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agsy · 08-21-2010, 02:50 PM

I think the K-x beats them all!

cwood · 08-21-2010, 03:52 PM

The latest Pentax cameras are adequate for most purposes but they remain far from superior. As someone else in this thread pointed out - if you are not filling the frame at a very wide aperture you are not really testing the AF of your camera.

These are shots that Pentax cameras would truly struggle with. I sold my Pentax 300mm F2.8 for a Canon version just so I could take these types of action photos. The DOF on these shots is only a few inches and the targets are moving VERY fast.

agsy · 08-21-2010, 04:15 PM

That is sick! Very nice photos

philbaum · 08-22-2010, 11:30 PM

Looking up the AF Specification line in Dpreview for these cameras:

K10: AF working range: 0 to 19 EV (at ISO 100, F1.4 lens)

K20: AF working range: -1 to 18 EV (at ISO 100, F1.4 lens)

K7: AF working range: -1 to 18 EV (at ISO 100, F1.4 lens)

What i find odd is that AF range is specified based on FA 50 F1.4 lens and the DA 55 F1.4. Very few current lenses have the light gathering ability of those 2 lenses, certainly all the zooms are F2.8 and less, although some limited primes dip down into the area below F2.8.

So now i'm wondering why more people aren't talking about aperture when their Pentax cameras don't seem to be focusing properly. Some folks talk about this lens being better than that lens for focusing, but it seems to me that one of the most important lens factors for focusing is the maxium aperture for that lens.

It does seem odd that Pentax has chosen to specify focusing performance range for a lens aperture that is very uncommon for the average Pentax lens. I have had one personal experience when trying to photograph in moonlight, that my f2.8 zoom would not focus while switching to the FA 50 successfully resolved the focusing issue.

It is disappointing that there aren't more primes that have a faster aperture than f2.8, for focusing performance reasons, e.g. DA 35 is F2.8, my F 28mm is F2.8, etc.

**eccentricphotography** · 08-23-2010, 02:00 AM

Not to mention the low light poor performance of Pentax. Love many aspects of Pentax, but auto-focus is not one of them.

08-22-2010, 11:30 PM	#64
philbaum Veteran Member Join Date: Oct 2007 Location: Port Townsend, Washington State, USA Posts: 3,659	What's the F1.4 mean for AF specification? Looking up the AF Specification line in Dpreview for these cameras: K10: AF working range: 0 to 19 EV (at ISO 100, F1.4 lens) K20: AF working range: -1 to 18 EV (at ISO 100, F1.4 lens) K7: AF working range: -1 to 18 EV (at ISO 100, F1.4 lens) What i find odd is that AF range is specified based on FA 50 F1.4 lens and the DA 55 F1.4. Very few current lenses have the light gathering ability of those 2 lenses, certainly all the zooms are F2.8 and less, although some limited primes dip down into the area below F2.8. So now i'm wondering why more people aren't talking about aperture when their Pentax cameras don't seem to be focusing properly. Some folks talk about this lens being better than that lens for focusing, but it seems to me that one of the most important lens factors for focusing is the maxium aperture for that lens. It does seem odd that Pentax has chosen to specify focusing performance range for a lens aperture that is very uncommon for the average Pentax lens. I have had one personal experience when trying to photograph in moonlight, that my f2.8 zoom would not focus while switching to the FA 50 successfully resolved the focusing issue. It is disappointing that there aren't more primes that have a faster aperture than f2.8, for focusing performance reasons, e.g. DA 35 is F2.8, my F 28mm is F2.8, etc.

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08-21-2010, 02:50 PM	#61
agsy Veteran Member Join Date: Aug 2010 Location: Florida Photos: Gallery \| Albums Posts: 551	I think the K-x beats them all!

08-21-2010, 03:52 PM	#62
cwood Veteran Member Join Date: Aug 2008 Location: California Posts: 851	The latest Pentax cameras are adequate for most purposes but they remain far from superior. As someone else in this thread pointed out - if you are not filling the frame at a very wide aperture you are not really testing the AF of your camera. These are shots that Pentax cameras would truly struggle with. I sold my Pentax 300mm F2.8 for a Canon version just so I could take these types of action photos. The DOF on these shots is only a few inches and the targets are moving VERY fast.

08-21-2010, 04:15 PM	#63
agsy Veteran Member Join Date: Aug 2010 Location: Florida Photos: Gallery \| Albums Posts: 551	That is sick! Very nice photos

08-23-2010, 02:00 AM	#65
eccentricphotography Site Supporter Join Date: May 2008 Location: Los Angeles Photos: Gallery \| Albums Posts: 182	Not to mention the low light poor performance of Pentax. Love many aspects of Pentax, but auto-focus is not one of them.

Anecdotal evidence for superior Pentax AF

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