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03-01-2011, 09:13 AM   #1
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Weird thing with AUTO-ISO and framerate...

Yesterday was shooting inside in very dim light and noticed a weired thing...

Here are the settings: K5 body + 18-135, RAW, AV, AF.S, burst-high, auto-ISO, highlights/shadow/lens correction OFF

The weird part is that whenever ISO goes over ~800, the actual framerate drops to ~3FPS... Unless AE-L is ON, where the camera would fire at full 7FPS regardless of the current ISO value... Same goes for Tav-mode... my shutter speed could be 1/500th... but at hight iso values the frame rate still drops to ~3fps...

If auto-iso is OFF, camera fires at full 7fps as well regardless of the current ISO setting...

No I haven't tried it yet with other lenses...

Could somebody try to replicate it please?

03-01-2011, 09:32 AM   #2
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Well I did make in TAv mode in burst mode pictures with high iso in 7 fps, so this is not my experience.
03-01-2011, 09:34 AM   #3
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I can't say this is surprising based on some early reports on the K-5. The file size goes up considerably after ISO 800 (see for yourself) so the camera can't go as fast as with the lower ISO's. Do you have the latest firmware?
03-01-2011, 09:49 AM   #4
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QuoteOriginally posted by macTak Quote
I can't say this is surprising based on some early reports on the K-5. The file size goes up considerably after ISO 800 (see for yourself) so the camera can't go as fast as with the lower ISO's. Do you have the latest firmware?
If I manually select the ISO, even at highest setting camera maintains full 7FPS... it's in AUTO-ISO that it drops... And the key thing is - DIM light... just tried it again in the office... has no issues of firing at 7FPS in well-lit environment, but as soon as I point the lens towards something dark, it slows down...

I'm just trying to find the logic behind it... AUTO-ISO takes a smoke-break after each frame????


Last edited by alexeyga; 03-01-2011 at 09:58 AM.
03-01-2011, 10:09 AM   #5
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Auto ISO requires more processing time?

When manufacturers quote specifications, that is generally going to be the best they can get out of the equipment in ideal conditions.
Change one parameter and the specification can change drastically.
03-01-2011, 11:40 AM   #6
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noise reduction?
03-01-2011, 06:05 PM   #7
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QuoteOriginally posted by Wheatfield Quote
Auto ISO requires more processing time?

When manufacturers quote specifications, that is generally going to be the best they can get out of the equipment in ideal conditions.
Change one parameter and the specification can change drastically.
It doesn't make any sense, though. Your camera doesn't adjust the iso between every frame when you are in continuous shooting mode, does it? The K7 will shoot at its max fps in continuous mode, whether you have auto iso on or, have selected iso manually. It only slows down when you go to AF-C.
03-01-2011, 11:46 PM   #8
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Aina voi nähdä unta paremmasta.


03-02-2011, 03:17 AM   #9
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Try turning in camera noise reduction off.
03-03-2011, 07:32 PM   #10
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Buffer clearence times slow down due the NR doing its thing so your buffer fills and frame rate drops to allow for it.
It's all documented in the manual.
Just been reading it as I only got my K5 three days back.

Nico.
03-03-2011, 08:14 PM   #11
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What does it have to do with the noise reduction if when AUTO-ISO is OFF, camera fires at full 7fps REGARDLESS of the current ISO value??? It's with the AUTO-ISO ON that things tend to slow down in darker conditions...
03-03-2011, 09:31 PM   #12
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QuoteOriginally posted by alexeyga Quote
What does it have to do with the noise reduction if when AUTO-ISO is OFF, camera fires at full 7fps REGARDLESS of the current ISO value??? It's with the AUTO-ISO ON that things tend to slow down in darker conditions...
If you have auto ISO selected on and NR is also on and just for this purpose say NR is in auto mode as well then as the ISO increases so does the amount of NR applied to each image.
So the higher the ISO the more time it takes to process each image with NR being applied at higher rates as the ISO goes up.

Refer to top of page 98 in the manual.

Hope this helps.

Just re-reading your post, is NR switched on when you manualy select higher iSO settings?

Nico.

Last edited by Nico13; 03-03-2011 at 09:34 PM. Reason: added text
03-04-2011, 06:47 AM   #13
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NR settings stay the same... I'm only changing ISO or shooting mode... So as far as i'm concerned, there's something going on with AUTO-ISO...

That being said... I can hardly imagine a situation where i'd want to gun anything in that little light anyways... just wanted to share some observations...
03-04-2011, 06:55 AM   #14
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I have not put much thought about this but perhaps in Auto ISO mode, it puts a metering step in each frame of the continuous mode.

If this is the case, it probably also has been done on other bodies as well, so this should be repeatable on any body not just the K5

I might try on my K7 to see if I get a similar reduced frame rate in AUTO ISO mode but I can gaurantee I would never have noticed this because I don't shoot auto ISO AT ALL.

the reason is simple, pentax has implemented the auto ISO function in a way that pushes ISO up first as the means of achieving any shot, as a result, you are always at the worst case grain and noise possible. Unless you clamp down on the upper limit of auto iso to a point where you are happy with the noise on a consistent basis, this can lead to a lot of disappointing shots. If you clamp the AUOT ISO doen that far, why not just set it there in the beginning?
03-04-2011, 08:10 AM   #15
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QuoteOriginally posted by Lowell Goudge Quote
the reason is simple, pentax has implemented the auto ISO function in a way that pushes ISO up first as the means of achieving any shot, as a result, you are always at the worst case grain and noise possible. Unless you clamp down on the upper limit of auto iso to a point where you are happy with the noise on a consistent basis, this can lead to a lot of disappointing shots. If you clamp the AUOT ISO doen that far, why not just set it there in the beginning?
Actually Pentax's implementation of AUTO-ISO is one of the best on the market... for an average Joe that is... When shutter speed is not fixed, it's a function of the current focal length. I don't remember about K7, but in K5 there are 3 different curves for the AUTO-ISO "aggressiveness" that you can define depending on your needs or shakiness of your hands... so at the slowest setting camera goes wondering into theoretical minimum shutter speed limit for that FL way before bumping up the ISO...

Having rather extensive experience with Nikon's auto-iso, my only wish so far is to have a way of defining the minimum shutter speed limit as I do sports and often don't want to go below 1/500th...
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