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04-22-2014, 03:15 AM   #16
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QuoteOriginally posted by PaulR100 Quote
I read somewhere that the ISO are not the same on different brands, with the Pentax being more accurate.
It was suggested that the ISO difference was perhaps to mislead regarding noise levels.
This would also affect the exposure accordingly.
I to have seen this.

QuoteOriginally posted by MJSfoto1956 Quote
I'm convinced that Pentax deliberately underexposes -- my JPEG previews look completely different than my RAW files when previewed in either ACR or DxO. In particular, I would say that on average, the JPEGs are almost exactly +1 stop "lighter" than the corresponding RAW images. Not that this is a problem per se -- the images clean up quite well, especially in DxO Optics Pro. But there is no question in my mind. You can see this most clearly when comparing Pentax RAWs to Nikon RAWs shot in the same conditions at the same exposures. As a side note, I won't use +1 to compensate because I use my JPEGs as "backup" and I want these to "properly" exposed in case of catastrophic failure of the RAW files or data storage.
I have seen that the RAWs in ACR always are darker compared to the Preview in ExifPro but did not think more about it until now. I shoot mostly only RAW but will try RAW+ and open both of them in ACR. Thank you for pointing this out.

04-22-2014, 03:32 AM   #17
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Sounds to me that people are shooting with highlight protection enabled then not using a 'Pentax' capable raw processor.

Highlight protection will shoot approx 1 stop under and correct during raw convertion, it writes pointers for the raw converter to also deliver this.

If the converter is not able to understand these directives you will have an image underexposed by about 1 stop.

One other thought is ensure your FW is up to date as I seem to remember my k3 with fw V1.0 was shooting slightly under.
04-22-2014, 03:43 AM   #18
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QuoteOriginally posted by awaldram Quote
Sounds to me that people are shooting with highlight protection enabled then not using a 'Pentax' capable raw processor.

Highlight protection will shoot approx 1 stop under and correct during raw convertion, it writes pointers for the raw converter to also deliver this.

If the converter is not able to understand these directives you will have an image underexposed by about 1 stop.

One other thought is ensure your FW is up to date as I seem to remember my k3 with fw V1.0 was shooting slightly under.
I am not using this feature. It is set to OFF.
04-22-2014, 06:48 AM   #19
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QuoteOriginally posted by awaldram Quote
Sounds to me that people are shooting with highlight protection enabled then not using a 'Pentax' capable raw processor.
Interesting hypothesis. I think it explains my observations (where that property is currently set to "auto" by default). However, what that means then is that by default Pentax is deliberately underexposing (to protect the highlights) then "pushing" the shadows -- a pretty common practice these days, with the result that shadows are "noisier" than if they were captured at base ISO. As I always bracket three exposures, I'd rather make the choice myself rather than software.

Michael

04-22-2014, 07:22 AM   #20
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Contact your authorized repair center - describe to them in detail the problem. They can probably look at a few sample images and tell you if there is a problem.
04-22-2014, 10:43 AM   #21
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Exposure problem

Highlight protection suggestion is interesting and I will have to check- I do shoot raw and dont see the underexposure in Lightroom that I see on the LCD or Irfanview (my quick check program) - I wonder if that is the problem

I spoke to the repair service today and they wondered if I didnt need calibration (but they didnt see images or adk for much in the way of details), I had called to see if I was covered by the warrant (I was)

Will check highlight protection and if not the problem send the body in to be checked

Steve

---------- Post added 04-22-14 at 01:46 PM ----------

by the way- I assume that the correction , if set to auto is "off"
Could someone more fully explain the highlight protection feature and its appropriate use
I think many would appreciate it

Steve
04-22-2014, 12:55 PM   #22
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QuoteOriginally posted by srock Quote
Highlight protection suggestion is interesting and I will have to check- I do shoot raw and dont see the underexposure in Lightroom that I see on the LCD or Irfanview (my quick check program) - I wonder if that is the problem

by the way- I assume that the correction , if set to auto is "off"
Could someone more fully explain the highlight protection feature and its appropriate use
I think many would appreciate it

Steve
If your HP is set to "auto" it isn't off, you are leaving it up to the cameras discretion when to utilize it and I venture to say most of the time you wouldn't know it was being applied..

Ok from what I know from my research and reading here's a very good explanation;

"If you start at ISO 200 and then enable HP, the exposure doesn't change - you get the same aperture & shutter speed. This is identical to setting ISO 100 and under-exposing by 1 stop.

You will see a change in exposure if you start at ISO 100, then enable HP. The camera can't reduce the analogue gain for the lowest ISO values, so halves the exposure and increases the ISO to 200 for correct metering. The dynamic range is unchanged (same as at ISO 100 without HP) though you have traded highlight range for shadow range by the effective under-exposure.

enabling highlight protection at ISO 160 or higher makes no difference to the indicated ISO, and no difference to the metered exposure. In Av mode, aperture and shutter speed are unchanged. What happens is that sensor gain is reduced, and the JPEG tone curve boosted to compensate in the mid-tones and shadows, while giving the highlights a softer roll-off. The raw file preserves the reduced gain linear data, which Jim's copy of Aperture 3 renders as under-exposed by 1 stop.

If HP did increase sensor gain and reduce exposure, the metered aperture and shutter speed would have to change, and this simply does not happen at ISO 160 and above. Only at ISO 80, 100 and 125 is the exposure reduced (and indicated ISO boosted by 1 stop), because it is not possible to reduce sensor gain for the lowest ISO settings."


I don't use HP since I have from my film days always compensated by using exposure bracketing or EV adjustments on the cameras that had that..

Last edited by Oldbayrunner; 04-22-2014 at 01:04 PM.
04-22-2014, 07:46 PM   #23
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Exposure problem

I turned highlight protection off and it may have helped. I need to more rigorously test in daylight, though

I'm not sure that I really understand Highlight protection, or shadow protection and what they do , what problems they solve and when they are helpful . I must admit I pretty much ignored the settings and left both on the default "auto"

Would appreciate some further explanation

Steve

04-22-2014, 08:02 PM   #24
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this behavior is a bit different than on Nikon cameras -- HDR and other image enhancements only apply to JPEGs -- RAWs are always left "pristine". So for me, this is a new, unexpected behavior. But it is easy enough to fix. So yes, if your primary image capture is RAW and you also always bracket (as I do now and did back in the film days) then turning off any automation is recommended.

Michael
04-23-2014, 03:35 AM   #25
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Exposure issue

I shoot raw and develop in lightroom

Would it be good practice to leave HP and SP off except perhaps in High-contrast low light situations.

Are there any other times when it could be helpful?

Steve

---------- Post added 04-23-14 at 07:17 AM ----------

I was thinking about it and then understood that this is the in-camera implementation of the maxim:

If there are blinkies , expose to the right.

Since I use that rule , I'm not sure where HP will be useful to me->OFF

Steve

Good explanation and examples here:

Pentax K-3 Review: Now Shooting! - Exposure
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