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10-26-2012, 05:08 PM   #46
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QuoteOriginally posted by DragonLord Quote
Okay, it is now clear that the f/2.8 high-precision point is in addition to, not in lieu of, the existing AF sensors.

--DragonLord
Fantastic! That means it should be as good with the slower lenses, and even better with fast lenses! And just today I've been suffering a bit trying to get my Sigma 50 F1.4 to be accurate on my k-x...

10-26-2012, 08:14 PM   #47
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QuoteOriginally posted by DragonLord Quote
Okay, it is now clear that the f/2.8 high-precision point is in addition to, not in lieu of, the existing AF sensors.
As I suspected...there would be no good reason for it to be otherwise.
10-27-2012, 03:21 AM   #48
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QuoteOriginally posted by JinDesu Quote
Fantastic! That means it should be as good with the slower lenses, and even better with fast lenses! And just today I've been suffering a bit trying to get my Sigma 50 F1.4 to be accurate on my k-x...
Yes, so every f/2.8 lens or faster should be more accurate.
10-27-2012, 04:41 AM   #49
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QuoteOriginally posted by Anvh Quote
Yes, so every f/2.8 lens or faster should be more accurate.
As a matter of fact, every f/4 lens or faster should focus more accurately.

Just like the f/5.6 sensors still work at f/8, the f/2.8 sensor will still work at f/4 (with only minor limitations compared to faster lenses).

10-27-2012, 06:06 AM   #50
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But the sensor isn't designed for it and it might very well not be active or used with slower lenses by firmware default.
10-27-2012, 07:11 AM   #51
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QuoteOriginally posted by Class A Quote
As a matter of fact, every f/4 lens or faster should focus more accurately.

Just like the f/5.6 sensors still work at f/8, the f/2.8 sensor will still work at f/4 (with only minor limitations compared to faster lenses).
This depends on how wide the AF sensor baseline is set. If the AF sensor baseline is so wide that there is no room for anything slower than f/2.8, this statement would be false. While f/4 lenses might not benefit, an f/3.2 lens (such as the DA 21mm f/3.2 Limited lens) will likely see an increase in accuracy.

Remember: Wider sensor baseline = longer distance between line sensors in a pair = higher accuracy and precision = faster aperture required.

--DragonLord
10-27-2012, 03:42 PM   #52
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QuoteOriginally posted by Anvh Quote
But the sensor isn't designed for it and it might very well not be active or used with slower lenses by firmware default.
What do you mean by "the sensor isn't designed for it"?
Is a f/5.6 sensor designed to be used with f/8 lenses? If not, why does it still work? <- Rhetorical question.

QuoteOriginally posted by DragonLord Quote
This depends on how wide the AF sensor baseline is set.
The length of the sensor baseline is specified by "f/2.8". A standard f/2.8 sensor will already be slightly vignetted when using a lens with a maximum aperture of f/4, but it will still work.
10-28-2012, 03:46 AM   #53
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There is a difference between just working and working well.

Vignetted has very little to do with the AF sensor, sure the light that falls on the sensor edges might be underexpose but with f/4 no light falls on the edges what so ever.
so... only a smaller proportion of the sensor can be used so the sensor can not function on all focus lengths.

10-28-2012, 05:29 AM   #54
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QuoteOriginally posted by Anvh Quote
There is a difference between just working and working well.
What makes you think that it won't work well enough?

QuoteOriginally posted by Anvh Quote
Vignetted has very little to do with the AF sensor, sure the light that falls on the sensor edges might be underexpose but with f/4 no light falls on the edges what so ever.
I'm talking about the AF sensors, not the imaging sensor.

An f/4 lens will cause slight vignetting on the f/2.8 sensors. Lenses that are even slower than that will make the f/2.8 completely black out (not unlike split-prism focusing aids black out when lenses become too slow).

An f/5.6 sensor will still continue to work up until f/8.


QuoteOriginally posted by Anvh Quote
so... only a smaller proportion of the sensor can be used so the sensor can not function on all focus lengths.
Focus distance (or focal length?) has nothing to do with when an f/2.8 sensor will stop working.
10-28-2012, 07:16 AM   #55
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A rough and ready low light K5 vs. K5II AF test is here on the tube.....
10-28-2012, 09:38 AM   #56
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Class A, yes sorry it is indeed focus distance.

As for the rest.
AF sensor is a strip, you can figure out what that means with smaller aperture and vignetting

Here is some help.
10-28-2012, 02:40 PM   #57
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QuoteOriginally posted by Anvh Quote
Class A, yes sorry it is indeed focus distance.
But neither focus distance nor focal lenght have an influence on when an AF area stops working.

What you may be referring to is the degree with which a subject is out of focus. At a certain point, the two images the AF module sees from the same portion of the scene have diverged too much from each other so that no AF prediction can be made anymore. In this case the lens will be racked as long as some overlap between the two images have been established. This situation can indeed occur more easily when a slow lens is pushing the AF module by causing partial vignetting on the AF sensors.

QuoteOriginally posted by Anvh Quote
Here is some help.
No offense, but maybe you are the one who needs to do a bit more reading/investigation.
10-29-2012, 10:18 AM   #58
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I think things got lost in translation here

If i need more reading then why do you say that it actually can be the case in your comment?

Like i said and the picture show, if a slower lens is used for example large enough to be half way the red indication inside the lens than that also means that only half of the red F/2.8 AF sensor is used.
So... the AF sensor might be able to still help in trying to get a focus but if the focus is too far off that it falls into the black spot of the AF sensor then the sensor won't work.
10-29-2012, 10:58 PM   #59
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QuoteOriginally posted by Anvh Quote
If i need more reading then why do you say that it actually can be the case in your comment?
Because "focus distance <> amount of being off-focus" and your earlier comment regarding "Vignetted has very little to do with the AF sensor".

All good.
10-30-2012, 10:37 AM   #60
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With vignetted i meant decrease in brightness but with slower aperture lenses you also have total blackout in the corners, in that case the AF sensor might have no image at all to work with.
Thats what i meant.
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