EOS Rebel T8i Av Mode photos feel overexposed compared to Manual

[stevet1]

I have run across a situation that has me puzzled. I have seen this on previous occasions.

I have a Canon T8i. The lens is an 18-135mm IS USM.

When I take a shot in Av mode, my pictures seem to come out (to my eyes anyway) slightly overexposed or washed out. If I take the exact same picture in Manual Mode, they are slightly darker and seem fuller.

Here's an example in Av Mode. The settings are 1/200th's of a second, f/9, Auto ISO at 500. The focal length is roughly 90mm. No post processing has been done on these other than to downsize them for web publishing purposes.

.

I went back into Manual Mode and dialed in these exact same settings 1/200, f/9. Auto ISO of 500.

If I go back to Av Mode and dial in a -1/3 stop of negative exposure compensation, I get this:

I don't know what to make of this.

Steve Thomas

[johnrmoyer]

you might check whether the "auto lighting optimizer" setting makes a difference https://cam.start.canon/en/C002/manual/html/UG-06_Shooting-1_0120.html  "

• If the effect of Auto Lighting Optimizer is too strong and results are not at your preferred brightness, set to [Low] or [Disable].

"

Another setting to check is "highlight tone priority" https://cam.start.canon/en/C002/manual/html/UG-06_Shooting-1_0130.html   "

Caution

• Noise may increase slightly.
• The available ISO range starts at ISO 200. Expanded ISO speeds cannot be set.
• [Enhanced] is not available when recording movies.
• With [Enhanced], results in some scenes may not look as expected.

"

[p4pictures]

Steve, please check what setting you have for the Auto Lighting Optimiser (ALO). With the camera default settings, ALO is automatically disabled when shooting in manual exposure mode. However the default for P, Tv, AV modes is the ALO is enabled with the standard setting. ALO automatically is applied to the JPG images in Av mode, and one of its functions is to adjust contrast and lighting. This is most likely the cause of your differences. You can choose to use ALO in manual mode if you wish, or also disable it in all modes.

Another potential setting that can change the look of an image is the Picture Style. When the default AUTO picture style is used the camera makes a decision about which of the Standard, Landscape and Portrait picture styles to apply. Picture styles also affect sharpness, contrast and colour rendition. I suggest you set the camera to the standard or even Fine Detail Picture style to eliminate the potential inconsistency here.

[stevet1]

John and Brian,

Thanks. ALO and Highlight Tone Priority are disabled in all occasions.

Brian, I use the Standard Picture Style, and I see this affect even in the RAW files.

I don't have another camera to compare this to, or if it's just a feature of the T8i.

Steve

[johnrmoyer]

One more to check is peripheral illumination correction

Good luck

[stevet1]

I pulled up the Exif files for both the AV RAW shot and the Manual RAW shot, and there is one line in the middle where, for Av shot it says, "Exposure Mode: Auto:, but for the Manual shot, it says, "Exposure Mode: Manual"

Av shot

FocalPlaneResolutionUnit - Inch

CustomRendered - Normal process

ExposureMode - Auto

White Balance – Manual:

SceneCaptureType – Standard

------------------------------------------------------------

Manual shot:

FocalPlaneResolutionUnit - Inch

CustomRendered - Normal process

ExposureMode - Manual

White Balance - Manual

SceneCaptureType - Standard

All other readings are identical.

I do not know if this has some kind of bearing.

Steve

[deebatman316]

Av (Aperture Priority) Mode is a semi Automatic mode in which the camera selects the shutter speed and ISO (If set to Auto). You select the aperture ie F/8 for instance. The exposure will be automatic. So it’s not incorrect. Full Manual is where you set the exposure manually ie the ISO, Shutter Speed and Aperture to get the proper exposure. 

[johnrmoyer]

It sounds to me like "exposure mode" is likely the answer.

Recent versions of exiftool will do a diff between two CR2 files. exiftool is capable of dumping most of the metadata and might show a difference in exposure between two photos. For example:

exiftool /Volumes/EOS_DIGITAL/DCIM/100CANON/IMG_8494.CR2  -diff /Volumes/EOS_DIGITAL/DCIM/100CANON/IMG_8496.CR2  | less 

======== diff < /Volumes/EOS_DIGITAL/DCIM/100CANON/IMG_8494.CR2 > /Volumes/EOS_DIGITAL/DCIM/100CANON/IMG_8496.CR2
< [System]        File Name                       : IMG_8494.CR2
>                                                 : IMG_8496.CR2
< [System]        File Modification Date/Time     : 2025:01:30 13:58:28-06:00
>                                                 : 2025:01:30 14:01:54-06:00
< [System]        File Inode Change Date/Time     : 2025:01:30 13:58:28-06:00
>                                                 : 2025:01:30 14:01:54-06:00

...

< [ExifIFD]       Exposure Time                   : 1/60
>                                                 : 1/100
...
< [ExifIFD]       Shutter Speed Value             : 1/64
>                                                 : 1/99
...
< [Canon]         Measured EV                     : 9.38
>                                                 : 10.00
< [Canon]         Target Exposure Time            : 1/64
>                                                 : 1/102
< [Canon]         Camera Temperature              : 23 C
>                                                 : 24 C
< [Canon]         Exposure Time                   : 1/64
>                                                 : 1/102
< [Canon]         Exposure Time                   : 1/64
>                                                 : 1/99
...
< [Canon]         AF Points In Focus              : 37,38,40,41,42
>                                                 : 13,14,20,21,28
< [Canon]         Measured RGGB                   : 596 1024 1024 612
>                                                 : 597 1024 1024 608
< [Canon]         WB RGGB Levels As Shot          : 1686 1024 1024 1739
>                                                 : 1689 1024 1024 1742
< [Canon]         WB RGGB Levels Auto             : 1686 1024 1024 1739
>                                                 : 1689 1024 1024 1742
< [Canon]         WB RGGB Levels Measured         : 1686 1024 1024 1739
>                                                 : 1689 1024 1024 1742
< [Canon]         Peripheral Lighting             : On
>                                                 : Off
< [Canon]         Peripheral Lighting Setting     : On
>                                                 : Off
< [Canon]         Peripheral Illumination Corr    : Off
>                                                 : On
...

[stevet1]

Just for the heck of it, I took a couple of pictures using a fixed ISO, rather than an Auto ISO.

While there was a sight difference (and I mean very slight) between the two pictures, it wasn't nearly as dramatic as using Auto ISO.

Steve Thomas