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05-15-2010, 06:24 AM - 1 Like   #1
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Best low light autofocus - k20,k7 or KX??

I had an assignment of shooting a year end award ceremony with my K20D rig last night ... in a dimly lit hall with teachers and kids dressed in a wide range of evening wear. My K20D/Tamron 17-50 XR DiII/Metz 58 setup fought me every step of the way, slowly hunting for a focus point as I missed shot after shot. It didn't matter if I was in constant focus or single shot focus. I finally went to manual focus, guestimated my distance to subject for the majority of the evening... at least I could get the camera to fire when handshakes were happening and awards were being handed off.

It was the first time I was truly and completely unhappy with my Pentax system.

So... okay, I've read on the forum that the K7 is "better" at autofocusing, and that the K-X is great in low light.... would anyone say that either of these bodies would be better for low light autofocusing in the scenario I've outlined here?

I'm going to have more of these types of shoots in the future, if this is indeed Pentax' weak point, I have a tough decision to make about staying with the system. Help!

Regards,

germar

05-15-2010, 10:07 AM   #2
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While the Pentax AF system may not be perfect, when the light gets dim any camera will struggle. Don't blame the Pentax system. Other camera systems can't perform miracles either. You could jump ship and still get the same result.

Your camera settings can make a big difference to AF performance - eg using spot AF will give better (ie more reliable) results in low-light than matrix. And if your flash has an AF assist beam, why not use that too to help out the camera's AF. Using a faster lens than the 2.8 Tammy may also help by feeding the AF more light when setting up the shot. It's also worth noting that stuff like having a filter on the lens can also make AF less reliable, esp in low-light. If you have a filter on that lens, ditch it in low-light.

But I don't understand why so afraid of MF when the light level is challenging. MF + understanding your DOF = good predictable results for me in low-light, and I shoot successfully in places a lot darker than relatively well-lit school halls.

The K-x is certainly a confident AF performer in low-light, more so than my K200D, and I'd venture to say that the K-7 is more confident than the K20D. Maybe both the K-x and K-7 have updated AF algorithms or faster chips than the K20 and K200D.

But technically, all the recent Pentax DSLR AF systems are rated to operate from -1 to 18 EV light levels (using a 1.4 lens). This isn't much different from comparable Canon or Nikon bodies - eg the AF on the Canon 550 is rated for -0.5 - 18 EV, and the Nikon D90's AF is rated to operate from -1 to 19 EV. That's something to be aware of.
05-15-2010, 11:00 AM   #3
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Every Pentax user i know, who has switched to canon 40/50D because of AF describe the difference as night and day. Even with the cheaper non USM/L lenses. It simply works, where others are just rated to work.

Still, all of them told me, that they would rather have stayed with Pentax unless they absolutely needed the specific AF performance (Very often low light or fast action tracking, paid work).

No matter what can be read, i suggest you trying out K-x, 40/50D and see what the speed feels like.
You should also put on paper and see the switching costs. To K-x vs whole system. Then think about the AF gain you get and features you loose.

From my experience im most confused, not when the AF is slow, but when it simply doesn't do anything. I half press the shutter button, and nothing happens - i have to repress it several times before it starts focusing. And i get no AF fail or anything.. camera meters but no AF.
05-15-2010, 12:28 PM   #4
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I have a K20D and was ready to abandon Pentax because of its poor low light AF. I was missing shot after shot that would be a cinch with my old Canon 20D.

Based on reviews, I got a K7.

Night and day difference. I spent a week on vacation in Las Vegas taking casual shots on the strip in the evening with the K7. No trouble.

Problem solved.

05-15-2010, 01:18 PM   #5
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QuoteOriginally posted by germar Quote
I had an assignment of shooting a year end award ceremony with my K20D rig last night ... in a dimly lit hall with teachers and kids dressed in a wide range of evening wear. My K20D/Tamron 17-50 XR DiII/Metz 58 setup fought me every step of the way, slowly hunting for a focus point as I missed shot after shot. It didn't matter if I was in constant focus or single shot focus. I finally went to manual focus, guestimated my distance to subject for the majority of the evening... at least I could get the camera to fire when handshakes were happening and awards were being handed off.

It was the first time I was truly and completely unhappy with my Pentax system.

So... okay, I've read on the forum that the K7 is "better" at autofocusing, and that the K-X is great in low light.... would anyone say that either of these bodies would be better for low light autofocusing in the scenario I've outlined here?

I'm going to have more of these types of shoots in the future, if this is indeed Pentax' weak point, I have a tough decision to make about staying with the system. Help!

Regards,

germar
I've owned and used all three cameras you're asking about and of them the K-7 is by far the best at autofocusing in both dark and other challenging lighting conditions (like focusing under tungsten light, something that can give the K20D and k-x fits). This is even without the green autofocus assist light on the K-7, which helps even more if you don't mind bothering people with the light from the camera. With the green assist light on I've focused on things in near darkness.

In the scenario you described above, the K-7 would be a big upgrade over the K20D in both focus speed and accuracy. Where people have criticized the K-7, I think somewhat unfairly, is that it isn't tons faster than the K20D in autofocusing under good lighting conditions. The K-7 is still faster than the K20D under all conditions, it's just not as fast as people wanted it to be to justify the upgrade.

Last edited by Urkeldaedalus; 05-15-2010 at 01:32 PM.
05-15-2010, 04:51 PM   #6
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QuoteQuote:
In the scenario you described above, the K-7 would be a big upgrade over the K20D in both focus speed and accuracy. Where people have criticized the K-7, I think somewhat unfairly, is that it isn't tons faster than the K20D in autofocusing under good lighting conditions. The K-7 is still faster than the K20D under all conditions, it's just not as fast as people wanted it to be to justify the upgrade.
Agree there for sure... AF is great in K-7. The other major difference I found is flash compatibilty with the K-7.. another problem solved for me.
05-15-2010, 10:31 PM   #7
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I do some low light photography outdoor and I found the K-7 AF excellent in low light. I cannot compare with another Pentax but I have been really impressed by the K-7 AF in low light conditions like before sunrise and shortly after sunset. No problem what so ever.
05-15-2010, 10:42 PM   #8
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I have a K20D and K-x. The K-x focusses much better in low light. The K20 hunts a lot and sometimes will not find the subject at all. I don't have a K-7 but it would be the best of these three considering it has a AF assist beam and is tungsten sensitive.

05-15-2010, 10:51 PM   #9
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I can't comment on the K-x, but I cut my teeth on the K20's slow low (and available) light Autofocus. I can attest that the K-7 is much much better. Give it a shot before jumping ship.
05-16-2010, 01:50 AM   #10
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Got all three, and K7 just kicks the other two in the dust... Faster in all conditions, better in low-light, green thingy is good...
Kx seems on par with the k20 (which is a rather good news!), for speed and low-light accuracy.
05-16-2010, 04:40 AM   #11
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I routinely shoot the Kx at ISO 6400 in tough stage light conditions using manual catch-in-focus. It virtually guarantees in focus shots. Several things that really help low light shooting are using RAW, spot metering, prime lenses and take A LOT of shots.

Last edited by tarsus; 05-16-2010 at 04:42 AM. Reason: Add In
05-16-2010, 10:11 AM   #12
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i get much less hunting with the Kx than the k20d, plus the iso performance...
i've never seen a k7 in the flesh let alone shot one.
05-16-2010, 12:23 PM   #13
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QuoteOriginally posted by dlacouture Quote
Kx seems on par with the k20 (which is a rather good news!), for speed and low-light accuracy.
Not what I found. When I received the K-x I tested both cameras with my slowest focussing lens, the DA 18-250. The K-x locked focus easily every time, the K20 hunted and at times would not lock. I have had trouble with the K20 and FA 35 in low light too, and never with the K-x, although I didn't compare head to head with the prime.

Note that I did not test focus accuracy. I'll have to do that some day.

Last edited by audiobomber; 05-16-2010 at 12:29 PM.
05-16-2010, 01:12 PM   #14
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QuoteOriginally posted by ytterbium Quote
Every Pentax user i know, who has switched to canon 40/50D because of AF describe the difference as night and day. Even with the cheaper non USM/L lenses. It simply works, where others are just rated to work.

Still, all of them told me, that they would rather have stayed with Pentax unless they absolutely needed the specific AF performance (Very often low light or fast action tracking, paid work).

No matter what can be read, i suggest you trying out K-x, 40/50D and see what the speed feels like.
You should also put on paper and see the switching costs. To K-x vs whole system. Then think about the AF gain you get and features you loose.

From my experience im most confused, not when the AF is slow, but when it simply doesn't do anything. I half press the shutter button, and nothing happens - i have to repress it several times before it starts focusing. And i get no AF fail or anything.. camera meters but no AF.
Perhaps it depends where you are coming from.
The K-7 does pretty well compared with the 40D. It is so much better than my K10D.

We did a 3 week tour through Zambia last year and we've done a lot of night and walking safari's.
A lot of wildlife and birdshooting around sunrise / sunset and in darkness with a flashlight. We were either by ourselves or with small groups (4-6).
Most other people we met were carrying Canons. So I did a lot of very low light shooting shoulder to shoulder with them.
I can tell you that a K-7 / DA*60-250mm combi is on par with Canon.
I worked a lot with a German gentleman who owned a 50D and a 28-300mm f3.5/5.6 zoom lens and my K-7 was faster and more often in focus.

Contineous AF is where the problem lies with the K-7.

Worked with Ian Murphy there as well, who shoots D3x with a 200mm f2 lens. That is a different class completely.

- Bert

A few low light examples:







I've got lots more like that.

Last edited by bymy141; 05-16-2010 at 01:19 PM.
06-26-2010, 02:22 PM   #15
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Follow up

As a follow up on my original post on this thread, I unboxed my new K7 this week and mounted my most troublesome low-light lens in regards to autofocus: my DA* 16-50.

I must tell you that results are STILL mixed.

I found that if I leave the camera with the AF point to AUTO, this lens will still hunt for a few seconds and almost always return a focus error. It is particularly bad if I'm running f2.8. HOWEVER, if I set it to center point focus, the instances of the problem is greatly, greatly reduced. I haven't shot enough to say it's been eliminated, but pretty close.

So, while I am HAPPY I upgraded to a K7 for 762 USD, I would have to say that it wasn't perfect.

It's still hard for me to have 1300+ of flagship camera and zoom lens and I can't count on it firing without hamstringing the focus.

Still takes wonderful images ... when it wants to actually fire.

Thanks

germar
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