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12-17-2014, 02:08 PM   #16
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Originally posted by jatrax:
Sorry, those are not real tests, those are snapshots, which will tell you nothing.

QuoteOriginally posted by Flugelbinder Quote
I have nothing but respect for your insights - for what I've been able to read here - but that kind of comments, without you knowing my skills, are just......
Could it be you meant to say "real LIFE tests"? Too many variables in the subjects/scenarios you're
describing to consider them quantitative tests, which is the point jatrax is trying to make.

12-17-2014, 02:12 PM   #17
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QuoteOriginally posted by tvdtvdtvd Quote
Originally posted by jatrax:
Sorry, those are not real tests, those are snapshots, which will tell you nothing.



Could it be you meant to say "real LIFE tests"? Too many variables in the subjects/scenarios you're
describing to consider them quantitative tests, which is the point jatrax is trying to make.
Maybe the title of the thread is misleading, it should mention focus inconsistency instead of accuracy, and I apologize for that...
12-17-2014, 02:15 PM   #18
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QuoteOriginally posted by pentaxpete Quote
He is not the only one -- I have been fed up with getting 'back focus' on my 2007 K10D both with the 18-55mm 'kit lens and my Pentax manual focus lenses.
1. The complaint was imprecision, not backfocus

2. I owned a K10D until this last Spring and AF was predictable and accurate during the entire seven years of ownership. My only focus complaints were AF speed, tracking and low light sensitivity.


Steve
12-17-2014, 02:18 PM   #19
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QuoteOriginally posted by Flugelbinder Quote
I know, that's why I'm stressing the af, to get some real results.
Stressing the AF to get real results is like using torture to get reliable and actionable intelligence. It is possible, but not advisable.

Beyond that, it appears you are letting the camera choose the focus point and as noted above, the camera is very poor at reading your mind.


Steve

12-17-2014, 02:34 PM   #20
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QuoteOriginally posted by stevebrot Quote
... appears you are letting the camera choose the focus point and as noted above, the camera is very poor at reading your mind.


Steve
I know, and that's what's worrying me... Camera is set to AFS on the dial...

One more thing that's starting to get on me, and I've asked about it before taking the plunge, is about metering consistency. It seems like it's behaving much like the af is... An example...

If focused on the wall above the window, gives me a correct exposure, but if focused on the tip of the wall, with part of the sky inside the (), the meter tells me I'm 6 stops over exposed?...

Last edited by Flugelbinder; 03-30-2015 at 02:03 PM.
12-17-2014, 02:37 PM   #21
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QuoteOriginally posted by Flugelbinder Quote
I have nothing but respect for your insights - for what I've been able to read here - but that kind of comments, without you knowing my skills, are just......
I am sorry, but Jatrax's suggests were spot on and possibly the best advice you have received on this thread to the point of your comment copied above. I have no idea what your skills are, but your original post and most of the comments that follow read like you are a bit of a noob.

My suggestion (explicit this time) is that you narrow your scope to determine if the base AF system is working and dialed in properly. To do so, follow Jatrax's advice. I also suggest that you seriously consider how you are using the AF system. These things the system will not do for you:
  • Determine what you want in focus (system cannot read minds)
  • Determine what point within the diameter of the AF sensor you want in focus (system will always lock at best phase match)
  • Perform at better than the system specification
That last is perhaps the most critical when determining acceptable results. The technical explanation is involved and would be 2000 words or more, but the summary only takes a few sentences. With the exception of the center focus point, the AF sensors on your camera have a focus sensitivity equal to f/5.6.* What that means is that the ability to detect out-of-focus is the same at f/2.4 (your DA 35/2.4 maximum aperture) as it is at f/5.6. At f/5.6 DOF is pretty generous and focus precision suffers as a result. The center focus point has a focus sensitivity of f/2.8. For best performance with a faster prime (like your DA 35/2.4) use fixed AF at the center point.

Good luck.


Steve

* The f/5.6 sensors are pretty much the industry standard with f/2.8 sensors less common and generally limited to higher end models. The K-5 has one f/2.8 sites and the K-3 has three. The K-30 and K-50 have f/5.6 sensors through-out.
12-17-2014, 02:40 PM   #22
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QuoteOriginally posted by Flugelbinder Quote
I know, and that's what's worrying me... Camera is set to AFS on the dial...

One more thing that's starting to get on me, and I've asked about it before taking the plunge, is about metering consistency. It seems like it's behaving much like the af is... An example...

If focused on the wall above the window, gives me a correct exposure, but if focused on the tip of the wall, with part of the sky inside the (), the meter tells me I'm 6 stops over exposed?...
It all depends what metering mode you are using, with spot metering, it 'should' behave exactly as you described, depending very much on your focus point; with center-weight, and matrix metering, you can change in custom setting 1.4 and 1.5. That again, is not inconsistency, it is how you set it.
12-17-2014, 02:41 PM   #23
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QuoteOriginally posted by aleonx3 Quote
It all depends what metering mode you are using, with spot metering, it 'should' behave exactly as you described, depending very much on your focus point; with center-weight, and matrix metering, you can change in custom setting 1.4 and 1.5. That again, is not inconsistency, it is how you set it.
Again I wasn't explicit, I apologize. I exclusively shoot with spot.

12-17-2014, 02:43 PM   #24
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QuoteOriginally posted by Flugelbinder Quote
I know, and that's what's worrying me... Camera is set to AFS on the dial...
AF-S means single exposure, not single focus point. You want AF-S (shutter will only fire when focus is attained) + single focus point, preferably center. This is the top selection on the switch on the back of your camera. AF-S is set using the switch on the side of the lens mount.


Steve
12-17-2014, 02:44 PM   #25
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QuoteOriginally posted by stevebrot Quote
I am sorry, but Jatrax's suggests were spot on and possibly the best advice you have received on this thread to the point of your comment copied above. I have no idea what your skills are, but your original post and most of the comments that follow read like you are a bit of a noob.

My suggestion (explicit this time) is that you narrow your scope to determine if the base AF system is working and dialed in properly. To do so, follow Jatrax's advice. I also suggest that you seriously consider how you are using the AF system. These things the system will not do for you:
  • Determine what you want in focus (system cannot read minds)
  • Determine what point within the diameter of the AF sensor you want in focus (system will always lock at best phase match)
  • Perform at better than the system specification
That last is perhaps the most critical when determining acceptable results. The technical explanation is involved and would be 2000 words or more, but the summary only takes a few sentences. With the exception of the center focus point, the AF sensors on your camera have a focus sensitivity equal to f/5.6.* What that means is that the ability to detect out-of-focus is the same at f/2.4 (your DA 35/2.4 maximum aperture) as it is at f/5.6. At f/5.6 DOF is pretty generous and focus precision suffers as a result. The center focus point has a focus sensitivity of f/2.8. For best performance with a faster prime (like your DA 35/2.4) use fixed AF at the center point.

Good luck.


Steve

* The f/5.6 sensors are pretty much the industry standard with f/2.8 sensors less common and generally limited to higher end models. The K-5 has one f/2.8 sites and the K-3 has three. The K-30 and K-50 have f/5.6 sensors through-out.
Maybe I should have mentioned that I'm only using the center point only and not even recomposing, just focus and shoot.
12-17-2014, 02:44 PM   #26
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QuoteOriginally posted by Flugelbinder Quote
If focused on the wall above the window, gives me a correct exposure, but if focused on the tip of the wall, with part of the sky inside the (), the meter tells me I'm 6 stops over exposed?.
Is it safe to assume you are still shooting in Spot meter mode? In that case that is what is expected.


Steve
12-17-2014, 02:45 PM   #27
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QuoteOriginally posted by stevebrot Quote
AF-S means single exposure, not single focus point. You want AF-S (shutter will only fire when focus is attained) + single focus point, preferably center. This is the top selection on the switch on the back of your camera.


Steve
Both set on single...

---------- Post added 12-17-14 at 02:46 PM ----------

QuoteOriginally posted by stevebrot Quote
Is it safe to assume you are still shooting in Spot meter mode? In that case that is what is expected.


Steve
Really? I would assume this from matrix... Shouldn't 'spot' cover around 1% of the VF?
12-17-2014, 02:49 PM   #28
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QuoteOriginally posted by Flugelbinder Quote
This seems to happen only when shooting from a distance
It's probably the lens. I have the same problem with the DA 35mm 2.4. If I want accurate focus towards infinity distance, I'm better off focussing manually.
12-17-2014, 02:49 PM   #29
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QuoteOriginally posted by Flugelbinder Quote
Again I wasn't explicit, I apologize. I exclusively shoot with spot.
That is where most problems arise.... spot metering can be a 'life-saver' but it can be very unforgiving, learn how to use and what not to use it.
12-17-2014, 02:51 PM   #30
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QuoteOriginally posted by Flugelbinder Quote
Really? I would assume this from matrix, or average, or whatever Pentax calls it...
Yes...spot. The spot meter region is bound by the () in the viewfinder. If that is the point of discontinuity, it would be good evidence of the mode. Oh...that and the exif indicates spot meter mode. What you experienced is expected. The only portion of the scene being metered is the space between the ( and the ). You put a piece of the sky into that space and it will throw the meter.


Steve
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