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12-23-2010, 01:15 PM   #1
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Pentax AF speed (again..) vs EOS 40D/50D

I have a K20D and some lenses. Particularly, I find AF to be rather slow with the FA50 and D-FA 100.

I would like to have faster AF in general. Was wondering how much better the K-r is (K-5 is a bit too rich for my blood).

I do have the option of scrounging a used EOS 40D or 50D. With the resale prices of Pentax lenses these days, I could actually afford a Canon 40D and some used ring drive lenses (85/1.8, 100/2.8 Macro) without spending much extra.

So.. how's the K-r autofocus? is it competitive with a Canon 40D or 50D with ring-drive lenses? I'm particularly interested in K-r + D-FA 100 vs 40D + 100mm macro ultrasonic (yes I know at macro ranges AF is always slow, but the Canon macro makes a good general purpose telephoto, while the D-FA 100 retains its slow AF even at telephoto distances, at least on the K20D).

12-23-2010, 01:52 PM   #2
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I don't have the K-r but the K-m & 40D. I would say the 40D with ring USM is just way ahead of any Pentax I have had. However, switching a system based merely on a single lens seems strange to me. You will be sacrificing SR too since you are buying the older Canon macro. If you are building up a complete system, then it would be different.
12-23-2010, 02:01 PM   #3
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My 40d and 17-85mm with ring USM is faster than my old K7.
12-23-2010, 02:15 PM   #4
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If you don't need SR and weather-sealing, I'd say go with the Canon.
Pentax is no longer a value proposition with the current lens prices and there is much less choice of affordable third-party lenses.
Sell your Pentax lenses into the demand and get a system with more competition and value.

12-23-2010, 02:28 PM   #5
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You're trying the slowest lenses too...only other slug to add to your collection is the DA35 IIRC :-)

That said, Canon pioneered ring motors (and screwed anyone who had screw drive lenses when they switched over because they totally dropped all support for that in their bodies :-) Because of their long experience, they'll be faster...even faster than Nikon. Sigma and Nikon are on their first generation ring motor technology. AFAIK, Pentax doesn't have any ring motor support yet, but the latest micromotor in the 18-135 is really fast and is probably the fastest lens currently out...
12-23-2010, 03:17 PM   #6
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In good light AF speed is mainly matter of the lens. And Canon still dominates that. But I'm happy with K-5's AF - Pentax lenses lags behind Canon ring USM lenses but on the other hand screw drive is faster than micro motors.

P.S.: I dont have DFA100 but my girlfriend had the EF100mm USM. No scientific comaprison yet, but a good IF lens like Sigma 180 can focus at similar speed with my K-5's screw drive.
12-23-2010, 05:12 PM   #7
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Thanks for the insights.

The 40D does have some degree of weather-sealing (probably not as good as the K20D, but good enough for light rain). Anyway weather-sealing is irrelevant to me because I don't have DA* lenses.

I know the Pentax ethos is the Limiteds (small, high-quality). Since I don't have any of those..

I did think about the Sigma 180 HSM (I assume modern Pentax bodies can use the ring drive on these lenses) but it's darn expensive!
12-24-2010, 02:38 AM   #8
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>The 40D does have some degree of weather-sealing (probably not as good as the K20D, but good enough for light rain).

Make no mistake, the 40D is not sealed at all. You can actually flashlight and peek inside from the seams near the strap lugs. There was hair and dust inside the mirror box mechanism when mine was disassembled cleaning the shutter release, and I didn't use it that much really. I can see why sand grit might kill the plastic gears. The plastic Pentax DSLRs have tighter seams w/o WR. To be fair, Limited lenses are dust suckers too.

12-24-2010, 03:37 AM   #9
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thanks.. that's good to know.

so those Canon folks aren't paranoid after all

picked up a 40D with 22K shutter count for $450 today. Since my last Canon was a 350D, using this thing is an eye-opener. I can see why people say "Canon DSLR's are designed by engineers, not photographers."

Although it certainly does a few things better than the K20D, which is about the same age..

1) Live View is a lot more useful, because the display is much finer (no gritty pixels when you zoom in); you can change exposure settings during LV mode; and the lag between shots is much less (mirror flips down then up, unlike the K20D where it goes down, up, down, then up again)


2) Metering with ancient lenses is way more accurate than the K20D! of course it can't stop down K lenses, but the metering with my M42 screw lenses is at most half a stop out (unlike the erratic, dependent-on-f-stop offset of K10D and K20D, which is 2 stops underexposed at f/2, bang-on at f/8, and overexposed at smaller apertures)


3) Subjectively, mirror blackout is much less, and the shutter is quieter (I understand the K-7 and K-5 fix this)



However, the lack of in-body SR / IS was an unwelcome surprise. I was wondering why my photos were unsharp at 1/8. Doh!

Anyway I still don't have any AF lenses, so the AF speed comparison will have to wait.
12-24-2010, 06:45 AM   #10
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I don't have a 40/50D but I do own the 5d and T2i.

I compared my T2i to my K20d AF recently and found them to be quite similar in speed. No real change as both were fast in good light, and struggled in very dark settings (the T2i seemed to hunt for longer before deciding to give up).

However, I must say the AF on the 5d is what I was, and still am impressed with (better be for double the cost of the K20d). It is quite a bit faster than the K20d especially with USM-type motors like the 100mm/f2. Even then, the Canon people say the 5D AF is ancient compared to the 1D and Ds series. But that's when we start getting into some pretty expensive gear.
12-24-2010, 10:45 AM   #11
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I believe the T2i is the 550D? the 400D, 450D, and all its successors also use the AF module of the 30D. Same for the 5D and 5D Mk II although I think the 5D's have a faster processor.. (the 40D, 50D, 60D, and 7D all use the same AF module, but the 50D and 7D have two DIGIC processors while the 60D has just one but faster than that on the 40D).

I'll be picking up a 100/2.8 Macro USM tomorrow, will be able to make a direct comparison soon..

Last edited by orly_andico; 12-24-2010 at 10:50 AM.
12-25-2010, 10:25 PM   #12
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I have my answer.

Even in good light, the EOS 40D + 100mm f/2.8 Ultrasonic Macro is way, way faster than the K20D + SMC D-FA 100mm f/2.8 Macro.

The big differences are

1) the Canon rotates, then stops. It very rarely hunts back and forth and only if there's cluttered background that confuses the AF sensor.

2) the Pentax rotates, gets the focus, then does some tiny nudges back and forth for another second or two before indicating in-focus. This is the big difference.

The ring USM drive also rotates faster, because the Canon macro can go from lock to lock significantly faster than the D-FA.

I'm going to try to sell off my DA/FA lenses. Where I can see my Pentax remaining useful is with Limited pancakes. If you compare the monstrous Canon 20mm f/2.8 with the DA 21 Limited.. that's where there's a major value-add.
12-26-2010, 01:23 AM   #13
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QuoteOriginally posted by orly_andico Quote
I have my answer.

Even in good light, the EOS 40D + 100mm f/2.8 Ultrasonic Macro is way, way faster than the K20D + SMC D-FA 100mm f/2.8 Macro.

I'm going to try to sell off my DA/FA lenses. Where I can see my Pentax remaining useful is with Limited pancakes. If you compare the monstrous Canon 20mm f/2.8 with the DA 21 Limited.. that's where there's a major value-add.
Or get a k-5 than try and see
12-26-2010, 04:02 AM   #14
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QuoteOriginally posted by TZH Quote
Or get a k-5 than try and see
A K-5 costs significantly more than I paid for both the EOS 40D body and 100mm Macro lens! specifically, about $400 more.
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