MattKing
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The Luna Pro SBC uses a 9 volt battery and an SBC cell - that video is for a Luna Pro.
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SR44/lR44 battery adapter
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The Luna Pro SBC uses a 9 volt battery and an SBC cell - that video is for a Luna Pro.
MattKing
Moderator
As far as I am aware, the CDS sensor is also voltage dependent.
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- Kodachromeguy
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- Reason: Why bother?
OP
OP
My sbc uses the button batteries, Gossen made these names in a confusion of nomenclatures.
(The marketing name nomenclature really can get confusing!) Are you referring to this one, named in th eUS as Luna Pro S?:
MattKing
Moderator
And in any case, that "S" model uses a CDS cell.
The "SBC" model(s) are the first of the Gossen meter line that switched to Silicon Blue Cells, and modern batteries.
Yes, of course you’re correct in these facts. We still are not sure which meter Eli has; hopefully a picture will be posted to fully resolve this apparent discrepancy of knowledge.
OP
OP
A picture might be forthcoming latter this week, my darkroom is inaccessible at the moment for hvac work at the moment.
Good luck with the HVAC work. That can be expensive and inconvenient, but when done very fulfilling.
So, I understand this argument, but I am not sure if it works for all meters in practice. I will try to rephrase it so that others can understand better.
First, the CdS photoresistor merely translates light levels into resistance. The idea is that if it's exposed to light at 1 lux, it has a resistance of (for example) 100 KOhms, and for light at 10 lux, it has a resistance of 10 KOhms. These are just example values. You can see an example photoresistor datasheet at https://cdn.sparkfun.com/datasheets/Sensors/LightImaging/SEN-09088.pdf (not very detailed). Typically the resistance has some inverse logarithmic slope as a function of lux, which the datasheet calls "gamma" = 0.7, for that particular CdS cell.
So, if a given amount of light corresponds to some particular LV and causes the cell to have a resistance of so many KOhms, then for a simple light meter, everything else in the circuit is just resistors. If you turn up the supply voltage from 1.35 to 1.5 volts, you should get an increase in the currents in each leg of the circuit by a factor 1.5/1.35. And the needle movement (galvanometer) is basically a current sensor. So the needle should deflect a little more, and mtjade2007's argument is that you can compensate by adjusting the ISO dial, in a predictable fashion.
(Most meters that used a mercury battery also used an analog needle indicator to my knowledge, not LEDs or semiconductor current sensing; I can't think of an exception, although there probably is one.)
I think the main problem here is that the meter circuit has to approximate the logarithmic relation of incident light to LV and thus to meter movement, using some imperfect CdS cell that has a log slope of resistance per lux that isn't 1. So there are some series and parallel resistors: voltage dividers with trimpots, etc, that roughly mock up the logarithmic function you want. And it's not guaranteed that increasing the supply voltage linearly, will get you the same approximated log function. I think this is why some cameras/meters are more sensitive to battery differences than others.
The CdS photoresistor is itself a semiconductor and I suppose there's a possibility that it is not ohmic (meaning current isn't completely linear V/R), but that's a little more exotic and I couldn't find any technical discussion of non-ohmicity in photoresistors.
That's not the relevant point.
The important consideration is the discharge curve of different type of battery chemistry as the battery ages.
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Yes, no doubt about this. However, an AI overviw from Google search revealed this:
Yes, the resistance of a Cadmium Sulfide (CdS) photo sensor (or Light Dependent Resistor - LDR) is somewhat sensitive to the voltage applied to it, but its primary and dominant sensitivity is to light intensity.
I believe the nolinearty of CDS due to the voltage variation is much insignificant than the voltage itself causing the current through the sensor to vary. I jusr did an experiment to see if my thought is valid or not.
I used two Gossen Luna Pro to do a measurement experiment. One meter has a weak battery and the other has a fairly fresh one of 1.55V. The battery check on the first meter showed the needle just slightly over the red zone on the scale of the meter. The 2nd meter showed the needle a bit more over the red zone. I set the film speed of the 2nd meter about 15% slower. Interestingly both meter gave me almost equaly measurement of a same light source.
This experiment may have a large error margin and need a more tight control of the measurement process. I suggest the Gossen Pro owners to test shoot some film with the film speed set to 15% slower on the meter and see if it makes the meter useful without using any adapters.
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Excellent point. I actually thought of that a long while back when the 15% idea came to mind. This was a complex issue too complicated to me so I simply put it aside untill I found it critical and can not be ignored.
The Galvanometer itself is never a linear device. We often saw for example analog volt meters with even scale on them. That makes everyone believe the meter is linear. The linearty of the meter actually varies a lot depend on the quality of the meter. I have quite a few Gossen Pro meters. I found them not really equal with each others.
Again why not give it a try and see if this 15% idea will work for you or not. I think Gossen meters were accurately calibrated when new. But over the years (50 or so?) many of them could have significant margin of error now. So the 15% reduction of film speed to compensate the baterry voltage increase may be questionable but it sure should help reduce the error margin I hope.
Most my 35mm cameras it's just removing the bottom cover. I put the diode where there is room, usually near the battery holder. You do need to make sure you put it in the right way. Getting it wrong doesn't hurt anything, camera just won't turn on. It involves cutting one of the battery wires and splicing the diode in. Make to insulate the diode leads.
OP
OP
Be sure you’re not shorting out the diode/camera and use shrink tubing.
There is also a guy selling tiny 1.35V and and 2.7V semiconductor regulator chips that can be wired in circuit.
We need not see a picture...the SBC model uses 9V battery; other models, which use CdS sensor, use mercuric oxide button cell.
Your earlier statement tells us enough information for clarity, "My sbc (wrongly identified) uses the button batteries."
But as my testing of Olympus OM-1 meter pointed out, it is important to test and see if the ***amount of meter error*** changes in LOW light vs in BRIGHT light, too!
And also determine if the error magnitude is altered by the change in battery Voltage as the battery ages.
I have no idea how well they work or how long they last, but since I have a rangefinder on the way that takes PX625 I looked on my local go-to battery shop's webpage and found these for around 1,60 euros a piece.
(I have never received expired batteries from them, they sometimes have old product photos on their website)
(I have never received expired batteries from them, they sometimes have old product photos on their website)
You might want to let us know what specific Brand and Model of camera!
PX625 battery was mercuric oxide 1.35V constant output, the PX625A was alkaline 1.5V and declining Voltage during its lifetime.
Some specific cameras CAN take 1.5V declining Voltage battery, and others CAN NOT.
Thank you! It's an Olympus 35 SP. All the links I saw said it uses PX625, but after seeing your post it appears to use the 1.3V version, which is not what I bought.
MattKing
Moderator
I have a friend with skills that I don't have who has, as a fun experiment for him, taken one of those alkaline 625 cels, pulled out the battery part and converted the housing to a voltage reducing adapter for smaller silver oxide cels.
From the sounds of things, it would be expensive to do that regularly.
From the sounds of things, it would be expensive to do that regularly.
CRIS in Arizona sells the MR9 adapter. I have one that I bought from them about 15 years ago and it's still working.
This might have been stated already, but….
I recently researched the same thing for my vintage Nikon.
The size difference can be overcompensated by installing a small plumbing o ring to take up the slack space. The thickness of the battery is fine, but it is too small. AI will tell you what size o ring to use. Ask it to give you both size and common name.
As for the slight voltage discrepancy, apparently my camera can tolerate this slight difference.
The higher voltage will affect readings, but if you have access to a light meter, adjust your camera iso to match the correct reading.
You should be golden.
Good luck.
I recently researched the same thing for my vintage Nikon.
The size difference can be overcompensated by installing a small plumbing o ring to take up the slack space. The thickness of the battery is fine, but it is too small. AI will tell you what size o ring to use. Ask it to give you both size and common name.
As for the slight voltage discrepancy, apparently my camera can tolerate this slight difference.
The higher voltage will affect readings, but if you have access to a light meter, adjust your camera iso to match the correct reading.
You should be golden.
Good luck.
OP
OP
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