ST-E2 as Focus Assist

I like to shoot low light/high ISO so I thought I'd use my ST-E2 to assist focusing..So I thought???

I found that with my ST-E2 turned on my exposures are underexposing when in AV or TV modes.. In manual mode the meter doesn't move when switching between ST-E2 on and off.. This happens with both my 50D and 20D but only in low light.. In brighter light this does not happen and with all my lenses..

Any thoughts??

First image with ST-E2 turned off..

Model = Canon EOS 50D
Exposure Time = 1/30"
F Number = F2.2
ISO Speed Ratings = 400
Exposure Bias Value = ±0EV

Second image with ST-E2 turned on..

Model = Canon EOS 50D
Exposure Time = 1/60"
F Number = F2.2
ISO Speed Ratings = 400
Exposure Bias Value = ±0EV

Notice,,a full stop difference in exposure..

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hah weird... is the focus assist light affecting the meter or do you think it is an internal electrical thing? I use mine for FA a lot but 99.9% in M so I wouldn't notice. I'll go check for you.

What metering mode are you using? I wonder if the assist beam is enough to affect the meter. It's just a thought, I have no experience with the ST-E2.

I'm sure It's NEVEC rearing it's ugly head.

When you have the ST-E2 mounted does the flash icon light up in the viewfinder? If so, what's happening is that the camera will underexpose by up to 1 stop whenever it sees that there's a flash mounted in the hotshoe.

If you do a search on NEVEC, you'll find a couple of threads that discuss the phenomenon in detail.

BTW, NEVEC is an acronym for Negative EValuative Exposure Compensation.

Wow, way to find a buried bug.

That is totally reproducible on my 1DS2. I didn't take the shot but the meter in AV was 1/8 sec @ f/2.8, ISO 1600. I turned on the ST-E2 and the exposure changes to 1/15 sec. On, off, on, off, same results every time. And that is without even focusing, just tapping the shutter to get an exposure.

TheHoff wrote in post #9137719
Wow, way to find a buried bug.

That is totally reproducible on my 1DS2. I didn't take the shot but the meter in AV was 1/8 sec @ f/2.8, ISO 1600. I turned on the ST-E2 and the exposure changes to 1/15 sec. On, off, on, off, same results every time. And that is without even focusing, just tapping the shutter to get an exposure.

It's not a bug. It's an undocumented feature of the EOS cameras. Just about all EOS DSLR cameras exhibit this behavior when a flash is mounted in the hotshoe.

Thanks Hoff.. My ST-E2 is pretty old but works great with my flashes.. When I switch to manual mode an turn the ST-E2 on and off, the camera's meter stays put,, doesn't move..

It only effects the exposure when when shooting in AV or TV.. In manual mode I no difference..

I thought of that also so I took an incident meter reading with my Sekonic handheld meter which confirmed the reading with the ST-E2 turned on is about 1 stop under..

I doubt the assist beam is strong enough to effect the meter reading.. Also the assist beam is red so I should have noticed a colour shift..

PacAce wrote in post #9137735
It's not a bug. It's an undocumented feature of the EOS cameras. Just about all EOS DSLR cameras exhibit this behavior when a flash is mounted in the hotshoe.

Interesting; thanks for the tip on NEVEC.

Thanks guys for your help.. It's no biggy.. I'll just have to remember to use the Exposure Compensation feature when shooting in AV or TV with the ST-E2 turned on..

PacAce,,thanks for the link,,I'll do some reading..

The camera does it since it assumes that flash will be added to the picture. Thus it can't expose the ambient at its nominal value, or all added flash light will give overexposure.

apersson850 wrote in post #11014912
The camera does it since it assumes that flash will be added to the picture. Thus it can't expose the ambient at its nominal value, or all added flash light will give overexposure.

Thanks Anders

I've already come to this conclusion..

Is it just due to the presence of a flash in the hotshoe, or does the flash also need to be turned on?

Shadowblade wrote in post #11018757
Is it just due to the presence of a flash in the hotshoe, or does the flash also need to be turned on?

Needs to be turned on.. I did tests with my ST-E2 both turned on and off..When turned on it gave me underexposure..

Shadowblade wrote in post #11018757
Is it just due to the presence of a flash in the hotshoe, or does the flash also need to be turned on?

Yes, the flash needs to be turned on. Otherwise, the camera will not know that the flash is there.

Hmm, I was just about to say, plug in the ST-E2 but disable flash from firing in the camera... I guess that doesn't work. I had an ST-E2 back in the day, and am (cross-out) WAS looking at getting one to help combat some of the 5D II focus problems.. I guess i'll have to look elsewhere.