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03-15-2015, 07:58 PM   #1
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645Z-difference between warning blinkies and actual exposure

Hi all,

a thing that puzzles me.
when I am in LV with the highlights alert on and reduce EXP to minimize it, take the shot and then review the file in camera, I get a lot bigger area to blink than in LV.
I basically end up overexposing if I trust the LV exposure preview.

anybody else having that problem?
Michael Reichmann has reported that the Pentax takes the histogramm from the actual RAW file and not from the JPG preview...

Stephan

03-15-2015, 08:14 PM   #2
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QuoteOriginally posted by zobeleye Quote
Hi all,

a thing that puzzles me.
when I am in LV with the highlights alert on and reduce EXP to minimize it, take the shot and then review the file in camera, I get a lot bigger area to blink than in LV.
I basically end up overexposing if I trust the LV exposure preview.

anybody else having that problem?
Michael Reichmann has reported that the Pentax takes the histogramm from the actual RAW file and not from the JPG preview...

Stephan
I have always assumed that the only histogram/blinkies that is what the sensor sees is the Live View histogram/blinkies and that the jpg preview has differences. That is the only reason there would be differences between the two in my view (not being all that technical, it's possible I'm wrong). I don't use Live View enough to compare notes, mainly because exposing using Live View tends to make it a spot meter. I will often use Live View to autofocus a third of the way in at F/11 to get close to hyperfocal distance.
03-16-2015, 03:19 AM   #3
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I think you will find that the raw file on Lightroom would be correctly exposed like that of the highlight warning.

The jpg compression will clip it off.

Try setting your JPEG settings to lowest contrast and see how you go.
03-16-2015, 09:21 AM   #4
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I agree with the posters above, it's a JPG preview issue, the blinks should be back to normal when you develop your RAWs. Setting JPG to lowest contrast helps but doesn't fix the issue in 100% of the cases. Best,

Vieri

03-16-2015, 03:40 PM   #5
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Guys,
I am aware of the fact that normally the histogramm is taken from the jpg preview.
I had just assumed that it could be different with the 645Z.
Michael Reichmann wrote in his in-depth review

<Fortunately the 645z has real-time highlight warning blinkies in Live View mode, and this is taken directly from the sensor. In other words, if something blinks red in Live View it’s blown. If it doesn’t, it isn’t. When displayed along with the histogram in Live View (which also has a red line to the right when anything is blown), you will be able to make technically optimum exposures.>

so to get clarity around that, I checked again.
turns out that the fact that the blinkies are taken from the sensor is spot on.
as you can see in the last pic, the blinkies( right in the middle on the book) coincide with the raw file brought into LR, if you compare first and last.
BUT, the histogram displayed in LV does not indicate that anything is blown, as the red line is not shown, so the blinkies and therefore clipping, occurs way before the LV histogram shows it.
any other histogram, displayed in camera, be it test shot or from the actual recorded file, is based on jpg preset selected and so far I have not been able to adjust any of the presets, so they show an approximation of the actual file in terms of highlight over exposure.
as far as highlight recovery from this sensor goes, so far it seems to be good, but I will further test this.
maybe for now I'll just go + 1 EV from where the blinkies appear, just to be safe I can get them back.
or I'll just let them go to hell and go shooting...��
cheers
Stephan

P.S. any further thoughts welcome
Attached Images
 

Last edited by zobeleye; 03-16-2015 at 04:03 PM.
03-16-2015, 04:20 PM   #6
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QuoteOriginally posted by zobeleye Quote
Guys,
I am aware of the fact that normally the histogramm is taken from the jpg preview.
I had just assumed that it could be different with the 645Z.
Michael Reichmann wrote in his in-depth review

<Fortunately the 645z has real-time highlight warning blinkies in Live View mode, and this is taken directly from the sensor. In other words, if something blinks red in Live View itís blown. If it doesnít, it isnít. When displayed along with the histogram in Live View (which also has a red line to the right when anything is blown), you will be able to make technically optimum exposures.>

so to get clarity around that, I checked again.
turns out that the fact that the blinkies are taken from the sensor is spot on.
as you can see in the last pic, the blinkies( right in the middle on the book) coincide with the raw file brought into LR, if you compare first and last.
BUT, the histogram displayed in LV does not indicate that anything is blown, as the red line is not shown, so the blinkies and therefore clipping, occurs way before the LV histogram shows it.
any other histogram, displayed in camera, be it test shot or from the actual recorded file, is based on jpg preset selected and so far I have not been able to adjust any of the presets, so they show an approximation of the actual file in terms of highlight over exposure.
as far as highlight recovery from this sensor goes, so far it seems to be good, but I will further test this.
maybe for now I'll just go + 1 EV from where the blinkies appear, just to be safe I can get them back.
or I'll just let them go to hell and go shooting...��
cheers
Stephan

P.S. any further thoughts welcome
In this forum you'll notice a discussion we had a few weeks back about banding in highlights, and whether it is a feature or fault of the camera. I haven't heard anything back from my contact at Pentax. many of us established that while the Z is amazing at shadow recovery, it struggles with highlight recovery. This has rarely been an issue for me, as I tend to expose to the left, ignoring normally held wisdom in exposing to the right. Shooting with a Canon, I'd definitely ETTR, but with the 645Z there is so much scope in shadow recovery there are few occasions when I wouldn't ETTL.
03-17-2015, 08:09 AM   #7
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QuoteOriginally posted by itshimitis Quote
... Shooting with a Canon, I'd definitely ETTR, but with the 645Z there is so much scope in shadow recovery there are few occasions when I wouldn't ETTL.
Second that - though not exactly what you (the OP) asked, this is a very valuable piece of information, and one which could save you all the pains you are going through trying to figure out a solution to your problem: since the 645z is AMAZING at recovering shadow detail, just keep on the safe side when it comes to exposure, don't blow your highlights and you'll be able to recover almost anything you throw at the 645z in the shadows

Best,

Vieri
03-17-2015, 08:32 AM   #8
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QuoteOriginally posted by itshimitis Quote
In this forum you'll notice a discussion we had a few weeks back about banding in highlights, and whether it is a feature or fault of the camera. I haven't heard anything back from my contact at Pentax. many of us established that while the Z is amazing at shadow recovery, it struggles with highlight recovery. This has rarely been an issue for me, as I tend to expose to the left, ignoring normally held wisdom in exposing to the right. Shooting with a Canon, I'd definitely ETTR, but with the 645Z there is so much scope in shadow recovery there are few occasions when I wouldn't ETTL.
There is information that I contributed there too, but here is the cliff's notes on 645Z dynamic range:



This graph I cooked up shows a visualization of the DR distribution that you get while exposing. You have very low highlight head room, an area that's clearly over-exposed in Lightroom can take about -10 highlights before you simply get a grey fill instead of detail. However, at ISO100, you can push the exposure slider all the way to the right and add +100 shadow recovery, with fairly usable results.

This is because the point that the camera considers to be "middle gray" is actually quite high up on the scale, and so all representations of the scene that you see only display the top half of your entire dynamic range. Canon cameras are set with a lower gray point, so you have a good 1~1.5 stops of headroom on something like a 5D3, while the Raw shadow range would have been your buffer to protect the image from noise and banding, but on the 645Z it's 100% usable data due to both a higher dynamic range and a nearly non-existent noise floor.

Even when shooting at higher ISO levels like 3200 or 6400 you still have a fairly good recovery margin without severely aggravating noise, and the noise profile of this camera's sensor seems consistent enough that even small levels of noise reduction can help.

Regarding Live View, the red blinks do show what will be blown out, while the preview blinks are already generated from the "cooked" jpeg. One thing to point out, is that once again unlike Canon cameras, the exposure simulation is actually biased by the metering system and does not display over/under exposure greater than 5EVs beyond what the system thinks is the "correct" exposure, a massive oversight by Pentax in my opinion, along with being unable to manually set auto-brightness or exposure sim for each shooting mode. Why would you want exposure sim in X-mode? the camera doesn't know how bright your flash is, so the scene will be extremely dark while trying to set focus.


Last edited by Kolor-Pikker; 03-17-2015 at 08:47 AM.
03-17-2015, 08:59 PM   #9
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Interesting reading...
thanks for all your thoughts and comments

just went back and checked the actual base iso of this sensor.
my sekonic says that the camera's actual iso is something like 37.5 😀.
back in photoschool they taught us, when you measure and expose for the grey card, then it sits right in the middle. at ZoneV for the those of us that still think analog.
or talking PS/LR at 128 resp. 50.
so doing this with the 645Z the middle grey gets me to 23, that's 1 1/2 stops below 50.
this tells me exposing in the studio I set my lightmeter to below 50 iso and I'm good and safe...
just saying

Stephan
03-18-2015, 06:01 AM   #10
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QuoteOriginally posted by zobeleye Quote
so doing this with the 645Z the middle grey gets me to 23, that's 1 1/2 stops below 50.
this tells me exposing in the studio I set my lightmeter to below 50 iso and I'm good and safe...
just saying

Stephan
I'm going to try that, thanks.
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