatly affect the focus I chose, because the actual distance to the subject is off/

What technique are you using? One thing I need to do is learn/remember to compose and then focus by selecting a focus point.

12-06-2013, 06:27 AM   #5
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@klkitchens: for the reason that you mention I do use all of the focusing points (manually selecting the best suited for the composition), to avoid focus->recomposing at the wide apertures since it, as you say, will affect the distances. Unfortunately the focusing points is somewhat cramped together in the middle, and the K-3 isn't any better in that regard.
12-06-2013, 06:48 AM   #6
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If shooting portraits from a tripod I would suggest using live view as you can select focus point over a much wider area, about 80% of the image I would guess. It is somewhat slower than focusing through the viewfinder but conversely selecting the right point looking at the LCD rather than through the viewfinder is actually much easier and quicker.
The live view focusing seems to be just as accurate as the viewfinder focusing as far as I can tell.

About using the centre point and recomposing there is of course the problem of distance changing when you tilt the tripod head (panning should be OK though) because the axis of rotation can never coincide with the lens axis on a normal tripod head. That can be fixed though with a Panoramic Head one of those whatsitsnames that are used for panoramic photos. A sort of pivoted bracket that makes the camera tilt along an axis that coincides with the lens axis. Can't remember what its called but I'll try looking it up. With that one could recompose without having to worry about changing distance, though it would of course still not cater for the subject moving in the time it takes to recompose. To fix that you might use this technique:


Last edited by lister6520; 12-06-2013 at 06:54 AM.
12-06-2013, 07:05 AM   #7
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@lister6520: I use live view when possible, but it is not an option for most portrait work. You want to be able to work freely and keep up with the model in different poses etc, and tripods won't work for that kind of shooting. I have used my K-01 with live view (only option) but the AF area is a bit to big even on smallest size (at least for full body shots). It is nice to be able to place the area freely though and live view is very precise, but you do loose contact with the model when you have too look on an LCD screen and it won't work very well in sunlight either. I feel that I know all of the various techniques, and I will use different methods when possible.

My question remains though, is the single point AF on the K-3 more precise (will generate more keepers)?
12-06-2013, 07:56 AM   #8
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QuoteOriginally posted by DonThomaso Quote
I was thinking that the new metering and white balance system would help the AF precision a bit
Metering and AF are completely decoupled.

QuoteOriginally posted by DonThomaso Quote
I have noticed that the focusing indicator on the K-5 seems to be a bit larger than the actual focusing point that the camera uses, and that they might not be 100% aligned either.
Indeed, the focus points are mostly filling the whole surface inside the brackets in the viewfinder. The red dots are indications, they are never 100% aligned and they are smaller than the actual areas the camera uses.

QuoteOriginally posted by DonThomaso Quote
Is the focus indicator on the K-3 of similar size compared to older cameras (just that there are more of them) or are they smaller too?
The indicators on the K-3 are the same size, so because each AF point is smaller (they are all within the same bracket as before) they will be more accurate.

Plus when you want to nail focus you can use live view with focus peaking and MF, a tremendously useful feature.

12-06-2013, 08:26 AM   #9
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@bdery

I was thinking that the AF was compensating for color temperature, strong backlight etc, and maybe it does but it does it internally within the AF system? An (extreme) example is that in infrared photography the focusing point is very different from visible light, but it will be different under visible light as well. My experience is that the keeper rate is higher under daylight than artificial light (even at reasonable EVs). Maybe this has to do with algorithms inside the SAFOX system, but then again, has it been improved?

As I said before, I do use live view and on my K-01 also focus peaking. It works well under some situations, but it is definitely not a replacement for traditional OVF use when you are working with a model.

The reason I ask i that a higher keeper rate during these conditions would be a big advantage for me and motivating the K-3. That and the dual sd-slots (backup for critical work). Image quality is more than enough from the K-5 IMHO.
12-06-2013, 08:50 AM   #10
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QuoteOriginally posted by DonThomaso Quote
My experience is that the keeper rate is higher under daylight than artificial light (even at reasonable EVs). Maybe this has to do with algorithms inside the SAFOX system, but then again, has it been improved?
This actually affects other camera systems as well...there were comments from D7000 users about BF/FF issues in tungsten light.

This was addressed in the K-5II IIRC.
Do you have a rental shop you can borrow a K-3 from to try for a weekend? Shoot w/ the 77Ltd all weekend and see what your keeper rate is. I'm fairly certain it'll be much higher than your K-5...

The narrow DOF BF/FF issue is something that has plagued Pentax for a while...I've always thought that was a huge reason they moved away from really fast lenses like the 85/1.4 and 50/1.2 and 135/1.8, though they've always claimed they wanted to avoid heavy/expensive lenses
12-06-2013, 09:28 AM   #11
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I think the K3 is quite a bit more accurate than the original K5 in poor-ish light. K5 II is about the same as the K3, except that the auto focus points are smaller on the K3 and so it can focus more precisely. Tracking is definitely better on the K3 than either of the preceding two cameras,
12-06-2013, 09:48 AM   #12
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QuoteOriginally posted by DonThomaso Quote
@lister6520: I use live view when possible, but it is not an option for most portrait work. You want to be able to work freely and keep up with the model in different poses etc, and tripods won't work for that kind of shooting. I have used my K-01 with live view (only option) but the AF area is a bit to big even on smallest size (at least for full body shots). It is nice to be able to place the area freely though and live view is very precise, but you do loose contact with the model when you have too look on an LCD screen and it won't work very well in sunlight either. I feel that I know all of the various techniques, and I will use different methods when possible.

My question remains though, is the single point AF on the K-3 more precise (will generate more keepers)?
I cannot tell you about how it compares to the K-5 as I don't have one. However it is very rare for me to get a shot with the K-3 that is not perfectly in focus in 'static' situations. But I can say the same of the K-30. I have also a K-r and that does occasionally miss getting the focus spot on, but even then I don't think it happens more than 5% of shots, if that. I must add though that I use almost exclusively the centre focus point, which may be more accurate than the others.

I wouldn't think the K-5 should be any worse and wonder if your specific copy could perhaps have some problem.

Where I do quite often get problems is with handheld macro photos. There I attribute the problem to my moving slightly between the time I acquired the focus and the time I fully press the shutter. In such cases I find that using continuous AF with tracking improves the situation somewhat, even if somewhat limited by the macro lens being a screw drive.
12-06-2013, 09:53 AM   #13
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I'm glad to see (sorry!) that someone else has the same focusing issues that I do with portraits and the K-5 FA77 combination. I would say my results are about the same. Very frustrating when you get that great expression on one shot, but the focus is off. I like the rendering of the FA77 at f2 and 2.4, but I generally go no wider than 2.8 to give a little more leeway in the focus.

I use center point and recompose focusing on the eye. Do you folks think that the change in distance is really significant in focus by using that method?
12-06-2013, 10:17 AM   #14
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QuoteOriginally posted by jake14mw Quote
I'm glad to see (sorry!) that someone else has the same focusing issues that I do with portraits and the K-5 FA77 combination. I would say my results are about the same. Very frustrating when you get that great expression on one shot, but the focus is off. I like the rendering of the FA77 at f2 and 2.4, but I generally go no wider than 2.8 to give a little more leeway in the focus.

I use center point and recompose focusing on the eye. Do you folks think that the change in distance is really significant in focus by using that method?
Depends on your depth of field. Wide open or zoomed focal length gives a shallow DOF so the margin of error is greater.

Check online for a depth of field calculator and see how sometimes an inch or so can kill you.
12-06-2013, 11:23 AM   #15
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Have you tried the technique of using AF-C and using the AF button? I found going to this method, rather than the half press has increased my keeper rate about 5x easily (if not more). You can use the selected focus point and hold the AF button and it will compensate for those micro movements from either yourself or you subject.

Here is an example of a difficult focus situation. My daughter doing spins. While not every shot is spot on focus wise, most are good enough. Was shot at f2.0, 1/1500, ISO 200. Admittedly it is with a K-3 which has a faster focusing system than the original K-5, but the OP's studio situations wouldn't be as extreme as this. Click image to go to high res version....



edit: was made using JPG's from the camera. No PP applied (other than in camera JPG processing)
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