F5: Beware, the camera's not really 2000 ISO...

You used the light meter to match f-stops on your lens and then looked at the ISO your meter was giving you right?

A lot of meters are calibrated for 12% not 18% grey as pointed out by Alister over on the Sony forums, and if that's the case it could mean you'd end up with different ISO's yet again.

The quest for the "right" ISO continues!
 
starcentral said:
The quest for the "right" ISO continues!
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Yes, Dennis, I know how to rate a camera. :-) And I didn't use gray, I used Kodak 90% white.

But I take issue with your statement above. It's not about the "right ISO" because that number means nothing whether it is displayed correctly or not. What matters is the best level to expose, and I'm sure that debate will continue.
 
All I can suggest is that users do some tests and that is different brightness in camera with different post recipes and come to their own conclusions.

S
 
But Doug how did you come up with the ISO? Even if you used white to match IRE on WFM and then did a meter read to get the ISO, most meters are set with lower grey reference point....
 
Hey Doug, did you use the incidence or spot meter on your L758?

Videocraft, (who sold me my camera) are loaning me another F5 next week to run a comparison using the same methodology, it'll be interesting to see how it compares.
 
Grug said:
Hey Doug, did you use the incidence or spot meter on your L758?

Videocraft, (who sold me my camera) are loaning me another F5 next week to run a comparison using the same methodology, it'll be interesting to see how it compares.
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I'm also curious. My L-508's spot meter is calibrated for 12% BUT the incident one is calibrated for 18%, I have to always remember that. Not sure if it is the case with L758.
I used L-508 and Minolta VI.

BTW, if someone runs this test and the aimed mapped IRE value used as a reference is the one for 18% grey and reflective metering method is used, then there is no need to use 18% target, just any neutral and uniform surface. One just has to illuminate it evenly, point the camera at it, adjust exposure with WFM so that the IRE value of that surface is the recommended one by Sony for 18% for the particular gamma, then take a reflective reading with the meter of that surface, then adjust the ISO in the meter until the displayed f-stop value matches that on the lens. The resulting ISO is the camera's sensitivity. That is of course if the meter is perfectly calibrated for 18%. The benefit of this method is that it eliminates speculation if the 18% grey card is really 18% and you don't need a calibrated target at all, any neutral and evenly illuminated surface is good (for example a white, grey or even very dark grey wall).
 
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Agree with brightonfilms, when I've rated cameras using a light meter the % grey on the card is not relevant because you adjust the lens iris until you get the right reading on the waveform monitor. So you WFM needs to be decent, hopefully folks are not trying this with the numberless thumbnail WFM built into the camera.
 
starcentral said:
But Doug how did you come up with the ISO? Even if you used white to match IRE on WFM and then did a meter read to get the ISO, most meters are set with lower grey reference point....
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Dennis, if you can find some kind of credible documentation that the Sekonic L-758C lighter meter is somehow flawed at reading light properly, I would sure like to see it.

First I set the aperture on the lens to exactly f/5.6 as it is aimed at the evenly lit Kodak white card.
Then I adjust the dimmer on the Litepanels Sola4 until the white card hits exactly 59% on the Leader WFM.
This WFM is way more precise than the camera's crappy little excuse for a WFM.
The Skeonic is set to match the camera's frame rate and shutter speed.
Then I use the Sekonic (in incident mode) to read the light to find out what ISO is required to get an f/5.6 exposure.
Then I confirm that ISO by randomly testing other f-stops and light levels.
The FS7 always comes up as 1600 ISO.
It's not rocket science.
 
Not that the light meter is flawed, only that there is lots of arguing on the internet about whether or not light meters are calibrated using 12% grey (ANSI standard) or 14% (Japan standard), or 18% as we've all been lead to believe is the "standard".

Just like in my 508 light meter manual, the 758 light meter manual says the the calibration constant for reflected light metering is 12.5. There is no unit of measurement. For incident light metering with the diffuser up the manual says C = 340. I have no idea what that means, I do know that there is half a stop or so difference between incident and reflected, so maybe it is 12% for reflected and around 18% for incident? Not sure.

I agree it would be nice to see some credible documentation. My camera rating process (same as yours) has also been subject to criticism by some so in a way I'm curious..
 
Doug Jensen said:
Dennis, if you can find some kind of credible documentation that the Sekonic L-758C lighter meter is somehow flawed at reading light properly, I would sure like to see it.

First I set the aperture on the lens to exactly f/5.6 as it is aimed at the evenly lit Kodak white card.
Then I adjust the dimmer on the Litepanels Sola4 until the white card hits exactly 59% on the Leader WFM.
This WFM is way more precise than the camera's crappy little excuse for a WFM.
The Skeonic is set to match the camera's frame rate and shutter speed.
Then I use the Sekonic (in incident mode) to read the light to find out what ISO is required to get an f/5.6 exposure.
Then I confirm that ISO by randomly testing other f-stops and light levels.
The FS7 always comes up as 1600 ISO.
It's not rocket science.
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Very strange that these cameras with similar sensors (and one would assume comparable architecture) generate such inconsistent results. Especially when Sony seemed to get things spot-on sensitivity-wise with the earlier Cinealtas (F35, F3, F65).

It'll be interesting to see how this second F5 compares next week. I'll see if I can throw an F55 into the mix as well.

starcentral said:
Not that the light meter is flawed, only that there is lots of arguing on the internet about whether or not light meters are calibrated using 12% grey (ANSI standard) or 14% (Japan standard), or 18% as we've all been lead to believe is the "standard".

Just like in my 508 light meter manual, the 758 light meter manual says the the calibration constant for reflected light metering is 12.5. There is no unit of measurement. For incident light metering with the diffuser up the manual says C = 340. I have no idea what that means, I do know that there is half a stop or so difference between incident and reflected, so maybe it is 12% for reflected and around 18% for incident? Not sure.

I agree it would be nice to see some credible documentation. My camera rating process (same as yours) has also been subject to criticism by some so in a way I'm curious..
Click to expand...

I definitely get about 1/2 stop difference between my spot meter and incidence meter on my L758-C. Which leads me to believe that the Spot is at 12% and the Incident at 18% on that meter (the fact that the camera's false colour and an incident reading from the Sekonic approximately match up, seems to bare that out)... now as to WHY Sekonic do it that way, who knows?!
 
I rarely use the spot meter on the Sekonic so I didn't even think to check the ISO with it earlier today. So I did it just now, and I get EXACTLY the same 1600 ISO when I meter off the gray side of the Kodak card. Those of you who are getting inconsistent results, you are probably using a poorly calibrated gray target.

Also, I like to put my light source at least 8' away from the chart because if the light is too close, that extra couple inches that the incident meter is closer to the light might make a little difference.
 
According to the article link I posted, if it is correct, using the K and C values published at the back of the manual for 508 and 758 light meters these meters are calibrated for around 11.2% grey with the lumisphere raised and 15.7% with the flat diffuser (lumisphere lowered).

This is the formula to calculate it for your particular light meter where K is the reflected light metering value, and C is the incident light metering constant (usually two values are provided for lumisphere raised or lowered) and n is equal to pie ie. 3.14159.

ζ = π x (K / C)

Now the majority of grey cards being sold are made using 18% grey reflectance. This includes "Kodak's genuine grey card". Even Sony white papers make reference to 18% grey to let us know what IRE or Code Value we should be getting from 18% grey.

So it does appear that if you are going to use a Sekonic 758 or 508 light meter (with lumisphere raised) to figure out the ISO it's going to be off by half a stop just because the meter is NOT calibrated to 18% grey. The only manufacturer that seems to come extremely close to 18% is Pentax and Minolta, but again you need to check the manual.


Here's a table of various manufacturer K values, but for the C value you'll need to look it up for your specific model and then go off and do some math:

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Dennis, you may very well be correct, but ultimately it doesn't matter to me anyway:

1) I have no plans to actually use my meter to set exposure so the ISO is irrelevant no matter what it is.

2) I never set exposure by gray so the debate about what percentage is appropriate does not apply to me.

3) If I am going to use my 758 meter in incident mode (the only way I would use it), I have proven to myself that I need to have it set for 1600 if I want it to get the right exposure. I'm 100% certain of that -- so the information in the chart is overruled by real world usage with the meter.

I appreciate the information though. But it's all academic.
 
Yep, as stated earlier, what the meter reads doesn't matter at all as long as you get your f-stops to match then you can go ahead and make meter reads and set your exposure accordingly if you wish.

But if anyone is interested to "properly" rate the ISO of the FS7/F5/F55 cameras and be scientific (and correct) about it, they will need to take the specific meter's constants into account and then test. Again, we're not changing the face of mankind here with this information but if we're going to discuss rating the camera accurately, then it seems there is a proper way to go about it.
 
I totally agree with all that. And I will stake my reputation (for whatever that is worth around here!) that the FS7 is 1600 and the F55 is 1250 on a Sekonic 758c if your goal is to put whites at 59% with S-LOG2 or 61% with S-LOG3.
 
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