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05-21-2009, 01:54 PM   #46
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Exactly

QuoteOriginally posted by Torphoto Quote
I think we have to take the Pentax Af systems performance in comparison with other similar cameras. Having played with the 40D and D300, I can tell you that AF tracking in AFs is as fast in good light. In low light the K20D can lock with out AF assist better than the 40D but both the 40D and D300 just kill the K20D in AFC ( also their AF assist especially on the D300 is better ), the K20D's AFC simply can not track subjects comming toward or going away from it, latteral tracking is no problem.

I further noticed that the lens I was mostly using was the 50-135mm, slowish AF vs the 40mm and 70mm limiteds. The limiteds faster AF made a huge difference as the faster AF from the lens enabled it to track better, much better than the 50-135 but still far behind the 40D or D300 with perpendicular subject movement.


From what I have gathered the AFC on the K7 is much improved vs the K20D, the question is how does it compare now vs the D90, 50D and D300.

I think that other than low light performance, you have hit on what I think is the prime source of the incessant AF whining concerning the Pentax AF system:

"both the 40D and D300 just kill the K20D in AFC"

Hopefully the AFC has dramatically improved, but there is very little noise about any improvement in this area, but lots of generalizations and marketing fluff about overall improvements to the system.

I have not seen one NDA'er or hands-on K7 user make a single claim about improved AFC.

That feels like an attempt to manage expectations to me.

Ray

05-21-2009, 02:04 PM   #47
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QuoteOriginally posted by Ray Pulley Quote
I think that other than low light performance, you have hit on what I think is the prime source of the incessant AF whining concerning the Pentax AF system:

"both the 40D and D300 just kill the K20D in AFC"

Hopefully the AFC has dramatically improved, but there is very little noise about any improvement in this area, but lots of generalizations and marketing fluff about overall improvements to the system.

I have not seen one NDA'er or hands-on K7 user make a single claim about improved AFC.

That feels like an attempt to manage expectations to me.

Ray
Not that I ever seem to use AF-C anyway, but I think assuming that there's something magical about other brands that wouldn't make an overall improvement yield better results in that mode...is mostly about people coming to do whatever they get out of bashing other brands and those that choose them.

I mean, really. Whatever it is, it's done. May as well see what they came up with.

Pentax has *never* billed itself as the action shooter's choice, and most of those who do it seriously and can't afford to own whatever they might want , want to be able to roll into a big town and rent something big and fast, and that's not on the table, here, right now. Stuff like that doesn't just drop out of the sky.
05-21-2009, 02:12 PM   #48
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Yes and No

QuoteQuote:
I think it means they added a new light source to the data range of phase-detection AF.
No.


QuoteQuote:
Actually, since they said 'data range' rather than 'detection range,' it's quite possible that they *didn't* add a new sensor, just the ability to receive and process more useful information from *a* sensor. Could even be the very same one, that just previously hadn't been fully utilized.
No. The sensor is clearly shown and discussed as being a color temperature sensor.



QuoteQuote:
Could have. . If having more useful data makes a positive lock easier under whatever set of conditions, then, there's less dithering to do. It's kind of like radar: a bigger antenna, so to speak.
Bad analogy, but there is some truth in this.




QuoteQuote:
An algorithm is a mathematical process that is the means by which something like AF data is turned from a bunch of light falling on a sensor, into commands for something like the AF or SR.

If there's a more-efficient way to get the same results out of fewer computer cycles, (and fewer times blipping the lens to get more data) yes, it happens faster. This is why computer speed is measured in Hertz.
No offense intended, but I am quite aware of what an alogrithm is.



QuoteQuote:
Agreed. But this is also all about the math the computer does and what information it has to process. There isn't like a separate 'predictive AF machine' someone sticks in a camera, ...just more math.
Yes and no, but mainly no. Other brands use many AF sensor points, many of them hidden, to create a predictive AF system that includes hardware (more sensors) and AI-like algorithms to manage the AF tracking. It is more like a closed-loop servo system.

The hidden sensors pick up and start tracking the object and because there are enough of them, they have enough data to start trying to predict where the object being tracked is headed. They hand off this work to other sensors as the object moves (so to speak) and keep passing this information to the AF system which drives the lens to where the object is PREDICTED to be, not where it was or is. At some point in the process the main AF sensors lock and you can take the image, but in the meanwhile the lens has never stopped driving to the focus point that the hardware and the software predict the object will be.

QuoteQuote:
Speed improvements come from that being fast and accurate, and from the machinery being able to respond as quickly as possible to it. The machinery can't go any faster than the calculations, though. So improving the calculations ....either with more computer power, a broader range of data, or more efficient ways to process it, certainly pays dividends.
Of course faster processing will always improve such a system, but all of this has little or nothing to do with low light focusing. If the processing were the problem in low light, the system would not be any faster at higher light levels than it is at low levels. The AF hardware has to be the main hold-up in low light.

You could, however, have the exact same arrangement as the K20D but emply 2 year newer AF sensors that are much more sensitive to light and get improvements in low light without making any other huge change to the overall system.

Ray
05-21-2009, 02:14 PM   #49
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QuoteOriginally posted by Ray Pulley Quote


No offense intended, but I am quite aware of what an alogrithm is.




Ray
No offense intended, but your pose of 'confusion' didn't make it sound like it, especially if you knew all that.


(Also, the claim that new 'data' is going into the AF system *doesn't mean Pentax is trying to deceive anyone about there necessarily being new or more hardware in there.)

05-21-2009, 02:26 PM   #50
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I have to be honest, I NEVER found a difference between Canon AF and the AF on the *ist DS (one of the oldest Pentax DSLRs), so I don't understand the complaints. Then again I rarely used it for moving subjects, but I did use it a lot in low light. Didn't hunt any more than the 30D.
05-21-2009, 02:28 PM   #51
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I compared the cameras on Imaging Resource and subtracted the shutter lag time at manual focus from the shutter lag time at full autofocus then subtracted the difference from the full auto focus number. If I'm thinking that through correctly the following numbers are the scientifically distilled auto focus speeds in order:

Nikon D700 = .045 seconds
Nikon D300 = .054 seconds
Nikon D90 = .061 seconds
Pentax K20D = .09 seconds
Pentax K10D = .181 seconds

Presumably these are AFS numbers on a tripod, not AFC tracking an active seven year old handheld. The K-7 speed tests have not been posted yet.

Edit to add:
Canon 5D Mrk II = .118
Canon 50D = .12 seconds

Last edited by GoldenWreckedAngle; 05-21-2009 at 02:38 PM.
05-21-2009, 02:31 PM   #52
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Eh, Golden. It'll do.

What's that make the complainers, sitting around waiting on a difference of .04 seconds? I must be getting old.

I think maybe why I'm tending to get a little peeved here is that it seems the message from all the, if you don't mind my saying, geekery, is, 'You can't unless you buy this, you can't unless you buy that.'

That's no way to teach or learn photography.

(So, sorry if it does cheese me off a little. I like talking about cameras, too. But I think there's a lot of loss of perspective about what really gets the job done involved. )

Last edited by Ratmagiclady; 05-21-2009 at 02:38 PM.
05-21-2009, 02:37 PM   #53
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QuoteOriginally posted by Ray Pulley Quote

BTW, accuracy over speed is fine with me too, but I would like better low light AF speed.

Ray
The way my K20D behaved more accuracy could led to faster AF even if AF is not as fast...
If accuracy eliminates low light hunting I don't care about AF speed, it will be faster !!!!

I fail to see how the AF motor in a lens can go faster than it is designed for... Somy gues is AF speed itsself is faster but as it hunts les, you gain time

05-21-2009, 02:42 PM   #54
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QuoteOriginally posted by janneman Quote
I fail to see how the AF motor in a lens can go faster than it is designed for... Somy gues is AF speed itsself is faster but as it hunts les, you gain time
Assuming it can take the additional load, more current through a motor will make it spin faster than less current. If the K-7 has more powerful batteries, it will can direct more current through the same motor (SDM lenses) or spin an existing motor at faster speeds, with more torque, than previously (non-SDM lenses). The former premise is assuming the SDM lenses weren't being pushed to rated limits to begin with.
05-21-2009, 02:48 PM   #55
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Uhhhhh

QuoteOriginally posted by Ratmagiclady Quote
No offense intended, but your pose of 'confusion' didn't make it sound like it, especially if you knew all that.
The operative word here being: "sound", meaning it sounded one way or another to you. Sorry, but I am not responsibile how you think things "sound".


QuoteQuote:
(Also, the claim that new 'data' is going into the AF system *doesn't mean Pentax is trying to deceive anyone about there necessarily being new or more hardware in there.)
Deceive? Who said anything about deception, or is this another one of those "sound" things of yours?

Ray
05-21-2009, 02:50 PM   #56
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The shutter lag at full auto focus is actually probably a more accurate number for real world shooting. This is kind of interesting:

Shutter lag at full auto focus:

Canon 50D = 0.131 (W) seconds
Pentax K20D = 0.174 (W) seconds
Nikon D700 = 0.197 (W) seconds
Canon 5D Mrk II = 0.206 (W) seconds
Nikon D90 = 0.208 (W) seconds
Nikon D300 = 0.227 (W) seconds
Pentax K10D = 0.254 (W) seconds
05-21-2009, 02:53 PM   #57
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Perhaps, Ray, you'd like to just rearticulate your original point, so as it's not about me?
05-21-2009, 03:01 PM   #58
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You see, where *I* got the idea you figured someone was trying to pull a fast one, was where you said:


QuoteOriginally posted by Ray Pulley Quote
Well, it IS a marketing release and has no specificity or data to back up the claims, so what does this statement really mean?

We know what the light source sensor does, and frankly I would be hard-pressed to believe that adding a sensor that has to be read and processed and then taking that data and using it to adjust the AF would make the whole process FASTER. After all, in the K20D no such sensor/calculation was included.

And where I got the idea you weren't clear on what an algorithm is, was when you said *this.*

QuoteQuote:
How do algorithms improve low-light focus speed?



Ray

From stuff I clipped out of these quotes for clarity, I don't think were at any so great loggerheads about what it all *means,* I was just saying it seems awfully early for some to doubt it's *possible* for the AF to have improved.

See where we are, there?


As far as trying to take it personal, believe it or not, I have some experience of guys talking down to me like I couldn't possibly understand anything technical, who might look at my choice or kludge of gear and say, "silly girl, you can't do that with that."

My customary response is: Watch me.

Last edited by Ratmagiclady; 05-21-2009 at 03:06 PM.
05-21-2009, 03:10 PM   #59
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AF-C on K7

Just to interject a comment here between the back-and-forth comments of Ray and the Ratmagiclady, an earlier poster in this thread mentioned that he had not seen anything mentioned about the speed of the K7's AF-C. Mark Dimalanta in his review reports that AF tracking in AF-C is "vastly improved". His review can be seen here:

chasing light...: Initial Impressions of the Pentax K7

CN
05-21-2009, 03:15 PM   #60
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This is a waste of time

QuoteOriginally posted by Ratmagiclady Quote
Perhaps, Ray, you'd like to just rearticulate your original point, so as it's not about me?
No it is already a waste of time.

Ray
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