Mark W
dazed and confused
OK after having been beat up for about 30 posts for the way I vented my pent up anger. After reading for years now about 1.35V batteries and the problems their loss to the camera world has caused I will repost my message.
No unmodified Canonet or other camera designed for a single 1.35V Mercury cell battery that does not have a built in voltage regulator can indicate the proper reading for any given amount of light.
This has nothing to do with if the meters mechanics are worn etc. A Cds light meter is simply a voltmeter the reading on the voltmeter is effected by the resistance to current flow caused by light on the cell. The more light hitting the cell the more resistance to flow.
If you use a higher voltage battery then the 1.35V the base voltage will cause an under exposure as the meter will misinterpret the high voltage as less light hitting the cell.
If you use a battery with Alkaline chemistry due to that batteries slow gradual discharge rate when the battery is new the higher 1.6 voltage of the new Alkaline cell will cause an underexposure if you set based on the meter reading. As the battery passes through 1.4-1.3 volts (the normal operating voltage of a Mercury cell) The meter will give and accurate reading and all will be fine. Once the voltage drops to about 1.2 Volts the meter will start giving a reading that if followed will result in an overexposure.
If a Silver Oxide cell a type of battery that has a much steadier discharge curve but at 1.55V is used the meter reading will remain constant almost until the cell is discharged but the whole life of the battery it will cause a meter reading that if followed will cause an underexposure.
Adjusting the ASA will not make up for this as the reading is not linear but based on a curve adjusted to the voltmeter/lightmeters reaction to a cell with 1.35Volts as it's base voltage.
SO if you can live with a meter reading as much as a full stop over or under then use what ever battery you want.
If on the other hand you would prefer to use the very fine Cds metering and excellent AE features of a camera like the Canon Canonet in it's various forms.
Them I strongly suggest you either.
1. Use a 1.35V merc. (my chosen option)
2. Have a qualified camera service tech modify your cameras circuitry to include a voltage regulator that will hold the voltage to a constant within the 1.4-1.3 voltage range.
3. Use an external voltage regulator like the type that fit in the battery compartment and hold a smaller Silver Oxide cell
4. Use either a Zinc air hearing aide battery with some type of spacer or one of the camera used designed Wein Air cells (which is a Zinc air cell)
5. Use you $400.00 Sekonic hand held that operates off of an easy to find 1.5Volt AA cell.
It was asked about camera that originally operated on stacked mercury cells or used multiple button cells. The reason these cameras have the higher voltage requirements has nothing to do with their meters it is due to the designers need for more current to operate AE features including electronically controlled shutters and variable diaphragms.
The meters in these camera still operate on 1.35V as a base so these cameras will already have within their circuits a voltage regulator that drops the feed voltage to the metering circuit to 1.35V.
Thus allowing a modern 1.5v or stack of 1.5V cells to work in the place of the original battery.
The Canon EF (FD mount AE body) uses two 1.35V PX-625 cells but since the meter still requires 1.35V to operate properly Canon put a Voltage regulator in the meter feed circuit thus allowing us now to feed the camera 1.5V cells Silver Oxides being the better choice of the two options in that size.
I hope this works better for those offended at my last post
No unmodified Canonet or other camera designed for a single 1.35V Mercury cell battery that does not have a built in voltage regulator can indicate the proper reading for any given amount of light.
This has nothing to do with if the meters mechanics are worn etc. A Cds light meter is simply a voltmeter the reading on the voltmeter is effected by the resistance to current flow caused by light on the cell. The more light hitting the cell the more resistance to flow.
If you use a higher voltage battery then the 1.35V the base voltage will cause an under exposure as the meter will misinterpret the high voltage as less light hitting the cell.
If you use a battery with Alkaline chemistry due to that batteries slow gradual discharge rate when the battery is new the higher 1.6 voltage of the new Alkaline cell will cause an underexposure if you set based on the meter reading. As the battery passes through 1.4-1.3 volts (the normal operating voltage of a Mercury cell) The meter will give and accurate reading and all will be fine. Once the voltage drops to about 1.2 Volts the meter will start giving a reading that if followed will result in an overexposure.
If a Silver Oxide cell a type of battery that has a much steadier discharge curve but at 1.55V is used the meter reading will remain constant almost until the cell is discharged but the whole life of the battery it will cause a meter reading that if followed will cause an underexposure.
Adjusting the ASA will not make up for this as the reading is not linear but based on a curve adjusted to the voltmeter/lightmeters reaction to a cell with 1.35Volts as it's base voltage.
SO if you can live with a meter reading as much as a full stop over or under then use what ever battery you want.
If on the other hand you would prefer to use the very fine Cds metering and excellent AE features of a camera like the Canon Canonet in it's various forms.
Them I strongly suggest you either.
1. Use a 1.35V merc. (my chosen option)
2. Have a qualified camera service tech modify your cameras circuitry to include a voltage regulator that will hold the voltage to a constant within the 1.4-1.3 voltage range.
3. Use an external voltage regulator like the type that fit in the battery compartment and hold a smaller Silver Oxide cell
4. Use either a Zinc air hearing aide battery with some type of spacer or one of the camera used designed Wein Air cells (which is a Zinc air cell)
5. Use you $400.00 Sekonic hand held that operates off of an easy to find 1.5Volt AA cell.
It was asked about camera that originally operated on stacked mercury cells or used multiple button cells. The reason these cameras have the higher voltage requirements has nothing to do with their meters it is due to the designers need for more current to operate AE features including electronically controlled shutters and variable diaphragms.
The meters in these camera still operate on 1.35V as a base so these cameras will already have within their circuits a voltage regulator that drops the feed voltage to the metering circuit to 1.35V.
Thus allowing a modern 1.5v or stack of 1.5V cells to work in the place of the original battery.
The Canon EF (FD mount AE body) uses two 1.35V PX-625 cells but since the meter still requires 1.35V to operate properly Canon put a Voltage regulator in the meter feed circuit thus allowing us now to feed the camera 1.5V cells Silver Oxides being the better choice of the two options in that size.
I hope this works better for those offended at my last post
Last edited:
kabkos
Established
A few minor corrections, a CDS cell has the resistance decrease as light levels increase. The meter with a constant voltage supply will read linearly across its operating range. Thus using a silver cell (which cause the meter to read higher , meaning under exposed pictures) than a mercury cell will but is equally applicable. This is due to the 1.55v vs. the 1.35v of the silver vs. mercury cells. A resetting of the ASA will accomodate this difference. The manufacturers designed the meter read out around a mercury battery because the mercury battery was about 1/10 the cost of a silver oxide battery. The manufacturer could have just as easily made the meter dials for silver oxide battery usage. Hence the resetting of ASA will work. A better solution would be to install a Schottsky diode in the battery circuit which will drop the 1.55v down to 1.35v, thus eliminating the confusion of remembering to reset the ASA value.
The statement that the meter cells are not linear and a difference in operating voltage can not be accomodated with a change in ASA is incorrect. Otherwise how would you design a meter that could accomodate various light levels. The lightmeter is basically a voltmeter where you are measuring the voltage drop across the CDS cell in the case of the battery driven lightmeters and where you are measuring the voltage from a selenium cell in the case of the selenium lightmeters. All the meter is doing is giving a linear relationship to the voltage across the meter windings.
The statement that the meter cells are not linear and a difference in operating voltage can not be accomodated with a change in ASA is incorrect. Otherwise how would you design a meter that could accomodate various light levels. The lightmeter is basically a voltmeter where you are measuring the voltage drop across the CDS cell in the case of the battery driven lightmeters and where you are measuring the voltage from a selenium cell in the case of the selenium lightmeters. All the meter is doing is giving a linear relationship to the voltage across the meter windings.
Duncan Ross
Say it with flashbulbs
I think I disagree about your point regarding ASA. I think in most cases compensating for that extra stop by adjusting your ASA is fine.
Light dependent resistors produces a more or less linear change in resistance across its working range as a function of the lux hitting it. As many cameras change their ASA setting by merely exposing more or less of then sensor to light this is a scalar change. I see no reason why scaling up the response with extra volts and scaling it back down with less light would dramatically change this, especially as such a tiny portion of the response of the sensor is actually 'in range'.
Have you any more detail on this effect? I would be very interested as it directly applies to my Rollei.
Many thanks,
Duncan
Light dependent resistors produces a more or less linear change in resistance across its working range as a function of the lux hitting it. As many cameras change their ASA setting by merely exposing more or less of then sensor to light this is a scalar change. I see no reason why scaling up the response with extra volts and scaling it back down with less light would dramatically change this, especially as such a tiny portion of the response of the sensor is actually 'in range'.
Have you any more detail on this effect? I would be very interested as it directly applies to my Rollei.
Many thanks,
Duncan
jlw
Rangefinder camera pedant
Mark is right that in most cameras, higher-voltage cells will not provide the same results as 1.35v cells. People need to learn to accept this fact. To summarize briefly, there are three problems with the substitute cells:
-- The voltage is different, leading to different meter readings.
-- The linearity is different, meaning that if you tweak the ISO dial to get a correct reading in bright light, it won't be correct in dim light, or vice-versa.
-- The output of alkaline cells isn't nearly as constant over time as mercury cells (silver cells are much better in this regard.) The variable output means that if you tweak your camera to give correct readings at some particular light level when your battery is fresh, it won't be correct a few weeks or months later.
However, lots of people do get away with using substitute cells. One reason they do is that a CdS cell is a resistor -- it has high "dark resistance" (lots of resistance in dim light, less in bright light.)
The effect of too high a voltage is to cause the meter to read too high, making the camera "think" there is more light than there really is, producing underexposure.
The voltage drop caused by the CdS cell depends on its resistance, so that in dim light (where the cell has more resistance) the voltage drops more, partially mitigating the effect of the substitute cell's higher voltage in the first place.
This means that although the meter reading will be wrong, it will be less wrong in dim light (where correct exposure matters more) and more wrong in bright light (where conditions may be more forgiving.) Such factors as slide film's preference for slight underexposure in bright light, the fact that old shutters may not give their full rated speeds, and the fact that non-18-percent-gray subjects may yield nonstandard exposures with a meter that reads wide areas may all conspire to help mask the effects of incorrect meter voltage (or not, if it's not your lucky day.)
Where this puts you is that if battery X gives you acceptable results for your kind of picture-taking most of the time, call yourself lucky and enjoy the feeling of getting away with it. Just be wary of trying to transfer the same exposure readings to a different camera, or comparing the readings from your substitute-battery meter to those from a different meter.
-- The voltage is different, leading to different meter readings.
-- The linearity is different, meaning that if you tweak the ISO dial to get a correct reading in bright light, it won't be correct in dim light, or vice-versa.
-- The output of alkaline cells isn't nearly as constant over time as mercury cells (silver cells are much better in this regard.) The variable output means that if you tweak your camera to give correct readings at some particular light level when your battery is fresh, it won't be correct a few weeks or months later.
However, lots of people do get away with using substitute cells. One reason they do is that a CdS cell is a resistor -- it has high "dark resistance" (lots of resistance in dim light, less in bright light.)
The effect of too high a voltage is to cause the meter to read too high, making the camera "think" there is more light than there really is, producing underexposure.
The voltage drop caused by the CdS cell depends on its resistance, so that in dim light (where the cell has more resistance) the voltage drops more, partially mitigating the effect of the substitute cell's higher voltage in the first place.
This means that although the meter reading will be wrong, it will be less wrong in dim light (where correct exposure matters more) and more wrong in bright light (where conditions may be more forgiving.) Such factors as slide film's preference for slight underexposure in bright light, the fact that old shutters may not give their full rated speeds, and the fact that non-18-percent-gray subjects may yield nonstandard exposures with a meter that reads wide areas may all conspire to help mask the effects of incorrect meter voltage (or not, if it's not your lucky day.)
Where this puts you is that if battery X gives you acceptable results for your kind of picture-taking most of the time, call yourself lucky and enjoy the feeling of getting away with it. Just be wary of trying to transfer the same exposure readings to a different camera, or comparing the readings from your substitute-battery meter to those from a different meter.
denishr
アナログ侘・&#
Thanks, Mark, for a very nice and comprehensive explanation 
We'll just forget about the other one, if you don't mind
Denis
We'll just forget about the other one, if you don't mind
Denis
Honu-Hugger
Well-known
Mark,
Very nicely put and I for one never disagreed with what you said originally -- it is all very logical and based in fact. Furthermore, I truly hope you didn't take any of the last thread personally. I should not speak for the group although I would be surprised if they did not share my feelings, but I was not only not offended by your post but I was just trying to have a little good-natured fun. If that resulted in anything otherwise then you have my sincere apology.
Very nicely put and I for one never disagreed with what you said originally -- it is all very logical and based in fact. Furthermore, I truly hope you didn't take any of the last thread personally. I should not speak for the group although I would be surprised if they did not share my feelings, but I was not only not offended by your post but I was just trying to have a little good-natured fun. If that resulted in anything otherwise then you have my sincere apology.
Duncan Ross
Say it with flashbulbs
...and above all remember that however much voltage curves and ASA adustments confuse you, the cds cells themselves get /really/ confused by colour so don't meter anything green!
taffer
void
Well, as I said in the other post, I got *consistent enough* results from my G-III 17 using a PX625 1.5V with 100 ISO slide film. Of course I'm not saying it's the correct way to go, only stating the fact that it worked for me on that occasion
Thanks for reposting your info Mark, there's also another option though (#5) in the shape of for example a small $25 second hand Gossen Pilot 2, which requires no batteries and does a pretty nice job on most 'normal' light conditions.
Regards,
Oscar
Thanks for reposting your info Mark, there's also another option though (#5) in the shape of for example a small $25 second hand Gossen Pilot 2, which requires no batteries and does a pretty nice job on most 'normal' light conditions.
Regards,
Oscar
back alley
IMAGES
see?
it's not necessarily what is said but HOW it is said.
and it did sound like a bunch of pent up anger which i was not about to accept as mine.
i like it when we all play nice.
joe
it's not necessarily what is said but HOW it is said.
and it did sound like a bunch of pent up anger which i was not about to accept as mine.
i like it when we all play nice.
joe
Solinar
Analog Preferred
As I have migrated to vintage cameras, which are mainly from the mid-1950's, I've become ever more appreciative of my Gossen Digisix. The battery free, pre-AE era cameras that I have usually offer better range finders than their 70's counter parts, most have lens interchangeabilty, and all of them make even my Olympus 35SP feel like a Johnny come lately.
Frankly, I get more consistent exposures from an incident reading than I ever did from even the best of reflective meters. You truly have to know where to point a reflective meter and still have to think of the variables, such as back lighting or off-gray colors.
Anyway, I still maintain three web pages giving information on the Olympus 35RC, 35RD and 35SP that are now four years old. Of the email I receive, 80% are enquiry with regards to replacement batteries. On each web page I clearly mention the Zinc Air cells and their trivial costs. What surprises me is how many people just do not read the info regarding replacement batteries.
Frankly, I get more consistent exposures from an incident reading than I ever did from even the best of reflective meters. You truly have to know where to point a reflective meter and still have to think of the variables, such as back lighting or off-gray colors.
Anyway, I still maintain three web pages giving information on the Olympus 35RC, 35RD and 35SP that are now four years old. Of the email I receive, 80% are enquiry with regards to replacement batteries. On each web page I clearly mention the Zinc Air cells and their trivial costs. What surprises me is how many people just do not read the info regarding replacement batteries.
back alley
IMAGES
gee andrew, while i have you here...i was wondeing about replacing those pesky batteries...
joe
joe
bmattock
Veteran
My Sekonic L-358 with 1 deg spot attachment didn't cost $400, and it doesn't use a AA battery. But it beats every vintage camera ever made for accuracy, when I need it to. Easy to carry, accurate, works as a reflected, incident, flash, spot, averaging, and so on. I have ONE Sekonic and HUNDREDS of vintage cameras to use it with, and that's my choice for dealing with the 1.35 volt mercury battery panic.
This is wrong how?
What *is* your problem? Even when you're trying to be nice, you have to stick in some shot across somebody's bow. It's starting to irritate me.
Best Regards,
Bill Mattocks
This is wrong how?
What *is* your problem? Even when you're trying to be nice, you have to stick in some shot across somebody's bow. It's starting to irritate me.
Best Regards,
Bill Mattocks
Solinar
Analog Preferred
All I can say is that I like my morning coffee and my hand-held meter. The rest doesn't worry me and I ain't goin to get irratated about it.
bmattock
Veteran
Solinar said:
MMMmmmm, coffee. Me like. Big pot of Ethiopian Harrar and I'm in good shape.
Best Regards,
Bill Mattocks
P
pshinkaw
Guest
As is sit here with my steaming mug of Mozart's Guatamalan, I recalled that six months ago I put tape over 2 of the 4 air holes in a hearing aid battery and installed it in my Gossen Super Pilot. It is still working well. On the first hearing aid battery I tried, I left all 4 holes open and it lasted about 4 weeks.
On this one I left all 4 holes open for 24 hours to get it started. Then I taped up 2 of them.
-Paul
On this one I left all 4 holes open for 24 hours to get it started. Then I taped up 2 of them.
-Paul
Honu-Hugger
Well-known
As perhaps another perspective: in spite of the best efforts of many that put way more energy into "exactness" or "precision" than I believe most of us are willing to do, this still is not an exact science.
I only know enough of this process to realize it is way too much trouble for me to bother with, but how many of us are using color temperature meters in place of conventional light meters -- and having them regularly and properly calibratred? How many of us are buying our film in bulk lots with consistent dye numbers and randomly testing rolls against constant color controls? In spite of these efforts, if you were to undertake them, you will still deal with variables on occasion.
Life is way too short for me to bother with this sort of nonsense -- bracketing is so much easier!!! Now, where's the coffee?
I only know enough of this process to realize it is way too much trouble for me to bother with, but how many of us are using color temperature meters in place of conventional light meters -- and having them regularly and properly calibratred? How many of us are buying our film in bulk lots with consistent dye numbers and randomly testing rolls against constant color controls? In spite of these efforts, if you were to undertake them, you will still deal with variables on occasion.
Life is way too short for me to bother with this sort of nonsense -- bracketing is so much easier!!! Now, where's the coffee?
cp_ste.croix
At the beginning again.
i'm not sure if it's been said before but Karen Nakamura mentions the battery issue on Photoethnography.com
"Although it uses the much hated PX625 mercury battery that is no longer available in the U.S., the Canon engineers did the Right Thing™ and made the circuitry voltage compensating. This means you can use a standard alkaline PX625A battery which you can buy at most larger drugstores or a LR/SR44 battery with liberal amounts of tin foil. Yippee."
Is she wrong? Is this something confined to the GIII? Am I merely stirring an overfilling pot ? I already feel sort of responsible for hitting the hornet's nest with a stone, as it were. I mean no harm.
"Although it uses the much hated PX625 mercury battery that is no longer available in the U.S., the Canon engineers did the Right Thing™ and made the circuitry voltage compensating. This means you can use a standard alkaline PX625A battery which you can buy at most larger drugstores or a LR/SR44 battery with liberal amounts of tin foil. Yippee."
Is she wrong? Is this something confined to the GIII? Am I merely stirring an overfilling pot
? I already feel sort of responsible for hitting the hornet's nest with a stone, as it were. I mean no harm.
K
Kin Lau
Guest
I've seen references to Karen's page on the GIII, and I think she's mistaken. I've heard of other's who taken apart their GIII's and did not find such a circuit.
Kim Coxon
Moderator
Hi, Just to add my thoughts:
It is actually quite difficult to make a voltage regulater for such small voltages with such a small difference and more so 30 years ago. Many of the SLRs of the time such as Pentax got round the problem by using a "bridged" circuit. In this there are effectively 2 "rails". One has the cell in it and the other a variable resistor controlled by the ASA/Speed dial. Correct exposure is indicated when there is zero difference between these ie the needle is in the middle. As the battery voltage is supplied to both rails, they are equally affected so the battery type doesn't matter. I recently "aquired" a Lynx 5000 and this appears to have this type of meter and doesn't seem to be affected by battery type. although this circuit design is better, it doesn't really lend itself to the shutter priority mode used by so many rangefinders. I suspect that the Canon SLRs had this type of circuit which is why there may have been some confusion
As far as the Canonets are concerned, I find by far the easiest and cheapest option is the pop the top off and adjust the variable pot just behind the winding flag. This must be done on a good sunny day. As has been mentioned earlier at low light levels the difference is so small it hardly matters and it is difficult to set. I don't think the aguments about non linearity hold scrutiny. Most cells are slightly different which is why there is a trim pot. By doing this and using silver cells, I don't have to remember to reset the ASA dial and most meter readings come out within a 1/2 stop which is good enough for most use. In fact tilting the camera up and down slightly can change the meter reading by up to 3 stops which is far worse. If you need really accurate meter readings, you almost have to use a good incident light meter as none of the inbuilt meters is that accurate.
Anyone know where the trimmer is on the Konica S2?
Kim
It is actually quite difficult to make a voltage regulater for such small voltages with such a small difference and more so 30 years ago. Many of the SLRs of the time such as Pentax got round the problem by using a "bridged" circuit. In this there are effectively 2 "rails". One has the cell in it and the other a variable resistor controlled by the ASA/Speed dial. Correct exposure is indicated when there is zero difference between these ie the needle is in the middle. As the battery voltage is supplied to both rails, they are equally affected so the battery type doesn't matter. I recently "aquired" a Lynx 5000 and this appears to have this type of meter and doesn't seem to be affected by battery type. although this circuit design is better, it doesn't really lend itself to the shutter priority mode used by so many rangefinders. I suspect that the Canon SLRs had this type of circuit which is why there may have been some confusion
As far as the Canonets are concerned, I find by far the easiest and cheapest option is the pop the top off and adjust the variable pot just behind the winding flag. This must be done on a good sunny day. As has been mentioned earlier at low light levels the difference is so small it hardly matters and it is difficult to set. I don't think the aguments about non linearity hold scrutiny. Most cells are slightly different which is why there is a trim pot. By doing this and using silver cells, I don't have to remember to reset the ASA dial and most meter readings come out within a 1/2 stop which is good enough for most use. In fact tilting the camera up and down slightly can change the meter reading by up to 3 stops which is far worse. If you need really accurate meter readings, you almost have to use a good incident light meter as none of the inbuilt meters is that accurate.
Anyone know where the trimmer is on the Konica S2?
Kim
martyr
Member
I remember going through this when my dad gave me my Minolta Hi-Matic 7SII and said, "You can't buy batteries for these old cameras anymore so the light meter isn't going to work. Good luck!" Why hasn't someone out there come out with a straight across replacement for the 625 battery that gives off a steady 1.35 volts of power for the life of the cell? Is it really that hard? Why all this talk of adapters and spacers and zinc-air cells that will last a couple months before they dry out? I can't believe someone hasn't stepped up and saved all the vintage camera enthusiasts of the world by supplying them with a straight across replacement for the 625 mercury battery (and all those other sizes too!) that all their cameras need to work properly. It just seems stupid to me but then again, I haven't really been dealing with the problem for very long and obviously don't know all the ins and outs of battery technology.