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03-30-2009, 07:47 AM   #31
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QuoteOriginally posted by pingflood Quote
So far I've seen the Pentax AF discussions devolve into
1) You should just manual focus like a REAL photographer
2) Pentax is more accurate
3) The head-in-the-sand approach, Pentax is as good as everything else
You forgot (4): it's fast enough for most situations (but most competitors are faster in low light and predictive AF) and there are workarounds like the AF-C hack that get you sorta closer

FWIW, I've seen complaints about Canon's 50/1.8 being useless for indoor photography on a 40D, people using AF-ON w/ the D700, etc., so a lot of it is "it depends". None of that means there aren't better systems if you need it though (the Canon 1DmkII kicks everyone's butt w/ predictive AF, etc.)...

03-30-2009, 07:55 AM   #32
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I shot this test portrait of my daughter yesterday afternoon with my K10D and DA 35mm f/2.8 Macro Limited. The light coming through the window wasn't bad as this was shot at ISO 100, f/2.8 & 1/80 second.


I focused on her left eye (camera right). Trying to get her (and me) to stand still long enough for the AF system to lock in and fire in AF-S mode wasn't working at all so I switched to MF and fired as soon as the AF indicator illuminated. After a few tries I was getting too much front & back focusing due to the short DoF so I tried AF-C mode and continuous shutter. After a burst of about 6 images I got this single keeper. (If you click the photo it should take you to my Picasa page where you can zoom in.)

Accuracy is important. So is speed. Sometimes we need both for even the most mundane shots.

So, how about if Pentax gave us the option of disabling the double focus check for those times when speed was more important than accuracy?
03-30-2009, 08:03 AM   #33
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Question about AF here in general. What detriments are there for including an active ultrasonic AF aid on-board? Speed? From my understanding contrast and phase detect are passive correct? Focus is based on the image projected on the AF module. Active AF would give the camera a starting point in terms of distance and then the contrast double check could lock quickly correct? Since I haven't been using an SLR for long I am unaware of the historical trends as to why certain widgets were chosen over other widgets. Thanks!
03-30-2009, 08:07 AM   #34
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QuoteOriginally posted by Robert S Donovan Quote
So, how about if Pentax gave us the option of disabling the double focus check for those times when speed was more important than accuracy?
Precisely what I suggested. Though I don't know if the "double check" process is crucial to achieving proper focus the way the Pentax AF system operates. It could be that the first move is a "rough approximation" and stopping at that point could be too far out of acceptable focus to work out. Some lenses will obviously have more allowable "slop" than others; e.g. a 16-45 f/4 will have more depth of field wide open than a 50/1.4...

Still, would be nice if we could get some info from Pentax on this -- either explain why they can't offer that option (because of technical issues), or offer it in a firmware update.

On a side note, the 24-105L arrived today and mommy, it's a nice piece of glass! My first IS lens, and it's pretty darn cool to throw the switch and watch the image stabilize in the viewfinder. Too bad you have to pay for it in each lens you buy though... (the autofocus is incredible on it for a zoom, almost as fast as my 85... not sure how they managed that but I'm happy!)

03-30-2009, 08:12 AM   #35
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You've made typical missassesment at choosing the af subject. In that situation camere tried to to choose somethig beetwen your doughter ear and the background, it could'nt be succesfull. Try to choose somethig bigger like her eye so to cover with the af sensor entire flat area... it was some thread about size of af point....
03-30-2009, 09:01 AM   #36
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QuoteOriginally posted by filorp Quote
You've made typical missassesment at choosing the af subject. In that situation camere tried to to choose somethig beetwen your doughter ear and the background, it could'nt be succesfull. Try to choose somethig bigger like her eye so to cover with the af sensor entire flat area... it was some thread about size of af point....
I was focusing on her eye using the center focus point (normally I focus on the eye, recompose and shoot). Slight camera and subject movement while shooting continuously in AF-C mode resulted (somehow?) in this perfect focus just off center.
03-30-2009, 09:11 AM   #37
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If you choose center focus point, it should be dead-on. Hmm.. have you ever checked that you may have a BF/FF problem? I did that on my K10D, it improves a lot in situations like that.
03-30-2009, 09:20 AM   #38
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QuoteOriginally posted by aleonx3 Quote
If you choose center focus point, it should be dead-on. Hmm.. have you ever checked that you may have a BF/FF problem? I did that on my K10D, it improves a lot in situations like that.
BF/FF is an accuracy problem, not a speed problem, no?

The problem with the shot above is that the AF just continuously hunted- "dut, dut, dut, dut"- while trying to lock focus on her eye. Neither of us were moving very much but obviously just enough to send the focus double check into an infinite loop. I definitely did not have this problem with my 5D.

On a related note, I want to make it clear that I am not bashing Pentax here in any way. I love my K10D (more so than my old Canon 5D). The AF performance is one of the very few areas I see that need improvement... and it's really not that bad most of the time. In fact, today I am shooting students in my class working in the wood shop and the K10D DA 35mm f/2.8 Macro Limited combination is working like a champ!

03-30-2009, 09:28 AM   #39
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QuoteOriginally posted by Robert S Donovan Quote
I was focusing on her eye using the center focus point (normally I focus on the eye, recompose and shoot). Slight camera and subject movement while shooting continuously in AF-C mode resulted (somehow?) in this perfect focus just off center.
Robert, I am curious: why are you using AF-C on a static subject?

Regards,
Marc
03-30-2009, 09:47 AM   #40
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QuoteOriginally posted by Robert S Donovan Quote
I was focusing on her eye using the center focus point (normally I focus on the eye, recompose and shoot). Slight camera and subject movement while shooting continuously in AF-C mode resulted (somehow?) in this perfect focus just off center.
Okay you were using center focus point, but the focus sensor there is much larger than her eye so it might have picked the hair locks just behind -- highest contrast against the bright face.
03-30-2009, 09:49 AM   #41
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QuoteOriginally posted by Robert S Donovan Quote
I was focusing on her eye using the center focus point (normally I focus on the eye, recompose and shoot). Slight camera and subject movement while shooting continuously in AF-C mode resulted (somehow?) in this perfect focus just off center.
I have just notice on my previous k10d and a little less with k20d that when you chooses a subject 3dimensional like a human face and AF point (bigest then on 5d) covers for instance eye and ear you won't be able to obtain good results. Exaggerating: if you take the picture of something with the black/dimmy background, what kind of contrasty situation do you have....? ....something vs undefined darkness?

Last edited by filorp; 03-30-2009 at 09:54 AM.
03-30-2009, 09:50 AM   #42
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I am quite bored today, so I will participate even when this horse has been beaten to death

I have used the Pentax Ist D, Ds, K100d and K20d. The first 3 have slowish but good AF-S in good light. Low light and continous AF was just rubbishing by today standards. The K20d improved on low light but it still very very far from the Canon 40d I also had.

The accuracy of focus of Pentax (over the rest of the brands) is good but it is overrated. The K100d with apertures larger than f2 was inconsistent to be generous. One thing that I remember it surprised me was that lenses that had accuracy problems in my K100d (particularly a 31 limited and a F50 f1.4) on a regular basis were much better on the K20d. THe K20d improved this area but still slightly inconsistent when shooting a f1.4 or f1.8 lens wide open in less than perfect light (with tripod) but that was being very very picky. AF on fluorescent light with fast lenses wide open was problematic with any pentax I have used. And peripheral points in low light were also problematic.

But not everything is shinny on Canon, the center point of the 40d was mondo-accurate in any light, but the peripheral points were very inconsistent on any light. Also the proportion of lenses that BF/FF on Canon is quite high and calibrations were needed to get the most of them (and I am talking about L lenses too). Once the lenses are calibrated they can be amazingly good.
03-30-2009, 10:16 AM   #43
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QuoteOriginally posted by Marc Langille Quote
Robert, I am curious: why are you using AF-C on a static subject?

Regards,
Marc
Normally I would not, but in this case I tried the spray-and-pray method as suggested in an earlier comment. Truth be told, neither the subject nor the photographer were truly static
03-30-2009, 10:18 AM   #44
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QuoteOriginally posted by kenyee Quote
You forgot (4): it's fast enough for most situations (but most competitors are faster in low light and predictive AF) and there are workarounds like the AF-C hack that get you sorta closer
I'm adding 5) Don't use it for things it wasn't intended for, like human faces.
03-30-2009, 10:20 AM   #45
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@Gruoso,
Thanks for joining in

Your experience pretty well mirrors mine. The only difference is that I rarely use anything other than the center focus point. The only camera I have used to date that even comes close to having perimeter focus points that are accurate enough is the Nikon D3. The problem there is that there are so many of them it becomes quite tedious to select the right one shot-to-shot. You can leave it in auto but... how does the camera know what I'm trying to do with my composition? Typically, it does not.

What I want is a lighting fast center focus point so I can focus, recompose and shoot before the shot gets away. This technique has worked for me for a very long time. I just struggle sometimes with my K10D...
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