Interesting experience testing my 35mm camera meters

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BHuij

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I've posted at length about getting my OM-1 and FTb cameras to match my spot meter, after modifying the circuits to use a 1.55v battery, and re-calibrating the meters in each. Both are working perfectly now.

Made me get curious about my other meters, since I actually have a fair number of 35mm cameras in the rotation. So I started testing them all tonight using the same method with a relatively high-CRI LED panel set to 5600k and various brightness levels.

Baseline against which all other meters were compared was my Reveni Labs Spot Meter. The FTb and OM-1 match it exactly since I recently worked on them. The AT-1 was off by 1/2 a stop. Hopefully I can tweak that a hair, but I probably wouldn't hesitate to use it for B&W film at least. The XA was off by 1/2 a stop. I don't intend to ever put slide film through that camera, so that difference is within an acceptable tolerance for me. The AE-1 meter is being weird since the last time I used it. That camera currently has all the light seals scraped out of it and is waiting on new ones to get it back in the fight. I'll see if I can get the meter working as it should when I next take it apart. It has worked in the past and given me good B&W negatives, but I haven't shot it in over a year due to light leaks. The OM-G was dead on, so near as I could tell - its meter readout only really gives you 1 stop increments to read, but it seemed more or less right on.

Here's the weird one - my Elan II. A couple of years ago, I noticed that the Elan II was spitting out thin negatives, and upon closer investigation of the problem, found the meter to be inexplicably, precisely 1 stop off in all "real world" metering situations. I've been offsetting that error by setting 1-stop slower ISO speed since then with good results. So I expected to see that same error tonight.

Instead what I found was... the meter absolutely will not detect anything when shining it at the LED panel at 12EV. I can be inches away from the panel, wide open at f/1.8, with a 20 second shutter speed, and the meter readout in the viewfinder will still be pegged at "-2" and blinking. If I point it at the extremely dimly lit wall in the room with those same settings, suddenly it swings to the opposite end of the scale, indicating (correctly) that I'm overexposing by more than 2 stops. If I increase the brightness, the meter will wig out and flip back and forth between -2 and +2 with no stops in between. It also seems confused about how brightly to illuminated the green meter readout in the viewfinder, and hops back and forth between them. But at 12EV, it's like that big rectangle of light is completely invisible to the camera. Something about that LED panel just doesn't play nicely with the (already weird) Elan II meter. Very odd.
 

koraks

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Your LED panel likely uses PWM to adjust color temperature and for sure it does for brightness. This means it basically flickers like mad, but too fast for you and me to notice it. Apparently the Elan does notice it...
 
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BHuij

BHuij

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Yeah, PWM could explain why the meter gets so wacky as brightness on the panel is adjusted. What's strange to me is that it will read the reflected light of the panel off of walls (though I don't know yet how accurate the reading is). Just not the transmitted light through the diffuser in front of the LEDs themselves.
 
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Yeah, PWM could explain why the meter gets so wacky as brightness on the panel is adjusted. What's strange to me is that it will read the reflected light of the panel off of walls (though I don't know yet how accurate the reading is). Just not the transmitted light through the diffuser in front of the LEDs themselves.

Is it perhaps polarised? I don't see why it would be, but that could explain the behaviour you describe. I believe some light meters don't like linear pol filters.
 

koraks

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Yeah, PWM could explain why the meter gets so wacky as brightness on the panel is adjusted. What's strange to me is that it will read the reflected light of the panel off of walls (though I don't know yet how accurate the reading is). Just not the transmitted light through the diffuser in front of the LEDs themselves.

Yes, that's odd. I was thinking about this and I can see how it might have something to do with the difference/balance between stray light in the room and your panel. If the camera 'sees' pretty much only the panel, the contrast between PWM ON vs. OFF is plenty of stops. It may be a lot less if you meter the indirect light bouncing off of a wall, where it's blended with other (non-PWM-ed) light. Just a wild thought though.
 

koraks

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It's puzzling for sure. So far I've been able to withstand the inclination to give it a try with one of my EOS30v's (which IIRC is the Elan 7ii). I use those quite a lot, but never noticed anything particular w.r.t. the metering system.
 

MattKing

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The Elan 7 probably employs a beam splitter in the metering system - so polarized light might be an issue.
Perhaps the 35 zone evaluative metering is confusing it.
 
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BHuij

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Other than finding it to be a stop too hot years ago, it has always behaved exactly as expected in actual shooting scenarios for me. Only when I decided to bench it did I find that my methodology for doing so is apparently incompatible with this specific meter :D

FWIW, I believe that the EOS 30v is the European name equivalent to the North American Elan 7NE. My Elan II would be called an EOS 50 in Europe. Whether the meters are meaningfully different from each other... I won't even hazard a guess.

Perhaps with this specific camera, I can skip all of the academic approaches to determining whether it's suitable for shooting slide film, and instead just go burn a roll of Ektachrome to arrive directly at that conclusion one way or another :smile:
 
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BHuij

BHuij

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The Elan 7 probably employs a beam splitter in the metering system - so polarized light might be an issue.
Perhaps the 35 zone evaluative metering is confusing it.

So far all my tests are using Partial metering mode, which should a 9.5% circle in the center of the frame. Still, there are any number of things that could be working in conjunction to cause this odd behavior.
 

koraks

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FWIW, I believe that the EOS 30v is the European name equivalent to the North American Elan 7NE. My Elan II would be called an EOS 50 in Europe. Whether the meters are meaningfully different from each other... I won't even hazard a guess.

Oh thanks for remembering or looking that up. I do have a 50e here that I use from time to time (also never noticed anything particular about it); I think that would have been the Elan IIe then, logically? I assume it has the same metering system as the Elan II/EOS50, since the only addition of the 'e' was the eye control autofocus.

Perhaps with this specific camera, I can skip all of the academic approaches to determining whether it's suitable for shooting slide film, and instead just go burn a roll of Ektachrome to arrive directly at that conclusion one way or another :smile:

I'd have no qualms whatsoever doing that, personally. I've used several EOS cameras, and they've always been solid, reliable performers!
 
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BHuij

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Yeah the EOS 50e = the Elan IIe, and I do believe the only difference between the cameras is the eye-controlled AF. I imagine the metering systems are identical.

If you get a chance, let me know if yours will register PWM-controlled LED panels :D
 

koraks

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Well, of course, no PWM-ed LED panel around when you need one...but there's always my enlarger, which is very much PWM-ed LED alright. Just had a go with the ESO50e and a EF 100/2, meter set to partial, camera in manual mode and see what the meter does. It seems to behave perfectly normally. I think the PWM frequency on my LED head is currently around 1kHz, although it might as well be 5kHz; I'm really not sure. Something in that range in any case. Whatever it is, it's not bothersome to this camera.

Really not sure what's up with the combination of the camera and that particular LED panel!
 
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