Erratic Exposures in Manual Mode (Canon 40D): Updated

chemosabe

chemosabe

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I've just returned from the Le Mans 24hrs and was browsing the photos I took. I've noticed that I'm getting some strange exposures on the full manual mode with the settings below with image sequences.

I've exposed for the 'lighter' apprearing shots. (Please ignore the image quality as they're not 100% in focus). The camera (I'm guessing) or lens then seems to underexpose some shots. This happens when panning or still when shooting at 6.5fps.

The ambient light cannot be a factor as it can't swap and change 6 times in one second, so I'm guessing there's some faulty processing going on.

I've spoken to Canon and I'm awaiting their technical support team to call me back, but I was wondering if this problem has been experienced by anybody here.

Any ideas???:shrug:

Chris

Camera: Canon 40D
Lens: EF 70-300 f/4-5.6 IS USM (set to IS setting no.2)
Mode: Manual, High speed continuous (6.5fps)


Sequence 1:

Tv: 1/400
Av: 5.6
ISO: 200
White Balance: Auto
Focal Length: 220mm

exposure_sequence.jpg



Sequence 2:

Tv: 1/500
Av: 5.6
ISO: 200
White Balance: Auto
Focal Length: 225mm

exposure_sequence_2.jpg
 
dunno if you noticed, but it seems to be every other shot is right, is it a bracketing mode you have activated?
 
I had exactly the same thing happening a little while ago and posted about it here.

It seems to have stoped since I changed from spot to whatever metering mode its on now so I'm wondering if that could have had anything to do with it :shrug: I did not have any exposure compensation or bracketing on so I know it was not that.
 
Is the metering mode used when in Manual mode?
 
I think manual use would only set the ISO aperture and shutter speed, the exposure would be set as spot/partial/average from the menu as a camera setting. I use Tv or Av though so I'm not 100% up on full manual use
 
Well I though manual mode would over-ride ISO (unless on auto), shutter and aperature
 
No there's no bracketing. There are other sequences where the photos are not alternating. It's just the sequence I've chosen to show has alternate under exposures.

It's on full manual, so the shutter speed, aperture, and iso are all fixed. The metering is there to give you an indication of what combination of shutter/aperture/iso you need for a 'correct' exposure, however in manual mode the metering value or type (spot/partial etc) does not play a part in the shot. Forgot to say the focus was also set to manual.

I'm going to try and do more test shots on the roads here with another lens as well.

The only thing on auto is the white balance.
 
Well thats blown my spot metering theory out then!! I had auto WB as well if that makes any difference.
 
Are the iris blades to set the aperture size? If so how do they play a part when the aperture is manually set as it's the shutter that takes the photo? If not what are they and what do they do?
 
The aperature stays fully open and then closes down when you take the shot.

There is a DOF button under the lens release button that closes them down. Dial it down to say f/22 and press the button whilst looking in to the lens and you'll see.

Hard to say if they're slow though with the naked eye, unless of course a few blades occassionally get stuck.

What lens is it?
 
if it was on spot metering and your values were correct for say the yellow car it is going to be over or under for say a darker car or the track unless you were constantly altering the settings
of course i could be wrong
try a test with a different metering mode
 
I'm trying to get a handle on this, so please correct me if I'm wrong.

In Manual (M) mode, the metering (matrix, spot, etc) is there to help you get the appropriate exposure according to your shutter speed, aperture, and iso.

The metering (in manual) is only there to show you if you are over/under/correctly exposed. It is up to the person taking the shot to decide what his/her exposure is, so once you've decided on your preferences, the shutter speed, aperture, and iso are fixed.

I take the photos in quick succession using high speed 6.5 fps, so there can't be any change in the ambient light conditions. There is no bracketing, and yet some of the shots are dark/underexposed.

The blades on the lens are to set the aperture size. Once the aperture size is set they don't move.

The camera's shutter opens and closes at the appropriate speed. Makes me wonder if the shutter on the camera is getting stuck when in high speed continous shooting as I've never experienced this at 3 fps.
 
chemosabe said:
The blades on the lens are to set the aperture. Once the aperture is set they don't move.
Click to expand...

When you press the release button, the aperature closes down to say e.g f/8, the mirror raises, then the shutter's first curtain opens, then the 2nd curtain finishes the exposure, then the mirror returns, whilst the aperature returns to the largest it can e.g f/2.8

Thats my understanding anyway
 
In the first sequence you are panning the subject, this could affect the exposure in each shot. Not sure on the 2nd sequence.
 
the blades will open and close to the preset aperture with each shot
the light conditions wont change but if you are a using spot it will only meter for the very centre of the exposure not the whole frame
that is assuming you were using spot

try rattling a few off on a fixed scene
 
But Mav, how will spot metering affect a camera set up in manual? The exposure, ISO and shutter speed won't change
 
That makes sense. At 220mm 5.0 is the maximum aperture. My aperture was set at 5.6 which is 1/3 stop, yet the underexposed images look more underexposed than 1/3 stop.

Perhaps it is sticking. I'd have to then do a sequence at the maximum aperture (5.0 at 220mm), so that the stepping down of the aperature isn't a factor in this.

Thanks, Chris

PS: Mav, the metering mode will not affect the exposure in Manual as you set the speed, aperture and iso. In Av or Tv or any of the other mode yes, the metering may decide to change one of those parameters.
 
why dont you forget manual for this and just test in in any old mode/

If there is something mechanically wrong it will be wrong in all modes.
 
Janice,

You may be right however, if there is something wrong, and it affects all modes, you still need to remove any variables. In manual mode, everything is fixed so the camera isn't altering the settings. If you are shooting the same scene with fixed settings, you should get similar exposures.

Trying any of the other modes would not prove anything as the camera's processor is continuously monitoring and altering the either the shutter, aperature or iso, so you will inevitably get slightly varying exposures and you wouldn't know if it was something sticking or just the camera changing a setting.

If I was using any of the other modes, I would expect there to be slightly different exposures, but in manual mode I wouldn't when shooting a burst of 6 shots in a second.

Chris
 
But Mav, how will spot metering affect a camera set up in manual? The exposure, ISO and shutter speed won't change

i may be wrong as i rarly use manual
i just tried this in my living room
i focussed on some darkish wall paper set shutter and aperture to give correct reading
then focussed on the light colored ceiling
nothing changed settings wise but was showing 1 1/2 stops over
 
mav said:
But Mav, how will spot metering affect a camera set up in manual? The exposure, ISO and shutter speed won't change

i may be wrong as i rarly use manual
i just tried this in my living room
i focussed on some darkish wall paper set shutter and aperture to give correct reading
then focussed on the light colored ceiling
nothing changed settings wise but was showing 1 1/2 stops over
Click to expand...

But it's only 'showing' a different light reading. It's not actually altering the exposure settings of the camera. If the camera is set to manual the only thing that will change the amount of light reaching the sensor is the light itself, ie. if the sun suddenly came shining through heavy cloud your shot would be drastically overexposed if you'd set the camera to have correct exposure whilst the sun was hidden by cloud..
 
That is odd - as mentioned above I too have had very similar when shooting with Spot in Av mode, but for it to happen in M is plain odd :| hope it is nothing serious :(
 
Presumably the fence and the car headlights do not contribute? :shrug:
 
admirable said:
Presumably the fence and the car headlights do not contribute? :shrug:
Click to expand...


This is what makes it so odd. With the camera in manual the exposure metering acts simply as an informative light meter, doing nothing to effect the actual exposure values. The photographer would normally set the ISO, aperture and shutter speed to bring the 'needle' to the somewhere near the centre of the scale. This means that once these variables have been set all exposures should be the same providing the strength of the 'light' stays the same. It does beg the question on just how consistant the shutter timings are on this camera.
 
Just wondering if 'Highlight Tone Priority' is enable and if it is if that would make any difference.
 
There's a chap on another forum that has had a similar problem (more or less identical in fact) and he has had a conversation with Canon who have told him that High Tone Priority will not cause it. They have asked for the camera to be returned to them so it will be interesting to hear what Canon have to say about this Chemosabe's camera.
 
Gofer said:
There's a chap on another forum that has had a similar problem (more or less identical in fact) and he has had a conversation with Canon who have told him that High Tone Priority will not cause it. They have asked for the camera to be returned to them so it will be interesting to hear what Canon have to say about this Chemosabe's camera.
Click to expand...

Any chance of a link to that so we can all keep an eye on it? I am really interested to see what they say.
 
OK test time

use the same lens set wide open on manual at a static subject -

I'm thinking camera on tripod in a house pointing at a bit of white paper blue-tacked to the wall, set the iso high so that you get a fast shutter speed 125th? the camera must be on manual to reduce the variables

set motor drive to fastest speed and shoot off 12 ish? frames at f5
then do the same at f16 - still with 125th - just adjust iso for the second set (possibly at max)

in both tests the shots should look consistent (on the pc - we are looking for brightness here focus and everything else do not matter)- if in the second they are not then you have a sticking iris


if they are both in-consistent in brightness then it may well be a shutter problem

the problems on the original photos are nothing to do with spot metering - you had the camera set to manual...
 
You haven't got the "shot saver" turned on in the custom functions? It will meter and make adjustments for under and over exposed shots, but not necessarily in any predicatable way!

I think its on by default...

I would test my theory by looking at the exif, but you havent kept it in those shots...
 
There is a thread over on POTN about a very similar issue - Looks like a fault with the camera according to a Canon 'person'.

Not sure if I'm allowed to link to a post from another (rival?) forum here, but if you visit POTN and do a search for "Problem with 40D? Light and dark images" you'll find it ;)

*&$%&^! - Just seen Gofer's post above - beat me to it :bang:
 
desantnik said:
You haven't got the "shot saver" turned on in the custom functions? It will meter and make adjustments for under and over exposed shots, but not necessarily in any predicatable way!

I think its on by default....
Click to expand...

i cant say Ive ever heard of that? tell me more!
 
isnt the iris in the lens? if so, perhaps try a different lens and see if it happens:shrug:

if it does, it your camera, if it doesnt its the lens.(no idea on this, but would seem logical)
 
My camera did it with 3 different lenss on, one Sigma and 2 Canon
 
Susie,

If you are using any of the other modes other than manual, you can expect to get a slight variation in the exposure, as the camera's processor will determine what settings to apply.

For example, if you're in Av mode, and have set the ISO, then the camera will adjust your shutter speed according to the metering of the scene. What you may notice, is that one shot is, say 1/200 sec and another is 1/250. That's because you are using an 'automatic' mode (albeit semi auto). So one shot may come out darker/lighter. The light in the scene may be constant, but if you're pointing the camera at a slightly different point, the camera's metering may decide there's more light or less light in the scene and adjust the shutter. This is why there are different metering modes. They each have their pluses and minuses. The metering you use depends on the type of photo you are trying to take.

Same applies in Tv mode, but the camera will alter the aperture (assuming the iso is set)

If, on the other hand you get this problem in manual mode, then either a) the light in the scene has changed, which would be the case if you're outdoors on a semi-cloudy day and one minute the sun is behind the clouds, and the next minute the sun is out the clouds b) there's a problem if this occurs when you're shooting in a burst, when the light in the scene can not change in the short space of time.

Then I guess one has to test all the lenses to figure out if it's the camera or the lens.

Chris
 
I have had it happen a few times now hence my thread a few weeks ago, like you it was when I was using it on burst and its unlikely the light would change at 6fps on an overcast day. The last time it happened I checked the exif and the speed, aperture and ISO had not moved between the shots, the focus point had not moved either as I had a stationary target! The problem is it seems to be intermitant so I cannot replicate it all the time. I'm pretty sure its camera because its happened with different lenses. I'm hoping to try the lenses on a different (1Dxx) camera in a couple of weeks so it will be interesting to see if it happens on that.
 
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