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1.55v vs 1.35v in classic rangefinders - light meters measure the same
Old 11-05-2019   #1
Cortexturizer
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Question 1.55v vs 1.35v in classic rangefinders - light meters measure the same

Continuation of my other thread - so I am puzzled as to why my Olympus 35RD, Hi-Matic 7S II and Auto S3 would all measure absolutely the same with either a fresh 1.55v alcaline and a steady 1.35v.

The lightmeter indicated exposure values (F stops in these cases) of all 3 just don't seem to differ between the two voltages at all. What gives? How can that be?

All 3 cameras are in pristine condition, innards are clean, etc.

Any thoughts?
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Old 11-05-2019   #2
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I’m lost in translation.
They show the same or they don’t change at all?
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Old 11-05-2019   #3
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Quote:
Originally Posted by Ko.Fe. View Post
I’m lost in translation.
They show the same or they don’t change at all?
all 3 cameras show the same values in the viewfinder with both voltages
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Old 11-05-2019   #4
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Is that the same in varying light conditions (dark, normal, bright)?
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Old 11-05-2019   #5
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Yes, tried it in various light
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Old 11-05-2019   #6
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Interesting!

I swapped the 1.5v battery in my Leica M5 for a 1.35v and the result was a different value at that time.

It's all magic anyway.
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Old 11-05-2019   #7
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I would SO appreciate it if maybe someone who has these cameras could do a test in theirs. Pretty please?
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Old 11-05-2019   #8
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Sounds like the meter cells themselves are dead. I get this problem once in a while in a camera I'm tinkering with. The battery will send current so the meter will look active but even if I shine a light right at the meter cell, nothing happens. I think 2 out of 3 Konica T3 & T4 SLRs I've worked on have this problem. Strangely enough I had a Konica Auto-Reflex with a meter that worked perfectly.
I've owned all the cameras you mentioned and the needles all reacted to changes in light.
Try cleaning your battery contacts with a pencil eraser and recheck.
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Old 11-05-2019   #9
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Quote:
Originally Posted by Cortexturizer View Post
all 3 cameras show the same values in the viewfinder with both voltages
Compare it with reference meter. If all four are the same, here is no problem.
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Old 11-05-2019   #10
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All 3 cameras take great pictures, the meter cells are fine. I just like them so much that I am aiming for perfection, or as perfect as metering can go with these primitive old meters.

All over the internet I've read that 1.5v makes a two stop underexposure difference. Seems like it makes no difference in my case.
I also tried just before today on my 35 RC. Absolutely no difference.

So at this point, after 4 cameras, I am challenging the internet-wide spread assertion that the new modern alcaline batteries make a difference.
Of course, their discharge curve is very different, but on full charge, I see no difference at all.
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Old 11-05-2019   #11
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I also edited my start of the convo post as upon repeated reading I realized that it may had sounded as the meters were dead.
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Old 11-05-2019   #12
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Maybe there's an excess potential being regulated to a lower operating voltage, making the result independent of terminal voltage, eg both the 1.5 and 1.35 are regulated down to 1.0V. To some degree it makes sense if you study the discharge curves of batteries.
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Old 11-05-2019   #13
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Quote:
Originally Posted by Cortexturizer View Post
All 3 cameras take great pictures, the meter cells are fine. I just like them so much that I am aiming for perfection, or as perfect as metering can go with these primitive old meters.

All over the internet I've read that 1.5v makes a two stop underexposure difference. Seems like it makes no difference in my case.
I also tried just before today on my 35 RC. Absolutely no difference.

So at this point, after 4 cameras, I am challenging the internet-wide spread assertion that the new modern alcaline batteries make a difference.
Of course, their discharge curve is very different, but on full charge, I see no difference at all.
What's the voltage of the various cells under load? How did you ensure the light value remained constant between tests? Did you rest the cells after bright light readings? Etc. Your four camera sample hasn't sold me, yet.
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Old 11-05-2019   #14
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Quote:
Originally Posted by Ricoh View Post
Maybe there's an excess potential being regulated to a lower operating voltage, making the result independent of terminal voltage, eg both the 1.5 and 1.35 are regulated down to 1.0V. To some degree it makes sense if you study the discharge curves of batteries.
This pretty much has to be the case. The cameras that show the same with either voltage, must have internal voltage regulation. Are they more recent than the Leica M5? If so, they probably use technology that wasn't available yet for the M5. A zener diode, maybe.
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Old 11-05-2019   #15
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Quote:
Originally Posted by Rob-F View Post
This pretty much has to be the case. The cameras that show the same with either voltage, must have internal voltage regulation. Are they more recent than the Leica M5? If so, they probably use technology that wasn't available yet for the M5. A zener diode, maybe.
There's various ways of playing the voltage regulation tune, eg use of a Schottky diode, a silicon p-n junction, or a simple resistive-bridge across the cell. However, without knowledge of the load, ie the light cell and beyond, it's difficult to reverse engineer the solution.
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Old 11-05-2019   #16
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Quote:
Originally Posted by Sarcophilus Harrisii View Post
What's the voltage of the various cells under load? How did you ensure the light value remained constant between tests? Did you rest the cells after bright light readings? Etc. Your four camera sample hasn't sold me, yet.
Used several scenes all with constant lighting, no TVs in the background, no cars passing buy throwing lights at certain moments, none of that stuff.
I am telling you the 1.35v it makes no difference at all.

And according to the I N T E R N E T Z it should be a mild difference at all, it should be straight visible as soon as the lower voltage is in.
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Old 11-05-2019   #17
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Quote:
Originally Posted by Ricoh View Post
There's various ways of playing the voltage regulation tune, eg use of a Schottky diode, a silicon p-n junction, or a simple resistive-bridge across the cell. However, without knowledge of the load, ie the light cell and beyond, it's difficult to reverse engineer the solution.
The cameras were not tinkered with prior. There are no diodes or anything, and I would know as I used to build guitar pedals so I know what one looks like

The only camera I haven't tried the mr44 1.35v thing in is my Yashica Minister 700, that is a very old camera so THERE it might make a difference. I'll try it later in the day and post findings.
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Old 11-05-2019   #18
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When the 1.35 mercury cells were banned, some cameras had bridge circuits so they could use silver oxide 1.5 volt cells.

The Schokky Diode is in the CRIS adapter and I had 5 at one time. They worked in some cameras, not in others as they do not pass enough current. Sometimes they worked in bright or dim light , forget which, and not the other. Depends on current draw of meter.

1.55 Alkaline battery has lower voltage as it ages. The banned mercury cells always put out 1.35 until it dies rapidly.

Hearing aid battery and O ring are cheapest solution.
Some cameras can be recalibrated to 1.5 V.

Bad news is your cameras probably have cds cells which are at or near their expected life . SBC cells have longer life.
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Old 11-05-2019   #19
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I've posted this before (as others have) many camera have circuits that compensate for voltage / resistance changes. They may read a stop or so off with a silver oxide battery but if you compensate for that (by changing the iso setting) the meter will read correctly. How do think camera technicians calibrate a camera that took mercury batteries for a silver oxide battery? They aren't changing out the meter circuitry, they simply adjust the resistor pots to get the correct high and low readings with the new battery.
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Old 11-05-2019   #20
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In all Konica Autoreflex T series cameras, the difference is obvious and profound. There is no way I would substitute a 1.5v battery, silver oxide or alkaline, in one of those cameras because they are very sensitive to voltage changes. Also remember that the light value is on a log scale so just adjusting the ISO won't be good enough if you're using slide film. Negative film, go for it. With a Konica T3 or T4 though, for example, I wouldn't even expose negative film without the proper voltage because I have seen a full two stop difference between 1.35v and 1.5v. Then again, I usually shoot meterless anyway so it doesn't matter. But the voltage has always made a difference in meters which require 1.35v. This is the whole reason Gossen makes the battery adapter for the LunaPro.
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Old 11-05-2019   #21
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Quote:
Originally Posted by Phil_F_NM View Post
In all Konica Autoreflex T series cameras, the difference is obvious and profound. There is no way I would substitute a 1.5v battery, silver oxide or alkaline, in one of those cameras because they are very sensitive to voltage changes. Also remember that the light value is on a log scale so just adjusting the ISO won't be good enough if you're using slide film. Negative film, go for it. With a Konica T3 or T4 though, for example, I wouldn't even expose negative film without the proper voltage because I have seen a full two stop difference between 1.35v and 1.5v. Then again, I usually shoot meterless anyway so it doesn't matter. But the voltage has always made a difference in meters which require 1.35v. This is the whole reason Gossen makes the battery adapter for the LunaPro.
Phil Forrest

Please note that I said many, not all
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Old 11-05-2019   #22
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I've never bothered with that voltage difference, its insignificant.
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Old 11-05-2019   #23
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My 35 RD was a recent acquisition, and I just (10 mins ago) received my scans - they are some of the nicest pics I have ever taken.

Perfectly exposed, 1.55v.

So I think I'll just sell the MR-44 on the after market now. Cause it really makes zero difference in my cameras.

Just to repeat once more - I checked using a multimeter that my 35 RD is indeed getting 1.35v from the MR-44 under load. (this was at time of testing the adapter yesterday, the roll of shots I mentioned above was done on lr44 fresh)
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Old 11-05-2019   #24
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Quote:
All over the internet I've read that 1.5v makes a two stop underexposure difference.
Here lies the problem. To the point that even faced with your own experimental data, you are troubled by the internet myths. Because so many people say the same, they must be right. But they are just parroting each other.

To elaborate sightly. Yes, some effect of voltage is to be expected. A significant parameter for CdS photoresistors is gamma=(%change_current)/(%change_light), or for the mathematically oriented, delta_log_current/delta_log_light. Typical value is 0.7. On the other hand, these devices have a linear current-voltage relation (photoresistor).

1.35-->1.55 is a +14% change, equivalent (according to the above) to a light change of:
14%x(1/gamma)=20% approx. That is less than 1/3 of a stop.

As a physicist, I agree that should subject the above to experimental verification. But so far I've used my RF's with built-in meter (35RC, 7sII), with an external meter. But in fact, you have provided independent (even better) verification.
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Old 11-05-2019   #25
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We need a sticky thread on which we can list all the myths; we could start by telling everyone that expensive cameras need servicing and that secondhand ones can be (very) dodgy.


Trouble is, too many idiots in the world and others scared to think for themselves...


Regards, David
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Old 11-05-2019   #26
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Quote:
Originally Posted by BernardL View Post
Here lies the problem. To the point that even faced with your own experimental data, you are troubled by the internet myths. Because so many people say the same, they must be right. But they are just parroting each other.

To elaborate sightly. Yes, some effect of voltage is to be expected. A significant parameter for CdS photoresistors is gamma=(%change_current)/(%change_light), or for the mathematically oriented, delta_log_current/delta_log_light. Typical value is 0.7. On the other hand, these devices have a linear current-voltage relation (photoresistor).

1.35-->1.55 is a +14% change, equivalent (according to the above) to a light change of:
14%x(1/gamma)=20% approx. That is less than 1/3 of a stop.

As a physicist, I agree that should subject the above to experimental verification. But so far I've used my RF's with built-in meter (35RC, 7sII), with an external meter. But in fact, you have provided independent (even better) verification.
Well, this wins as my favorite post

Thanks for the responses guys, very useful. I hope it helps someone else who starts obsessing over this voltage difference.

Cheers
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Old 11-05-2019   #27
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I am reading that when metering the same target the meters on the 3 cameras are invariant no matter whether a 1.35v or a 1.55v battery is inserted and both battery types are delivering correctly metered values. Is my interpretation correct? I only ask as some people seem to be interpreting the question differently though to me the question being asked seems obvious.

A final question is does anyone know if the cameras involved have the same kind of balanced bridge circuit as the Pentax Spotmatic which can happily run on a variety of battery voltages without messing up the metering?

I am told the metering circuit diagram of the Spotmatic looks like this (though to me it is gibberish as I have no training in the field it may mean something to others better endowed in this department than I):

Per this thread...... https://www.pentaxforums.com/forums/...-wanted-2.html

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Old 11-05-2019   #28
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Quote:
Originally Posted by Beemermark View Post
I've posted this before (as others have) many camera have circuits that compensate for voltage / resistance changes. They may read a stop or so off with a silver oxide battery but if you compensate for that (by changing the iso setting) the meter will read correctly. How do think camera technicians calibrate a camera that took mercury batteries for a silver oxide battery? They aren't changing out the meter circuitry, they simply adjust the resistor pots to get the correct high and low readings with the new battery.
+1 on this. It depends on the camera. Seems my OM1 can cope with this in a reasonable way (meter reading is more on the same ballpark with 1.55 and with MR-44. On the other hand, my Leica M5, there is a big difference when using MR-44 and the 1.55 batteries.

Marcelo
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Old 11-05-2019   #29
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Quote:
A final question is does anyone know if the cameras involved have the same kind of balanced bridge circuit as the Pentax Spotmatic which can happily run on a variety of battery voltages without messing up the metering?

I am told the metering circuit diagram of the Spotmatic looks like this (though to me it is gibberish as I have no training in the field it may mean something to others better endowed in this department than I):
Granted, the bridge circuit that I believe (internet, no hands-on experience) to be implemented in the Spotmatic and possibly other cameras is by its principle immune to changes in battery voltage, the only impact of a voltage decrease being a lesser precision of the adjustment (random error, not systematic error). Please keep in mind that this requires a human intervention to "close the loop", with the photographer's hands moving the speed and aperture settings until the photographer's eye and brain are satisfied that the bridge is balanced.

I do not see how this could be applied to an auto-exposure camera relying, like so many Japanese cameras of the seventies, on a trapped needle; I believe the electrical circuit of such cameras is just a series connection of battery, photoresistor, and galvanometer, with maybe a couple potentiometers thrown in to cancel the dispersion in the opto-electrical properties of the CdS cells. Ditto for the match-needle systems in metered manual exposure, such as Canon FT of Minolta SRT101. I could find in my documentation the service manual for the Oly 35DC, with a fairly clear electrical schematic attached. The red ovals show (1) battery; (2) photocell; (3) galvanometer with a current limiting resistor. The other elements belong to battery check, flashmatic, and backlighting correction, not essential in the present discussion. Not an exhaustive proof for all auto-exposure compacts of the seventies, but still better than Interweb Rumor.
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Old 11-05-2019   #30
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Many of these vintage cameras use a CdS sensor (photoresistor) and a galvanometer in a Wheatstone bridge circuit:


Credit: DCACLab

A Wheatstone bridge allows to measure the resistance of a component independently of the circuit's supply voltage. In other words, the small needle on your camera will deviate according to the light received by the photoresistor and not according to the voltage supplied by the battery.

That's the reason why many of these cameras can accommodate 1.5V alkaline batteries instead of 1.35V mercury batteries without requiring any recalibration or modification.

Cheers!

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Old 11-05-2019   #31
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Quote:
Originally Posted by Cortexturizer View Post
Used several scenes all with constant lighting, no TVs in the background, no cars passing buy throwing lights at certain moments, none of that stuff.
I am telling you the 1.35v it makes no difference at all.

And according to the I N T E R N E T Z it should be a mild difference at all, it should be straight visible as soon as the lower voltage is in.
"...according to the I N T E R N E T Z..."
Oh well OK, case closed, then.

You miss my point entirely. I'm not disputing your reported findings from your own cameras. I don't have access to yours, to test myself. All I am saying is that, what you've proved, is the way your four cameras respond to the cells you have put in them, in the circumstances in which you've tested them. Beyond that, you haven't established anything with veracity.

If you really want to be more definitive, get hold of a calibrated standard light with known accuracy and colour temperature and run some tests across a wide range of light values, using cells that have been load tested to ensure the circuitry is receiving the nominal voltage each cell is meant to provide. That would be a start. Being fortunate enough to own a camera tester with a calibrated standard light source I'm aware of the benefits this provides for consistency and repeat-ability, critical for accurate interpretation of results.
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Old 11-07-2019   #32
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What would be useful would be a sticky thread in which we posted what kind of circuitry was in each camera. Finding that information is going to be a problem...


Regards, David
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Old 11-07-2019   #33
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Just gonna toss this in:
An originally factory calibrated Rollei 35S light meter WILL be off by 2 stops if its fed with a 1.55v battery instead of the original 1.35v battery.

Yes some cameras can and were recalibrated,
Yes some cameras were designed with this bridging circuit that Abbazz mentions.
The younger the camera the more likely this is.

What is true for one camera isn't necessarily true for another.
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