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08-25-2008, 07:03 AM   #16
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QuoteOriginally posted by Wheatfield Quote
Quoted from another forum:

"First the boring stuff...

EVERY decent control system has a certain amount of hysteresis. Hysteresis
is created when a *small* distance about "perfect" accuracy is designated as
having sufficient accuracy for acceptable performance (this is often called
"deadband") and wherein active control is suspended. This is done to prevent
chatter or excessive "hunting". Chatter or excessive "hunting" greatly
increases wear, is hard on mechanical equipment and often creates excessive
noise and vibration. The autofocus in your camera is a type of control
system because most folks greatly dislike vibration and noise in their
cameras. Further, they would be greatly dismayed if the life of the bearing
surfaces wore out in months instead of decades; therefore hysteresis is
actually a good thing. You know that your AF system has built in hysteresis
because the lens does not continue to hunt (forever) on a stationary due to
sensor noise and continuous slight overshoots.

What the boring stuff means...

This means that your autofocus system will NEVER focus on EXACTLY the same
spot every time because the AF will stop when it determines that focus error
is within the deadband and therefore "good enough". Now DOF, in distance
units, changes with several parameters. This also means that the deadband,
in distance units, is different for every focal length, every maximum
aperture and every focus distance.

Autofocus is a convenience (and a great one at that), but it will never be a
substitute for critical manual focusing to accurately and critically
position your DOF about the subject. Some AF systems may be better than
others or have different features, but this is true for *all* AF cameras,
regardless of brand or model."

My understanding is that Pentax AF in the K10 and prior models allowed for a lot less
allowable hysteresis than what Canon was allowing. This made Canon AF faster, Pentax AF more accurate. I think they loosened up a little bit with the K20, it certainly locks focus faster than the K10, but I have found wide aperture performance to be a little soft from time to time.

great info ---- thank you so much for this

kman

08-25-2008, 07:14 AM   #17
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QuoteOriginally posted by kmanlaker Quote
great info ---- thank you so much for this

kman
Yer welcome.
08-25-2008, 07:17 AM   #18
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QuoteOriginally posted by Wheatfield Quote
This made Canon AF faster, Pentax AF more accurate. I think they loosened up a little bit with the K20, it certainly locks focus faster than the K10, but I have found wide aperture performance to be a little soft from time to time.
Canon AF is less accurate? i'm not sure (1D III issues asside). it's definitely faster
08-25-2008, 07:26 AM   #19
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QuoteOriginally posted by Wheatfield Quote
Quoted from another forum:

"First the boring stuff...

EVERY decent control system has a certain amount of hysteresis. Hysteresis
is created when a *small* distance about "perfect" accuracy is designated as
having sufficient accuracy for acceptable performance (this is often called
"deadband") and wherein active control is suspended. This is done to prevent
chatter or excessive "hunting". Chatter or excessive "hunting" greatly
increases wear, is hard on mechanical equipment and often creates excessive
noise and vibration. The autofocus in your camera is a type of control
system because most folks greatly dislike vibration and noise in their
cameras. Further, they would be greatly dismayed if the life of the bearing
surfaces wore out in months instead of decades; therefore hysteresis is
actually a good thing. You know that your AF system has built in hysteresis
because the lens does not continue to hunt (forever) on a stationary due to
sensor noise and continuous slight overshoots.

What the boring stuff means...

This means that your autofocus system will NEVER focus on EXACTLY the same
spot every time because the AF will stop when it determines that focus error
is within the deadband and therefore "good enough". Now DOF, in distance
units, changes with several parameters. This also means that the deadband,
in distance units, is different for every focal length, every maximum
aperture and every focus distance.

Autofocus is a convenience (and a great one at that), but it will never be a
substitute for critical manual focusing to accurately and critically
position your DOF about the subject. Some AF systems may be better than
others or have different features, but this is true for *all* AF cameras,
regardless of brand or model."

My understanding is that Pentax AF in the K10 and prior models allowed for a lot less
allowable hysteresis than what Canon was allowing. This made Canon AF faster, Pentax AF more accurate. I think they loosened up a little bit with the K20, it certainly locks focus faster than the K10, but I have found wide aperture performance to be a little soft from time to time.
So maybe K30D could have an adjustable dummy parameter for this that the user could adjust between more accurate/slow and less accurate/faster? Wouldn't that be useful? Much like we are allowed control over how much sharpening/filtration that the camera do to the pictures. More personal choices and a possibility to tune up the AF to higher speed when I need it, for a price of course.

08-25-2008, 07:33 AM   #20
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QuoteOriginally posted by Jonson PL Quote
Iíve got my hopes up for a Pentax 135 mm one day. Would love it to be f/2.
QuoteOriginally posted by roentarre Quote
135L is in deed a very good lens and I would love pentax to produce one. Canon 135L autofocuses soooo fast and accurately. Light and affordable. Perfect to do theatre or stage play shots.
It's not like if they would have to invent a new good lens solution. "Just" take the A*135/1.8 and give it SDM and new coatings.
08-25-2008, 07:37 AM   #21
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QuoteOriginally posted by k100d Quote
Canon AF is less accurate? i'm not sure (1D III issues asside). it's definitely faster
I don't have first hand experience here, I'm mentioning what a couple of friends who use Canon have gleaned off some of the Canoncentric forums, and a few germs of information I've picked up from other sources.
Remember that a lot of slight AF inaccuracy will be masked by depth of field, and this is an area where a very small amount of allowance will give a very large performance increase.

You realize that by mentioning that Canon AF is definitely faster, you will be burned at the stake as a witch by the Alter of Pentax zealots that are rampant on this forum?
08-25-2008, 07:45 AM   #22
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QuoteOriginally posted by Douglas_of_Sweden Quote
So maybe K30D could have an adjustable dummy parameter for this that the user could adjust between more accurate/slow and less accurate/faster? Wouldn't that be useful? Much like we are allowed control over how much sharpening/filtration that the camera do to the pictures. More personal choices and a possibility to tune up the AF to higher speed when I need it, for a price of course.
Nice theory, but the end results would be pretty predictable. A bunch of (l)users would turn their AF speed up as high as possible, and then flood the forums with a bunch of complaints about 1) innacurate AF, 2) AF that doesn't work, 3) AF that isn't as good as manual focus, 4) when did Pentax stop making good lenses? I just can't seem to get a sharp picture, even though the AF says it's in focus.

Remember the Philbert complaints that Pentax Jpegs weren't as sharp as Nikon's? It never seemed to occur to him that turning the sharpening up a notch put the Pentax files on the same page, and that you could take the sharpening way farther than a normal person would want to.
People tend to be idiots, the internet has given them a home where they can bleat at the whole world from their soapbox.
08-25-2008, 09:10 AM   #23
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QuoteOriginally posted by Wheatfield Quote
You realize that by mentioning that Canon AF is definitely faster, you will be burned at the stake as a witch by the Alter of Pentax zealots that are rampant on this forum?
the forum isn't that bad... i'm sure everyone would love faster AF

08-25-2008, 09:33 AM   #24
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QuoteOriginally posted by Douglas_of_Sweden Quote
So maybe K30D could have an adjustable dummy parameter for this that the user could adjust between more accurate/slow and less accurate/faster? ...
While you're at the drawing table...

How 'bout a smart parameter that lets everything from 1cm to infinity be in absolute perfect focus in every single shot. Then in RAW processing decide on where the OOF area starts and ends, with 3rd party bokeh plug-ins and emulation plug-ins for bokeh master lenses of 'yore?
08-25-2008, 01:57 PM   #25
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QuoteOriginally posted by Wheatfield Quote
Nice theory, but the end results would be pretty predictable. A bunch of (l)users would turn their AF speed up as high as possible, and then flood the forums with a bunch of complaints about 1) innacurate AF, 2) AF that doesn't work, 3) AF that isn't as good as manual focus, 4) when did Pentax stop making good lenses? I just can't seem to get a sharp picture, even though the AF says it's in focus.

Remember the Philbert complaints that Pentax Jpegs weren't as sharp as Nikon's? It never seemed to occur to him that turning the sharpening up a notch put the Pentax files on the same page, and that you could take the sharpening way farther than a normal person would want to.
People tend to be idiots, the internet has given them a home where they can bleat at the whole world from their soapbox.
But we do get that sort of stupid questions anyway, don't we? Threads like: "I just put a 2x converter on my 80-300 lens to try to take some bird pictures on my backyard, but I can't seem to get any sharp pictures, why on earth is this, should I buy a canikony instead?" And it usually turns out they shoot hands-free on 1/60th of a second, so the main reason wasn't even the bad converter on a bad mediocre zoom. Just an example. When I was the youth section leader in my local photo-club in the 80's I was teaching kids and teenagers to use fully manual cameras (Praktika etc), but after all instructions on how aperture and exposure time related etc I still had people who could come to me having open the camera without (manually in this case) rewinding the film and in a complaining way ask me why there were no pictures on the film! Probably the same people now in a grown up shape have a canikony happily watching the live-view without destroying anything, but always wondering why they can't light up the Eiffel-tower with the built in flash on their nocturnal tourist tour in Paris etc. You will never get rid of this, no matter of how many or how few things they can interfere with on the camera.

And I would like that adjustable AF between accurate and fast, I don't care that some will use it less wisely.
08-25-2008, 02:38 PM   #26
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QuoteOriginally posted by Douglas_of_Sweden Quote
It's not like if they would have to invent a new good lens solution. "Just" take the A*135/1.8 and give it SDM and new coatings.
Unfortunately I am one of the unforgiveable that dislikes A* 135mm f1.8

The lens is fringeholic and not sharp in the centre until f2.8 or so. The bokeh are little busy most of the time. Yes, more improvement on that optical design would be great. But I think I am dreaming ...
08-26-2008, 02:52 PM   #27
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QuoteOriginally posted by Douglas_of_Sweden Quote
It's not like if they would have to invent a new good lens solution. "Just" take the A*135/1.8 and give it SDM and new coatings.
The A 135/1.8 doesn't really have that super a reputation. Needs to be stopped down a lot.

What I would really love to see, would be a DA* version of the 20/1.4 prototype :
K 20/1.4 AL

08-26-2008, 04:16 PM   #28
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QuoteOriginally posted by kmanlaker Quote
Also has anyone ever thought of why all these Canon shooters are using all of these funky adapters to put all of these non-Canon glass on their cameras??? I do not see the Pentax forums full of how do I grind the mirror off of my K10d to mount a Canon L lens. And no I did not grind my mirror on my 5D ---- I decided to sell it and move on !!!
Are you saying that some Canonites are willing to grind the mirror off of their $2000+ 5Ds so that they can use Pentax lenses on them? If that's the case, then that is FUNNY!

Why don't they just lay their Canon pride down and sell their 5Ds? Depending on what they can get for a used one, they can pick up a K20 and a lens or 2. We'll protect them from the Canon Mafia that may come around to take them out because they left the dark side.

Heather
08-26-2008, 04:37 PM   #29
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QuoteQuote:
I still had people who could come to me having open the camera without (manually in this case) rewinding the film and in a complaining way ask me why there were no pictures on the film! Probably the same people now in a grown up shape have a canikony happily watching the live-view without destroying anything, but always wondering why they can't light up the Eiffel-tower
Very funny Douglas.
08-26-2008, 05:45 PM   #30
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QuoteOriginally posted by Douglas_of_Sweden Quote
but always wondering why they can't light up the Eiffel-tower with the built in flash on their nocturnal tourist tour in Paris
QuoteOriginally posted by nulla Quote
Very funny Douglas.
You may laugh, but I've actually seen several people trying this with Big Ben in London, then staring at the LCD and frowning.
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