70D min shutter speed not working as expected.

Instead of shooting in T more in low light, I tried to shoot in A mode with min shutter speed as 1/125 sec. 70D is choosing 1/160 instead of 1/125 most of the times. Some times it chooses 1/125 sec. Some times I have try stopping lens by 1/3 or 2/3 stop to force 1/125. I am trying to understand how does camera determines min shutter speed needed in this case.

Trying to see if I am missing something. A mode gives me little flexibility to stop lens down to get more sharper pictures and dop. It also allows me to use EC which is not possible with M mode.

Which lenses are you using when this is happening?

Mine does the same, I think its a slight incompatibility with sigma, it doesn't happen on my canon 85.

Nothing worry about.

jimeuph1 wrote in post #17436277
Which lenses are you using when this is happening?

Mine does the same, I think its a slight incompatibility with sigma, it doesn't happen on my canon 85.

Nothing worry about.

Thanks Jim. I also noticed with sigma lens (30mm 1.4 and 17-50 2.8). I will check with 18-135 is stm and see how it behaves.

well it's a semi auto mode, so you're at the mercy of the algorithm. In the grand scale of things, 160 vs 125 isnt a huge deal, and just go full manual if you want a little better control.

something like manual with exposure comp would be the best for you, however you'll have to settle for the camera having a mind of it's own. Minimum shutter speed option is great when you're going from indoors to outdoors, however if one type of shooting scenario, it's better to have manual with exposure comp. Sadly, I have one camera that can only do one type, and the other camera also can only do one type. I like the minimum shutter of the canon version a little bit more.

It sounds like you may be misunderstanding min shutter speed, it just means it wont go below that speed. Like others have said try semi-manual, control dial in manual and auto iso, this works on the 70D, you just wont have exp comp with it.

Charlie wrote in post #17436361
well it's a semi auto mode, so you're at the mercy of the algorithm. In the grand scale of things, 160 vs 125 isnt a huge deal, and just go full manual if you want a little better control.

something like manual with exposure comp would be the best for you, however you'll have to settle for the camera having a mind of it's own. Minimum shutter speed option is great when you're going from indoors to outdoors, however if one type of shooting scenario, it's better to have manual with exposure comp. Sadly, I have one camera that can only do one type, and the other camera also can only do one type. I like the minimum shutter of the canon version a little bit more.

Thanks Charlie. I do not have EC with full manual. Canon just started implementing this from 7d2. I guess, they won't update 70d.

Varago wrote in post #17436699
It sounds like you may be misunderstanding min shutter speed, it just means it wont go below that speed. Like others have said try semi-manual, control dial in manual and auto iso, this works on the 70D, you just wont have exp comp with it.

Thanks Varago. I will check with canon lens and make sure it is not a lens issue. Do you mean, when I set min shutter speed to 1/125, it is not gong to chose 1/125 or slower. It consistently sets shutter speed to 1/160 and some times 1/125 before start pushing up ISO.

For this picture, 70D selected 1/160 , ISO 1000 with F2.2. My expectation is to get 1/125, ISO 800 with F2.2 when min SS set to 1/125.

IMAGE LINK: https://flic.kr/p/re6S​6D

khwaja wrote in post #17436916
...Do you mean, when I set min shutter speed to 1/125, it is not gong to chose 1/125 or slower...

No, you've got it backwards it will only choose 1/125 and higher speeds. But I understand what you are saying, you want it to choose 1/125 before starting to raise the ISO and shutter speeds. It assumes that you are okay with SSs higher than 1/125 so that you would rather have something higher than 1/125 since you chose that as the slowest that you would allow. Try choosing 1/90 or 1/80 as the minimum and see if it will choose 1/125. The only downside is that it will choose 1/90 or 1/80 sometimes.

No what he is saying is that he focuses, it tells him ISO 800, 1/125, f2.8. The exposure is supposedly set at that point when you are in evaluative metering.

Then he recomposes, while the exposure should be set at the point of exposure lock, he clicks the shutter and it has chosen ISO 800 1/160 f2.8.

It shouldn't be making last minute tweaks after focus is set.

All I can think is that the scene changes enough for the camera to say right hang on I actually need to just under expose a little, this guy is trying to fool me.

It can't go to ISO 640 1/125 f2.8 because that would under expose too far, the shift from 1/125 to 1/160 is the closest thing to the user controlled exposure value.

jimeuph1 wrote in post #17437099
It shouldn't be making last minute tweaks after focus is set.

It doesn't if you use evaluative metering combined with One Shot AF. In such a case exposure is determined on half-press of the trigger button. But in any other combination of AF and exposure metering mode, the exposure will be determined at the moment you press the trigger button completely.

You can override the latter effect by using a separate AE lock procedure. You can't change the behavior of One Shot AF in combination with evaluative metering, though. Which is as it should, since anything else doesn't make sense.

The exposure time limit just makes sure the time will be no longer than what you ask for. Since 1/160 is shorter than 1/125, the camera succeeded. You should also be aware that the camera rounds the actual value to the nearest it can display. The display resolution is never better than 1/3 of a stop, but the internal setting is.

You certainly do have EC in manual mode. Shut off the auto-ISO.

Turning Auto-ISO on is the only way to activate EC in manual mode, provided the camera you use is one of the few supporting it. Otherwise there's none, and when not in Auto ISO, you don't need any either. You simply set the exposure away from the meter's centerpoint.
Some cameras do have EC in manual mode, even cameras for film. But then it applies a consistent offset to the meter shown in the viewfinder, so that if you set EC to -2, you can still center the meter and get two stops of underexposure. It works as a metering offset in such cameras.

jimeuph1 wrote in post #17437099
No what he is saying is that he focuses, it tells him ISO 800, 1/125, f2.8. The exposure is supposedly set at that point when you are in evaluative metering.

Then he recomposes, while the exposure should be set at the point of exposure lock, he clicks the shutter and it has chosen ISO 800 1/160 f2.8.

It shouldn't be making last minute tweaks after focus is set.

All I can think is that the scene changes enough for the camera to say right hang on I actually need to just under expose a little, this guy is trying to fool me.

It can't go to ISO 640 1/125 f2.8 because that would under expose too far, the shift from 1/125 to 1/160 is the closest thing to the user controlled exposure value.

It is not a recompose issue. I am not recomposing that much with 70D which lets me change focus points quickly. What I mean, camera meters exposure values to ISO 1000, 1/160, f 2.2 instead of ISO 800, 1/125, f2.2. It should make use of shutter speed headroom before start pushing up ISO. That is what it is going to do without min shutter speed limit. It will reduce shutter speed all the way to 1/FL before start pushing up ISO (I am going to test this out confirm again).

apersson850 wrote in post #17437245
Turning Auto-ISO on is the only way to activate EC in manual mode, provided the camera you use is one of the few supporting it. Otherwise there's none, and when not in Auto ISO, you don't need any either. You simply set the exposure away from the meter's centerpoint.
Some cameras do have EC in manual mode, even cameras for film. But then it applies a consistent offset to the meter shown in the viewfinder, so that if you set EC to -2, you can still center the meter and get two stops of underexposure. It works as a metering offset in such cameras.

That's what I meant.

Yes, I understood. But since exposure compensation as a feature in the camera is something different, it's important to keep the two methods apart.