MR-9 Adapter 1.55V to 1.35V

kwyjibo · Jun 14, 2023

Has anyone had any experience with this adapter?

I recently purchased one and prior to install it in one of my cameras I tried to measure the voltage with a voltimeter:

But I cannot see such voltage reduction.

Looking carefully at the manufacturer site (http://www.kantocamera.com/english/adapter/adapter_en.html) there is a disclaimer that reads:

In order to measuer the voltage transform adapter using a digital tester, put a 10Kohm resistance between the measurement terminals.

I then tried that also:

Without better results...

Maybe is only when installed in the camera when the voltage conversion will take place correctly due having an actual load?

koraks · Jun 14, 2023

Welcome to Photrio, @kwyjibo

I think the type of adapter you have there simply places a small Schottky diode in series with the camera's circuitry and the battery. The voltage drop of a Schottky diode depends on a number of parameters, especially current and temperature (and of course the exact type and model diode used). As a result, the output voltage of this adapter (with battery installed) will fluctuate a bit - it may only hit exactly 1.35V under optimal conditions. To make matters worse, the output voltage will still follow the voltage of the battery used, and it is quite possible that the camera won't present a constant impedance to the adapter, meaning that the voltage will fluctuate a little bit depending what the camera is doing (e.g. how much light its meter is currently seeing).

There's a decent chance that the camera you intend to use this in will work fine nonetheless, although the accuracy of any in-built light meter may not be as good as with the original type of battery. You could try and compare the meter with a known-good external light meter and compensate for the difference.

kwyjibo · Jun 14, 2023

Thanks for the reply.

That is exactly my next test, use a lightmeter and compare against the camera readings.

Any other suggestions anyone can have are welcome

xkaes · Jun 14, 2023

Be very careful that the camera and the meter are metering the exact same thing in the exact same way. Your meter doesn't have a lens.

benjiboy · Jun 14, 2023

I have 2 MR 9 adaptors, one for each of my Canon F1ns and have been using them for more than ten years. I suggest that before you tie yourself in knots with testing them and worrying, you put the adaptor and battery in your camera and use it.
I don't think you will be disappointed with the results.

Sean Mac · Jun 14, 2023

In theory it is intended for use with a silver oxide battery. Like a SR44.

These apparently have a flatter discharge curve than a LR44.

The forward voltage of the diode is fixed according to the diode type.

dynachrome · Jun 14, 2023

Many of my cameras have been converted to 1.5 volts but I still have and use a number of MR-9 adapters. They generally work well. With some cameras, the thickness of the MS76 or equivalent will not allow the battery cover to screw in all the way. For those cameras I use a 386 silver oxide battery. It's slightly slimmer.

reddesert · Jun 14, 2023

Schottky diodes (like most/all diodes) have a forward voltage drop that depends on the current through the diode. It usually rises weakly with current at small currents and then changes more steeply at currents that are much larger than anything an MR9 adapter would ever see. For example, here's a plot from the datasheet for a BAT54 Schottky diode, I've rotated it so forward voltage is on the Y-axis. You can see that the Vdrop is about 0.15 V at 0.01 mA and 0.25 V at 1 mA. When you hook a digital voltmeter up to it, which probably has an input resistance of hundreds of Kohms or more, you're measuring with a current draw of a few micro-amps or even nano-amps.

Probably, the designer of the MR9 picked a diode that drops about 0.2 V under a typical current draw of perhaps a few milli-amps. Understand that most older light meter circuits are pretty simple, often using a few resistors and a light-sensitive element to approximate logarithmic sensitivity, not a precision laboratory instrument. Bottom line, most users are happy with the adapter.

Brad Deputy · Jun 14, 2023

I just received one for my Olympus 35 RC. I put in an SR44 and it's fat, but fits ok. SR43 is recommended.

Haven't tested accuracy yet but its working (aperture is varying depending on light). I'll know when I finish the roll in there.

BobD · Jun 14, 2023

kwyjibo said:
But I cannot see such voltage reduction.

Reduction from what?

I don't see that you measured the voltage of the battery by itself without the adapter so how would you know what the reduction is?

If you used an LR44, they are often about 1.6v or even a bit higher when new. So, a reduction from 1.6v to 1.4v would be about right.

But, you shouldn't use LR44 or any alkaline battery with these adapters because their voltage drops continually in use.

Use a silver oxide S76 type. Their voltage curve is much flatter.

And, I would measure with a better quality meter like a Fluke for example. When you're trying to measure tenths of a volt you need an accurate meter.

chuckroast · Jun 15, 2023

I use many of these in a variety of cameras and meters. As has been noted here, the required voltage drop only occurs under actual load.

Moreover, it's not as critical as you think. The built in meters in old SLRs and TLRs are not precision devices. They get you in the ballpark, but a battery variation of a few tenths of a volt from nominal 1.35V isn't going to make much practical difference. This variability was there when these meters were new. That's why things like Zone System have you figure out your "personal ASA" - to account for your meter, your thermometer, your water, your agitation style and so on. Analog photography is far less about absolute accuracy and far more about repeatability and predictability.

I've actually taken apart quite a few old Luna Pros and recalibrated them (against a known good meter) to use modern 1.5V batteries.

As someone noted, you should be using Silver batteries wherever possible. The fail almost instantly. Alkalines will drift down in voltage and slowly give you bad readings leading to incremental overexposure.

Nitroplait · Jun 15, 2023

The Kanto adapter is specifically made for SR43 and works fine for its intended purposes in my experience.

kwyjibo · Jun 15, 2023

reddesert said:
Schottky diodes (like most/all diodes) have a forward voltage drop that depends on the current through the diode. It usually rises weakly with current at small currents and then changes more steeply at currents that are much larger than anything an MR9 adapter would ever see. For example, here's a plot from the datasheet for a BAT54 Schottky diode, I've rotated it so forward voltage is on the Y-axis. You can see that the Vdrop is about 0.15 V at 0.01 mA and 0.25 V at 1 mA. When you hook a digital voltmeter up to it, which probably has an input resistance of hundreds of Kohms or more, you're measuring with a current draw of a few micro-amps or even nano-amps.

Probably, the designer of the MR9 picked a diode that drops about 0.2 V under a typical current draw of perhaps a few milli-amps. Understand that most older light meter circuits are pretty simple, often using a few resistors and a light-sensitive element to approximate logarithmic sensitivity, not a precision laboratory instrument. Bottom line, most users are happy with the adapter.

Thanks, I should have taken a look at some diode datasheets from the start

BobD said:
Reduction from what?

I don't see that you measured the voltage of the battery by itself without the adapter so how would you know what the reduction is?

If you used an LR44, they are often about 1.6v or even a bit higher when new. So, a reduction from 1.6v to 1.4v would be about right.

But, you shouldn't use LR44 or any alkaline battery with these adapters because their voltage drops continually in use.

Use a silver oxide S76 type. Their voltage curve is much flatter.

And, I would measure with a better quality meter like a Fluke for example. When you're trying to measure tenths of a volt you need an accurate meter.

Look at the first picture, where I am taking a reading of the battery without the adaptor.

Thanks everyone for the comments, I was afraid that the adaptor was doing nothing but clearly is working as expected.

BobD · Jun 15, 2023

kwyjibo said:
Look at the first picture, where I am taking a reading of the battery without the adaptor.

Yes, but not with the resistor. Direct readings of batteries without a load resistor are not accurate

Brad Deputy · Jun 15, 2023

BobD said:
Yes, but not with the resistor. Direct readings of batteries without a load resistor are not accurate

Huh? I mean, a battery will give vastly different voltage readings based on load and its chemistry, so normally they're measured open circuit.

Do you mean to measure voltage while the meter is active, both with and without the adapter?

kwyjibo · Jun 16, 2023

BobD said:
Yes, but not with the resistor. Direct readings of batteries without a load resistor are not accurate

That is the second picture.

Ivo Stunga · Jun 16, 2023

I use it in my OM-1n for years now. It's clear to me: plain silver button battery shows values different than when it's in its adapter, so it works. And my exposures are stable, so it works.

BobD · Jun 16, 2023

kwyjibo said:
That is the second picture.

But, the second picture shows you measuring WITH the MR-9! Obviously, you don't get what I'm saying.

But, I wish you well with your photographic adventures.

koraks · Jun 16, 2023

BobD said:
But, the second picture shows you measuring WITH the MR-9!

You mean he should measure the battery with just the 10kOhm load, then measure it with the 10kOhm load and the MR-9 adapter, and compare the difference, right?

Ian C · Jun 16, 2023

I removed the TN metered finder from my Nikon FTN, removed the battery cover and measured the resistance of the battery contacts at 16.8kΩ with the power switch in the “ON” position.

This seems to indicate that using a 10KΩ resistor in the circuit to measure the loaded voltage of the cell-plus-converter might be too small. I consulted a resistor catalog and found that resistors of 17KΩ are available. Even a 20KΩ resistor might give a more meaningful result, as they are closer to the measured 16.8KΩ resistance of my FTN finder's meter.

[I edited the errors in the above paragraph. Originally given as "1.7KΩ" and "2.0KΩ" respectively (misplaced decimal point).]

My FTN finder’s meter gives readings inflated by 3 to 4 stops with 1.5-volt alkaline replacement cells for the old 625 mercury cells. When I use two 1.55 volt silver oxide cells in MR9 converters, the FTN reads about the same as do my more modern Nikons: EL2, FE, FE2, and FA.

koraks · Jun 16, 2023

@Ian C I'd consider 16k8 as close enough to 10k. Or did you measure 1k68 instead of 16k8?

Ian C said:
I consulted a resistor catalog and found that resistors of 1.7KΩ are available. Even a 2KΩ resistor might give a more meaningful result.

For experiments like these, it can be worthwhile to purchase a resistor kit. By placing several values in series and/or parallel, it's possible to approximate just about any value quite closely with a limited set of standard values. E6 series kits are sold in several places (or can easily be assembled from a catalog), quite affordable and handy to keep around. Get 1/4 or 1/2W types; they're fine for most low power purposes.

BobD · Jun 16, 2023

koraks said:
You mean he should measure the battery with just the 10kOhm load, then measure it with the 10kOhm load and the MR-9 adapter, and compare the difference, right?

Right. And, a better quality meter wouldn't hurt. We're talking about a few tenths of a volt here. You need good accuracy.

BrianShaw · Jun 16, 2023

Ivo Stunga said:
I use it in my OM-1n for years now. It's clear to me: plain silver button battery shows values different than when it's in its adapter, so it works. And my exposures are stable, so it works.

Ditto, but in a Ricoh Singlex TLS

Ditto but in a Canonet

And I wish all well in their electrical measurement adventures!

MattKing · Jun 16, 2023

BrianShaw said:
And I wish all well in their electrical measurement adventures!

Me too!
If nothing else worthwhile, this probably helps people understand that it is not particularly simple to measure some of these things to the accuracy that matters.

reddesert · Jun 16, 2023

(Beating a dead horse) Today's $10 digital volt meter can give results that are very good, especially since we are trying to measure a difference rather than an absolute calibration. The more important thing is understanding your measuring tool. One of the reasons the $10 DVM is useful is that it has a relatively high input impedance, so it doesn't load the circuit under test (maybe 1 megohm, compare to the my first Radio Shack analog VM at 2000 ohms/volt, so 30kohms on the 15V scale, which was totally standard amateur kit in the 1980s).

However, this means you have to load the battery yourself to measure the voltage under real operation. Measure the battery under load, and then the battery + adapter under load.

The impedance load a lightmeter presents to the battery will vary depending on the intensity of light. That's the justification for needing these adapters. So it doesn't really make sense to measure the resistance of a single camera lightmeter and then try to match that resistance exactly (IOW the difference between using a 10K resistor and a 17K resistor should not be material.) You just have to get in the right ballpark of operating current.

Or, you can put the adapter in the camera and check the results at a couple of different light levels, like sunny outside and dim inside. Remember that light meters are not precision measuring circuits, not precisely linear nor logarithmic.

I've had some cameras where I got along fine without the adapter, but the adapter is a technologically superior method of dealing with the battery issue.

MR-9 Adapter 1.55V to 1.35V

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