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12-16-2010, 08:36 AM   #16
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Best possible exposure?

QuoteOriginally posted by Thesorus Quote
IMO, The best way to take advantage of it is to shoot with the best possible exposure.
You'll get more than one opinion, I'll bet, on what "best possible exposure" means. Here's what I think it is:
  • Slowest shutter speed that will freeze the action in the scene
  • Widest aperture that will still get the desired DOF
If, at base ISO, those settings blow highlights, increase the shutter speed, or decrease the aperture, or add a neutral density filter.

The approach that I just outlined will put the most light on the sensor, consistent with the photographer's objectives for DOF and freezing action. In contrast, the popular expose-to-the-right (ETTR) technique makes no sense in most situations.

Consider this example:
  • f5.6 is needed for DOF
  • 1/125 is needed to prevent motion blur
  • At base ISO, with those settings, the histogram is on the left side
In order to ETTR in this situation, what can the photographer do? Neither a longer shutter speed nor a wider aperture are options, and increasing ISO only adds gain, not exposure. Increasing ISO will move the histogram to the right, giving the impression that the photo has been exposed to the right, but that's an illusion, since the actual exposure has not changed.

Jeff

12-16-2010, 09:22 AM   #17
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QuoteOriginally posted by Jeff Charles Quote
You'll get more than one opinion, I'll bet, on what "best possible exposure" means. Here's what I think it is:
  • Slowest shutter speed that will freeze the action in the scene
  • Widest aperture that will still get the desired DOF
If, at base ISO, those settings blow highlights, increase the shutter speed, or decrease the aperture, or add a neutral density filter.

The approach that I just outlined will put the most light on the sensor, consistent with the photographer's objectives for DOF and freezing action. In contrast, the popular expose-to-the-right (ETTR) technique makes no sense in most situations.

Consider this example:
  • f5.6 is needed for DOF
  • 1/125 is needed to prevent motion blur
  • At base ISO, with those settings, the histogram is on the left side
In order to ETTR in this situation, what can the photographer do? Neither a longer shutter speed nor a wider aperture are options, and increasing ISO only adds gain, not exposure. Increasing ISO will move the histogram to the right, giving the impression that the photo has been exposed to the right, but that's an illusion, since the actual exposure has not changed.

Jeff
The theoretical reason for exposing to the right is that you get more tonal levels in a fully exposed image than in an uderexposed one. However, the human eye/brain may not be able to perceive the tonal differences, according to GordonBGood over on the dpreview forum. So, although I agree with Jeff in principle, I would point out that one frequently has latitude in aperture and shutter speed to achieve the desired results. This allows one to avoid severe underexposure, even if it is possible to recover deep shadow with the K-5. I agree with those who say that one should aim to avoid clipping highlights in all three color channels, whenever possible. In any case, the huge DR of the K-5 really makes exposure issues much simpler.

Rob

Last edited by robgo2; 12-16-2010 at 10:51 AM.
12-16-2010, 11:50 AM - 1 Like   #18
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QuoteOriginally posted by nanok Quote
a jpeg, straight from the raw (without blending or tonemapping) will _not_ contain the whole dinamic range, regardless what iso you shoot at, or how well you exposed (hint: 8bits is still 8 bits, and definitely not 14).
Correct, as long as you undertstand that an 8-bit JPEG (with 24-bit colour) can contain more than 8 stops of DR. The encoding in the JPEG is non-linear – a Tone Response Curve (TRC) with gamma compression is applied. According to GordonBGood, the max. possible DR for 8-bit JPEG with a sRGB TRC is 11.7 stops.

Remove space in first two URLs:
http://forums.dpreview .com/forums/read.asp?forum=1018&message=25074654
http://forums.dpreview .com/forums/read.asp?forum=1036&message=36849343

Tone reproduction - Wikipedia, the free encyclopedia

Gamma correction - Wikipedia, the free encyclopedia
"In any case, binary data in still image files (as JPEG) are explicitly encoded (that is, they carry gamma-encoded values, not linear intensities)"
...
"almost all standard RGB color spaces and file formats use a non-linear encoding (a gamma compression) of the intended intensities of the primary colors of the photographic reproduction; in addition, the intended reproduction is almost always nonlinearly related to the measured scene intensities, via a tone reproduction nonlinearity."

JPEG - Wikipedia, the free encyclopedia
"Many JPEG files embed an ICC color profile (color space). Commonly used color profiles include sRGB and Adobe RGB. Because these color spaces use a non-linear transformation, the dynamic range of an 8-bit JPEG file is about 11 stops"

Dan.

Last edited by dosdan; 12-16-2010 at 11:58 AM.
12-16-2010, 04:18 PM   #19
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I also have auto exposure bracketing set to the RAW button for quick movement between taking a single shot to multiple exposures when the scene looks like it could be blown either with sky or white/bright objects etc

Great feature

12-16-2010, 06:15 PM   #20
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QuoteOriginally posted by nulla Quote
I also have auto exposure bracketing set to the RAW button for quick movement between taking a single shot to multiple exposures when the scene looks like it could be blown either with sky or white/bright objects etc
Nulla, an excellent use for the raw button, since the K-5 don't have a Exposure Bracketing button like the K20D does.

It's a pity the raw button can't be reconfigured in the K20D for another function. I never use it.

Dan.
12-17-2010, 03:06 AM - 1 Like   #21
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QuoteOriginally posted by robgo2 Quote
The theoretical reason for exposing to the right is that you get more tonal levels in a fully exposed image than in an uderexposed one. However, the human eye/brain may not be able to perceive the tonal differences, according to GordonBGood over on the dpreview forum.
This is an often quoted reason by many to dismiss ETTR. However, ETTR as promoted by the late Bruce Fraser (which is where I learnt about it) was meant as a way to expose for RAW files, not JPGs. During processing the exposure level of these RAW files needs to be adjusted to what's visually perceived as correct exposure, resulting in a better tonality compared to a RAW that was exposed as you would a JPG for straigh out of the camera use.

The required adjustment can be positive as well as negative BTW. ETTR could mean:
- underexposing to get detail in otherwise blown out highlights (requiring exposure push in PP). Here Gordon's remark may hold true for near white colours as the PP will render invisible some of the gained highlight detail, while potentially losing detail in shadows.
- overexposing to get better details in shadows of a scene without (relevant) highlights (requiring exposure pull in PP). Here PP may bring partially blown (one or two colour channels) part of the image back with a slightly off colour.
In either case the trade-off needs to be considered, and the application of ETTR to be applied with the necessary care, taking into account all colour channels.

Thinking a bit out of the box, ETTR doesn't even need to apply to the histogram of the entire scene you're photographing. If a bright background will be overexposed anyway, you may want to overexpose yet a little more to get a better distributed histogram for your foreground subject. In this case you will ignore the peak at the right of the histogram but will try to bunch up the Gaussian curve left to this peak as much as possible to the right without merging it with the peak. Be careful of sensor bleeding however...

In my book, the science behind ETTR holds, it's just the understanding and application by many that fails IMHO...

just a few random thoughs.

Wim

Last edited by Ishpuini; 09-28-2011 at 11:54 PM.
12-17-2010, 04:00 AM   #22
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QuoteOriginally posted by dosdan Quote
Nulla, an excellent use for the raw button, since the K-5 don't have a Exposure Bracketing button like the K20D does.

It's a pity the raw button can't be reconfigured in the K20D for another function. I never use it.

Dan.
Nor do I use the RAW button... maybe because of the known lack of use of the RAW button by users this feature was added Dan.


cheers

Neil
12-22-2010, 10:38 PM   #23
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thanks a lot guys for your inputs! Just got back from a 5 day trip to the wizarding world of HP, saw 0 pentax shooters... when I tried to shoot the Hogwarts, the k-7 was not able to do the job...

Happily reading this thread after 5 days, I really learned a lot, I cannot fully understand some of the explanations at this time though... thanks again!

12-22-2010, 11:30 PM   #24
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the k-7 was not able to do the job? i honestly doubt that. perhaps you should give more detail and maybe some examples (pictures)
12-23-2010, 12:12 AM   #25
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sorry, I mean to shoot the Hogwarts at 10:00pm...
12-23-2010, 12:48 AM   #26
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I'm a digital capture newbie, so have read this thread with interest. To get a little more background I did a search and came across this piece in Luminous Landscape that helped me better understand the fundamental issues that I think underpin much of this discussion, at least as related to ETTR. Perhaps it may help others as well.

Expose Right

Thanks to all of you who are taking the time to help the rest of us.
05-19-2011, 07:43 AM   #27
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The discussion has been mostly centered on the getting the high DR if shooting in RAW. But I've been trying to find out how to not waste the K5 high DR capability while converting into Jpeg in the camera. I thought that the whole range of internal settings should somehow provide a desired high DR output in a final Jpeg image. After doing a thorough search I found the following thread. I made several tests myself and found these settings very useful. In some situations they can be much easier then using HDR or exposure bracketing with PP. In case the thread is removed over the time, I am putting the settings also here below:

Highlight Correction: ON
Shadow Correction : HIGH
Image tone: Bright
Saturation : +1
High/low key adj: -3
Contrast: -4
Contrast Highlight adj: +4
Contrast Shadow adj: +4

Then you can store these into a User preset for easy access.
Any thoughts about these settings?

Cheers

Last edited by Divecat; 05-19-2011 at 08:04 AM.
05-19-2011, 10:40 AM   #28
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QuoteOriginally posted by shang Quote

my question is what the best way is to make full use of K-5's wonderful DR?
Easy question, use 80 ISO.
05-19-2011, 10:54 PM   #29
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Using ISO 80 will not effect much the in-camera Jpeg output. Neither it will help in a very high contrast (deep shadows and the sky) scenes. For such scenes the Jpeg output gives very dark shadows if exposing for not burning highlights. When using the above mentioned settings, you get a much balanced histogram with both highlights and shadows well recognizable. Will be interesting to hear your thoughts on what happens to the jpeg output when these setting are applied.
05-20-2011, 01:11 AM   #30
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QuoteOriginally posted by Divecat Quote
Using ISO 80 will not effect much the in-camera Jpeg output. Neither it will help in a very high contrast (deep shadows and the sky) scenes.
OP is already stating that, nor intending to use in-camera jpeg for getting most of the DR. Let me put is this way this time, shooting RAW with lowest ISO and using a RAW file processing software afterwards will get you most of the DR.

DR is on the fourth tab, you can check.

DxOMark - Pentax K-5
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