How does Pentax AF-C compare to other brands?

**clackers** · 03-28-2019, 03:07 AM

Originally posted by Rondec

Most of the time when I am using AF-C I use the center point and try to keep that centered on my subject and just track them. I just have had way more success with that than choosing one of the auto modes and letting the camera figure things out for itself.

But I don't know if that is the "right" way to do things.

That's what I'll generally do, with Expanded so the camera will also do some tracking when I miss.

**reh321** · 03-28-2019, 05:32 AM

Originally posted by sutherland

What apertures are required to enable autofocus, including cross-type or high-precision focusing, on Canon DSLR cameras? - Photography Stack Exchange

'Canon EOS Digital Rebel (original, 300D), Digital Rebel XT (350D), Rebel XS (1000D), Rebel T3 (1100D), D30, D60, 10D
All points function to f/5.6; the center point is normal-precision cross-type (it is both vertical- and horizontal-sensitive to f/5.6 and is not high precision at f/2.8). All other points are single-line (EOS D30 and D60: vertical sensitive only). Autofocus does not function below f/5.6.'

Canon EOS Digital Rebel XTi (400D), Rebel XSi (450D), Rebel T1i (500D), Rebel T2i (550D), Rebel T3i (600D), Rebel SL1 (100D), Rebel T5 (1200D), Rebel T6 (1300D), 20D, 30D
All points function to f/5.6. The center point is cross-type, and all other points are single-line. The center point is high-precision dual cross-type with f/2.8 or faster lenses. Autofocus does not function with lenses narrower than f/5.6.

Could be camera/af system specific. This first excerpt is regardless of lens, just setting specific. The second excerpt specifies lenses narrower than f/5.6 (perhaps lenses with a max of f/5.6 or paired with a TC resulting in f/5.6 or narrower).

I had a "Digital Rebel XT", which I routinely used at f/8 or f/9.5, and it always achieved autofocus; these words clearly do not refer to the aperture setting at the time the photo was taken. Since the lens is wide open at time of focusing/composing, and shifts to shooting aperture {"stops down"} only as exposure is made, clearly maximum aperture of lens is what they are referring to.

**reh321** · 03-28-2019, 05:42 AM

Originally posted by sutherland

Perhaps on paper. In use, focusing to a scene that has already passed (especially in fast shooting situations when panning with a moving subject) could be the difference between a shot in focus and one that is mis-focused.

The cameras that use this method are focusing while they record.

beholder3 · 03-28-2019, 06:35 AM

Originally posted by BrianR

Lenses perform their autofocusing wide open and that aperture is what will determine which focusing points will be active. The first excerpt you quoted will be referring to the wide open aperture, and not the setting you use for taking the photo. Note they also say "Autofocus does not function below f/5.6". If this referred to the f-stop you took the photo at, there would be heaps and heaps and heaps of problems.

A "lens narrower than f5.6" means wide open possibility, not the temporary stopped down situation.

BrianR · 03-28-2019, 09:54 AM

Originally posted by beholder3

A "lens narrower than f5.6" means wide open possibility, not the temporary stopped down situation.

Is that not what I said?

kkoether · 03-28-2019, 08:14 PM - **1 Like**

I always use center point when shooting boat racing. Backgrounds are too busy to do otherwise. This and the other shot I posted where using my DA* 60-250 with the Pentax HD 1.4x teleconverter then cropped on top of that. I've been real happy with the auto focus with that combo on my K-3. It took some figuring out at first. This shot is f8, 1/1600, 640 ISO. DOF with the teleconverter is definitely narrower than without. Still need to play some more this spring to find the sweet spot. The Pentax T/C was definitely worth the extra $$$. It communicates properly with the camera and takes some of the guesswork out of things.

**clackers** · 03-28-2019, 08:26 PM

Originally posted by kkoether

I always use center point when shooting boat racing. Backgrounds are too busy to do otherwise. This and the other shot I posted where using my DA* 60-250 with the Pentax HD 1.4x teleconverter then cropped on top of that. I've been real happy with the auto focus with that combo on my K-3. It took some figuring out at first. This shot is f8, 1/1600, 640 ISO. DOF with the teleconverter is definitely narrower than without. Still need to play some more this spring to find the sweet spot. The Pentax T/C was definitely worth the extra $$$. It communicates properly with the camera and takes some of the guesswork out of things.

Nice work, Keith - that guy's travelling!

kkoether · 03-28-2019, 08:47 PM - **1 Like**

Originally posted by clackers

Nice work, Keith - that guy's travelling!

Thanks! Vintage Hydroplane exhibitions can be exciting even though "technically" they are not racing. The guys and girls who drive them sure have a lot of fun though. This boat raced in the late 60's and 70's when I was a kid. It currently runs in the American Power Boat Association's Vintage & Historic division.

beholder3 · 03-29-2019, 02:40 AM

Originally posted by BrianR

Is that not what I said?

Maybe I just misunderstood what you wanted to say.

03-28-2019, 05:32 AM	#107
reh321 retired sw engineer Join Date: Nov 2014 Location: South Bend, IN, USA Photos: Gallery \| Albums Posts: 14,999	Originally posted by sutherland What apertures are required to enable autofocus, including cross-type or high-precision focusing, on Canon DSLR cameras? - Photography Stack Exchange 'Canon EOS Digital Rebel (original, 300D), Digital Rebel XT (350D), Rebel XS (1000D), Rebel T3 (1100D), D30, D60, 10D All points function to f/5.6; the center point is normal-precision cross-type (it is both vertical- and horizontal-sensitive to f/5.6 and is not high precision at f/2.8). All other points are single-line (EOS D30 and D60: vertical sensitive only). Autofocus does not function below f/5.6.' Canon EOS Digital Rebel XTi (400D), Rebel XSi (450D), Rebel T1i (500D), Rebel T2i (550D), Rebel T3i (600D), Rebel SL1 (100D), Rebel T5 (1200D), Rebel T6 (1300D), 20D, 30D All points function to f/5.6. The center point is cross-type, and all other points are single-line. The center point is high-precision dual cross-type with f/2.8 or faster lenses. Autofocus does not function with lenses narrower than f/5.6. Could be camera/af system specific. This first excerpt is regardless of lens, just setting specific. The second excerpt specifies lenses narrower than f/5.6 (perhaps lenses with a max of f/5.6 or paired with a TC resulting in f/5.6 or narrower). I had a "Digital Rebel XT", which I routinely used at f/8 or f/9.5, and it always achieved autofocus; these words clearly do not refer to the aperture setting at the time the photo was taken. Since the lens is wide open at time of focusing/composing, and shifts to shooting aperture {"stops down"} only as exposure is made, clearly maximum aperture of lens is what they are referring to. Last edited by reh321; 03-28-2019 at 07:56 AM. Reason: "stops down"

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03-28-2019, 03:07 AM	#106
clackers Loyal Site Supporter Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 13,480 Original Poster	Originally posted by Rondec Most of the time when I am using AF-C I use the center point and try to keep that centered on my subject and just track them. I just have had way more success with that than choosing one of the auto modes and letting the camera figure things out for itself. But I don't know if that is the "right" way to do things. That's what I'll generally do, with Expanded so the camera will also do some tracking when I miss.

03-28-2019, 05:42 AM	#108
reh321 retired sw engineer Join Date: Nov 2014 Location: South Bend, IN, USA Photos: Gallery \| Albums Posts: 14,999	Originally posted by sutherland Perhaps on paper. In use, focusing to a scene that has already passed (especially in fast shooting situations when panning with a moving subject) could be the difference between a shot in focus and one that is mis-focused. The cameras that use this method are focusing while they record.

03-28-2019, 06:35 AM	#109
beholder3 Pentaxian Join Date: Dec 2011 Posts: 2,333	Originally posted by BrianR Lenses perform their autofocusing wide open and that aperture is what will determine which focusing points will be active. The first excerpt you quoted will be referring to the wide open aperture, and not the setting you use for taking the photo. Note they also say "Autofocus does not function below f/5.6". If this referred to the f-stop you took the photo at, there would be heaps and heaps and heaps of problems. A "lens narrower than f5.6" means wide open possibility, not the temporary stopped down situation.

03-28-2019, 09:54 AM	#110
BrianR Pentaxian Join Date: Dec 2010 Location: Ontario Photos: Gallery Posts: 3,332	Originally posted by beholder3 A "lens narrower than f5.6" means wide open possibility, not the temporary stopped down situation. Is that not what I said?

03-28-2019, 08:14 PM - 1 Like	#111
kkoether Pentaxian Join Date: Jul 2008 Location: Huber Heights, OH, USA Photos: Gallery \| Albums Posts: 611	I always use center point when shooting boat racing. Backgrounds are too busy to do otherwise. This and the other shot I posted where using my DA* 60-250 with the Pentax HD 1.4x teleconverter then cropped on top of that. I've been real happy with the auto focus with that combo on my K-3. It took some figuring out at first. This shot is f8, 1/1600, 640 ISO. DOF with the teleconverter is definitely narrower than without. Still need to play some more this spring to find the sweet spot. The Pentax T/C was definitely worth the extra $$$. It communicates properly with the camera and takes some of the guesswork out of things.

03-28-2019, 08:26 PM	#112
clackers Loyal Site Supporter Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 13,480 Original Poster	Originally posted by kkoether I always use center point when shooting boat racing. Backgrounds are too busy to do otherwise. This and the other shot I posted where using my DA* 60-250 with the Pentax HD 1.4x teleconverter then cropped on top of that. I've been real happy with the auto focus with that combo on my K-3. It took some figuring out at first. This shot is f8, 1/1600, 640 ISO. DOF with the teleconverter is definitely narrower than without. Still need to play some more this spring to find the sweet spot. The Pentax T/C was definitely worth the extra $$$. It communicates properly with the camera and takes some of the guesswork out of things. Nice work, Keith - that guy's travelling!

03-28-2019, 08:47 PM - 1 Like	#113
kkoether Pentaxian Join Date: Jul 2008 Location: Huber Heights, OH, USA Photos: Gallery \| Albums Posts: 611	Originally posted by clackers Nice work, Keith - that guy's travelling! Thanks! Vintage Hydroplane exhibitions can be exciting even though "technically" they are not racing. The guys and girls who drive them sure have a lot of fun though. This boat raced in the late 60's and 70's when I was a kid. It currently runs in the American Power Boat Association's Vintage & Historic division.

03-29-2019, 02:40 AM	#114
beholder3 Pentaxian Join Date: Dec 2011 Posts: 2,333	Originally posted by BrianR Is that not what I said? Maybe I just misunderstood what you wanted to say.

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