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06-11-2010, 09:45 AM   #1
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FPS slows down during AFC

my kx slows down in FPS during AFC mode and i believe this is also true w/ the K7

is this a PRIME II limitation?

does the competition (aka Nikon, Canon, Oly, Sony) have the same slowing down issue or is this specific to Pentax?

06-11-2010, 10:04 AM   #2
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QuoteOriginally posted by opiedog Quote
my kx slows down in FPS during AFC mode and i believe this is also true w/ the K7

is this a PRIME II limitation?

does the competition (aka Nikon, Canon, Oly, Sony) have the same slowing down issue or is this specific to Pentax?
afc adds an additional function between frames with respect to re-focusing, this adds to the time. put the camera in MF with no auto features, ISO, WB etc as all of these take time.

No it is not a prome II limitation because the image processor has nothing to do with AF and frame rate.
06-11-2010, 10:17 AM   #3
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I bet it's a voltage issue- AFC uses power, and thus slows down continuous shooting. Either that, or it's too much for the processor to handle.

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06-11-2010, 06:12 PM   #4
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anyone with a non-pentax dslr care to comment if it's the same phenomenon?

06-11-2010, 06:46 PM   #5
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My 50D slows down in AFC as well. It's focusing, snapping, refocusing, snapping...etc. Even with my USM lenses it would slow a bit. It's a limitation on how much can be done in a second. Since focusing still requires a physical change to be made before it fires the shutter (also remember the camera has to lock first).

I will note though, my 50D slowed less often than my K7 does. It's not enough to bother me. If you are trying to AFC something coming at you fast, you'll find most cameras have trouble with this as well as missed focus shots. It probably slows down more than I'd want it to, but that's not my brand of photography anyway.
06-12-2010, 04:33 AM - 1 Like   #6
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QuoteOriginally posted by opiedog Quote
my kx slows down in FPS during AFC mode and i believe this is also true w/ the K7
There are two ways to read your question:

1. Your camera slows down during continous shooting.

This is due to limited buffer sizes and as soon as the buffer is full (a few shots only for the K-x) the camera slows down to a speed as defined by your SD card.

A crazy feature is that the K-7 can actually maintain FULL 5.2fps for 14.6MP images and an unlimited amount of time. Just make sure everything is on manual, JPG compression is high (1 star) and the SD card is fast (Sandisk Extreme III).


2. Your camera's framerate in AF.C is lower than in AF.S.

Well, 5.2fps are 192ms per shot and the camera needs about 0.14s to refocus between shots (YMMV). Add the 140ms and you end up with 332ms per shot or 3.0fps. That's normal. The 0.14s are no constant though. On the K-7, I've seen slightly better and significantly worse, depending on the subject and uniformity of motion. Eventually, the K-7 will give up on refocus and just fire. But it may only be after twice the time (0.3s) making it slow down to 2 fps and delivering out of focus shots. However, that's normal procedure again. Most AF.C implementations give up quicker though.

Some cameras (with higher fps) have a faster mirror too. The K-7 mirror though is dampened and swings about 50ms when returning down. This makes it loose about 30ms compared to a harder mirror slap.

Last edited by falconeye; 06-12-2010 at 04:40 AM.
06-12-2010, 06:30 AM   #7
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My Nikons slow down too

Both my Nikon D80 and D300S slow down when shooting in AFC. It is not just a Pentax issue.
06-12-2010, 07:04 AM   #8
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QuoteOriginally posted by Adam Quote
I bet it's a voltage issue- AFC uses power, and thus slows down continuous shooting.
That would be a VERY bad design and a mistake that not even a first years student in electronics would make.

06-12-2010, 12:11 PM   #9
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thanks for all that replied. at least i know it's not just pentax that has this issue.

all i thought was that during AFC, the camera doesn't need an AF lock to fire so in theory you could fire and get OOF shots(or hope the DOF takes care of it ),
but the frame rate would remain at 5.2 or 4.7 fps

that's the theory, but in reality as falk describes it, there's that time for AF before the shutter clicks.
06-12-2010, 12:43 PM   #10
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QuoteQuote:
all i thought was that during AFC, the camera doesn't need an AF lock to fire so in theory you could fire and get OOF shots(or hope the DOF takes care of it ),
but the frame rate would remain at 5.2 or 4.7 fps
Yeah, one of the tricks I used to use was to set my DoF wider so I could catch more in focus shots. Sometimes the camera thinks it has a lock and fires or locks on to something you didnt want it to... then the subject moves significantly and where it locked just a split second ago is no longer in focus.

Last edited by kalison; 06-12-2010 at 03:14 PM.
06-12-2010, 03:06 PM   #11
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Falconeye summarised nicely the situation. Very little need to be added. Further there have been several relevant threads in this forum on continuous shooting that are relevant to this discussion:
https://www.pentaxforums.com/forums/pentax-dslr-discussion/98964-k-7-continuo...nuous+shooting
https://www.pentaxforums.com/forums/pentax-dslr-discussion/96995-my-secure-di...nuous+shooting
https://www.pentaxforums.com/forums/pentax-beginners-corner-q/95892-k-x-conti...nuous+shooting
https://www.pentaxforums.com/forums/camera-studio-accessories/95705-high-spee...nuous+shooting
https://www.pentaxforums.com/forums/pentax-dslr-discussion/93186-k7-high-spee...nuous+shooting
...

The Pentaxian experience with Hi continuous shooting is that AF.C must be avoided to achieve Hi (5.2 fps) rate.

Last edited by hcc; 06-12-2010 at 03:07 PM. Reason: Typos
06-13-2010, 05:29 AM   #12
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Get yourself a 17mm/11 Takumar. Everything in focus from 3 meters to infinity (or something like that Yep, you must live with the fisheye effect but that's a small sacrifice
06-13-2010, 07:32 AM   #13
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QuoteOriginally posted by falconeye Quote
A crazy feature is that the K-7 can actually maintain FULL 5.2fps for 14.6MP images and an unlimited amount of time. Just make sure everything is on manual, JPG compression is high (1 star) and the SD card is fast (Sandisk Extreme III).
K-x is able to also do that, I've tried with 2-stars JPEG.

QuoteOriginally posted by falconeye Quote
2. Your camera's framerate in AF.C is lower than in AF.S.

Well, 5.2fps are 192ms per shot and the camera needs about 0.14s to refocus between shots (YMMV). Add the 140ms and you end up with 332ms per shot or 3.0fps. That's normal.
The annoying thing I've found is that even if the subject is stationery the camera needs time to confirm focus. It means that as soon as you switch to AF-C the camera will never get any higher than about 3fps whatever the subject.
06-13-2010, 08:41 AM   #14
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QuoteOriginally posted by ManuH Quote
It means that as soon as you switch to AF-C the camera will never get any higher than about 3fps whatever the subject.
In my tests, I had up to 14 images within 3.6s. But you're right, that's about the limit. A high contrast target helps a bit.
06-13-2010, 01:25 PM   #15
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QuoteOriginally posted by ManuH Quote
K-x is able to also do that, I've tried with 2-stars JPEG.



The annoying thing I've found is that even if the subject is stationery the camera needs time to confirm focus. It means that as soon as you switch to AF-C the camera will never get any higher than about 3fps whatever the subject.
that's what i don't understand. i thought in AF-C, the shutter will fire even if the subject is not in focus so in theory, the kx should be able to do 4.7fps, but it doesn't
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