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10-02-2017, 01:38 PM   #1
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Exposure offset in exif?

Hi I was using an fa lens earlier in manual on my K5 and I noticed it was telling me + - up to 2 or 3 stops the difference between the exposure I had set and the exposure it recommended.

Is this offset recorded in the exif and can it be brought up in lightroom?

10-02-2017, 02:12 PM   #2
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Look for ExposureCompensation in the EXIF to get the configured exposure compensation, and LightValue for the light meter reading in EV. Note that if you shot in M mode, you may have to do some calculations if you want to know by how much you underexposed relative to the camera's reading.

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10-02-2017, 10:03 PM   #3
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I don't believe the offset of your actual settings from the recommended nor the means to effectively calculate is captured in the EXIF, but let's take a look. This we have*, that I am aware of:
  • Shutter speed
  • Aperture
  • ISO
  • EffectiveLV (camera-calculated light value**, but includes exposure compensation)
  • LightValue (convenience composite tag reported by ExifTool and other tools, calculated LV = 2 * log2(Aperture) - log2(ShutterSpeed) - log2(ISO/100)
  • AEMeteringSegments (output from each of the meter sensors in the matrix array, 77 for the K-5, expressed as LV)
Comparing EffectiveLV or LightValue to the average of values in AEMeteringSegments might do it.

Taking a step back, what is your intent? Are you wishing to do forensics for exposure experimentation? If so, a pocket notebook and/or voice memo might be easier than working with the EXIF. Many software products allow notes to be entered as comments into XMP metadata during PP.


Steve

* The tag names I listed are those used by ExifTool for Pentax cameras. They may not be the same used by other tools. (The makernotes section has no established tags.)

** Light Value (LV) is the similar to Exposure Value (EV) except normalized to ISO 100. Technically, EV is based on the camera actual settings (shutter speed and aperture) while LV gives an approximation of illuminance within the frame. Meters often include the option of output as LV. Usage in the EXIF context is mildly incorrect unless based on the meter reading.

Last edited by stevebrot; 10-02-2017 at 10:10 PM.
10-04-2017, 07:46 AM   #4
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QuoteOriginally posted by stevebrot Quote
I don't believe the offset of your actual settings from the recommended nor the means to effectively calculate is captured in the EXIF, but let's take a look. This we have*, that I am aware of:
  • Shutter speed
  • Aperture
  • ISO
  • EffectiveLV (camera-calculated light value**, but includes exposure compensation)
  • LightValue (convenience composite tag reported by ExifTool and other tools, calculated LV = 2 * log2(Aperture) - log2(ShutterSpeed) - log2(ISO/100)
  • AEMeteringSegments (output from each of the meter sensors in the matrix array, 77 for the K-5, expressed as LV)
Comparing EffectiveLV or LightValue to the average of values in AEMeteringSegments might do it.

Taking a step back, what is your intent? Are you wishing to do forensics for exposure experimentation? If so, a pocket notebook and/or voice memo might be easier than working with the EXIF. Many software products allow notes to be entered as comments into XMP metadata during PP.


Steve

* The tag names I listed are those used by ExifTool for Pentax cameras. They may not be the same used by other tools. (The makernotes section has no established tags.)

** Light Value (LV) is the similar to Exposure Value (EV) except normalized to ISO 100. Technically, EV is based on the camera actual settings (shutter speed and aperture) while LV gives an approximation of illuminance within the frame. Meters often include the option of output as LV. Usage in the EXIF context is mildly incorrect unless based on the meter reading.
I was shooting the other day in manual and using an incident light meter, badly it seems. A lot of over exposed shots resulted. However I noticed that the camera was metering and telling me how far out I was. I was hoping that the camera recorded how far out my exposures were, lightroom was only showing me 0EV for exposure compensation. It would have been interesting to see how far to adjust the exposure to get the camera's idea of correct exposure.

10-04-2017, 11:55 AM   #5
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Am I misunderstanding something? EXIFToolGUI:
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10-04-2017, 12:15 PM   #6
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QuoteOriginally posted by bxf Quote
Am I misunderstanding something? EXIFToolGUI:
That shows the EC setting, but does not show the suggested (metered) EV for manual mode. Here is my interpretation of the OP's request:

Example:
  • "M" mode
  • No EC set
  • Exposure settings made per a hand-held meter
  • Image is OK, but user is curious about the internal meter's reading and what settings might have been made if that had been used


Steve
10-04-2017, 01:15 PM   #7
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QuoteOriginally posted by stevebrot Quote
That shows the EC setting, but does not show the suggested (metered) EV for manual mode. Here is my interpretation of the OP's request:

Example:
  • "M" mode
  • No EC set
  • Exposure settings made per a hand-held meter
  • Image is OK, but user is curious about the internal meter's reading and what settings might have been made if that had been used


Steve
Exactly, thank you. It's a pity I can't edit the thread title. I can spell exposure

The metering segment values are in the exif I think they read top left to bottom right (7 rows of 11 maybe) there are 3 methods for evaluating them matrix centre weighted and Spot but I don't know how Pentax gets from A to B. It's just way to much work to figure out the values.

I just need to meter better. I only wish Pentax firmware was better than it is or there was an exif analyser, still its academic. practice , practice, practice the camera isn't going to tell me how i messed up

10-04-2017, 02:25 PM   #8
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QuoteOriginally posted by blackest Quote
I just need to meter better.
Learning the "ins and outs" of exposure is easy for the basics and quite the art once one gets into it.

QuoteOriginally posted by blackest Quote
I only wish Pentax firmware was better than it is or there was an exif analyser,
What you are looking for would be handy, but its absence from the metadata is not an indication that Pentax was sloppy. In general, the stuff in the makernote section of the EXIF is not intended for general consumption and has no published documentation. It is just a collection of numbers with no labels or key. Pentax captures those data for their own purposes, not ours.

That being said, the authors of utilities such as ExifTool have done a very good job of determining the purpose and meaning of the Pentax makernotes and to them we are very thankful.* For those who are interested, the Pentax makernote tag reference for ExifTool may be found at:

Pentax Tags


Steve

* The tag names are the author's best guess as to purpose and they have done a mighty fine job. When reading that section of the EXIF metadata, it is good to remember that the labels and interpretation are deemed reliable, but potentially not accurate.
10-04-2017, 03:17 PM   #9
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QuoteOriginally posted by stevebrot Quote
Learning the "ins and outs" of exposure is easy for the basics and quite the art once one gets into it.



What you are looking for would be handy, but its absence from the metadata is not an indication that Pentax was sloppy. In general, the stuff in the makernote section of the EXIF is not intended for general consumption and has no published documentation. It is just a collection of numbers with no labels or key. Pentax captures those data for their own purposes, not ours.

That being said, the authors of utilities such as ExifTool have done a very good job of determining the purpose and meaning of the Pentax makernotes and to them we are very thankful.* For those who are interested, the Pentax makernote tag reference for ExifTool may be found at:

Pentax Tags


Steve



* The tag names are the author's best guess as to purpose and they have done a mighty fine job. When reading that section of the EXIF metadata, it is good to remember that the labels and interpretation are deemed reliable, but potentially not accurate.
Yes I know, it's just little things like why no other focus point other than centre on manual focus lenses. the focus points are part of the camera not part of the lens. With screw drive the body adjusts the lens helicoid in or out to get focus, there is no real reason my left hand can't replace the screw drive ok not so fast admittedly (although smooth use of catch in focus...). On canon with an adapted lens and dandelion chip you can use your focus points.

You might even think that mostly the same routines used on AF lenses could be reused. A firmware extension might be possible on the sdcard. I guess it might be that Sony controls some of the firmware for the camera and sensor so Pentax / Ricoh are limited on what they can do. I'd love better manual lens support but that doesn't sell lenses, although it might sell bodies... Right now the only step I want to take from my K5 is a K1. Better manual lens support on a new aps-c body I could be tempted
10-04-2017, 05:52 PM   #10
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QuoteOriginally posted by blackest Quote
Yes I know, it's just little things like why no other focus point other than centre on manual focus lenses. the focus points are part of the camera not part of the lens.
That is reasonable. It is not a feature I have missed despite having mostly manual focus lenses, but that is a reasonable request.

QuoteOriginally posted by blackest Quote
I guess it might be that Sony controls some of the firmware for the camera and sensor so Pentax / Ricoh are limited on what they can do.
Pentax may be a Sony customer for image sensors, but it is unlikely that they control camera features.

QuoteOriginally posted by blackest Quote
I'd love better manual lens support but that doesn't sell lenses, although it might sell bodies...
That is a good point. I know many people who purchased the original A-7 Sony primarily because of the breadth of manual focus lens support. OTOH, Sony does not feature manual focus confirmation on that model.

As I mentioned above, I have never wished for the ability to choose focus confirmation point for manual focus*, though it just occurred to me that the benefits might be less than appears. Much depends on one's eyesight. Even the stock focus screen will outperform PDAF at other than the center column of AF points found on higher model Pentax cameras.


Steve

* One of the reasons may be that from 1970 to 2007, I used manual focus SLRs having focus aids positioned at center. About 2008, I equipped my K10D with a Katz Eye focus screen having similar focus aids and my K-3 continues that practice. The best focus with my Pentax is done using either PDAF at center, manual focus using my peepers, or magnified live view.
10-04-2017, 06:12 PM   #11
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QuoteOriginally posted by blackest Quote
It's a pity I can't edit the thread title
Fixed.
10-04-2017, 07:14 PM   #12
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Is exposure compensation possible in M? I thought not.
10-04-2017, 07:17 PM   #13
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Before I started using EXIFTool I was using another program, whose name I am unable to recall. I actually have a post in PF somewhere referencing that program, but it is a very old post and I can't see it. That program, if I remember correctly, actually showed an EV map of the various sections of the image.

Could be useful here, if I could only remember the name. It is old, and had not been updated for ages, hence lost popularity, I guess.

Got it! PhotoME is the name, but seems to not work on Win10 x64.

Last edited by bxf; 10-04-2017 at 07:25 PM.
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