[blackest]

You are making the unwarranted assumption that EffectiveLV is influenced by the light meter and may be used to back-calculate the aperture. To evaluate, I did some test exposures.

K-3, M-mode, XR Rikenon 50/2 (no mount contacts), f/5.6, 1/30s, ISO 3200, EC = 0, M-mode

Case 1: evenly-lit blank wall, metered exposure determined using DOF preview in M-mode
EffectiveLV = 23.5

Case 2: evenly-lit blank wall, non-metered exposure after power cycle from Case 1
EffectiveLV = 23.5

Case 3: lens cap on after power cycle from Case 2
EffectiveLV = 23.5

Case 4: same as for Case 3 except changing the shutter speed to 1/40s
EffectiveLV = 23.9

Exif F Number = 0 for all four cases
Actual LV for all but Case 4 should have been 5.0 (f/5.6 @ 1/30s @ ISO 3200)*
Back-calculated aperture for 23.5 LV = f/3557**

Conclusions:

• EffectiveLV does not change in relation to exposure metering or light intensity
• EffectiveLV does vary by shutter speed (did not test for ISO)
• EffectiveLV represents the camera's exposure settings (i.e. is calculated from aperture, shutter speed, and ISO)
• EffectiveLV calculation by the camera apparently fails over to use an arbitrarily large f-number for the case when actual aperture is unknown (i.e. could not be set by the body)
• The assumption the EffectiveLV may be used to calculate aperture when that value is unknown to the camera is false.

Steve

* Confirmed with a Pentax-A 5/1.7 mounted with the same exposure settings.
** SQRT((2^28.5)/30)

Thank you for your research EffectiveLV appears to be linked to Shutter speed
This is a series at iso 100
ELV - shutter speed fraction

2.5 2000 Pd 8000
2.0 1500
1.5 1000, 1000
1.0 750, 750 Pd 3000
0.5 500
0.0 350 pd 1500
-0.5 250
-1.0
-1.5 pd 500
-2.0 90, 90
-25 pd 250
-3.0 45, 45, 45
-3.5 30 pd 125
-4.0 20
-4.5 15
-5.0 10

Looks to be a likely relationship

If you run

exiftool -s -ExposureTime -EffectiveLV on ISO 100 exposures what do you get?
I think its likely iso will be a factor in effectiveLV

I ran the same query on the previous days results (pd)
same base iso but as you can see the shutter speeds are way different but the intervals are the same. now it was a lot brighter yesterday than today

--This needs more consideration

---

Last edited by blackest; 03-28-2017 at 08:51 AM. Reason: more info

[stevebrot]

You can do it simply by feeding the data from the 4050 metering segments recorded in the EXIF into something as simple as Excel, and using conditional formating to highlight the values in a way that lets you visualize the results, like so:

Thanks for jumping in. I remember thinking the first time I saw this that it was just too cool. Have you ever tried using the actual numeric data (use -n option) rather than LV calculated by ExifTool?


Steve

[stevebrot]

Thank you for your research EffectiveLV appears to be linked to Shutter speed

Ummm...yes. When all three settings (aperture, shutter, and ISO) are known, EffectiveLV is calculated from those with a correction thrown in for EC. I did the forward and backward calculations to determine the expected LV and the calculated f-number.


Steve

[rawr]

Have you ever tried using the actual numeric data (use -n option) rather than LV calculated by ExifTool?

Never looked into it. I kind of got something usable, so I stopped there.

[blackest]

Ummm...yes. When all three settings (aperture, shutter, and ISO) are known, EffectiveLV is calculated from those with a correction thrown in for EC. I did the forward and backward calculations to determine the expected LV and the calculated f-number.


Steve

Ok so to make an exposure you need an iso a shutter speed and an aperture and the amount of light measured determines the exposure value where the other 3 can dance around but must agree to reach an exposure value.

What does the camera know?
it has a light value in EV calculated from the light metering sensors it has a fixed iso because we won't let it change it.
So based on the light falling on the meter the camera calculates which speed to use for the available light.

shutter speeds from 1/8000 to 1 second (2nd column 1/2 stops)
------------
8000 6000
4000 3000
2000 1500
1000 750
500 350
250 180
125 90
60 45
30 20
15 10
8 6
4 2
1

The camera has to adjust its shutter speed to suit the stopped down value and it seems to be using a series of stops to figure it out.
but it also means something different in different light ...

[stevebrot]

Ok so to make an exposure you need an iso a shutter speed and an aperture and the amount of light measured determines the exposure value where the other 3 can dance around but must agree to reach an exposure value.

What does the camera know?
it has a light value in EV calculated from the light metering sensors it has a fixed iso because we won't let it change it.
So based on the light falling on the meter the camera calculates which speed to use for the available light.

shutter speeds from 1/8000 to 1 second (2nd column 1/2 stops)
------------
8000 6000
4000 3000
2000 1500
1000 750
500 350
250 180
125 90
60 45
30 20
15 10
8 6
4 2
1

The camera has to adjust its shutter speed to suit the stopped down value and it seems to be using a series of stops to figure it out.
but it also means something different in different light ...

I read back through your posts. It appears you have been pondering the matter of "A" pins, apertures, EXIF, and exposure for a number of years. Good luck getting it all figured out.


Steve

[blackest]

I read back through your posts. It appears you have been pondering the matter of "A" pins, apertures, EXIF, and exposure for a number of years. Good luck getting it all figured out.


Steve

Yes to be fair it is a bit of a source of annoyance that Pentax couldn't have gone a little further in supporting old lenses.

I've been doing some more this evening

LensModel is free , you can call it anything you want. Thats

dx0 is picky it needs the focal length and aperture to be within range of what it thinks the lens is capable of.

LensType sets a LensModel and LensID I think.... I'm getting tired, Anyway
Learnt a few things and tried a few and
at least now I can put a lens model and f-stop in the exif thats an improvement and I can con Dx0 into processing with the wrong modules
I think I should write a batch file or 2 so exiftool only returns useful tags currently there are 260 if you don't specify which tags.

[blackest]

You are making the unwarranted assumption that EffectiveLV is influenced by the light meter and may be used to back-calculate the aperture. To evaluate, I did some test exposures.

K-3, M-mode, XR Rikenon 50/2 (no mount contacts), f/5.6, 1/30s, ISO 3200, EC = 0, M-mode

Case 1: evenly-lit blank wall, metered exposure determined using DOF preview in M-mode
EffectiveLV = 23.5

Case 2: evenly-lit blank wall, non-metered exposure after power cycle from Case 1
EffectiveLV = 23.5

Case 3: lens cap on after power cycle from Case 2
EffectiveLV = 23.5

Case 4: same as for Case 3 except changing the shutter speed to 1/40s
EffectiveLV = 23.9

Exif F Number = 0 for all four cases
Actual LV for all but Case 4 should have been 5.0 (f/5.6 @ 1/30s @ ISO 3200)*
Back-calculated aperture for 23.5 LV = f/3557**

Conclusions:

• EffectiveLV does not change in relation to exposure metering or light intensity
• EffectiveLV does vary by shutter speed (did not test for ISO)
• EffectiveLV represents the camera's exposure settings (i.e. is calculated from aperture, shutter speed, and ISO)
• EffectiveLV calculation by the camera apparently fails over to use an arbitrarily large f-number for the case when actual aperture is unknown (i.e. could not be set by the body)
• The assumption the EffectiveLV may be used to calculate aperture when that value is unknown to the camera is false.

Steve

* Confirmed with a Pentax-A 5/1.7 mounted with the same exposure settings.
** SQRT((2^28.5)/30)

23.5 on my camera is 1 second at iso 100 but i found that the same effectiveEV value was used 4
stops higher at 1600 so
2 at 200
4 at 400
8 at 800
16 at 1600
32 at 3200

The values are all 1/2 stop intervals unless your camera is set for 1/3 stop intervals.
At ISO 100

23.5: 1 second
24.0: 7/10
24.5: 1/2 second
25.0: 3/10ths
25.5: 1/4 second
26:0: na
26.5: 1/8 second
-5.0 : 1/10th
-4.5: 1/15th
-4.0: 1/20th
-3.5: 1/30th
-3.0: 1/45th
-2.5: 1/60th
-2.0: 1/90th
-1.5: 1/125th
-1.0: 1/180th
-0.5: 1/250th
000: na(1/350th)
+0.5 na (1/500th)
+1.0 na(1/750th)
+1.5: 1/1000th
+2.0: na(1/1500th)
+2.5: na (1/2000th)
+3.0: na (1/3000th)
+3.5: na(1/4000th)
+4.0: na(1/6000th)
+4.5: na(1/8000th)

It may be worth comparing with Charts of camera Nominal and Exact Precise Shutter speed, f/stop and ISO values

So what do we know now, effectiveEV relates to a shutter speed at iso 100

23.5 is 1 second at iso 100, 2 seconds at iso 200, 4 seconds at iso 400, 8 seconds at iso 800, 15 seconds iso 1600, 30 seconds iso 3200

There is a bit of a problem with the values I think, if you look at the bytes that are being read

exiftool -v2 -EffectiveLV -ShutterSpeed -ISO _IGP3620-2.dng
exiftool -v3 -EffectiveLV -ShutterSpeed -ISO _IGP3620-2.dng

look for 25) to find EffectiveLV
one gives a -decimal value and the other a HEX value

-1 :FC00:-1024
-2 :F800:- 2048
-3 :F400:- 3072
-4 :F000:- 4096
-5 :EC00:-5120

-1.5:1D18:-1536
-4.5:EE00:-4608

I thought I had it figured as between each stop there is a 1/3 a 1/2 and a 1/3 it would have been nice if -1.5 had been FA00 but its not
But it's fairly clear that each byte pair doesn't relate directly to the displayed value of EffectiveEV. The whole number hex values look like 1KByte offsets maybe a table? and I think that the 1/2 stop and 1/3rd stop values are in another set.

I will keep plugging away to see if I can figure this out

[wombat2go]

I think I should write a batch file or 2 so exiftool only returns useful tags currently there are 260 if you don't specify which tags.

Yes, you can add your own granularity something like this (linux bash):

#!/bin/bash
PR_wkdir=.
for file in $PR_wkdir/*; do
if [ ${file: -4} == ".DNG" ] || [ ${file: -4} == ".dng" ] || [ ${file: -4} == ".jpg" ]|| [ ${file: -4} == ".JPG" ]
then
PR_name=${file%\.*}
PR_name=$(basename "$file" | cut -d. -f1)
exiftool -a -u -g $file >$PR_name"_All_TAGS.txt"
cat $PR_name"_All_TAGS.txt" |grep Exp >$PR_name"_My_TAGS.txt"
cat $PR_name"_All_TAGS.txt" |grep LV >>$PR_name"_My_TAGS.txt"

fi
done

[blackest]

I think I have been going about this the wrong way.

The light meter in the camera measures the light it see's and figures out an exposure to perfectly expose mid gray.
But what aperture is the camera at when its metering? With a small aperture not much light is getting though and with a large aperture more is getting through so when the camera meters 7.5 the question has to be at what aperture.

when the camera knows what the aperture is it can adjust its metered light reading accordingly so if you have a 1.4 lens and a 2.8 lens the metered value of light will be two stops less on the 2.8 lens as compared with the 1.4 the raw light value on the 2.8 is 2 stops less than on the 1.4 lens so the camera adds 2 stops compensation more to the 2.8 than the 1.4

Ok so now it has a lightvalue to work with whats it going to do?

Try to perfectly expose middle gray of course.

So if its bright out , the exposure will need to be shorter and if its darker it will be longer. right.

So it needs to calculate a shutter speed with the current iso that will expose mid gray as mid gray in the current lighting conditions.
now lets say you want the shutter to close a couple of stops now the camera needs to expose for 2 stops longer.

Ok now what do the metered values mean without a known aperture , they don't there has to be an aperture to give the readings meaning.
I am pretty sure if a Pentax doesn't know the max aperture it assumes F1.2 doesn't matter a great deal to be fair but you need some number to calculate a light value yesterday my camera was mostly working on around 7.5 +/- half a stop now it wasn't that dark but in reality it was around 10 EV.

So if we know the speed it chose and the light it measured then all that is needed is to find out what exposure value it was going for.
then we can figure how much compensation it applied for the aperture used. Really that should be a constant as it trys to perfectly expose mid gray.

---------- Post added 03-29-17 at 05:37 PM ----------

Yes, you can add your own granularity something like this (linux bash):

#!/bin/bash
PR_wkdir=.
for file in $PR_wkdir/*; do
if [ ${file: -4} == ".DNG" ] || [ ${file: -4} == ".dng" ] || [ ${file: -4} == ".jpg" ]|| [ ${file: -4} == ".JPG" ]
then
PR_name=${file%\.*}
PR_name=$(basename "$file" | cut -d. -f1)
exiftool -a -u -g $file >$PR_name"_All_TAGS.txt"
cat $PR_name"_All_TAGS.txt" |grep Exp >$PR_name"_My_TAGS.txt"
cat $PR_name"_All_TAGS.txt" |grep LV >>$PR_name"_My_TAGS.txt"

fi
done

Thank you for that I will give it a go.

Any idea's how to find the 39th metering segment
Its a real pain I ended up copying the metering segments into a text file replacing all the spaces with commas then bringing it into libre office
then each photo got its own line and i had to count to find which was the 39th column and then highlight that column.

still has to be an easier way than that. I think i might have figured out how the exposure gets set

[wombat2go]

Any idea's how to find the 39th metering segment

Give me a string or something and i will have a go.
Being old timer, I love fooling around with bash scripting

[Oakland Rob]

Just a practical note that is based on the info already provided, and more detailed info: be careful of messing in exif with lens ID info.

I have used exiftool to write in lens names or even IDs so I could find them in Lr. But it borked DxO's ability to identify the body/lens combo. They use some fairly sophisticated sleuthing to verify the lens/body combo, and it can be defeated by mere mortals attempts to mess with the lens info. So now I just use keywords to ID the lens when it isn't automatically found, like with old manual lenses.

[blackest]

Give me a string or something and i will have a go.
Being old timer, I love fooling around with bash scripting

Ok

AEMeteringSegments : 8.8 8.8 8.9 8.8 8.8 8.6 8.8 8.8 8.9 8.9 8.8 9.0 8.9 8.6 8.6 8.6 8.8 8.8 8.8 8.8 8.9 8.9 8.9 9.0 8.6 8.5 8.5 8.5 8.6 8.6 8.6 9.0 9.1 8.6 8.9 8.6 8.5 8.5 8.8 8.8 8.6 8.8 8.9 8.8 8.6 8.8 8.8 8.8 8.8 8.5 8.6 8.8 9.0 8.9 8.9 8.5 8.4 8.6 8.8 8.5 8.5 8.6 8.8 8.9 8.8 8.6 8.2 8.5 8.8 8.9 8.8 9.0 9.0 9.0 9.0 8.6 8.5

I've a pretty good Idea that works out to be 9

Metering an exposure seems to be light + 1/2 a stop.

This should be accurate as this was a da lens so it knows the aperture it is measuring the light at.

I actually think I have cracked the problem

with a given light level the camera will pick an aperture shutter iso combination to expose for mid gray + 1/2 a stop. The actual light level isn't that important its just what is coming into the lens and what combo will produce an accurate mid gray exposure. Stopping down just adds some more duration to the exposure by a number of stops. it doesn't actually matter where it starts from.

[blackest]

Just a practical note that is based on the info already provided, and more detailed info: be careful of messing in exif with lens ID info.

I have used exiftool to write in lens names or even IDs so I could find them in Lr. But it borked DxO's ability to identify the body/lens combo. They use some fairly sophisticated sleuthing to verify the lens/body combo, and it can be defeated by mere mortals attempts to mess with the lens info. So now I just use keywords to ID the lens when it isn't automatically found, like with old manual lenses.

It's not too bad when you write to a tag exiftool makes a copy and labels the original, original.

Dx0 can only be as complicated as good as the exif information is.

E.g I set a 55mm km lens as a fa 50mm it needed the max aperture and focal length to match and the LensID and a valid fnumber
you can do this in realtime too
e.g the picture is open in dx0 and you change a value it refreshes if it stays gray it doesnt have a matching module if it goes red it has a number of matches and if it is green it matched.

[wombat2go]

Ok

AEMeteringSegments

This script will print to file all seg numbers and their values. You can also select one for printing
Could be adapted to any tag which has multiple space separated vars.

#!/bin/bash
PR_wkdir=.

PR_search1="Exp"
PR_search2="LV"
PR_segtag="AEMeteringSegments"
PR_segnum=10


for file in $PR_wkdir/*; do
if [ ${file: -4} == ".DNG" ] || [ ${file: -4} == ".dng" ] || [ ${file: -4} == ".pef" ]|| [ ${file: -4} == ".PEF" ]
then
PR_name=${file%\.*}
PR_name=$(basename "$file" | cut -d. -f1)
exiftool -s -a -u -g $file >$PR_name"_All_TAGS.txt"
cat $PR_name"_All_TAGS.txt" |grep $PR_search1 >$PR_name"_My_TAGS.txt"
cat $PR_name"_All_TAGS.txt" |grep $PR_search2 >>$PR_name"_My_TAGS.txt"


while read -r PR_line; do
PR_stringarray=($PR_line)
if [[ ${PR_stringarray[0]} = *$PR_segtag* ]]
then
echo $PR_name"_"$PR_stringarray >>$PR_name"_My_TAGS.txt"
echo $PR_name"_"$PR_stringarray
j=1
for i in "${PR_stringarray[@]}"; do
((j++))
echo "SegNum= "$((j - 1 ))" Val= "${PR_stringarray[$((j+0 ))]} >>$PR_name"_My_TAGS.txt"
done

echo "My_Meter_Seg="$PR_segnum" Val= "${PR_stringarray[$(($PR_segnum + 1 ))]}>>$PR_name"_My_TAGS.txt"
echo "My_Meter_Seg="$PR_segnum" Val= "${PR_stringarray[$(($PR_segnum + 1 ))]}
fi
done < $PR_name"_All_TAGS.txt"
fi
done