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05-05-2013, 01:46 PM   #1
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K30 sensor profile. Latitude still like reversal film, 5 stops? RAW. Always RAW.

I'm wondering if any tech nerds with a K30 have profiled their K30 and figured out the sensor latitude. I could be asking the wrong question the wrong way but want to know how many stops of latitude I would program into a light meter. I know the general rule about digital being about the same as reversal film but that rule is getting a bit long in the tooth and sensors have come a long way. I don't want to just program in 5 stops without knowing whether or not it's really an accurate measure of the K30 sensor's latitude. I'd rather not use the feature until I can use it accurately.

05-05-2013, 02:18 PM   #2
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Do you mean how much the light meter can get the measurements wrong? I don't know personally, and I don't even know if this helps you, but at ISO 100, the K-30 captures tones about 13EV apart (max) and you can probably get a stop from the highlights and at least three from the shadows in post
05-05-2013, 02:24 PM   #3
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meter a mid-tone textured surface and then take pictures at +3 e.v. + 4 e.v., etc. and -3 e.v., -e.v., etc. Do this at a few iso values. Open in your raw software and check what range works for you.There are reported dynamic ranges for K30 but is less on high end, and anyway may not be to your criteria for noise. Nice thing about digital you can do this yourself, and w/o hassle of developing film. I did not check but likely about 8 stops to 12 stops for 1600 iso to 100 iso w/o recovery in camera raw.
05-05-2013, 02:30 PM   #4
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DXO mark has it as 13 to 10 stops for iso 100 to 1600. But again:
this is not symmetric
does not include (if you want) recovery in raw
and likely will not match what you get when you test it

05-05-2013, 02:32 PM   #5
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I mean how many stops in either direction above 18% grey can the sensor render detail properly exposed. For instance, if middle grey is f8.0 how far in either direction do I have before clipping, before my highlights blow out or my shadows block up. For the longest time I've read it's the same as reversal film, about 5 stops. DxO labs measures DR but, as far as I can tell, they don't profile the sensor to the degree where one can determine latitude.
05-05-2013, 02:37 PM   #6
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And that is what I was addressing!
05-05-2013, 03:09 PM   #7
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QuoteOriginally posted by dms Quote
DXO mark has it as 13 to 10 stops for iso 100 to 1600. But again:
this is not symmetric
does not include (if you want) recovery in raw
and likely will not match what you get when you test it
So the "middle" of 10 -13 stops would be 5 - 6 1/2 above or below middle grey. Is that what you mean? That would pretty much fall into the old reversal film / digital rule with 1 1/2 stop extra to account for technological advances in sensor design. I guess I didn't really think deeply about the DxO ratings beyond some recent 1 to 1 comparisons I made. That's embarrassing but thanks for helping me picture it in real world terms. I'm still a noob in most ways.

The lack of symmetry you're referring to relates to how much more latitude you have with shadows than with highlights, yes? Expose for highlights?
05-05-2013, 03:38 PM   #8
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There is more latitude in the shadows then highlight with Pentax, it sort off already expose to the right already.

Also lightmeters don't meter to 18% grey you will be about 2/3th of a stop off most likely.

05-05-2013, 03:44 PM   #9
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I don't use/know the details for the K30, but for argument sake, if about 3-4 stops above middle gray is where the maximum, and maybe 6-8 stops below middle gray is the minimum. That's why I say not symmetric. But staying with this example if you simply do a 1 2/3 e.v. exposure reduction (e.g., think raising the iso from 100 to 320) you can make it symmetric. Although for most scenes you want the asymmetry. After all the brightest will not get brighter--but areas in shade will get much darker.
05-05-2013, 03:52 PM   #10
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Anvh's point about 18% not being middle gray is also my understanding. Prior to general/universal (?) acceptance of Ansel Adams zone system I think middle gray was more often taken as 10-12%, and I believe that is the calibration for most light meters.

Not that the zone system isn't just as useful if zone V is 10% instead of 18% reflectance, but anyway, either by testing, or experience, you should modify it to your needs.

But from 10% to 100% is about 3 1/3 stops, and 18% to 100% is about 2 1/2 stops--either way you want more range for low exposure--except for example stage lighting where much hotter spots may be present.
05-05-2013, 04:06 PM   #11
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Perhaps one more suggestion--if you meter for the brightest acceptable tone, and let the darkest fall where they will--you have likely a more generally satisfactory approach. The only additional caution is for color a few areas actually being in glare adds highlights and should not be metered.
Notwithstanding what I said above--for my K20d I actually often use an incident meter and simply expose at +1 e.v. for outdoors. Maybe my point being use the instant feedback of digital to work out a scheme.
05-05-2013, 04:36 PM   #12
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QuoteOriginally posted by Anvh Quote

Also lightmeters don't meter to 18% grey you will be about 2/3th of a stop off most likely.
I thought it was a 1/2 stop. Nevertheless, I know that debate rages on. To make matters more complicated my meter , as stated in the manual, is calibrated for 18% grey but the spot metering is calibrated to "midtone". What is the value of this midtone? Who knows? The manual doesn't say.
05-05-2013, 08:35 PM   #13
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Okay guys, thanks to your insight I have a much better understanding of latitude. Even more, your insight led me to a few websites (more refined searches thank you) that helped me understand spot metering much better and how it differs quite a bit from incident metering. I'm still getting my head around the whole idea of using a spot meter to chose one's own "mid-tone" based on a particular scene. As Spock would say, "Fascinating."

I also just found out whilst writing this that Firefox's spell checker recognizes, "Spock", as a proper name to be capitalized.

Thanks again.
05-06-2013, 03:33 AM   #14
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I haven't tried it yet with my K-30 but with the narrower DR K100D at air shows using RAW, I used to matrix meter on the sky, add +1.33EV compensation and lock the exposure for all my shots unless the light changed. No chance of blowout and pretty consistent exposure all round, underexposure being the only risk but always recoverable if it happened.
05-06-2013, 07:28 AM   #15
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Sorry if this is off-topic but this looks like a good place and time to ask this question: Does Pentax matrix metering favor correct exposure of high brightness parts of the image at the risk of overall underexposure? I ask as it seems exposure is usually a little lower in matrix metering vs center-weighted.
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