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05-15-2012, 09:15 AM   #1
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AF performance with 35/2?

Hey folks.

I recently purchased the K-01, and I truly believe it has reignited my passion for Pentax equipment. I recently took the wee-beastie on a trip to India (pics coming soon), with an SMC-A 20/2.8 and an SMC-FA 35/2.0.

I've had some concerns with the 35/2.0. This is my first Pentax AF camera (moving from a Super-Program and an LX), and I may have been spoiled with my previous gear (Canon EOS), so I'm not sure what to expect for AF performance. The AF seems to hunt a lot as it tries to find the correct lines to focus on. This is pretty consistent in low and normal light situations, with a variety of scenes (scenes with a lot of lines to focus on, scenes without many lines, etc.).

I do understand that the SMC-FA 35/2.0 is an older lens. Do newer lenses (e.g., the ones with built in motors) improve the AF performance at all? Or is Pentax's AF just not that good?

Other than the AF performance, the camera performed like a champ. Metering was much better than I expected, and when I managed to program the Green and Red buttons, things really started to fly. My primary concern (lack of a viewfinder) wasn't really a worry -- except for some very rare situations (e.g., on the roof of a 30-story building in direct sunlight), the screen was always adequate. Battery life was great (with minimal use of the playback), AE lock is wonderful, and I was able to get some great shots with the SMC-A 20/2.8.


05-15-2012, 09:26 AM   #2
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You are trying to compare Apples to Oranges. The EOS you used in the past has Phase Detect AF. The K-01 lacks a mirror, therefore it has to use Contrast Detect AF. Contrast detection is more accurate than Phase detection, but it is slower. This is something that affects all mirror less cameras, except the Nikon 1 which uses some sort of hybrid system.

Autofocus - Wikipedia, the free encyclopedia
05-15-2012, 09:56 AM   #3
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I use the FA 35mm f2 on my K-5 and consider it very fast.
05-15-2012, 10:01 AM   #4

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QuoteOriginally posted by boriscleto Quote
Contrast detection is more accurate than Phase detection, but it is slower

Brief, but well written.

Might I add in... I've also seen focus speed and ability effected by aperature range (also noting the original poster used the f2.0 and noticed the timing in it). IF one uses a lens that has either a starting aperature OR an aperature that drops below (defined later....) a certain point, then focusing may be more of an issue. Cases in point... With an aperature starting at about f4.5 to (example) f5.0; this naturally would not be as good as a f2.8 lens. This also applies to zoom lens. If the lens starts out at about f3.9 and then goes down to 5.5 when zoomed further out - then... It would focus better at the better aperature, not quite as fast or accurate at the lower aperature - even though fully opened at f5.5.

IF only I could get around to posting a video example of this

05-15-2012, 10:39 AM   #5
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Use your focus peaking when needed

I find the K-01 with the FA35 about equal to the K20D in terms of AF speed in most conditions. However, the K-01 is a tad more consistently accurate in AF.

I don't expect great AF performance with Pentax; even the highest-performing K5 is not up to the Canon EOS line in that regard. The major reason photojournalists (especially sports shooters) have Canon is that these are the most advanced AF systems in the world at any given price point. I still use a Canon 20D with fast lenses when I need to shoot sports or other fast action - and that's an old body.

Given that you are already shooting an MF wide angle lens with good success, you might want to get into the habit of shooting the FA35 in MF in bad light. With the wider aperture and longer focal length, you'll find the focus peaking far more useful and accurate than with the other lens. You have to switch the body to MF, as the FA35 has to have the screw drive released. Damping is a bit light, unfortunately.

By the way, as you shoot longer and faster lenses, the focus peaking is a huge benefit. On the K20D with a high quality VF magnifier, my 85mm f/1.4 achieved critical accuracy in dark concert situations about 35% of the time; with the K-01 I'm up to about 75% and expect to improve on that as I acclimate (and remember to wear my readers!). Focus peaking was the biggest reason for me to pick the K-01 over the K5 - as I enjoy shooting MF when the situation demands it.
05-15-2012, 11:43 AM   #6
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Here's a link to the crowd-sourced autofocus performance thread on a number of popular Pentax lenses on the K-01. FA35/2 was characterized by all contributors as good in all conditions (Indoor/Outdoor, Bright/Dim light), whichn was my conclusion. FA35/2 is my most-used lens on K-01, followed by DA40/2.8 Limited and F35~70(for video).
05-15-2012, 01:10 PM   #7
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The K-01's AF isn't as fast as that of a DSLR. WIth that said, older (screwdrive) lenses with short throw generally outperform Pentax SDM lenses.

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