Question on Aperture Priority

Marcel

Marcel

Happily retired
Staff member
Super Mod
BackdoorHippie said:
That's not the thing, Marcel. Regardless of what the meter is suggesting as the proper exposure, the exposure settings should fall within those specified in the Auto ISO settings. If he has a minimum Shutter Speed set to 1/125sec then it shouldn't drop below that without hitting the Maximum ISO setting first (in this case 3200). With those parameters set and Auto ISO turned on it should be impossible to get a shot at 1/40, f8 and ISO 400 in Aperture Priority mode.
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If I remember correctly, the meter will overcome the limits and the shutter speed could go lower BUT when it does that, the display turns to RED in the viewfinder. Now I'm not 100% certain and don't have the time to check this morning, but I think this is what happens when you run out of enough light.
 
BackdoorArts

BackdoorArts

Senior Member
Marcel said:
If I remember correctly, the meter will overcome the limits and the shutter speed could go lower BUT when it does that, the display turns to RED in the viewfinder. Now I'm not 100% certain and don't have the time to check this morning, but I think this is what happens when you run out of enough light.
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Exactly!! But he's not running out of light because ISO isn't close to maxed out according to the settings. It will lower it when the available exposure parameters need to be overridden, and that's not the case.
 
Marcel

Marcel

Happily retired
Staff member
Super Mod
BackdoorHippie said:
Exactly!! But he's not running out of light because ISO isn't close to maxed out according to the settings. It will lower it when the available exposure parameters need to be overridden, and that's not the case.
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You are right. I wonder if the "mode A" works like it should with auto-iso.
 
L

Lawrence

Senior Member
Jake has got it figured exactly - in Aperture mode with ISO-A set (at maximum 3200), shutter speed minimum 1/125 to my way of thinking the shutter speed should never drop below 1/125 yet it is. And it isn't a light issue as I was sitting in a mall that had both natural lighting from a large window behind me and the usual lighting you get in these malls.
I am going to post one of the shots so you can see exif.
Give me 20 minutes - to haul one out.
 
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Lawrence

Senior Member
OK here is one - bugger all editing done

As shot .jpg

ISO was 640
Shutter 1/30
f4.0

So ISO was NOT maxed out to cause the shutter to drop to such a slow speed
 
W

WayneF

Senior Member
Lawrence said:
Doing what you suggest with aperture on f 1.8 and minimum shutter speed on 1/125 the shutter jumps around to 1/60 and 1/80th as I move the camera around - it is night time here so I am under artificial light but that shouldn't cause this.
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Is a flash involved? Flash Maximum Shutter Speed With Flash affects regular front curtain sync (in A and P mode). Also Slow Sync or Rear Curtain Sync affects shutter speed, ignoring Auto ISO shutter speed.
 
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Eyelight

Senior Member
There is auto settings and then there is choosing auto as the ISO setting. I'll ask the dumb question.. Is ISO set to auto?
Sent from Somewhere using Tapatalk
 
Marcel

Marcel

Happily retired
Staff member
Super Mod
Now you guys got me confused... Of course you can say it eventually always comes with age, but I'm not quite there yet. :)

I think that all auto-iso does is raise the iso to your maximum to "TRY" to keep the shutter speed over your fixed limit. But when there is not enough light, the shutter speed will go wherever it needs to and you'll still be able to take a picture. But I did notice some kind of blinking in the viewfinder when that happens. And when I reviewed the picture on the camera with infos showing, the iso was in RED.
 
L

Lawrence

Senior Member
Marcel said:
Now you guys got me confused... Of course you can say it eventually always comes with age, but I'm not quite there yet. :)

I think that all auto-iso does is raise the iso to your maximum to "TRY" to keep the shutter speed over your fixed limit. But when there is not enough light, the shutter speed will go wherever it needs to and you'll still be able to take a picture. But I did notice some kind of blinking in the viewfinder when that happens. And when I reviewed the picture on the camera with infos showing, the iso was in RED.
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Marcel if that is the case then I have to ask why, in the photo posted above, did it decide to use an ISO of 640 instead of 3200? Had it done this then the shutter speed could have been increased to way more than 1/30
This whole thing doesn't make sense to me
 
D

Don Kuykendall_RIP

RIP :(
I use minimum shutter speed and set it for each lens I use. I also use Auto ISO and set the maximum normally to 6400 on my D7100 or higher if needed. I normally works as advertised like my friend Lawrence things it should. I use this same setup in aperture mode, Program mode and auto ISO in the manual mode when I need specific shutter speed and aperture like for Bird in Flight.
 
Marcel

Marcel

Happily retired
Staff member
Super Mod
Lawrence said:
Marcel if that is the case then I have to ask why, in the photo posted above, did it decide to use an ISO of 640 instead of 3200? Had it done this then the shutter speed could have been increased to way more than 1/30
This whole thing doesn't make sense to me
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You are quite right to ask because I can't understand it either. Maybe there is another setting needed to activate this option. Could be hidden somewhere that we haven't thought of yet. When you find out, just make sure to shed light our way too. :)
 
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Lawrence

Senior Member
Local camera shop guy gave me some answers.
Not sure that I agree with him as he wasn't 100% convincing and disappeared into the back room to "Google it".

Anyway he says that the minimum shutter speed does not apply at all when in aperture mode and that this feature is for use with video.
Then he mumbled something about synch with flash. I had the feeling he was happy to get me out of the shop.

I wil look into it some more but that's where I am at - best to shoot in auto with aperture and shutter speed on what I want and have ISO on auto.

Who said "Candid Street Photography" was going to be easy?
 
BackdoorArts

BackdoorArts

Senior Member
He's just in over his head. Aperture Priority Mode is exactly where minimum shutter speed applies. Sorry he couldn't shed light on it.

Try the green button restart and see if it helps.
 
W

WayneF

Senior Member
Lawrence said:
Local camera shop guy gave me some answers.
Not sure that I agree with him as he wasn't 100% convincing and disappeared into the back room to "Google it".

Anyway he says that the minimum shutter speed does not apply at all when in aperture mode and that this feature is for use with video.
Then he mumbled something about synch with flash. I had the feeling he was happy to get me out of the shop.
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Those were my concerns, but you said no flash involved.

Minimum Shutter Speed with Flash (default 1/60 second) certainly does apply to camera mode A or P (and surely Auto and Scenes too). The models like D300 and D7100 and up have a menu E2 for this. The default 1/60 second Minimum can be slowed, but not increased.

You can see this kick in, like indoors (less bright than sunshine), and take an exposure reading in A or P mode (in dimmer light, it will be slower, like 1/4 to 1/10 second maybe). Pop open the internal flash, and then the shutter speed jumps to 1/60 second (the default Minimum with flash). Exceptions are that if Slow Sync or Rear Curtain Sync, the Minimum is ignored, and the shutter speed necessarily stays slow, because that is the point of those sync modes.

Video takes 30 frames a second, therefore shutter speeds longer then 1/30 second are impossible. In dimmer light, it will be 1/30. If in better light, 1/60 is considered to be better.


I have no clue about your Auto ISO issue. Your opinion sounds very correct, I can't imagine why it is not happening.
 
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aroy

Senior Member
I also had a problem with auto ISO (it would first max out and then change the speed/aperture, as the setting demanded), so now a days I have stopped using it. If set to a fixed ISO, then aperture priority will change the speed.

With auto ISO it depends on the algorithm used in the body. The way I figure it is, if the subject seems to be stationary, then it may change speed even below the maximum (it is trying to have a clean picture), if the subject is moving then it will change the ISO first and speed next.
 
BackdoorArts

BackdoorArts

Senior Member
aroy said:
I also had a problem with auto ISO (it would first max out and then change the speed/aperture, as the setting demanded), so now a days I have stopped using it. If set to a fixed ISO, then aperture priority will change the speed.

With auto ISO it depends on the algorithm used in the body. The way I figure it is, if the subject seems to be stationary, then it may change speed even below the maximum (it is trying to have a clean picture), if the subject is moving then it will change the ISO first and speed next.
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Do you make this stuff up or does someone give it to you? There is no motion-specific algorithm, it's as basic a decision making process as can be...


  • Can I get a proper exposure at current ISO without dropping below the minimum Shutter Speed?
    • Yes - Take the picture
    • No - Have I hit Max ISO?
      • Yes - Drop shutter speed to fastest possible for Aperture and ISO and take the picture.
      • No - Raise ISO one step and go back to the beginning

Don't believe me? https://support.nikonusa.com/app/answers/detail/a_id/14130/~/how-does-the-auto-iso-feature-work?
 
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