Fast Auto-ISO

starstuff · 06-30-2011, 07:08 AM

Could someone please explain to me the practical use(s) of Fast/Normal/Slow Auto-ISO? I've fiddled with these settings and can't really see what difference they make. Thanks.

dlacouture · 06-30-2011, 08:15 AM

Practical example, if you are using Av mode :
- "Slow" will use half the shutter speed, thus using a one stop lower ISO.
- "Fast" will double the shutter speed, thus using a one-stop higher ISO.

Same goes if you are in Tv mode but with obviously the aperture as a variant...

Trickier still, if you use P-mode with "sport" as P-line, you'll be able to tweak the lowest speed used.

starstuff · 06-30-2011, 09:52 PM

Thanks for trying, but I'm still not getting this, sorry; and the manual says so little. Try again? Or can anyone point me to an explanation? Thanks.

twitch · 06-30-2011, 10:00 PM

"Fast" means the camera is "Fast" to increase ISO so it can maintain a high shutter speed or a large DOF. So in Av mode, as the light drops, the camera will pump up ISO rather than sacrifice shutter speed.

So for a 70mm lens in Av mode:
FAST may result in ISO3200, 1/250
Normal may result in ISO1600, 1/120
Slow may result in ISO800, 1/60

Or there abouts

Skog · 07-01-2011, 06:49 AM

Choose fast if you want the camera to increase ISO rather then use a larger aperture or slower shutter. This will give you images with more ISO noise/grain, but keep your fast shutter speed and/or small aperture (large depth of field)

Use slow if you want the camera to keep the ISO low, and rather adjust the other two parameters. This setting will give you less ISO noise/grain, but at the expense of depth of field and/or shutter speed.

Normal is normal

Something in between.

Fast, normal or slow indicates the priority in which the camera changes ISO. In P mode the fast setting would be "shutter speed & aperture priority", and the camera changes the ISO before it messes with shutter or aperture. Where as in "low" it's a "ISO priority" and the camera alters your shutter speed and aperture rather then turning up the ISO.

I hope you understood me (English is not my first language). Someone please correct me if I'm wrong.

starstuff · 07-01-2011, 11:15 AM

Twitch and Skog -- thank you!! Got it!! (whew... makes sense now)

06-30-2011, 07:08 AM	#1
starstuff Forum Member Join Date: Jun 2009 Location: San Francisco Posts: 57	Fast Auto-ISO Could someone please explain to me the practical use(s) of Fast/Normal/Slow Auto-ISO? I've fiddled with these settings and can't really see what difference they make. Thanks.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[Auto-ISO] so, is the K5 and Kr brave enough to use max iso?	Reportage	Pentax K-5 & K-5 II	13	10-24-2010 03:30 PM
Auto ISO...do you use it?	Reportage	Pentax DSLR Discussion	76	09-30-2010 05:27 PM
Auto iso - k10d	stevewig	Pentax DSLR Discussion	10	03-25-2010 05:32 PM
Auto-iso on Pentax K-7	consiglieri	Troubleshooting and Beginner Help	5	11-27-2009 12:35 PM
For Sale - Sold: Tokina 28-70mm f/2.8-4.3 fast auto-aperture lens	wallyb	Sold Items	10	07-28-2009 11:02 AM

06-30-2011, 08:15 AM	#2
dlacouture Veteran Member Join Date: Jul 2008 Location: Var, South of France Photos: Albums Posts: 1,074	Practical example, if you are using Av mode : - "Slow" will use half the shutter speed, thus using a one stop lower ISO. - "Fast" will double the shutter speed, thus using a one-stop higher ISO. Same goes if you are in Tv mode but with obviously the aperture as a variant... Trickier still, if you use P-mode with "sport" as P-line, you'll be able to tweak the lowest speed used.

06-30-2011, 09:52 PM	#3
starstuff Forum Member Join Date: Jun 2009 Location: San Francisco Posts: 57 Original Poster	Thanks for trying, but I'm still not getting this, sorry; and the manual says so little. Try again? Or can anyone point me to an explanation? Thanks.

06-30-2011, 10:00 PM	#4
twitch Veteran Member Join Date: Nov 2009 Posts: 4,571	"Fast" means the camera is "Fast" to increase ISO so it can maintain a high shutter speed or a large DOF. So in Av mode, as the light drops, the camera will pump up ISO rather than sacrifice shutter speed. So for a 70mm lens in Av mode: FAST may result in ISO3200, 1/250 Normal may result in ISO1600, 1/120 Slow may result in ISO800, 1/60 Or there abouts

07-01-2011, 06:49 AM	#5
Skog Inactive Account Join Date: May 2010 Posts: 167	Choose fast if you want the camera to increase ISO rather then use a larger aperture or slower shutter. This will give you images with more ISO noise/grain, but keep your fast shutter speed and/or small aperture (large depth of field) Use slow if you want the camera to keep the ISO low, and rather adjust the other two parameters. This setting will give you less ISO noise/grain, but at the expense of depth of field and/or shutter speed. Normal is normal Something in between. Fast, normal or slow indicates the priority in which the camera changes ISO. In P mode the fast setting would be "shutter speed & aperture priority", and the camera changes the ISO before it messes with shutter or aperture. Where as in "low" it's a "ISO priority" and the camera alters your shutter speed and aperture rather then turning up the ISO. I hope you understood me (English is not my first language). Someone please correct me if I'm wrong.

07-01-2011, 11:15 AM	#6
starstuff Forum Member Join Date: Jun 2009 Location: San Francisco Posts: 57 Original Poster	Twitch and Skog -- thank you!! Got it!! (whew... makes sense now)