Auto ISO & minimum shutter speed

Started 11 months ago | Questions
D Mac
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Auto ISO & minimum shutter speed
11 months ago

Not sure if this has been asked already, but if I put the camera in auto-ISO  with a minimum shutter speed of 1/125 and then put the shutter dial to automatic, is that supposed to keep the shutter speed from dropping below 1/125?  I've  tried a couple test shots with those settings but the shutter speed drops below 1/125th.

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Limburger
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Re: Auto ISO & minimum shutter speed
In reply to D Mac, 11 months ago

You basicly work with aperture priority. When the light runs out for propper exposure it only then will go slower than you have set it.

You can try by choosing a wider aperture or get more scene luminance.

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a l b e r t
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Re: Auto ISO & minimum shutter speed
In reply to D Mac, 11 months ago

When you hit the highest Auto ISO value and the exposure is still under, the camera will try to reduce shutter speed to keep exposure correct.

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bigpigbig
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Re: Auto ISO & minimum shutter speed
In reply to a l b e r t, 11 months ago

a l b e r t wrote:

When you hit the highest Auto ISO value and the exposure is still under, the camera will try to reduce shutter speed to keep exposure correct.

Let me see if I can get my head around this.

I choose and Aperture and put the SS dial to A (aperture priority mode) then Auto ISO (let's say 3200). If the minimum SS is set to 1/125 then will the camera start at ISO 100 (or 200 in RAW) and as long as the SS is faster than 1/125 it will shoot. If the SS would need to be lower than 1/125 at ISO 100 it will set the shutter speed to 1/125 and increase the ISO up to 3200 at which point:

IT WILL DECREASE SHUTTER SPEED??

this seems wrong. If I am shooting a subject that requires a 1/125 shutter speed to avoid motion blur, it seems I would rather have an underexposed photo at 1/125 and ISO 3200 than a blurry photo.

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Limburger
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Re: Auto ISO & minimum shutter speed
In reply to bigpigbig, 11 months ago

bigpigbig wrote:

a l b e r t wrote:

When you hit the highest Auto ISO value and the exposure is still under, the camera will try to reduce shutter speed to keep exposure correct.

Let me see if I can get my head around this.

I choose and Aperture and put the SS dial to A (aperture priority mode) then Auto ISO (let's say 3200). If the minimum SS is set to 1/125 then will the camera start at ISO 100 (or 200 in RAW) and as long as the SS is faster than 1/125 it will shoot. If the SS would need to be lower than 1/125 at ISO 100 it will set the shutter speed to 1/125 and increase the ISO up to 3200 at which point:

IT WILL DECREASE SHUTTER SPEED??

this seems wrong. If I am shooting a subject that requires a 1/125 shutter speed to avoid motion blur, it seems I would rather have an underexposed photo at 1/125 and ISO 3200 than a blurry photo.

It makes perfect sense. The camera wasn't set to underexpose but to try keeping 1/125s as long as possible at given aperture and scene luminance. By dialing in -EC you tell the camera it's ok to underexpose (when hitting your upper iso and lower shutter limits) and it by then will do so.

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dengx
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Re: Auto ISO & minimum shutter speed
In reply to D Mac, 11 months ago

D Mac wrote:

Not sure if this has been asked already, but if I put the camera in auto-ISO with a minimum shutter speed of 1/125 and then put the shutter dial to automatic, is that supposed to keep the shutter speed from dropping below 1/125? I've tried a couple test shots with those settings but the shutter speed drops below 1/125th.

A few days ago I've explained it here:

http://www.dpreview.com/forums/post/52610244

Regards

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bigpigbig
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Re: Auto ISO & minimum shutter speed
In reply to Limburger, 11 months ago

Limburger wrote:

bigpigbig wrote:

a l b e r t wrote:

When you hit the highest Auto ISO value and the exposure is still under, the camera will try to reduce shutter speed to keep exposure correct.

Let me see if I can get my head around this.

I choose and Aperture and put the SS dial to A (aperture priority mode) then Auto ISO (let's say 3200). If the minimum SS is set to 1/125 then will the camera start at ISO 100 (or 200 in RAW) and as long as the SS is faster than 1/125 it will shoot. If the SS would need to be lower than 1/125 at ISO 100 it will set the shutter speed to 1/125 and increase the ISO up to 3200 at which point:

IT WILL DECREASE SHUTTER SPEED??

this seems wrong. If I am shooting a subject that requires a 1/125 shutter speed to avoid motion blur, it seems I would rather have an underexposed photo at 1/125 and ISO 3200 than a blurry photo.

It makes perfect sense. The camera wasn't set to underexpose but to try keeping 1/125s as long as possible at given aperture and scene luminance. By dialing in -EC you tell the camera it's ok to underexpose (when hitting your upper iso and lower shutter limits) and it by then will do so.

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Cheers Mike

Thanks Mike.

But what "makes sense" is always personal (unless physics or math is involved). To me, I would only ever set a minimum shutter speed and Auto ISO in variable lighting or luminance scenarios when the shutter speed minimum is CRITICAL to getting in focus images. People walking on a sidewalk for example. Dialing in EC to raise shutter speed seems to defeat the purpose of "Auto" with MINIMUM SHUTTER SPEED.  What does the camera do if I set the shutter speed to 1/125, aperture to "A" and Auto ISO 3200 in a case of insufficient light and maximum aperture? I am guessing it underexposes. No? I would hope it doesn't go up past ISO 3200, I can do that in post.

Sorry, I am in a hospital bed at the moment and can check for myself. ACL reconstruction, good fun.  :/

But I would use minimum shutter speed, for me, in a similar way to manual mode when minimum SS is critical and variable light or luminance makes it difficult to shoot in manual Mode. I don't want to be shooting away and find that the SS has dropped below a value that assures my subjects are in focus (not blurred). If I have to keep looking at the shutter speed it defeats the purpose (for me) of going to Auto in the first place.

What am I missing? Why and how would you use it? Scenarios?

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dengx
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Re: Auto ISO & minimum shutter speed
In reply to bigpigbig, 11 months ago

bigpigbig wrote:

What does the camera do if I set the shutter speed to 1/125, aperture to "A" and Auto ISO 3200 in a case of insufficient light and maximum aperture? I am guessing it underexposes.

Yes, it underexposes in that case.

Sorry, I am in a hospital bed at the moment and can check for myself. ACL reconstruction, good fun. :/

Hope you'll get well soon!

Regards

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Limburger
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Re: Auto ISO & minimum shutter speed
In reply to bigpigbig, 11 months ago

Hey, first I hope you will be out of hospital soon. Hospital is no fun but ACL (had to look it up not knowing what it was) seems to be not life threatening...anyways hospital is no fun unless you work there.

As for the auto iso and such, well... why not go full manual. It's an automated mode but only works in good light.

In full auto 1/125 is 1/125 no matter the exposure.

You're missing nothing imho, it's an overestimated conveniance mode.

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bigpigbig
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Re: Auto ISO & minimum shutter speed
In reply to dengx, 11 months ago

dengx wrote:

bigpigbig wrote:

What does the camera do if I set the shutter speed to 1/125, aperture to "A" and Auto ISO 3200 in a case of insufficient light and maximum aperture? I am guessing it underexposes.

Yes, it underexposes in that case.

Sorry, I am in a hospital bed at the moment and can check for myself. ACL reconstruction, good fun. :/

Hope you'll get well soon!

Regards

Thank, that's good..

Six months of rehab should give me time to sort out the best way to use Auto ISO.

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bigpigbig
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Re: Auto ISO & minimum shutter speed
In reply to Limburger, 11 months ago

Limburger wrote:

Hey, first I hope you will be out of hospital soon. Hospital is no fun but ACL (had to look it up not knowing what it was) seems to be not life threatening...anyways hospital is no fun unless you work there.

As for the auto iso and such, well... why not go full manual. It's an automated mode but only works in good light.

In full auto 1/125 is 1/125 no matter the exposure.

You're missing nothing imho, it's an overestimated conveniance mode.

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Cheers Mike

most of time I shoot in manual mode. But occasionally letting the camera do the metering is helpful. for example, a city street with shady areas and sunny areas.

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D Mac
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Re: Auto ISO & minimum shutter speed
In reply to dengx, 11 months ago

Thanks, makes sense to me now.

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