[pundit]

I've noticed some odd behaviour when using video mode on my K5.

I always lock my exposure using the usermode/AE-L method.

For example I will ensure my shutter speed is 1/50th sec and aperture is set to manual (say F4) and with an ISO of say 400.

I always do a custom white balance and will spot meter a grey card in order to obtain the correct exposure based on a shutter speed of 1/50thsec.

After locking the exposure in usermode with AE-L and then switching to video mode the exposure remains locked and consistent while shooting regardless of any change in lighting.

There is one exception however.
If I rack focus between a light and dark object I notice a temporary shift in exposure as I refocus which then settles back to normal as soon as I stop focusing.

When changing lighting conditions have no effect on exposure when the exposure is locked with AE-L why would changing the focus cause a temporary exposure shift? I'm guessing it is the ISO that is changing.

Got me beat?

[enoeske]

I've noticed some odd behaviour when using video mode on my K5.

I always lock my exposure using the usermode/AE-L method.

For example I will ensure my shutter speed is 1/50th sec and aperture is set to manual (say F4) and with an ISO of say 400.

I always do a custom white balance and will spot meter a grey card in order to obtain the correct exposure based on a shutter speed of 1/50thsec.

After locking the exposure in usermode with AE-L and then switching to video mode the exposure remains locked and consistent while shooting regardless of any change in lighting.

There is one exception however.
If I rack focus between a light and dark object I notice a temporary shift in exposure as I refocus which then settles back to normal as soon as I stop focusing.

When changing lighting conditions have no effect on exposure when the exposure is locked with AE-L why would changing the focus cause a temporary exposure shift? I'm guessing it is the ISO that is changing.

Got me beat?

Most lenses change focal length ever so slightly when the focus changes. Assuming the aperture remains physically the same size, this could result in a change in exposure.

[pundit]

Most lenses change focal length ever so slightly when the focus changes. Assuming the aperture remains physically the same size, this could result in a change in exposure.

I understand there may be some change in EV with non constant aperture zooms but I'm having this occur with primes.

The exposure change does not occur if the near and far objects are similar in reflectivity. It only occurs when there is a reasonable contrast difference.

Rack focussing from a dark foreground object to a light background object and back again causes a brief change in exposure which then settles back once the rack focussing stops.

If, for example, I rack focus between two middle grey objects no change in exposure occurs. This indicates to me that this symptom is not directly caused by a change focal length/lens speed.

It seems that the camera briefly loses AE-L and resorts to auto mode then back to AE-L again once I finish rack focussing.