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**Kobie** · 04-08-2021, 07:49 PM

Something I've noticed regarding PENTAX vs all other brands is that PENTAX uses a different term for their AF system.
PENTAX calls it Phase Matching, all other brands call it Phase Detect. Is this just crafty wording on the PENTAX side or is there an actual difference between the 2?
I've tried looking it up but only get Contrast detect vs Phase detect articles.

stevebrot · 04-08-2021, 09:21 PM - **1 Like**

Originally posted by Kobie

PENTAX calls it Phase Matching, all other brands call it Phase Detect. Is this just crafty wording on the PENTAX side or is there an actual difference between the 2?

You got me. Pentax has used that terminology going back as far as their first SF-series of AF film cameras. What I do know is that the detector uses PDAF, regardless of what they call it. FWIW, I don't know why they call it phase detect. The principle is similar to that of a split-image rangefinder where the discrepancy between the two elements of a split image are compared to determine degree of OOF as well as direction to correct.

Steve

**Kobie** · 04-08-2021, 09:58 PM - **1 Like**

Originally posted by stevebrot

The principle is similar to that of a split-image rangefinder where the discrepancy between the two elements of a split image are compared to determine degree of OOF as well as direction to correct.

Steve

So basically, the two elements have to "match" the image to know it's in focus. Hmmm, I guess both terminologies say the same thing. One (Phase detect) is detecting the difference between the two split images and Phase Matching is saying the same thing but talking about once it's in focus (both split images match). Different for the sake of being different I guess lol.

beholder3 · 04-09-2021, 03:48 AM - **1 Like**

Originally posted by Kobie

Something I've noticed regarding PENTAX vs all other brands is that PENTAX uses a different term for their AF system.
PENTAX calls it Phase Matching, all other brands call it Phase Detect. Is this just crafty wording on the PENTAX side or is there an actual difference between the 2?
I've tried looking it up but only get Contrast detect vs Phase detect articles.

They all work exactly as an electronically analyzed "split image focussing screen".

Whatever they call it, they compare images (actually now pixel rows) from the left and right edges of the image circle.

If you understand how a split image screen focusing works you know how "PDAF" works. Instead of your own eyes watching the two prisms and you turning the focus ring it is photo diode pixels and a motor.

**DonV** · 04-09-2021, 09:16 AM

One has to "detect" the phases before they can be "matched"; it is just "semantics".

zapp · 04-11-2021, 05:49 AM

It is a lot more than semantics, but just by looking at the wording, you will not find out what each system does exactly or what the difference may be. Phase correlation is another possible name. Bring two sets of information on top of each other and align them as good as possible for an exact alignment. The algorithm should do that quickly. Quick and reliable calculation plus prediction where to find the best match is the art behind the math.

**DonV** · 04-11-2021, 06:21 AM

The wording/description is definitely semantics; but , you are quite correct that the execution of the phase "whatever" focus system is the key to performance.

04-08-2021, 07:49 PM	#1
Kobie Site Supporter Join Date: Oct 2014 Location: Bowmanville Photos: Albums Posts: 1,211	Phase Matching AF or Phase Detect AF, one in the same? Something I've noticed regarding PENTAX vs all other brands is that PENTAX uses a different term for their AF system. PENTAX calls it Phase Matching, all other brands call it Phase Detect. Is this just crafty wording on the PENTAX side or is there an actual difference between the 2? I've tried looking it up but only get Contrast detect vs Phase detect articles.

04-08-2021, 09:21 PM - 1 Like	#2
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Kobie PENTAX calls it Phase Matching, all other brands call it Phase Detect. Is this just crafty wording on the PENTAX side or is there an actual difference between the 2? You got me. Pentax has used that terminology going back as far as their first SF-series of AF film cameras. What I do know is that the detector uses PDAF, regardless of what they call it. FWIW, I don't know why they call it phase detect. The principle is similar to that of a split-image rangefinder where the discrepancy between the two elements of a split image are compared to determine degree of OOF as well as direction to correct. Steve Last edited by stevebrot; 04-08-2021 at 09:35 PM.

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04-08-2021, 09:58 PM - 1 Like	#3
Kobie Site Supporter Join Date: Oct 2014 Location: Bowmanville Photos: Albums Posts: 1,211 Original Poster	Originally posted by stevebrot The principle is similar to that of a split-image rangefinder where the discrepancy between the two elements of a split image are compared to determine degree of OOF as well as direction to correct. Steve So basically, the two elements have to "match" the image to know it's in focus. Hmmm, I guess both terminologies say the same thing. One (Phase detect) is detecting the difference between the two split images and Phase Matching is saying the same thing but talking about once it's in focus (both split images match). Different for the sake of being different I guess lol.

04-09-2021, 03:48 AM - 1 Like	#4
beholder3 Pentaxian Join Date: Dec 2011 Posts: 3,112	Originally posted by Kobie Something I've noticed regarding PENTAX vs all other brands is that PENTAX uses a different term for their AF system. PENTAX calls it Phase Matching, all other brands call it Phase Detect. Is this just crafty wording on the PENTAX side or is there an actual difference between the 2? I've tried looking it up but only get Contrast detect vs Phase detect articles. They all work exactly as an electronically analyzed "split image focussing screen". Whatever they call it, they compare images (actually now pixel rows) from the left and right edges of the image circle. If you understand how a split image screen focusing works you know how "PDAF" works. Instead of your own eyes watching the two prisms and you turning the focus ring it is photo diode pixels and a motor.

04-09-2021, 09:16 AM	#5
DonV Site Supporter Join Date: Jan 2017 Location: Near Charlotte NC Photos: Albums Posts: 695	One has to "detect" the phases before they can be "matched"; it is just "semantics".

04-11-2021, 05:49 AM	#6
zapp Pentaxian Join Date: Jul 2011 Posts: 2,389	It is a lot more than semantics, but just by looking at the wording, you will not find out what each system does exactly or what the difference may be. Phase correlation is another possible name. Bring two sets of information on top of each other and align them as good as possible for an exact alignment. The algorithm should do that quickly. Quick and reliable calculation plus prediction where to find the best match is the art behind the math.

04-11-2021, 06:21 AM	#7
DonV Site Supporter Join Date: Jan 2017 Location: Near Charlotte NC Photos: Albums Posts: 695	The wording/description is definitely semantics; but , you are quite correct that the execution of the phase "whatever" focus system is the key to performance.

Phase Matching AF or Phase Detect AF, one in the same?

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