Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-01-2008, 04:01 AM   #1
Inactive Account




Join Date: Jul 2008
Location: Sydney, Australia
Posts: 9
K20d under exposing

I am finding my K20d is under exposing on some shots. I am shooting a lot with exposure compinsation at +1 or +2. Is any one else having this problem? if so how can I fix it? I have attached an example!

Attached Images
 
11-01-2008, 04:08 AM   #2
Senior Member




Join Date: Dec 2007
Location: Perth Australia
Photos: Gallery | Albums
Posts: 293
The exposure is fine if you used other than spot metering.
I would have used centre spot focussing with spot metering point tied to the focus point.
Focus on the the boats on the far side of the river. The sky will be almost white, the river will be very pale but the boats and the far bank will brighten up a lot.
Try multiple exposures using the 3 positions on your metering mode switch and try the different focussing modes.
It's easy to do this quickly with the K20D.
11-01-2008, 04:34 AM   #3
Veteran Member
ftpaddict's Avatar

Join Date: Jan 2008
Location: Yurp
Photos: Gallery
Posts: 4,669
This type of scene is notoriously difficult to meter. You can never get the sky and the boats properly exposed in a single shot, because of sensor limitations. This is common with all cameras; digital and film alike, and is not a shortcoming of the K20D alone.

Pentax has always had conservative metering; favouring highlights over shadow areas.
11-01-2008, 05:55 AM   #4
Veteran Member




Join Date: Nov 2006
Location: Hong Kong
Posts: 1,934
Your example shot is *perfectly* exposed!

QuoteOriginally posted by mattyjm Quote
I am finding my K20d is under exposing on some shots. I am shooting a lot with exposure compinsation at +1 or +2. Is any one else having this problem? if so how can I fix it? I have attached an example!
Just look at the histogram, both the shadows and highlights are not clipped and they both reach the extreme left and right of the histogram, for the overall brightness.

In fact, it preserves the highlight very well but without any room in the right which just means perfect exposure in your this case!

As for the individual colour channel, all RGB channels are not clipped and the WB is also right in your this pic and so do the metering accuracy as well (no colour channel is clipped).

Would be you show us more of your "underexposed" examples by the K20D? Also, what lens(es) did you use? Pls specify when you post more.

Attached Images
 
11-01-2008, 07:03 AM   #5
Veteran Member
jeffkrol's Avatar

Join Date: Sep 2006
Location: Wisconsin USA
Photos: Gallery
Posts: 8,435
Yeaaahh more FUD.....
Anyways I look at the mean. One thing to remember is that the camera has to boil all exposure measurements down to 1 number which it uses to set the f stop and shutter speed.
Each metering mode involves different math to arrive at that number (barring spot metering which should expose the spot metered at 110 in RGB scale.
Matrix metering is a separate beast all together. Center weighted is just that. Exposure of objects in the center take priority.
As to if your meter is functioning correctly, just take a moderately well illuminated monotone surface (a white or grey wall is preferred though any very light tone is fine).
Shoot the picture, and check the histogram. It should have a strong peak LEFT of dead center which will measure 90(older models)-115. As is your average in your shot.
ALWAYS remember these words from a Leica expert:
The exposure meter is calibrated to some clearly defined standards and the user needs to adjust his working method and his subject matter to these values. It does not help to suppose all kinds of assumptions that do not exist.'

Erwin Puts

BTW: please ignore RH. He seems to have some misguided notions on Pentax metering and the ANSI standards used to calibrate them......as well as a biased opinion in their regard.....
The camera looks to exposed fine if you understood what the camera was seeing.
There are some lenses that are a bit "dark" in their exposure ie old kit lens.
PLEASE look at this article:
CameraHobby - Digital Metering and Histograms
11-01-2008, 07:43 AM   #6
Veteran Member
creampuff's Avatar

Join Date: May 2007
Location: Singapore
Photos: Gallery
Posts: 3,955
There is nothing wrong with your camera.

Looking at the image that was posted, it is clear that the a large proportion of the scene is very bright (the sky). Naturally the camera's meter will be influenced by the bright portions to expose correctly for the sky but leaving the stands underexposed a little. The choice of metering mode can partially mitigate the problem but this can be avoided by mentally assessing the proportion of bright vs dark when looking in the viewfinder and making the appropriate EV compensation or manual adjustments.
11-01-2008, 07:52 AM   #7
Veteran Member
benjikan's Avatar

Join Date: Jan 2007
Location: Paris, France
Photos: Gallery
Posts: 4,312
Is this what you were looking for?

Ben
Attached Images
 
11-01-2008, 08:58 AM   #8
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
As everyone else has pointed out, this scene is not underexposed in any technical sense - the camera did a fantastic job of not clipping highlights while still preserving shadow detail, getting the scene to average a little darker than an 18% gray card - all the things a metering system is *supposed* to accomplish.

Of course, there is also little doubt that this is not the exposure you'd want. That's what exposure compensation is *supposed* to be used for. To say, "I *want* you to blow out the highlights in order to lighten the part of the scene I care about", or "I don't *want* this scene to come out looking as dark as a gray card on average - I want it to come out lighter".

Or, you could simply get the camera to meter off just the part of the scene you want to see nicely exposed. If you don't want the foreground darkened in order to preserve the sky, then don't include the sky in the scene when metering. Point at somethng darker, then hit AE-L to lock the exposure, then reframe and take the shot.

11-01-2008, 09:57 AM   #9
Senior Member




Join Date: May 2007
Location: Philadelphia, PA
Posts: 167
maybe I got all of you all wrong but I disagree:

If he used spot metering the scene should be brighter since the center is underexposed. If he used multi-segment metering the scene should be brighter as well- Isn't the whole point of multi-segment that the camera recognizes the kind of scene and than exposes it right? Here this would have been simple: bright sky on top with darker scene in the middle- the camera should have tried to expose the middle just right without blowing out to much of the sky - and failed by underexposing.

I have the same problem with my K20 as well, I tend to have the compensation set to +1. But than there are differences between lenses which makes everything more complicated.
11-01-2008, 10:11 AM   #10
Veteran Member
jeffkrol's Avatar

Join Date: Sep 2006
Location: Wisconsin USA
Photos: Gallery
Posts: 8,435
QuoteOriginally posted by chse Quote
maybe I got all of you all wrong but I disagree:

If he used spot metering the scene should be brighter since the center is underexposed. If he used multi-segment metering the scene should be brighter as well- Isn't the whole point of multi-segment that the camera recognizes the kind of scene and than exposes it right? Here this would have been simple: bright sky on top with darker scene in the middle- the camera should have tried to expose the middle just right without blowing out to much of the sky - and failed by underexposing.

I have the same problem with my K20 as well, I tend to have the compensation set to +1. But than there are differences between lenses which makes everything more complicated.
Not to get into the downfalls of Pentax Matrix metering, which is probably no where near advanced as N/C but 1) if the spot was on the water then it exposed it to 12% as it should. Same w/ the sky. If the spot was in the shadows then the sky would have turned completely white probably.
2) you have 3 major band bright/dark/bright and unless some LUT tells you it's "water scene" it will probably fail.
BTW, lately I have seen some images showing the meter coverage. It is nowhere near 100% as far as I can tell. I thik this adds to the lens differences particularily w/ fast glass.
11-01-2008, 11:56 AM   #11
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by chse Quote
If he used spot metering the scene should be brighter since the center is underexposed.
I rather doubt he used spot metering - he would probably have said so if he did. And of course, if he used spot metering, he may well have metered off the water, in which case this is pretty much correct.

QuoteQuote:
If he used multi-segment metering the scene should be brighter as well- Isn't the whole point of multi-segment that the camera recognizes the kind of scene and than exposes it right?
That's part of it - but you have to define what "right" means in this context. It doesn't mean "read the photographer's mind and interpret the scene the way he might have wanted". It means many other things that are much more objectively determinable, and among these is "under no circumstance allow any highlight to be blown, even if that makes the rest of the scene very dark". The clouds are on the edge of clipping already - any more exposure and they'd be blown. The metering performed this job admirably - as it pretty much always does.

QuoteQuote:
I have the same problem with my K20 as well, I tend to have the compensation set to +1.
Again, there is *not* a problem here - the camera is working exactly as it was designed to work, and indeed the way any book on photography will describe.

Rather than leaving positive compensation permanently enable, you should learn what types of scenes need it and apply compensation then only, otherwise you'll end up with overexposed scenes and/or blown highlights in scenes that don't require compensation. High contrasts scenes where the area of interest in the shadow are the *classic* textbook example of scenes that require positive compensation.

The other solution is to use substitute metering where you are careful to meter off the area of the scene you *want* to represent as a middle value. That's what I do - it seems far more natural than trying to guess how much compensation might be needed for a given highlight.
11-02-2008, 04:30 AM   #12
Inactive Account




Join Date: Jul 2008
Location: Sydney, Australia
Posts: 9
Original Poster
Thanks for your replys every one. Some of that technical stuff has just gone over my head!!!!! I am not convinced that you can call this normal. I have used Canon digital Slr's and have not had this problem. I generally take my pictures on center weighted metering as I did with that sample one I posted. I find I also have the same problem with nigh photos. I have attached more samples.
The nigh pic shutter speed was 30 sec. The area this image was taken, was much brighter than the image displays.
Attached Images
View Picture EXIF
PENTAX K20D  Photo 
View Picture EXIF
PENTAX K20D  Photo 
11-02-2008, 05:40 AM   #13
Veteran Member
jeffkrol's Avatar

Join Date: Sep 2006
Location: Wisconsin USA
Photos: Gallery
Posts: 8,435
QuoteOriginally posted by mattyjm Quote
Thanks for your replys every one. Some of that technical stuff has just gone over my head!!!!! I am not convinced that you can call this normal. I have used Canon digital Slr's and have not had this problem. I generally take my pictures on center weighted metering as I did with that sample one I posted. I find I also have the same problem with nigh photos. I have attached more samples.
The nigh pic shutter speed was 30 sec. The area this image was taken, was much brighter than the image displays.
Many older Canon DSLR's underestimated their "iso" by 1/2 stop. Therefore images exposed were ""brighter" then other camera models...
Not sure about the nightshot though.
Did you read the article I linked to?
Sample Nikon image in matrix Exposure comp. Your shots are very similar to the snow shot. White everywhere.

http://www.camerahobby.com/Digital_Metering.htm
Histogram is your friend.....Nikon on the left....
BTW: If you shoot in RAW you may be amazed (I was the first time) what you can "fix".

Last edited by jeffkrol; 11-02-2008 at 09:56 AM.
11-02-2008, 10:05 AM   #14
Veteran Member
morfic's Avatar

Join Date: Feb 2008
Location: San Antonio, TX
Photos: Gallery
Posts: 428
QuoteOriginally posted by jeffkrol Quote
Not to get into the downfalls of Pentax Matrix metering, which is probably no where near advanced as N/C but .
No but, i find the K20D Matrix Metering far more usable than the 30D's Evaluative Metering ever was. Just because you find other metering methods to work better for you, don't think Canon does a better job at the equivalent metering type, can't comment on Nikon as i never handled one, chances are it too is not perfect.
No metering mode takes away the responsibility to make decisions regarding what we perceive as the correct exposure, especially on highly contrasting scenes.
11-02-2008, 10:09 AM   #15
Veteran Member
morfic's Avatar

Join Date: Feb 2008
Location: San Antonio, TX
Photos: Gallery
Posts: 428
QuoteOriginally posted by benjikan Quote
Is this what you were looking for?

Ben
Nice save, and people think you can't work with jpegs.
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, dslr, k20d, photography
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K20d Constainly over exposing layfsphoto Troubleshooting and Beginner Help 7 04-26-2010 12:28 PM
Pentax Da*16-50 over exposing tunarudi Pentax SLR Lens Discussion 2 03-24-2010 08:27 AM
exposing to the right VincenTC Troubleshooting and Beginner Help 10 02-03-2010 02:21 AM
sigma 28-300mm over exposing? kauaiguy Pentax SLR Lens Discussion 2 09-18-2008 05:30 PM
exposing for RAW Gooshin Photographic Technique 15 03-25-2008 01:15 AM



All times are GMT -7. The time now is 03:52 PM. | 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