Auto ISO in the Pentax K-5 in Av mode

philbaum · 05-26-2012, 02:17 PM

I'm not getting the same results in AV with auto-iso.

I just happened to have a DA300 on when i tried to duplicate your results. Aperture F8,

A. with auto-iso on Slow, i'm getting 1/200s shutter, about .7 *FL

B. with auto-iso on Fast, i'm getting 1/800s shutter, about 2.7*FL

SR position doesn't matter to the above.

Am i doing something wrong or is the camera calculation more complicated than suggested?

Edit:
Aperture also figures into it. 1/800s was the fastest shutter i could get out of AV with auto-iso, until i rolled it all the way open to F4. F4 now reduces my max fastest shutter to 1/640s. Thank the divinities for TAV and manual, this is too much to keep track of, IMO.

Last edited by philbaum; 05-26-2012 at 02:23 PM.

**jeffshaddix** · 05-26-2012, 02:39 PM

Auto-iso also behaves differently for pre-F lenses (I.e. any lens that you have to input the focal length). It does not rely on the focal length you give it, instead slow is fixed at 1/60, normal at 1/125, and fast at 1/200. Quite lame that it doesn't use the input FL from the user.

IMO, auto iso is sub-optimal, we should just be able to set the minimum shutter speed with the front dial.

beholder3 · 05-27-2012, 02:11 AM

[[deleted]

05-26-2012, 02:17 PM	#16
philbaum Veteran Member Join Date: Oct 2007 Location: Port Townsend, Washington State, USA Posts: 3,659	Are you sure about this? I'm not getting the same results in AV with auto-iso. I just happened to have a DA300 on when i tried to duplicate your results. Aperture F8, A. with auto-iso on Slow, i'm getting 1/200s shutter, about .7 FL B. with auto-iso on Fast, i'm getting 1/800s shutter, about 2.7FL SR position doesn't matter to the above. Am i doing something wrong or is the camera calculation more complicated than suggested? Edit: Aperture also figures into it. 1/800s was the fastest shutter i could get out of AV with auto-iso, until i rolled it all the way open to F4. F4 now reduces my max fastest shutter to 1/640s. Thank the divinities for TAV and manual, this is too much to keep track of, IMO. Last edited by philbaum; 05-26-2012 at 02:23 PM.

05-27-2012, 02:11 AM	#18
beholder3 Pentaxian Join Date: Dec 2011 Posts: 3,112 Original Poster	[[deleted] Last edited by beholder3; 08-11-2013 at 07:30 AM. Reason: [deleted]

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05-26-2012, 02:39 PM	#17
jeffshaddix Site Supporter Join Date: Jun 2010 Location: Colorado Posts: 1,473	Auto-iso also behaves differently for pre-F lenses (I.e. any lens that you have to input the focal length). It does not rely on the focal length you give it, instead slow is fixed at 1/60, normal at 1/125, and fast at 1/200. Quite lame that it doesn't use the input FL from the user. IMO, auto iso is sub-optimal, we should just be able to set the minimum shutter speed with the front dial.

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