1D Mark IV is randomly under-exposing photos

Have not been able to figure this out yet. Sometimes, while shooting AV with a manual ISO, the camera just under exposes a handful of shots. The histogram is way to the left, and it's just dark. Then it will snap out of it and shoot a few dozen shots at proper exposure, same scenes even.

Anyone seen this?

Thanks in advance!

Is safety shift enabled ? Have you tried disabling it?

Check the lens is properly secured.
I was getting over-exposure on a 7D2 the other day- found the lens was loose. A twist to lock it fixed the problem.

I did read you have an over exposure problem, I'm wondering if the aperture setting isn't being received by the lens and it is stepping down? In my case it was stepping up- I don't know if all lenses work the same way when disconnected.

trekgod3 wrote in post #18878530
Is safety shift enabled ? Have you tried disabling it?

No, it's disabled. Unchanged in the 4 years I've had the camera (this is a new problem).

Capn Jack wrote in post #18878569
Check the lens is properly secured.
I was getting over-exposure on a 7D2 the other day- found the lens was loose. A twist to lock it fixed the problem.

I did read you have an over exposure problem, I'm wondering if the aperture setting isn't being received by the lens and it is stepping down? In my case it was stepping up- I don't know if all lenses work the same way when disconnected.

This happens with four lenses, including one with a mechanical aperture selection ring (shooting AV).

Does the shutter sound the same when this happens, compared to when good pictures are taken?

I'm thinking maybe it moves, but incorrectly, so it doesn't open when it moves.

apersson850 wrote in post #18878987
Does the shutter sound the same when this happens, compared to when good pictures are taken?

I'm thinking maybe it moves, but incorrectly, so it doesn't open when it moves.

Interesting thought. I'll have to try to notice this -- nothing that caught my attention. What does shutter failure look like?

Examining a few photos, it appears that it usually happens for all shots in a series, and the EXIF shows that the shutter speed is way too fast on the dark shots. One series will be at 1/8000, for instance, underexposed, and the next series in the same conditions/subjects will be at 1/3200. So it seems that the camera recognizes what it's doing, so it feels like a metering problem. I have been shooting with "center weighted averaging" for years, including in these shots.

A simple test...aim the camera at a featureless uniformly colored and uniformly illluminsted wall, and take a lot of shots in succession.
Do this in Av, then in M (using same settings as indicated by the meter while in Av). All should result in uniformly dense exposures.
Variations while in M will indicate shutter deviations; variations in AV mode will indicate meter induced variations

Wilt wrote in post #18879151
A simple test...aim the camera at a featureless uniformly colored and uniformly illluminsted wall, and take a lot of shots in succession.
Do this in Av, then in M (using same settings as indicated by the meter while in Av). All should result in uniformly dense exposures.
Variations while in M will indicate shutter deviations; variations in AV mode will indicate meter induced variations

Thanks. I'll see if I can set something up.

At any rate, this doesn't seem like a common problem.

Two things pop into my mind.

1: What setting do you use for Metering, Spot metering ?

2: Do you have the vertical grip switch on ?
When I have the vertical grip on, I occasionally press the * button with my hand when in normal position.
And because I have the "Hail Mary" settings from CyberdyneSystems enabled, the camera behaves different when pressing *.
https://photography-on-the.net …showthread.php?​p=17951424
CyberDyneSystems post #4812
Switching off the vertical grip and everything is back to normal.

1: Center Weighted Average
2: Yes, vertical grip is on. I don't have hail mary set up -- but may be bumping * -- will check if that's causing this somehow.

Thanks!

Canon Amateur wrote in post #18879307
Two things pop into my mind.

1: What setting do you use for Metering, Spot metering ?

2: Do you have the vertical grip switch on ?
When I have the vertical grip on, I occasionally press the * button with my hand when in normal position.
And because I have the "Hail Mary" settings from CyberdyneSystems enabled, the camera behaves different when pressing *.
https://photography-on-the.net …showthread.php?​p=17951424
CyberDyneSystems post #4812
Switching off the vertical grip and everything is back to normal.

Wilt wrote in post #18879151
A simple test...aim the camera at a featureless uniformly colored and uniformly illluminsted wall, and take a lot of shots in succession.
Do this in Av, then in M (using same settings as indicated by the meter while in Av). All should result in uniformly dense exposures.
Variations while in M will indicate shutter deviations; variations in AV mode will indicate meter induced variations

Thanks, I did the test this morning on my 1DMKIV and it passed with flying colors.

2cruise wrote in post #18883210
Thanks, I did the test this morning on my 1DMKIV and it passed with flying colors.

Good news: it passed the recent tests
Bad new: What caused the problem when it occurred?!

You still have no idea if the metering is somewhat flakey, or if the shutter is somewhat flakey! The purpose of my suggested test was to help determine the root cause of the exposure change that you had observed.

Wilt wrote in post #18883284
Good news: it passed the recent tests
Bad new: What caused the problem when it occurred?!

You still have no idea if the metering is somewhat flakey, or if the shutter is somewhat flakey! The purpose of my suggested test was to help determine the root cause of the exposure change that you had observed.

The OP didn't reply that they passed with flying colors, it was someone else. As to the root cause of the OP, I have to assume metering mode is the culprit. AF point linked metering vs not could cause unexpected results.

TeamSpeed wrote in post #18883309
The OP didn't reply that they passed with flying colors, it was someone else.

As to the root cause of the OP, I have to assume metering mode is the culprit. AF point linked metering vs not could cause unexpected results.

Good point. Although I have never owned/used a 1Dn body, it would seem that spotmetering using the AF zone + focus-recompose could really confuse things!