[tduell]

Hello All,
I have experienced some odd exposure metering recently with both the K-3 II and the K-1 when shooting white birds in bright sun.
In both instances each camera was fitted with the HD-D FA 150-450 + HD-DA AF rear converter 1.4x.
In the K-3 II case the camera was set for AF-C, spot metering, -0.3EV, Av mode, 800 ISO, and the camera set the shutter at 1/8000. The image was underexposed and required +0.98EV in post.
In the K-1 case the camera was set for AF-C, spot metering, -0.3EV, Av mode, 800 ISO, and the camera set the shutter at 1/8000. The image was underexposed and required +1.66EV in post.
Has anyone else experienced similar, and able to offer an explanation as to what might have caused this behaviour?
[edit] I should have added that in both cases the aperture was set at f/8.0 (wide open for this combination).
Cheers,
Terry

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Last edited by tduell; 03-04-2017 at 03:36 PM. Reason: Added info

[stevebrot]

spot metering

The image was underexposed and required +0.98EV in post.

spot metering

The image was underexposed and required +1.66EV in post.

I would have expected about +2 or +3 EV in Post. The expected spot-metered exposure of your sunlit white birds should yield a rendering close to "middle gray" if the "spot" was on the bird. That is how non-evaluative metering (e.g. spot and center-weighted) works.* As has been mentioned in other recent posts, spot metering is a specialized tool and requires some knowledge of how you wish to place exposure. In the future, you may want to read an 18% gray card in advance using M mode and center-weighted metering. Use the resulting setting until the light or subject changes.** Regular multi-segment (evaluative) metering in Av, Tv, or TAv mode may also provide an acceptable exposure with perhaps +1 EC.

BTW...why the -0.3 EC?


Steve

* The meters are calibrated to an 18% "middle" gray standard. As a result, white with texture (bird feathers, snow, beach sand, etc.) will result in an exposure 2-3 EV below what one may like.

** To test out a workable solution, I would suggest some backyard work with a clean white terrycloth towel. What works with the towel should work with white birds.

[tduell]

I would have expected about +2 or +3 EV in Post. The expected spot metered exposure of your sunlit white birds should yield a rendering close to "middle gray" if the "spot" was on the bird. That is how non-evaluative metering (e.g. spot and center-weighted) works.* As has been mentioned in other posts, spot metering is a specialized tool and may requires some knowledge of how you wish to place exposure. In the future, you may want to meter an 18% gray card in advance using M mode.


Steve

* The meters are calibrated to an 18% "middle" gray standard. As a result, white with texture (bird feathers) will result in an exposure 2-3 EV below what one may like.

Thanks for that explanation, and good to know that it isn't some corner case in the firmware that isn't handled correctly.
I asked because the reported behaviour is quite inconsistent with what I seen on many occasions in the past, but given your explanation, in those cases the metering spot may have missed the bright white.

Cheers,
Terry

[UncleVanya]

Do you have links to the files you can post? First I'd say white subjects can be hard for the camera to guess exposure for. The amount of the scene covered by the subject, the type of metering pattern used, and the fact the camera meters for gray conspire against accurate whites.

Since I can't see the shots yet I'm imagining them as bird filling the frame shots. In that case most of the time if shooting in Av mode I would expect that increasing - not decreasing - exposure would be the norm to attempt to correct the meter's assumption that the scene is gray. So if that is the case a -0.3EV biased the exposure the wrong direction. Second if I were you I'd turn the ISO down some if the lens is wide open and hitting 1/8000. You likely could get by with ISO 100 at 1/2000.

Lastly the adjustment amounts aren't large particularly if you take the -0.3 into account.

---------- Post added 03-04-17 at 05:59 PM ----------

Just saw you used spot metering. This fits the same model of exposure. The camera tried to turn the white birds gray. You need to spot meter and overexpose a touch without blowing out the highlights. This is where watching your histogram comes in. You may want to see if highlight protection is enabled also.

---------- Post added 03-04-17 at 06:00 PM ----------

This may help. How do I get proper exposure when photographing white subjects? - Photography Stack Exchange

[tduell]

Do you have links to the files you can post? First I'd say white subjects can be hard for the camera to guess exposure for. The amount of the scene covered by the subject, the type of metering pattern used, and the fact the camera meters for gray conspire against accurate whites.

No links, I haven't posted the photos anywhere.

Since I can't see the shots yet I'm imagining them as bird filling the frame shots. In that case most of the time if shooting in Av mode I would expect that increasing - not decreasing - exposure would be the norm to attempt to correct the meter's assumption that the scene is gray. So if that is the case a -0.3EV biased the exposure the wrong direction. Second if I were you I'd turn the ISO down some if the lens is wide open and hitting 1/8000. You likely could get by with ISO 100 at 1/2000.

The bird pretty much filled the frame in the K-1 case, and the well lit whites where a fair portion of the centre of the image in the K-3 II case.
The camera only hit 1/8000 for one shot in about 3 in one case and one in about 8 for the other, so that sneeked in and wasn't something easily caught, so from all the forgoing I assume that the spot was catching different parts of the subject for some of the shots

Lastly the adjustment amounts aren't large particularly if you take the -0.3 into account.

---------- Post added 03-04-17 at 05:59 PM ----------

Just saw you used spot metering. This fits the same model of exposure. The camera tried to turn the white birds gray. You need to spot meter and overexpose a touch without blowing out the highlights. This is where watching your histogram comes in. You may want to see if highlight protection is enabled also.

---------- Post added 03-04-17 at 06:00 PM ----------

This may help. How do I get proper exposure when photographing white subjects? - Photography Stack Exchange

Thanks for your help.

Cheers,
Terry

[stevebrot]

in those cases the metering spot may have missed the bright white.

No, the spot metering was right on the money. The expected behavior is for the meter to return an exposure value appropriate to render your birds at middle gray. What was "off" was the expectation that the metered exposure would place them at white.

I know, this is a little bit tricky in that we expect the exposure system to be smarter than we are. With the multi-segment evaluative metering it usually does a very good job, particularly with the K-3 and K-1 where the sensor can do actual scene analysis. However, when using spot or center-weighted metering you are thrown back about 40 years to the "good old days" where the exposure systems were much less "smart".

Sorry to say, but in its more primitive "dumb" modes the meter thinks that everything you point it at should be rendered towards the center of the histogram. The center represents the middle between black and white in a 11-stop scale, so-called middle or 18% gray.

To illustrate, take a white towel into full sun and compose a shot as follows:

• Av exposure mode
• Center-weighted meter mode
• 0.0 EC
• Towel fully filling the frame

Make an exposure and note that the histogram is centered and that the towel is rendered rather gray. Add +3 EV exposure compensation and redo the shot. Note that the histogram is shifted significantly to the right and the that towel is now rendered white and that its texture is still evident. Add an additional 1 EV exposure compensation and note that the texture is now gone and the highlights are clipping.

In some ways this is quite inconvenient in that dim subjects are often overexposed and bright subjects are often underexposed. In other ways, it is very cool in that one can leverage this behavior to use even an in-camera meter creatively. For example:

• I mentioned a gray card in the comment above. It is useful for white balance calibration and also for metering the incident light, the light striking the subject rather than the light reflected. Meter the gray card and hit the exposure lock -or- switch to M mode and simply set exposure off the gray card directly. When you take the photo, most of the elements of the scene will magically "fall" where they should be.Whites will be white and blacks will be black even if the scene has elements that might fool even evaluative metering.
• The histogram is useful when using the gray card in that it lets you know if there is "clipping" of both highlights and shadow. Use the histogram to adjust the exposure up or down as needed.
• If you need finer control, the spot meter is your friend in that it allows you to read a small part of the scene and place the exposure of that part where you want it. The easy example is a girl in a white dress with a background of dark foliage. Set exposure compensation at +3 EV, place the center spot on the dress, and press exposure lock. Take the photo and evaluate the histogram for highlight clipping. If present, back the EC off 1 stop. If you are interesting in the face and don't care about the dress, Caucasian skin is about +1 EV compensation and darker skin 0 EV.

Don't worry if this all sounds quite exotic. There are whole books on the subject.


Steve

[tduell]

No, the spot metering was right on the money. The expected behavior is for the meter to return an exposure value appropriate to render your birds at middle gray. What was "off" was the expectation that the metered exposure would place them at white.

I think you misunderstood what I was saying. There were a number of cases for each of the series of shots I have talked about, where the exposure was pretty much correct, so for those cases the spot must have missed the whites, otherwise, as per the above explanations, those images would have been underexposed as well.

Cheers,
Terry