Auto Exposure/ISO Design Criteria?
I'm curious as to whether anyone can explain what the design criteria is behind the auto setting of exposure by the D7000. For example, I have "ISO sensitivity Settings" set to On with a max of 3200 and a min speed of 1/40. This morning taking a shot with a 50mm 1.8 with a mildly cloudy sky, the camera sets a shutter speed of 1/500 at an ISO of 1600. If I had done this by hand the ISO would have been 400, maybe 200 and (without doing a hasty calculation here) the speed would have ben closer to 1/60 or whatever. With my settings (which I have saved as U1) I consistently get a "high" ISO, a fairly high shutter speed and a mid-range aperture. And overall, pretty decent results.
Are there any menu settings that I can change to force the camera into a lower ISO and retain the auto aspect of it for these grab shots. That is, still maintaing the max high ISO and min low speed in the sensitivity setting? Or am I just going to have to go with my natural inclination and pay attention to ISO, shutter speed and aperture just like I have over the years and manually adjust as necessary? BTW the pictures don't really suffer too much as I do get nice, sharp results which is a testament to the capabilities of the camera versus the good old days of 400 speed film and whatnot. The only real issue is that if I want to enlarge I can run into a grain situation if I go a bit too extreme for what the camera gave me. Obviously, if the camera had used ISO 200, etc. I might have a bit more room to work in this respect.
Any road, any words of wisdom would be appreciated.
#1. "RE: Auto Exposure/ISO Design Criteria?" | In response to Reply # 0jvaidya Nikonian since 19th Apr 2011Wed 02-May-12 07:16 PM
I had this problem on a walkabout last summer when bright blue skies were being shot at 1600 ISO, till I realized that my default ISO was set too high. You might want to make sure that the ISO is set to the base before you switch on Auto ISO.
My understanding is that it starts at the ISO you start it with and bumps it up if it hits the shutter speed limit.
Must admit I havent used Auto ISO much so I may be way off here.
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#2. "RE: Auto Exposure/ISO Design Criteria?" | In response to Reply # 0Vlad_IT Nikonian since 21st Sep 2011Wed 02-May-12 07:30 PM
the camera should slow down on shutter until it hits preset minimum (1/40 in your case) and only then should start bumping ISO.
the things are a bit more complicated when speadlight is in use.
In your case i think your U1 mode was saved a manual and not "S"/"P" mode, or, as pointed above, you base ISO was set to ISO 1600, going upto 3200
#3. "RE: Auto Exposure/ISO Design Criteria?" | In response to Reply # 0MotoMannequin Registered since 11th Jan 2006Wed 02-May-12 07:35 PM
In P or A mode, if shutter speed is above the minimum setting, then it should shoot at minimum ISO. ISO should not increase unless it's required to get good exposure at the minimum shutter speed. Then ISO will increase unless it hits the max setting, at which point shutter will slow further.
Given the auto-ISO settings you describe, it seems the camera should have shot at 1/40" ISO 130 (which is equivalent exposure to 1/500" ISO 1600).
Why didn't it do this? I can think of a couple possibilities:
The "minimum ISO" according to the manual (pg 103) should be automatically set to 100. If however you change the ISO setting then it's possible the camera uses your new setting as the minimum. I've seen different Nikon bodies behave differently this way. First, make sure ISO is set to 100.
The other possibility is that you're not in P or A mode. Because you say you're using "User" setting, we really have no idea what exposure mode you're in. (I hate the U1/2 implementation on the D7000 but that's a different rant).
I'd suggest you go into "A" mode, set ISO to 100, then enable auto-ISO. Try shooting that way. You should never see ISO over 100 unless shutter is at the minimum setting. Once you're comfortable with the way it's working, save those settings to U1, then see if it still works the same there.
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#4. "RE: Auto Exposure/ISO Design Criteria?" | In response to Reply # 0Wed 02-May-12 08:01 PM | edited Wed 02-May-12 08:09 PM by billross
Thanks, everyone. Great suggestions and I'll see how they work out.
Edit: Yep, as you guys suggested base ISO was set at 1600. Doh!
#5. "RE: Auto Exposure/ISO Design Criteria?" | In response to Reply # 4TheDraftsman Registered since 20th Jan 2011Thu 03-May-12 10:21 AM
With a lot of experiance now with both my D90 and D7000, you'll be much happier turning on your Easy ISO (Custom settings "d3") and using your dials to change ISO on the fly.
I think "Auto ISO" is not that helpful for the advanced user.
#6. "RE: Auto Exposure/ISO Design Criteria?" | In response to Reply # 5Thu 03-May-12 04:08 PM
>With a lot of experiance now with both my D90 and D7000,
>you'll be much happier turning on your Easy ISO (Custom
>settings "d3") and using your dials to change ISO on
>I think "Auto ISO" is not that helpful for the
Thanks for the suggestion.
I actually have both. That is, by default, Auto ISO starts at 100 until the camera changes it or I change it using "Easy ISO". This way I can grab a shot and not worry about it, or tweak the ISO to get the shutter speed and/or aperture I'm after. Seems to work OK, but I do need to remember to turn ISO back to the 100 base setting if I do change it via Easy ISO since the U settings do not revert to a saved base ISO when the camera is turned on, only the last set.