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Meter Caliberation


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#1 abhijitabde

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Posted 18 June 2007 - 03:58 PM

i bought a new sekonic L 758 cine,,,, my incident and spot reading differ by .3 when metered on a grey card,,,
id like to know please if that much difference is fine and also should it be the same with my new meter or anyways
thanx
abhijit
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#2 Stuart Brereton

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Posted 18 June 2007 - 04:22 PM

Have a look at this thread:

www.cinematography.com/forum2004/index.php?showtopic=23633

BTW, you have to use a (real) first & last name on this forum. You can change it in My Controls
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#3 Jonathan Bowerbank

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Posted 18 June 2007 - 07:13 PM

...my incident and spot reading differ by .3 when metered on a grey card...


Honestly, I'd only be alarmed if both readings were exactly the same. Incident & reflective light are two different things, so in my opinion, you should be getting different readings. Just use them both enough to know which works best for you and to figure out what each reading REALLY means once you get your results back

:)
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#4 abhijitabde

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Posted 19 June 2007 - 07:33 AM

hi jonathan
thanx a lot for ur input. but i really felt that on a grey card both the incident and the reflected spot should be almost same, of course if they differ now i will have a reading done n use either as and when it suits me.
thanx again

abhijit abde

Honestly, I'd only be alarmed if both readings were exactly the same. Incident & reflective light are two different things, so in my opinion, you should be getting different readings. Just use them both enough to know which works best for you and to figure out what each reading REALLY means once you get your results back

:)


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#5 abhijitabde

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Posted 19 June 2007 - 07:39 AM

hi Stuart

i had checked the link u sent me ,, thanx
and sorry i will use my full real n last name henceforth

Abhijit Abde

Have a look at this thread:

www.cinematography.com/forum2004/index.php?showtopic=23633

BTW, you have to use a (real) first & last name on this forum. You can change it in My Controls


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#6 Laurent Andrieux

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Posted 25 June 2007 - 06:01 PM

Just my 2 cents... Mind that your grey card is not a bit old... Get a brand new one for checking your meter's calibration. A 0.3 of a stop is within the usual range, so that the chart could be the cause...
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#7 Chris Keth

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Posted 25 June 2007 - 06:57 PM

I wouldn't change a thing.

Try this: have someone hold a greycard outdoors for you. Meter it while they tilt it in several different directions. See how the reading changes? It probably varies by a stop or more if it goes into shadow.

Which of these angles is correct? Who knows. You really shouldn't base anything on the difference between those readings because they are simply different beasts.
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#8 Laurent Andrieux

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Posted 25 June 2007 - 07:07 PM

Well, if the grey card is turned into shadow, it will of course, change your reading, but the card is designed to follow the Lambert law, meaning that it equally luminates in every direction... If the source is making an angle, say, from 30° to 45° to the camera direction and the card is facing the lens, the reading shouldn't change even if you tilt it a bit.
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#9 Chris Keth

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Posted 25 June 2007 - 09:39 PM

Well, if the grey card is turned into shadow, it will of course, change your reading, but the card is designed to follow the Lambert law, meaning that it equally luminates in every direction... If the source is making an angle, say, from 30° to 45° to the camera direction and the card is facing the lens, the reading shouldn't change even if you tilt it a bit.


It may be meant to follow that law but they generally don't. Try it. I can usually get a full stop or at least 2/3 of a stop of difference by tilting it around in the light.
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#10 janusz sikora

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Posted 26 June 2007 - 10:47 AM

Incident and Spot readings off the Grey Card should be the same.
By the way... this is the only instance when they are the same (not including reading in total darkness)
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#11 Chris Keth

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Posted 26 June 2007 - 12:34 PM

Incident and Spot readings off the Grey Card should be the same.
By the way... this is the only instance when they are the same (not including reading in total darkness)


Theoretically they should be the same. In practice, they rarely are. It also complicated things when you figure that most meter companies calibrate their spotmeters to more like 16% grey rather than 18%
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#12 abhijitabde

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Posted 27 June 2007 - 02:19 PM

Theoretically they should be the same. In practice, they rarely are. It also complicated things when you figure that most meter companies calibrate their spotmeters to more like 16% grey rather than 18%

hello Chris
u mean its ok if im getting that difference of .3 ?? and yea u r right bout some companies caliberating the grey card to 16% n not 18% ..
thanx a lot nways
abhijit abde
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#13 abhijitabde

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Posted 27 June 2007 - 02:22 PM

Just my 2 cents... Mind that your grey card is not a bit old... Get a brand new one for checking your meter's calibration. A 0.3 of a stop is within the usual range, so that the chart could be the cause...

Hello Laurent

i thought so bout the grey card and i checked it with a newer grey card tooo but it still is giving a difference of .3 , is that all right practically ?? theoritically it must be the same with incident n spot ,,
advise pls
abhijit abde
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#14 Laurent Andrieux

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Posted 28 June 2007 - 02:34 PM

;)

theoritically it must be the same with incident n spot


I would say so. Have your meters calibrated. You also can take a correction in account, based on the one you trust must. But I would trust the grey card and consider the spotmeter metering should give the same result as the incident light meter.
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