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Pawlowski6132
29-Nov-2014, 11:04
At ISO 400 and EV 9, at f8, my Pentax digital spot gives 1/30 exposure. My sekonic twinmate gives 1/8. Why would these be different?..

Am I missing something?.

I'm pretty sure the sekonic scale is right but they should be equal.

ic-racer
29-Nov-2014, 11:39
EV value on the Pentax is always referenced to ISO/ASA 100 (oddball quirk with that lightmeter). Look in the manual under "Special Features" number 10.

Set the Sekonic to 100 and see if they now match.

Pawlowski6132
29-Nov-2014, 11:46
EV value on the Pentax is always referenced to ISO/ASA 100 (oddball quirk with that lightmeter). Look in the manual under "Special Features" number 10.

Set the Sekonic to 100 and see if they now match.

Thanx for the reply. But my Pentax has an adjustable ISO.

Pawlowski6132
29-Nov-2014, 11:56
https://www.icloud.com/photostream/#AAJRveFpF7VJH

Pawlowski6132
29-Nov-2014, 13:27
This table tells me Pentax scale is correct?

http://en.m.wikibooks.org/wiki/Basic_Photography/Exposure_tables

ic-racer
29-Nov-2014, 16:56
Thanx for the reply. But my Pentax has an adjustable ISO.
Yes and in spite where the ISO is set, the EV is always referenced to ISO 100.

Bill Burk
29-Nov-2014, 16:59
Yet this table shows the Sekonic Twin-Mate is correct.

I'm afraid we have a case where the same two letters of an abbreviation for the same two words are used for two completely different purposes.

Quite an interesting mess the light meter people have given us isn't it?

http://en.wikipedia.org/wiki/Exposure_value

Bill Burk
29-Nov-2014, 17:01
ic-racer, are they only the same at EI 100?

Pawlowski6132
29-Nov-2014, 21:22
Yes and in spite where the ISO is set, the EV is always referenced to ISO 100.

That shouldn't matter in this case. The scales should match and they don't.

Right?

Bill Burk
29-Nov-2014, 23:13
Pawlowski6132,

I guess you figured something out? It looks to me like the Pentax scale should be labeled EV@EI=100 because that's what the numbers are.

ic-racer
30-Nov-2014, 07:28
My theory is that Pentax did not intend on making a meter that only gives EV at a single ISO. However, if you look at the way they designed and constructed the barrel of the meter's lens, it seems as if they were forced in the situation. It looks as if linking the ISO to the EV scale would have been difficult. Just a guess, however.

Pawlowski6132
30-Nov-2014, 08:12
My theory is that Pentax did not intend on making a meter that only gives EV at a single ISO. However, if you look at the way they designed and constructed the barrel of the meter's lens, it seems as if they were forced in the situation. It looks as if linking the ISO to the EV scale would have been difficult. Just a guess, however.

Wouldn't that mean anyone using a film with an ISO other than 100 would get erroneous reading?

Pawlowski6132
30-Nov-2014, 08:21
Fwiw, I just metered a grey card with both meters. Suggested exposures are VERY CLOSE.


EV indications are still two stops off.

Mr Racer, I guess it doesn't matter if the Pentax is stuck using ISO 100 (although I still don't understand that) to calculate EV. That number becomes irrelevant if the recommended exposure is true.

ic-racer
30-Nov-2014, 09:58
That number becomes irrelevant if the recommended exposure is true.
Exactly!

Randy Moe
30-Nov-2014, 10:28
Yet this table shows the Sekonic Twin-Mate is correct.

I'm afraid we have a case where the same two letters of an abbreviation for the same two words are used for two completely different purposes.

Quite an interesting mess the light meter people have given us isn't it?

http://en.wikipedia.org/wiki/Exposure_value

EV to me is a mess. I grew up using ASA which is now ISO and they damn bear match. BS!

I never metered for decades as I didn't have one. I used the directions on the box of Kodak film. Sunny 16 was never mentioned. Then Kodak dropped the inside the box instructions. Cost savings BS.

In 1996 I got a camera with a meter and it used ISO and could be used manually or in various auto methods. Big improvement but no mention of 'EV'. Technology works BS.

Then I used both digital and 35 mm cameras for years until I noticed 'Pros' using something called EV and EI. Professional BS.

By now I knew to use faster or slower ASA or ISO to allow a wider aperture of faster shutter. OK, I got it. Hobbyist BS.

But then I get a Retina RF and it has some indecipherable 50's jargon where the normal lens setting used to be. Tech BS.

Then I notice everybody is adjusting their DSLR's by changing ISO which obviously is like changing film ISO. Sorta BS.

Later I notice my DSLR has exposure compensation control by a dial that does what, changes what? I know it is good for bracketing. More features BS.

Now my dear film friends talk of personal EI, which is a combination of all the above, adding in shutter speed irregularities, film developing methods and God know what else. Total BS.

Why all the obfuscation in the name of simplicity?

I continue to think about exposure in the way printed inside the yellow box. Less BS.

Only 3 variables, ISO, actual shutter speed and actual aperture. Same old BS, but it works.

danno@cnwl.igs
30-Nov-2014, 10:40
Randy, I think you've nailed it !;)

Bill Burk
30-Nov-2014, 11:03
I agree Randy Moe, EV made a mess out of something that we already were accustomed to. It takes too much explaining. By the time the convenience of "one setting" became important, full automation arrived.

My analog Pentax spotmeter makes one needle sweep from 1 to 19 which is labeled on the dial as "Linear Scale". There is no mechanical linkage between the dial and the meter.

I think the Pentax meter scales are calibrated as EV at EI=100.

At least the Pentax needle scale "means something". It's a step ahead of other meters where the scale is an arbitrary unit.


You can easily see that holding the Sekonic dial in place so that f/stops and shutter speeds are locked... and turning it, changes the ISO but not the EV number.
-Sekonic defines EV as the mechanical linkage of f/stop and shutter speed combinations.

But do the same with the Pentax and both EV AND ASA
-Pentax defines EV as the mechanical linkage of f/stop and shutter speed combinations at IE=100.

These definitions are implemented mechanically, you can feel them as you turn the dials.

Bill Burk
30-Nov-2014, 12:12
A similar discussion is taking place on APUG and this reference "explains" the confusion...

="http://camerapedia.wikia.com/wiki/Light_and_Exposure_Values_(LV_%26_EV)"http://camerapedia.wikia.com/wiki/Light_and_Exposure_Values_(LV_%26_EV)

kintatsu
1-Dec-2014, 09:22
I've personally found that measuring the luminance of an object and using the exposure formula works quite well.

I like being able to measure at ISO 64 f/8 and go from there. That gives me the luminance for my notes, and then changing the ISO and f/stop to what I plan to use gives me my exposure. The highest value placement gives me my development.

I can't quite get my head around EV/LV, as these things don't make sense to me. Sometimes, the old ways are there because they work. Just my 2 cents.

Randy Moe
1-Dec-2014, 10:13
A similar discussion is taking place on APUG and this reference "explains" the confusion...

="http://camerapedia.wikia.com/wiki/Light_and_Exposure_Values_(LV_%26_EV)"http://camerapedia.wikia.com/wiki/Light_and_Exposure_Values_(LV_%26_EV)

Bill, your link is broken.

Bill Burk
1-Dec-2014, 10:23
Fixed URL...


http://camerapedia.wikia.com/wiki/Light_and_Exposure_Values_(LV_%26_EV)

Luis-F-S
1-Dec-2014, 10:26
If you calibrate your film speed to whatever meter you want to use, then this discussion becomes mute......L

Randy Moe
1-Dec-2014, 10:40
Fixed URL...


http://camerapedia.wikia.com/wiki/Light_and_Exposure_Values_(LV_%26_EV)

Thanks Bill.

Absolutely hilarious! :)

ic-racer
2-Dec-2014, 08:21
If you calibrate your film speed to whatever meter you want to use, then this discussion becomes mute......L

The discussion is somewhat mute because LF shutters, in 99% of cases, are not set with EV values. The f-stop & shutter speed combinations of the Pentax meter are OK at all ISO settings. The issues would be if you are using the Pentax meter to set the EV value on your Rolleiflex E (not allowed discussion here) and you forgot that the Pentax EV values are referenced always to ISO 100.

towolf
2-Dec-2014, 09:05
Proper notation would be 12 EV_100 equals 14 EV_400. _100 denotes subscript.

I have my Sekonic 508 always in EV mode. I like the equal spaced EV scale much more than the weird log scales. I’ve also learned that digital cameras calculate in APEX (http://dougkerr.net/Pumpkin/articles/APEX.pdf), which translates shutter speed, aperture, and sensitivity into equidistant stop increments as well.