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10-16-2012, 07:04 AM   #1
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Is it normal for the CDAF image to be sharper than PDAF?

Hello!
I have been doing some tests, and i have noticed that my K-30 frontfocuses with the kitlens (blerg, i'm so unlucky), and i've been using -10 adjust to correct it.
As a test to see if it is now ok, i focus using liveview, go out of LV and half press the shutter button to make it refocus.
If there is any movement, i assume it is frontfocus. There is only movement without adjustment at around 24mm (i would say from 22mm to 30, something like that).
Even though using 0 adjustment there is no movement at 55mm, for example, using -10 there is also no movement.
I've adjusted my camera to apply -10 to the kitlens, and noticed that CDAF images are always a BIT (a very small bit) sharper than the PDAF ones.
Is that normal and i'm too paranoid, or is that a sign that my adjustment isn't good enough?
(i'll try to exchange my 18-55 for a 18-55 WR, that may also solve the frontfocusing problem, since it only seems to affect the kit lens)
Thank you

10-16-2012, 07:09 AM - 1 Like   #2
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10-16-2012, 07:19 AM   #3
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Contrast Detect ignores all front/back focus issues in the lens. It's supposed to be 100% accurate - therefore, the sharpest image you can get without focus issues.
10-16-2012, 07:29 AM   #4
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Well, that was actually funny HAHAHAHAHAHA
It even looks like the poster underlined that part to answer my question hahahahah
Thank you for the quick answer. I'm too paranoid for sure

QuoteOriginally posted by JinDesu Quote
Contrast Detect ignores all front/back focus issues in the lens. It's supposed to be 100% accurate - therefore, the sharpest image you can get without focus issues.
But, i'm my head, a properly focusing camera would generate an image that is as sharp using PDAF as it is with CDAF



BIZARRE QUESTION : Am i using punctuation correctly? English is not my main language, and i might be doing it incorrectly.


Last edited by GabrielFFontes; 10-16-2012 at 07:40 AM.
10-16-2012, 07:33 AM   #5
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This is why I don't understand why they don't find some way of using CDAF while using the OVF. Or why they don't just use EVF w/o mirrors and just devope faster CDAF.

I know PDAF will always be faster, because it knows which way to focus, but I'd rather have superacurate then superfast.
10-16-2012, 07:34 AM   #6
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What I mean, by my post, is that CDAF is going to be the most accurate focus you get. So therefore, if your PDAF pictures are not as sharp - given the same conditions for both - your PDAF pictures are most likely a little bit off, focus-wise.

So yes - if your PDAF was spot on, it'll be the same as your CDAF. In fact, there are several articles that advise using CDAF to check your PDAF's accuracy.
10-16-2012, 08:05 AM   #7
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There should be a way to use CDAF and OVF nicely. There is actually a simple way. The light reflected to the AF sensor could be reflected to a image sensor that would do the AF, but the problem is that only 30% of the light (i guess) is reflected, so the CDAF would have to work with only a bit of light.
The perfect system should be a CDAF-checked-PDAF. The camera would focus using PDAF and would use the CDAF to check the accuracy. Of course, you would have to do that REALLY quickly, but i'm sure that is possible.
10-16-2012, 08:06 AM   #8
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QuoteOriginally posted by GabrielFFontes Quote
There should be a way to use CDAF and OVF nicely. There is actually a simple way. The light reflected to the AF sensor could be reflected to a image sensor that would do the AF, but the problem is that only 30% of the light (i guess) is reflected, so the CDAF would have to work with only a bit of light.
The perfect system should be a CDAF-checked-PDAF. The camera would focus using PDAF and would use the CDAF to check the accuracy. Of course, you would have to do that REALLY quickly, but i'm sure that is possible.
They use a similar system on the Nikon V1/J1, and supposedly on the EOS-M. It's very quick on the V1/J1.

They do it by using PDAF sensors within the image sensor - so it's only good on mirrorless cams. One benefit of the PDAF sensor in a DSLR is that we don't run the sensor all the time, and save on power. To use CDAF will require the entire sensor to be on.

10-16-2012, 08:14 AM   #9
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QuoteOriginally posted by JinDesu Quote
They use a similar system on the Nikon V1/J1, and supposedly on the EOS-M. It's very quick on the V1/J1.

They do it by using PDAF sensors within the image sensor - so it's only good on mirrorless cams. One benefit of the PDAF sensor in a DSLR is that we don't run the sensor all the time, and save on power. To use CDAF will require the entire sensor to be on.
Oh, the PDAF on the sensor uses CDAF to confirm? That's nice
The problem with those cameras is that they will use CDAF only in low light conditions, and the PDAF is only activated in good lightning conditions, from what i've read.
Why is that?
10-16-2012, 08:19 AM   #10
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QuoteOriginally posted by GabrielFFontes Quote
Oh, the PDAF on the sensor uses CDAF to confirm? That's nice
The problem with those cameras is that they will use CDAF only in low light conditions, and the PDAF is only activated in good lightning conditions, from what i've read.
Why is that?
They use PDAF for the speed, then CDAF for the accuracy. The Nikon V1 and J1 have fantastic fantastic AF for small mirrorless cams. I have heard the EOS-M implementation sucks though.

Re: Lighting conditions -

Not sure about that. I thought CDAF sucks in low-light because it's harder for it to find contrast - especially as the sensor needs to increase sensitivity and is exposed to noise. For example, the new k-5II's -3EV PDAF works down to -3EV, where I don't think CDAF will even see anything.
10-16-2012, 04:38 PM   #11
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QuoteOriginally posted by GabrielFFontes Quote
BIZARRE QUESTION :
QuoteOriginally posted by GabrielFFontes Quote
Am i using punctuation correctly? English is not my main language, and i might be doing it incorrectly.
No, you need to capitalize "I" and change your verb tenses.

Punctuation does not really matter here...
10-16-2012, 05:39 PM   #12
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The OP's English is perfectly clear, better than many native speakers!

I like Gabriel's idea of CDAF focus checking. The camera could work out how much to microadjust the focus by comparing CDAF and PDAF. And perform the necessary adjustments automatically, stored for each lens.
10-16-2012, 06:03 PM   #13
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I've noticed the same thing, no matter what Fine AF adjustment I applied the DA*55 will always adjust the focus point to a further distance when switching from LV to the viewfinder. But I've also noticed, using LV is giving a better exposure also. I noticed this several times when testing the AF (cause I'm having changing AF issues day to day), but using LV was protecting the highlights better than the using the OVF (AV mode, I noticed 1/45 on one and 1/60 on the other repeatedly). It's drove my nutz enough that I'm thinking about sending it in once my Q arrives (there's something on the sensor that won't come off {wet clean or air blown} also from day 1), the K5 is less than 2 months old, and I didn't have these issues with the K7.
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