| Author |
Message |
    
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 6
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, January 06, 2009 - 09:56 pm: | 
|
I picked up the above light meter at a local camera store yesterday. The owner said it was off by four stops and sold it to me for $5. I didn't really need it, but I couldn't let it sit there for that price.
I already own a Luna Pro F, so I put a fresh 9v battery in the SBC and take it outside and start comparing readings. No way is it four stops off, unless my F is also. They read within 1/3 stop of each other, whether pointing the meters at a scene or using the diffuser. Each of these meters has an adjustment screw on the back to tweak the reading, but since I didn't know which was closest to being correct, I just left the screws alone.
So, I get out my only camera with a trustworthy meter -- my digital EOS XS, and start doing some comparisons. That's when things started getting interesting. I was getting readings between the two meters and the XS that varied from almost identical to as much as 1-2/3 stops off. I had the XS's zoon set to a focal length that most closely corresponds to that of a "normal" lens, but I'm wondering if its evaluative metering pattern might be leading me astray.
I don't have any sort of calibrated light source or whatever it is that a tech would use to check a meter, so I'm having to do with what I've got around here. The weather's been pretty bad lately, so I'm hoping for a sunny day soon where I can meter blue sky with the camera and both meters and see if I still get the same difference. I've got an 18% gray card around here somewhere, but I've no idea where it is at the moment.
So, given no test equipment, is there a halfway reliable way to test then calibrate one of these meters?
Best,
Michael |
Ethostech
Tinkerer
Username: Ethostech
Post Number: 103
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 07, 2009 - 05:53 am: |
|
The variances between your two Luna Meters is minuscule.
Such could be accounted for by as little as not having first ensured that each meter is correctly zeroed.
The angle of acceptances between the Lunas and the EOS in evaluative mode with a 50mm lens would probably acount for the Luna/EOS differences.
In theory - light values are absolute but in practice there are abundant variables such as component tolerances, battery diode regulation accuracy, and of course the progressive changes in ambient light which the eye does not reasily perceive.
If your EOS gives good results - trust it. Electronic cameras with sophisticated integrated metering seldom produce the readings which are identical with those taken with an external meter - so the EOS is not a good reference point for evaluation of your Lunas. One third of a Stop is innocuous given the lattitude of modern films. It is a difference which you would be unable to detect upon super-lupe examination of the resultant negatives or positives. Sounds to me like you are in good shape to take award-winning photographs.
Happy New Year |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 7
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 07, 2009 - 02:12 pm: |
|
Thanks for the feedback.
As fortune would have it, today's weather is beautiful. Not a cloud in the sky. So got out both meters and the EOS and metered a patch of blue sky, well away from the sun (had my back to it, in fact).
Once again, the F and SBC were reading within 1/3 stop of each other. Metering with the EOS XS, using all three metering patterns, achieved identical results. And the EOS's meter agreed exactly with the F's. So, cool! I picked up a perfectly functioning SBC for $5!
After playing around with it some, I think I know where the folks at the camera store messed up. The SBC's outer dial, which normally adjusts shutter speed, also has an inner ring that can be turned independently. This is useful for EV compensation. The inner ring had been displaced from its "zero" point. When this is done, a red parallelogram is revealed, which is usually covered by a parallelogram on the ring. I guess they didn't notice that the ring wasn't zeroed.
Best,
Michael |
Puderse
Tinkerer
Username: Puderse
Post Number: 24
Registered: 09-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 08, 2009 - 08:04 am: |
|
When all else fails read the instructions! |
|
