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12-23-2011, 08:05 AM   #1
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When the light get low why my pentax is slow?

OK, I have a bit of a theory about why autofocus speed with pentax tends to fall of more quickly as the light gets lower than other brands. Maybe some of the smart people on this forum can tell me if this makes sense. I little while ago I looked though the D700 view finder and to my surprise it did not seem as bright as I thought it would be. Anyway as light comes through the lens most of the light is reflected up to the view finder while part of it is refracted down to the autofocus sensor. Could nikon use a mirror that refects a larger percentage of light towards the phase detect autofocus system. This would explain why pentax is just as quick in good light but falls off more quicky in low light.

???

12-23-2011, 08:12 AM   #2
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I'm pretty sure it's still because their AF technology is more advanced and refined, and they have more processing power. A less translucent mirror would only reduce light by a constant factor, and all you'd need is a more sensitive af module.

Pentax AF still isn't as quick or accurate in bright light, especially when there is low contrast. It also depends on your lens- the faster, the better the performance.
12-23-2011, 08:13 AM   #3
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Isn't the D700 a full frame camera? Could that be the difference?
12-23-2011, 08:32 AM   #4
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Not just full frame

I used my friends T2i last week in lowish light and it seemed faster than my K5. In brighter light my K5 is fast it is just in low light that there is a problem. The T2i certainly shouldn't have a more safisticated autofocus system than the K5. Yes more sensitive autofocus detectors probably would have helped alot.

12-23-2011, 08:37 AM   #5
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I think there were some tests relitive to AF performance that looked at speed accuracy and light level.

part of this may be technology limited, but unless the camera makers are each building their own phase detectors, (which is unlikely) then you are either down to selecting different hardware based upon cost (possible but incremental cost would be minimal) or you are dealing with software and processor speeds, which are all probably different.

I think the results I read basically compared speed and accuracy, the canikons were faster the pentax more accurate,

it is all about perception in my mind. To be sure, I have never really had a complaint about any of my pentax AF cameras starting with the PZ1 in low light. In fact, they have always been able to focus in conditions when I had a hard time just seeing,
12-23-2011, 08:50 AM   #6
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better iso

Well as high iso shooting improves we are shooting in lower light conditions than ever befor. Autofocus improvements have not kept up, I find having to switch to contrast detect at times in lower light. When you shooting young kids in lower light you need good autofocus. I think the K5 is great, the low light autofocus is my only complaint.
12-23-2011, 09:11 AM   #7
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QuoteOriginally posted by Belnan Quote
Well as high iso shooting improves we are shooting in lower light conditions than ever befor. Autofocus improvements have not kept up, I find having to switch to contrast detect at times in lower light. When you shooting young kids in lower light you need good autofocus. I think the K5 is great, the low light autofocus is my only complaint.
what about the AF assist light in the K5 or K7. that should help, but note that regardless of make, none of the AF systems have kept up with the sensors.

in my perspective this is the big advantage of good fast MF lenses. you can see well enough to focus them manually.

Note that the contrast detect (i assume you mean live view) is so slow that if you need a shot in a hurry, forget it. same is true of all AF systems, regardless of make, the instant shot is lost in low light.
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