1.55v vs 1.35v in classic rangefinders - measure the same

Phil_F_NM said:
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
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Please note that I said many, not all
 
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)
 
All over the internet I've read that 1.5v makes a two stop underexposure difference.
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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.
 
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
 
BernardL said:
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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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
 
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...nsidering-spotmatic-some-advice-wanted-2.html

280846d1441317686-considering-spotmatic-some-advice-wanted-circuit.jpg
 
Beemermark said:
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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+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
 
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):
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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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Many of these vintage cameras use a CdS sensor (photoresistor) and a galvanometer in a Wheatstone bridge circuit:

Wheatstone-Bridge-_1.jpg

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!

Abbazz
 
Cortexturizer said:
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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"...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.
 
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
 
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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