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M6 LM and Voltage Dependency?


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Just checked the battery in my 'new' M6, a lithium DL 1/3 N of unknown age. Measured a terminal voltage of 2.9V using a high impedance DVM.

 

Just wondering what dependency there is compared to say a fresh set of D357's, each having a terminal voltage of 1.55V (total 3.1V)

 

If I was to blindly set exposure based on the light meter reading (against a 18% grey card) it would result in an under exposure compared to a calibrated handheld L-758, but that's calibrated against my M240 so I won't know where I stand until I get the film back, but the question here is primarily about battery voltage dependency.

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From my decades of using M6, never notice that the light meter accuracy depend on battery voltage (or dropping of).

When the batteries (I mostly use silver 2 x SR44) drop in voltage, a warning is the LED is less bright, that is time to change batteries.

With lithium battery, it may be more or less gradual, but if the LED is visible, the meter stay consistent.

 

Experience is easy, when the LED balance is less bright, just replace the battery, then the same LED balance (for same LV) is just brighter.

 

In my Kodachrome day, I calibrate each M6 with known result and it depend on "actual speed shutter of that said M6" (mechanical one is 15-25% accurate), so I used 80 ASA or 50 ASA for K 64 (only 1/3 to be on the safe side) and bracketing was my friend for slides.

 

Have fun.

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Thank you a.noctilux. Since the LEDs are bright, I think I'll save my money and carry on using the existing lithium battery supplied with the camera.

 

As said earlier, I have calibrated my Sekonic L-758 to match the light meter in my M240, so there's no way of making an informed judgement of whether the light meter in the M6 is correct, other than viewing images taken of a 18% reference card, backed up by accurate SS measurements. As it stands, say the Sekonic indicates 1/250 at f8, the M6 at 1/250 requires f11 (I'm using the spot meter on the Sekonic, and allowing the 18% card to fill the M6 frame).

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Thank you a.noctilux. Since the LEDs are bright, I think I'll save my money and carry on using the existing lithium battery supplied with the camera.

 

As said earlier, I have calibrated my Sekonic L-758 to match the light meter in my M240, so there's no way of making an informed judgement of whether the light meter in the M6 is correct, other than viewing images taken of a 18% reference card, backed up by accurate SS measurements. As it stands, say the Sekonic indicates 1/250 at f8, the M6 at 1/250 requires f11 (I'm using the spot meter on the Sekonic, and allowing the 18% card to fill the M6 frame).

 

When working with different cameras it is the Sekonic meter that should be the datum point, not least because it is most likely to have a better linear response over a much wider range. So calibrating it to match your M240 is just plain wrong. If you want readings to match decide how much exposure compensation your M240 needs and dial that into the camera.  

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When working with different cameras it is the Sekonic meter that should be the datum point, not least because it is most likely to have a better linear response over a much wider range. So calibrating it to match your M240 is just plain wrong. If you want readings to match decide how much exposure compensation your M240 needs and dial that into the camera.

 

Not according to Sekonic. The L-758 was designed to be calibrated to 'see' the same as your camera's sensor. No two cameras, even the same model of camera from the same production run necessarily 'see' the same. With the 758 trained to see as my 240 I can take an incident or spot measurement and know the picture will be exposed correctly (for 18% grey, as for all light meters). Part of the calibration procedure against the Sekonic Target II is for the meter to 'learn' the DR range and clipping points of the chosen camera (separate profiles can be set for different cameras), useful when spot metering for highlights and shadows. Edited by Steve Ricoh
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