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11-03-2020, 08:24 AM   #1
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TAv Priority - overexposure: AE/AF Point Lock?

Hi everyone,

I've been using TAv shutter speed and f stop priority mode a lot when taking photos outside during changing light conditions and activities like hiking or sailing where I can't always stop and take my time with fully manual exposure settings.

It's worked great on very bright days and in shade.
However, I used it on a cloudy, yet bright late afternoon (as sun was setting) and found a lot of my photos where the grey, pretty sky was in my background and dark rock was in my foreground, the ISO got set to 3200 and the resulting overexposure and additional noise was very disappointing!

I have my AE/AF points set in menu to be "linked", and AF set to center spot.

I like having my AF point being central so I can train my camera around, hit AEL button or half press to focus, switch into manual focus or hold, and the re-frame to shoot. I find moving the focus point with the 4-way buttons very arduous.

Can someone let me know if de-linking the AE/AF points would help, and if there's a way to set AE point to scene average while retaining the AF point as a central spot? I can only seem to find the settings for the AF type - perhaps because the AE/AF link setting is still set to YES?

Thank you!

11-03-2020, 08:30 AM   #2
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What settings are you using for metering and white balance?

Spot or center metering could cause that, multisegment should not. I mention white balance even though it won't really cause your problem, but it can be helpful using multi auto WB on some situations like that, more when you have multiple light sources, like full sun on the right, and shaded sun on the left.

Last edited by ramseybuckeye; 11-03-2020 at 08:46 AM.
11-03-2020, 09:00 AM   #3
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The fact that your images are overexposed suggests to me that you are focussing on (and metering) the darker foreground. As a start, I think that you should try decoupling AE and AF. Use the AE/AF button for AE lock only and use multi-segment metering for AE. See what that does for your images.

Another approach would be to keep your settings as you currently have them but set your AE metering to Spot mode. Set exposure compensation to -2 or -3. Focus and meter as you have done with AE and AF coupled. This method will ensure that your darker foreground won't be overexposed.
11-03-2020, 10:01 AM   #4
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QuoteOriginally posted by Emirena Quote
I have my AE/AF points set in menu to be "linked", and AF set to center spot.
Unlink them

QuoteOriginally posted by Emirena Quote
I like having my AF point being central so I can train my camera around, hit AEL button or half press to focus
Once you hit the AEL button you are locking the exposure.

Change the setting to Matrix metering and try that out. I do use spot metering occasionally, but to get a number of readings and average them, especially when using ND Grad filters.

11-03-2020, 12:31 PM   #5
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QuoteOriginally posted by Emirena Quote
the ISO got set to 3200 and the resulting overexposure and additional noise was very disappointing!
Yes, that is one of the hazards of using TAv mode. Edit: We can blame the noise on TAv mode setting the highish ISO. The overexposure was probably metering.

QuoteOriginally posted by Emirena Quote
Can someone let me know if de-linking the AE/AF points would help, and if there's a way to set AE point to scene average while retaining the AF point as a central spot?
The default is to have the two separate. If you are set to have them linked, uncouple them using:
menu --> C1 --> 5 Link AE and AF point
As for metering choices, they run as follows:
  • Multi-segment (exposure based on scene evaluation over 77 segments)
  • Center weighted (brightness of the scene is averaged with emphasis given to the center portion)
  • Spot (exposure based on the center only)
My experience is that multi-segment works well for almost everything. Center weighted is good if your general subject is more in the center and stuff away from center might be present that will skew the metering. Spot metering is a specialized tool and is not appropriate for general photography. I think it is safe to say that the majority of help requests on this site related to poor exposure can be traced to use of spot metering or linking AE to the AF point.


Steve

(...uses spot metering to place exposure to a particular value when using M mode and never for anything else...)

Last edited by stevebrot; 11-03-2020 at 02:06 PM.
11-03-2020, 01:04 PM   #6
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QuoteOriginally posted by stevebrot Quote
Yes, that is one of the hazards of using TAv mode
Just to clarify Steve (for others, not you.....I know you know this), while noise from high ISO is one of the hazards of the TAv mode in poor light, overexposure is not.

Although both over/under exposure are possible in this mode, you are more likely to see underexposure if you have set a limit for AUTO-ISO in your camera and you are using too optimistically a setting for shutter/aperture.

TAv mode is the same as Manual mode, but with auto ISO. If the selection for shutter speed and aperture is not thought out properly, you will get poor results.
11-03-2020, 02:04 PM   #7
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QuoteOriginally posted by pschlute Quote
Just to clarify Steve (for others, not you.....I know you know this), while noise from high ISO is one of the hazards of the TAv mode in poor light, overexposure is not.
Thank you! The overexposure was probably due to the exposure settings based on how the scene was metered.


Steve
11-03-2020, 02:12 PM   #8
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QuoteOriginally posted by pschlute Quote
Although both over/under exposure are possible in this mode, you are more likely to see underexposure...
You have touched on an interesting aspect of TAv. The low end limit even without limiting range, is fairly easy to attain when shooting wide open with a fast lens. The display will blink if ISO 100 is not low enough and will simply overexpose if the user does not notice and takes the shot anyway.


Steve

11-03-2020, 02:53 PM   #9
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QuoteOriginally posted by stevebrot Quote
You have touched on an interesting aspect of TAv. The low end limit even without limiting range, is fairly easy to attain when shooting wide open with a fast lens. The display will blink if ISO 100 is not low enough and will simply overexpose if the user does not notice and takes the shot anyway.


Steve
Correct.

As I tend to use this mode mainly for moving subjects (my dogs in the garden), I am usually using a long lens and setting a reasonably fast shutter speed combined with a medium aperture in order to capture their movement with. This invariably leads to a high ISO which can often bump against any limit I have set in camera. If typical usage for this mode is anything like mine, I suggest under-exposure is more likely to be seen rather than overexposure. Although both are possible of course.
11-03-2020, 06:44 PM   #10
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QuoteOriginally posted by pschlute Quote
Correct.

As I tend to use this mode mainly for moving subjects (my dogs in the garden), I am usually using a long lens and setting a reasonably fast shutter speed combined with a medium aperture in order to capture their movement with. This invariably leads to a high ISO which can often bump against any limit I have set in camera. If typical usage for this mode is anything like mine, I suggest under-exposure is more likely to be seen rather than overexposure. Although both are possible of course.

This my experience as well.
11-06-2020, 02:34 PM   #11
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For what it is worth I tend to use manual and have in mind a range of f stops for various conditions so I can roll the wheel while I am shooting. The beauty of digital is that I can practice this at not cost!
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