50D shutter speed

[FWG]

I have just purchased a 24 - 70mm f2.8L USM lens to go with my 50D which is letting me use much higher shutter speeds but I have noticed that when I take the shot the indicated speed in the camera view finder is much lower than the speed indicated by the metadata when I view the picture. The difference is not constant but can be as much as 100%!  I always use Camera Raw as the camera format. Why am I seeing this difference? The photos are correctly exposed so one part of me says "why worry" but I am puzzled.

[TotoEC · Accepted solution]

Your "Safety Shift" is enabled.

See pg 175 of your manual.  "When the subject's brightness changes erratically and the correct autoexposure cannot be obtained, the camera will change the exposure settiing automatically to obtain a correct exposure."

[cicopo]

Just a guess but is the camera set to auto ISO?

[FWG]

No, I set the ISO to suit the general light and subject.;

[TCampbell]

We might need an example image with metadata included.  

I'm wondering if you're thinking of focal ratio differences rather than shutter speeds.

The shutter is inside your camera -- not in the lens.  The available shutter speeds are the same regardless of which lens you use.  But the 24-70 f/2.8L may be allowing you to use a lower focal ratio.  The focal ratio is determined by the lens.  Changing a lens would have an effect on the focal ratios available.

What mode are you using when you meter and shoot?  (e.g. are you in full auto, Tv, Av, or M, etc.?)

[FWG]

Thanks Tim - I tend to use mostly Av or Tv and I am aware of the speed of the shutter being controlled by the camera. I did try to up load an image but this site does not like PSD or RAW files and to convert to JPEG would defeat the object.

The sympoms are very much like the camera saying "I know what you want but I have a better idea!". I should say in all cases where I have noted the speed difference I have been using Av. When I use Tv I get indicated apatures which do not exist in the normal increments. In these cases the appature indicated in the metadata are smaller than in the view finder. The photos are correctly exposed.

If I set both appature and speed manually the meta data agrees with the values I have set!

As I always shoot in RAW is this the "problem" that my PC programs make automatic adjustments. I use PSCC and Lightroom 5 to view and edit my photos.

[Skirball]

So you’re setting to either Tv or Av, with set ISO, and the free variable (e.g. shutter speed in Av) of what the camera estimates during sampling (half push of shutter) doesn’t match with the final photo as viewed on your computer?  Is that right?  What about if you review a photo in camera, I assume that shutter speed matches the meta-data on your comp?

And no, it's not RAW.  Your comp can't change the exposure values that the picture was taken at.  It can adjust the exposure, but it can't change the actual values.

[FWG]

For those who are trying to help me with this question. This morning I did a "controlled" test. ISO 3200 Tv 1/320 sec camera indicated appature f10.  I used spot metering. The camera and PC metadata both agreed! It is a dull day (as indicated by the data!).

On the days I noticed the difference it was very bright and I was using spot metering and I therefore wonder if at the moment I press the shutter  the camera adjusts for my hand shake as I move the focal point slightly. The pictures were of high contrast (yellow flowers against an out of focus green foliage back ground).

In an earlier post I wondered if the camera knows best - perhaps it does!

By the way the 24 - 70 f2.8 usm lens is stunning even if a bit expensive. I was previously using an 18 - 200 zoom which is very versatile but the new lens puts literally a different light on my pictures!

[TotoEC · Accepted solution]

Your "Safety Shift" is enabled.

See pg 175 of your manual.  "When the subject's brightness changes erratically and the correct autoexposure cannot be obtained, the camera will change the exposure settiing automatically to obtain a correct exposure."

[FWG · Accepted solution]

Thanks - I always tell my children to read the instructions!!!!!!!!!!