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02-19-2008, 01:47 PM   #1
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exposure test.

I was having some issues with exposure and saw a test where they measure the exposure using a grey chart:

RiceHigh's (Pentax) DSLR and Lens Measurbation Page on Exposure Accuracy and More..

Any ideas? I don't want have to send the camera (K10d) in if it don't need to be and wasn't sure how accurate this test was

02-19-2008, 01:49 PM   #2
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Don't listen to anything RiceHigh says first off. What is your issue? Is the camera consistently under or over exposing? If so, this isn't a big problem really, just use the EV compensation to adjust for it.
02-19-2008, 01:58 PM   #3
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QuoteOriginally posted by jjfdvm72 Quote
I was having some issues with exposure...
What issues? In what way is the camera behaving contrary to your expectations?

Will
02-19-2008, 03:41 PM   #4
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QuoteOriginally posted by jjfdvm72 Quote
I was having some issues with exposure and saw a test where they measure the exposure using a grey chart:
Just take a picture of a white wall (any uniform light color will do actually) and see if the peak on the histogram is LEFT of dead center. This is where the meter is calibrated to. If you want a number, it is 110 (+/- 10 points). The rest is up to you.


QuoteOriginally posted by jjfdvm72 Quote
Any ideas? I don't want have to send the camera (K10d) in if it don't need to be and wasn't sure how accurate this test was
Are you trying to continue this thread????
https://www.pentaxforums.com/forums/pentax-dslr-discussion/19187-underexposed-pics-k10d.html

What parts or part aren't you satisfied with????????
http://doug.kerr.home.att.net/pumpkin/Exposure_metering_18.pdf
Now, where can we get such a gray card of 12.8% reflectance? It
isn’t easy. But we can easily acquire a gray card whose reflectance is
18%—all photo supply houses sell them. If we follow the scenario
above with such a card as our “metering target”, the exposure1
recommended or set by the metering system will be 1/2 stop less than
needed to produce the effect we seek. (The greater illuminance seen
from the 18% card will cause the metering system to feel that a lesser
exposure1 is required than we need, by 1/2 stop.)
So, after we see the exposure1 that the metering system recommends

CameraHobby - Digital Metering and Histograms
Most of us know that in-camera meters are calibrated for a middle-tone grey (which could be either 18% a la Ansel Adam's Zone metering and Kodak grey cards, or it could 12 or 13% per ANSI standards, but this is a debate for another time). What this means is that if your subject matter is predominantly of a middle grey value, your in-camera meter will provide perfect exposure. However, if your subject matter is not predominantly of a middle grey tone, your in-camera meter will err and it will attempt to still render the scene or subject as middle grey.
CameraHobby - e-Book on Metering, Chapter 3
Just HAD to add this chart......Thanks to Iliah Borg...
http://pochtar.com/KodakQ13Values.htm
Re: Testing your exposure metering: Nikon D300/D200/D100 Forum: Digital Photography Review


Last edited by jeffkrol; 02-19-2008 at 08:22 PM.
02-19-2008, 05:32 PM   #5
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QuoteOriginally posted by jjfdvm72 Quote
I was having some issues with exposure and saw a test where they measure the exposure using a grey chart:

RiceHigh's (Pentax) DSLR and Lens Measurbation Page on Exposure Accuracy and More..

Any ideas? I don't want have to send the camera (K10d) in if it don't need to be and wasn't sure how accurate this test was
Haven't we been here before (as pointed out by Jeff)? I like Ken Rockwell's description of "Measurebation" (see Bottom Level 1) Seven Levels of Photographers 2005 KenRockwell.com

Seriously, no DSLR is this hard to use. The k10d is not a finicky piece of equipment that constantly has to be tweaked and calibrated to get a good exposure. Get the thing checked out so you can start enjoying it.
02-19-2008, 06:38 PM   #6
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QuoteOriginally posted by jjfdvm72 Quote
I was having some issues with exposure and saw a test where they measure the exposure using a grey chart:

RiceHigh's (Pentax) DSLR and Lens Measurbation Page on Exposure Accuracy and More..

Any ideas? I don't want have to send the camera (K10d) in if it don't need to be and wasn't sure how accurate this test was
I have found that I can determine best exposure by using the LCD with the blinkies turned on. The best exposure seems to be with just one or two specular highlights blinking. This seems to retain the most detail in the image. I suspect that I am just using the camera to use ETTR metering. Once you have determined if the meter is off the correct exposure for your needs, you can just dial in exposure compensation to bring the exposure where you want it.

Good luck and happy shooting!
02-20-2008, 10:24 AM   #7
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I'm good at reading the histogram but I've yet to use the 'blinkies'.. The K10D is a very full-featured camera and although I have taken some amazing photos with it, there always seems to be one more thing to explore within it. I'm gonna mess with the blinkies this week.
02-20-2008, 10:31 AM   #8
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QuoteOriginally posted by Canada_Rockies Quote
I have found that I can determine best exposure by using the LCD with the blinkies turned on. The best exposure seems to be with just one or two specular highlights blinking.
Yes, the blinking feature is, in my opinion, more useful than the histogram on the camera.

Will

02-20-2008, 10:31 AM   #9
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QuoteOriginally posted by travis_cooper Quote
Don't listen to anything RiceHigh says first off. What is your issue? Is the camera consistently under or over exposing? If so, this isn't a big problem really, just use the EV compensation to adjust for it.
Totally agreed on all points.

Explain more and maybe a shot or 2 as examples. We'd need to know the lenses you have seen this with as well. Older K mount or M42's will need a little understanding to get the best out of them. There are so many variables that more info is needed. 97% of the time, it's just not using or understanding the camera correctly.
02-20-2008, 11:52 AM   #10
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QuoteOriginally posted by jjfdvm72 Quote
I was having some issues with exposure and saw a test ...(snip)...

I agree with Travis. You need to understand that very little RiceHigh says is based on accurate, consistent, or reliable method. For example, the "test chart," on the page you linked to, could vary dramatically (color, etc) depending on the printer used. And RiceHigh admits this, in his website disclaimer, by saying the "author has no responsibility of any kind on the accuracy or whatsoever on all the information and data provided here." In other words, he posts a bunch of negative junk and then denies any responsibility for it.

And I also agree with Travis, Will, Peter, and others, who asked you to provide details so the forum members here can work with you to solve any perceived issues. I suspect that will turn out to be a far more accurate and reliable method of gaining assistance.

stewart
02-20-2008, 12:36 PM   #11
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As jeffkrol pointed out earlier in this thread, this is a continuation of the following thread where there are many sample pictures posted:

https://www.pentaxforums.com/forums/pentax-dslr-discussion/19187-underexposed-pics-k10d.html
02-20-2008, 01:55 PM   #12
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I did post a previous thread about my perceived problems with exposures and did not mean to write a duplicate thread. Sorry if it turned out to be redundant in contents. I basically was curious on how different K10D would perceive the same image in terms of exposure, but understand that this could be affected by the printers ability to print the colors.

I do have some pics on the other link that show what I was talking about. I didn't posted b/c I didn't want to come off like I was posting the same thread twice, so I wanted to see the response about the "Exposure test"

Sorry if the thread seemed redundant...
02-21-2008, 03:09 AM   #13
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just have to say, in regards to rh GG Ignore List
02-21-2008, 06:35 AM   #14
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To get the thread back on track, if you are having exposure issues (and I will not dwell on whether the K10D has them or not) you need to perform a series of tests to understand how each of your lenses work.

start by selecting a uniform field of view, grey to white in color. I find a paved road or concrete path/wall work best.

Take a series of exposures with all settings in the camera set to neutral (JPEGS are OK for what we are doing). The series of photos are at each F stop on each lens, with the camera metering (either manually or automatically) to set the shutter speed.

Divide the photos with a 3x3 grid (i.e. into 9ths) and with the center 9th, measure the average grey scale value.

Plot grey scale vs f stop for each lens.

With all camera settings neutral, the camera should meter int eh 110-120 range for grey scale, and each stop is about a grey scale value of 45.

This will tell you exactly how your camera is performing with each lens.

Notes:
1) My experience is that the K10D will meter and expose correctly using AE lenses, but will have problems with non AE lenses, where at F1.4 it will under expose by 1 stop, and this moves to over exposure of 1 to 1.5 stops by F5.6, over exposure of 2 stops by F 11 and a gradual improvement to between 1 and 1.5 stops by f22/32.

2) From experience, I have found that the K10D has relitively linear response (grey scale), between a reading of 25 and 230 with 5 stops of exposure lattitude contained in this region, with 1.5-2 stops non linearly compressed into the top and bottom 25 grey scale values
The center region is compressed to 4 stops of lattitude with contrast set to max, and 6 stops of lattitude in this region with contrast set to minimum.

Once you understand how your camera works, you are then in a position to just go out and take photos.
02-21-2008, 07:56 AM   #15
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More Information

QuoteOriginally posted by jjfdvm72 Quote
I was having some issues with exposure and saw a test where they measure the exposure using a grey chart:

RiceHigh's (Pentax) DSLR and Lens Measurbation Page on Exposure Accuracy and More..

Any ideas? I don't want have to send the camera (K10d) in if it don't need to be and wasn't sure how accurate this test was
I suppose you have been facing the underexposure problem of your camera but I'm afraid this tendency is just normal for ALL Pentax DSLRs (same or different models AND same or different units) which I have used since 2003.

Here are more test samples and evidence that re-verify and re-confirm the case:-

RiceHigh's Pentax Blog: Underexposure Tendency of K10D and K100D

As for the solution to the problem, as I have said in my homepage, is to use fixed pattern metering and apply proper +EV compensation for each of the Pentax lenses you own and know about the compensation value for each of the conditions, e.g., outdoor or indoor, daylight or tungsten etc.

Below is a direct link to the measured test data for the K100D for its exposure accuracy, I found that the Centre-weighted average metering is the most consistent in results. As such, if it will be more easy to apply a fixed EV compensation without worrying to change the value significantly from frame to frame so oftenly if you use the CWA metering:-

RiceHigh's Pentax K100D Full Review

In short, as a few others responses have pointed out, you need to ADAPT for your DSLRs. Frankly, if you have a Pentax film SLR or a Canon / Nikon DSLR, the results would be more close to be correct or at least more acceptable by default in different situations or with different lenses and life will be much easier as such when much less compensation and adjustment works are required *during* shooting.

Another way to "solve" the problem is to shoot RAW and then compensate when convert, but you will never get the best image with more grey details and least noise if you do so, just see again the famous Luminous Landscape article below:-

Expose Right
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