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02-26-2015, 12:07 AM   #1
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Control exposure on Pentax DSLRs?

For K3 : "TTL open aperture metering using 86K pixel RGB sensor"

For K-2S: "TTL open-aperture 77 segment metering "

What does each?
Is it a significant quality difference between these two ways of measuring exposure?
Is it more precise the K3 control exposure system?

02-26-2015, 12:54 AM   #2
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QuoteOriginally posted by edri Quote
For K3 : "TTL open aperture metering using 86K pixel RGB sensor"

For K-2S: "TTL open-aperture 77 segment metering "

What does each?
Is it a significant quality difference between these two ways of measuring exposure?
Is it more precise the K3 control exposure system?
Yes, it's a higher-end metering system. The K-3's is generally more accurate, and it delivers superior white balance, especially at night.

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02-26-2015, 01:53 AM   #3
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This illustrates the difference between the 86k segment RGB metering and 77 segment grayscale metering.
But it also depends on how well the software in the camera can interpret what the metering is seeing.

02-26-2015, 02:08 AM   #4
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TTL open-aperture 77 segment metering

it's a zone metering system, you can think at it so: the image is divided in 77 zones pattern for measuring exposure

TTL open aperture metering using 86K pixel RGB sensor

RGB sensor can better recognize your scene, the colors, the brightness, has a great precision, can make accurate scene analysis, etc

since the k3 is very accurate in measuring exposure, I think that firmware interpret well what the metering is seeing...

02-26-2015, 04:48 AM   #5
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Is the difference noticeable when using spot metering and center weighted metering?
02-26-2015, 06:11 AM   #6
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To my taste , the K-5 was underexposed , the K3 is also underexposed, and for many years I had the impression that Pentax is more conservative than Canon.
So, recently, I bought a Sekonic light meter, and my conclusion is: the exposure with either K-5 (77 seg) or K-3 (86K) is not as good as the exposure done with the light meter. K-3 is more accuratly underexposed I would say....
02-26-2015, 08:10 AM   #7
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What does it mean "K-3 is more acuratly underexposed "? Not very clear to me.
02-26-2015, 08:35 AM   #8
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QuoteOriginally posted by edri Quote
What does it mean "K-3 is more acuratly underexposed "? Not very clear to me.
Sorry for the spelling mistakes. I meant "K-3 is more accurately under-exposed" .
Yes you ask a very good question.
In camera metering (reflected light metering) allow the algorithms of the camera to calculate the exposure parameters (exposure time, iso, aperture ... as you know, depending on the mode you select Tv, Sv, Av etc...).
As specified, the difference between the K-5 and K-3, is that they are a different light sensor; the K-3 having more resolution and RGB, so the K-3 light meter provides more information to the algorithm.
But how about the accuracy of the algorithm that interpret the meter from the light sensors?
It seems that the algorithm from Pentax produces more underexposed photographs (more conservative to prevent blown high lights) compared to Canon, regardless of 77 segments or 86K RGB. If you compare K-3 images with D810 image , you'll also notice that the D810 are just exposed correctly and the K-3 images are always slightly underexposed. We a separate light meter , I get slightly better exposed photographs , similar to what I observed on photographs from the D810 (the D810 also has a 86K light sensor).

02-26-2015, 08:35 AM - 1 Like   #9
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I found that K3 in multi-segment and center weighted metering underexpose for about 1/3 stop; K3 is very careful not to overexpose highlight, and I think this is a good thing and... Pentax philosophy
02-26-2015, 08:41 AM   #10
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QuoteOriginally posted by teoprome Quote
I found that K3 in multi-segment and center weighted metering underexpose for about 1/3 stop; K3 is very careful not to overexpose highlight, and I think this is a good thing and... Pentax philosophy
Yes, I share your findings, approx. 1/3ev underexposed as well. Slightly underexposed is more safe, it depends... at least it's better to be aware of this fact.
02-26-2015, 08:45 AM   #11
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QuoteOriginally posted by biz-engineer Quote
Yes, I share your findings, approx. 1/3ev underexposed as well. Slightly underexposed is more safe, it depends... at least it's better to be aware of this fact.
completely agree : better to be aware of this fact
then everyone knowing this makes his choices
02-26-2015, 07:27 PM   #12
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QuoteOriginally posted by biz-engineer Quote
So, recently, I bought a Sekonic light meter, and my conclusion is: the exposure with either K-5 (77 seg) or K-3 (86K) is not as good as the exposure done with the light meter.
Incident or reflected light measurements with the Sekonic? A properly used hand-held meter or spot-meter will almost always outperform a built-in meter system unless the optical path has unusually low transmittance. The reason is that there is no such thing as accurate exposure. There is proper exposure, but attaining such requires that there be some intelligence as part of the measurement process and some foresight as to how the image will be processed after the capture.

Steve

(...shoots a fair amount with non-metered cameras...)
02-27-2015, 11:51 AM   #13
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I wouldn't read too much into the technical differences at this level. It is far more important to evaluate performance in demanding field conditions.

When I got the K-3, I thought about just how sophisticated and complex the metering systems were, and told myself that once I master them I'll be getting even better exposure consistency than previous cameras. Well, after working with all the exposure options at a fairly deep level I came to the conclusion that - hey - the K-30 was far less likely to get fooled in high contrast situations than the K-3. Not only did the K-30 rarely get fooled like the K-3 does on occasion, but you didn't have to routinely dial in -.3 or -.7 to avoid the blown highlights (typically in Tav, and almost always with Auto Highlight Compensation enabled).

Not that the K-3 is poor for metering, but it is engineered toward Expose-to-the-Right in an age when that's not such a good idea. Let me deal with the noise issue on my own, but there's nothing I can do about a blown highlight. I had far fewer problems with the much simpler design of the K-30. This kind of reminds of the differences between Auto flash systems, and the engineering in pTTL which has had its share of problems. Sometimes simplicity works best.
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