Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-02-2014, 01:26 PM   #1
Pentaxian




Join Date: Jul 2010
Location: Lyngby, Copenhagen
Photos: Albums
Posts: 742
The K-3 multisegment meter is too smart for me

Since getting a K-3 I've been giving the multisegment meter another chance. I didn't like the K-5 multisegment meter, I found it too unpredictable and just used centerweighted and exposure compensation instead.

The K-3 meter is better than the K-5 one, no doubt about that. It chooses brighter exposures that push further to the right of the histogram and it's clever about dark backgrounds and uneven lighting.

But then this happened the other day that left me scratching my head.

The following two crappy snapshots are taken within three seconds of each other, on shutter priority and auto ISO. I used the viewfinder, not live view.
Metering was multisegment, exposure compensation was 0 for both shots.

The framing, light and everything are essentially identical, yet the latter shot is 2 stops brighter than the first!

1/125, f/2.8, ISO 160


1/125, f/2.8, ISO 640


What is going on here? Did the multisegment metering see the face in shot 2 and decided to expose for it? Does the K-3 do that, like the Nikon D800?

If this behaviour is commonplace (I've seen it twice now), I think I'm going back to centerweighted.

Regards,
--Anders.


Last edited by asp1880; 09-02-2014 at 01:28 PM. Reason: clarified viewfinder use.
09-02-2014, 01:38 PM   #2
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 41,603
The K-3 doesn't have face detection through the viewfinder, so I think it's just the scene as a whole that affected the metering result. After all, the camera has no way of knowing what you want to ensure is properly-lit, so it basically has to guess based on some simple heuristic.

Adam
PentaxForums.com Webmaster (Site Usage Guide | Site Help | My Photography)



PentaxForums.com's high server and development costs are user-supported. You can help cover those costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

09-02-2014, 02:40 PM   #3
Pentaxian




Join Date: Jun 2009
Location: GMT +10
Photos: Albums
Posts: 10,720
QuoteOriginally posted by Adam Quote
The K-3 doesn't have face detection through the viewfinder
While it may not have proper face detection via PDAF, there is a possibility that the metering system could be programmed to detect skin tones.

In these pictures, I think the issue is that the subject is mobile and dynamic, as is the lighting.

The histograms for both photos would be interesting.
09-02-2014, 02:53 PM   #4
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 26,612
QuoteOriginally posted by Adam Quote
The K-3 doesn't have face detection through the viewfinder, so I think it's just the scene as a whole that affected the metering result.
I agree, though I too believe that there is logic in place based on color mix and also on small-scale contrast mix. I have found it to be very sensitive to small changes in framing with some subjects, though the result is usually nicely acceptable.


Steve

09-02-2014, 03:02 PM   #5
Pentaxian
aleonx3's Avatar

Join Date: Jul 2007
Location: Brampton, Ontario
Photos: Gallery | Albums
Posts: 3,880
If you have this setting "Link AE to AF point" set to ON for multi-segment metering, then the exposure may change due to the focus point changed (in this case, perhaps, the face).
09-02-2014, 03:08 PM   #6
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 26,612
QuoteOriginally posted by asp1880 Quote
What is going on here? Did the multisegment metering see the face in shot 2 and decided to expose for it?
According to the exif the image is an in-camera JPEG. Face Detect was turned ON with one face detected at a location appropriate to the subject. That might explain it.


Steve
09-02-2014, 03:28 PM   #7
Pentaxian
Tjompen1968's Avatar

Join Date: May 2012
Location: Norrköping, Sweden
Photos: Gallery | Albums
Posts: 1,307
QuoteOriginally posted by stevebrot Quote
According to the exif the image is an in-camera JPEG. Face Detect was turned ON with one face detected at a location appropriate to the subject. That might explain it.


Steve
May I ask what program you are using for reading the exif?
09-02-2014, 05:09 PM   #8
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 26,612
QuoteOriginally posted by Tjompen1968 Quote
May I ask what program you are using for reading the exif?
Phil Harvey's ExifTool.


Steve

---------- Post added 09-02-14 at 05:39 PM ----------

Hmmm...

I have been able to replicate "face detect on with live view off", but don't see that it makes any difference in exposure.


Steve

09-02-2014, 06:30 PM   #9
Site Supporter




Join Date: May 2012
Location: Adelaide
Photos: Gallery | Albums
Posts: 1,085
QuoteOriginally posted by stevebrot Quote
Hmmm...

I have been able to replicate "face detect on with live view off", but don't see that it makes any difference in exposure.

Steve
It would be sensible programming that, if face detect was switched on, metering would give priority for correctly exposing the area it detected as representing the face. Afterall, if focus was asked to be prioritised to a face, then it would be logical Captain for the user to also want correct exposure for the face to a priority. In shot 1, with only one eye visible, this would have been unlikely to have been identified as a face so the metering most likely defaulted to prioritising general protection of highlights and gave a shorter exposure.
09-02-2014, 06:59 PM   #10
Pentaxian
gmans's Avatar

Join Date: Dec 2012
Location: Hunter Valley,NSW, Australia
Photos: Gallery
Posts: 1,469
T
QuoteOriginally posted by asp1880 Quote
The following two crappy snapshots are taken within three seconds of each other,
The first shot looks good to me, the exposure is very good, the soft window light on the boys face is a great effect. The second shot is really blown and I have had similar experiences with my K3 overexposing. I thought it was something to do with fast lens and centre weight compensation but only guessing.
09-02-2014, 07:35 PM   #11
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 26,612
QuoteOriginally posted by southlander Quote
It would be sensible programming that, if face detect was switched on, metering would give priority for correctly exposing the area it detected as representing the face. Afterall, if focus was asked to be prioritised to a face, then it would be logical Captain for the user to also want correct exposure for the face to a priority. In shot 1, with only one eye visible, this would have been unlikely to have been identified as a face so the metering most likely defaulted to prioritising general protection of highlights and gave a shorter exposure.
That is what I would have thought, but that is not what I am seeing. It makes no difference unless shot in live-view. In live view with face recognition enabled, exposure is tailored to the face. I am not seeing that when live view is turned off.


Steve
09-02-2014, 09:30 PM   #12
Site Supporter




Join Date: May 2012
Location: Adelaide
Photos: Gallery | Albums
Posts: 1,085
Steve, on reflection, I must admit that I don't know how a dslr would be able to perform face detection with the mirror down and phase detect focus in use. Phase detect has nowhere near enough measurement points to work out whether there was a face in the frame. The 77000 point exposure module might still be struggling with enough sample points. Liveview on the other hand has the full readout of the sensor to work with. I've not thought too much about face detection algorithms - does it seek patterns that suggest eyes and/or significant contiguous areas of certain colors that might suggest skin, I don't know. Curious now and off to do some research on this question.

But back to the OP's question, if face detection is not involved, I'd be inclined to think about technique, specifically whether the OP was focusing and then recomposing while the shutter button was half pressed. This could lead to unexpected exposure results from shot to shot if the camera is set up to lock exposure on the half press.
09-03-2014, 01:19 AM - 1 Like   #13
Veteran Member




Join Date: Nov 2006
Location: Norway
Photos: Gallery
Posts: 385
QuoteOriginally posted by southlander Quote
Phase detect has nowhere near enough measurement points to work out whether there was a face in the frame.
This is the image reduced to what the lightmeter in K-3 see. It is 86000 pixels.

09-03-2014, 05:32 AM   #14
Site Supporter




Join Date: May 2012
Location: Adelaide
Photos: Gallery | Albums
Posts: 1,085
Reading the K-3 manual, it looks as though Face Detect autofocus is only available in Live View (as Adam indicated in his response). Thus it would seem we can discount face detect as having any influence on the OP's experience with the two posted images. I'm back to pondering the AE-L or Link AE with AF Point settings on Custom settings area of the camera's menu. Or whether the differences in lighting between shot 1 and 2 was simply enough to trigger the camera to go down a different logic path (eg in shot 2 the proportion of very dark to very light was enough for the camera to assume a backlit scene where as in shot 2, it didn't see enough of this to trigger the back lighting logic. Overall, I'd say the lighting found in the OP's situation was not easy for a camera to determine what was required and would be the sort of scene where exposure bracketing could be helpful..
09-03-2014, 05:46 AM   #15
Site Supporter
savoche's Avatar

Join Date: Jun 2011
Location: Lowlands of Norway
Posts: 7,954
QuoteOriginally posted by StigVidar Quote
This is the image reduced to what the lightmeter in K-3 see. It is 86000 pixels.
Yes, I was wondering, too, if there could be a metering face detection algorithm - not at all related to the live view focus face detection.

Pure speculation, of course.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, compensation, d800, detection, dslr, entries, exif, exiftool, exposure, f/2.8, focus, iso, k-3, k-3 multisegment meter, k-5, k3, labels, max, meter, multisegment, pentax k-3, shot, steve, subject, tags, view
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: Hahnel Smart Charger for K-10D or K-20D Sigmoid Sold Items 2 04-04-2014 06:52 PM
Is the k511s too much camera for the 16-45 abd the 55-300? Flyfisher22 Pentax K-5 4 02-10-2013 11:59 PM
How Good is the Meter in the ME? zx-m Pentax Film SLR Discussion 4 05-27-2010 11:28 AM
Is my equipment too good for me RHW698 Troubleshooting and Beginner Help 27 05-17-2010 02:23 PM
Are we too odd as well as too few or is it just me? jptreen Pentax DSLR Discussion 72 10-09-2009 02:59 AM



All times are GMT -7. The time now is 10:31 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top