QL17 : +1 at low light, -1 at bright

[tog0710]

Hello, I just bought myself a Canonet QL17 for parts, which I think I managed to repair (at least for the most part).

However, I still have one problem with the light meter.
In low light it overexposes a little more than 1 stop, and at the same time it underexposes the same amount in high light.

Should I try to solve the problem (the potentiometer behind the light meter for example) or do I give up?

Does anyone know what this potentiometer actually sets? I have the impression that it acts mainly on highlights.

Thank you for your help.

 

[Chriscrawfordphoto]

The light meter is no longer "Linear." One that is linear will give correct exposure at all light levels. Most cameras have separate adjustments for bright light and dim light, but the Canonet does not. A bad metering cell can cause non-linearity in any camera.


Keep in mind, too, that this camera was made for mercury batteries that are not made anymore; using modern alkaline or silver oxide batteries will give incorrect exposure, though modern batteries usually cause under exposure at all levels.

 

[oftheherd]

I think Rick Oleson has a page on fixing the QL 17. Sorry I can't seem to find it right now, so I don't know how useful it might be.

 

[oftheherd]

Chris,

Don't the silver batteries work in the XA?

 

[dourbalistar]

I think Rick Oleson has a page on fixing the QL 17. Sorry I can't seem to find it right now, so I don't know how useful it might be.

Not sure which model the OP has, but here is Rick Oleson's page for the Canonet G-III 17:
http://rick_oleson.tripod.com/index-30.html

 

[tog0710]

Thank you all, with your explanations and the final link, i think now that my light meter is accurate (as possible as it could be).
I have the new QL17 which is very similar to the GIII.
Thank again to you all.

 

[Chriscrawfordphoto]

Chris,

Don't the silver batteries work in the XA?

Yes, the Olympus XA was designed for silver-oxide batteries. The OP was asking about the Canonet, though. It requires mercury batteries.

 

[oftheherd]

Yes, the Olympus XA was designed for silver-oxide batteries. The OP was asking about the Canonet, though. It requires mercury batteries.

Oops. Sorry. I had left my computer but left it on, and when I got back to it I had my threads mixed up. But thanks for the response and clarification.

 

[willie_901]

So how come voltage and amperage are a function of battery composition?

How does the meter circuit know how the voltage and amperage are generated?

Any data?

 

[Chriscrawfordphoto]

So how come voltage and amperage are a function of battery composition?

How does the meter circuit know how the voltage and amperage are generated?

Any data?

Different battery types produce different voltages.


Alkaline: 1.5 volt


Silver Oxide: 1.55 volt


Mercury: 1.35 volt


The camera does not know the voltage, it assumes it to be the voltage produced by the battery it was designed to use. So, the Canonet assumes the use of a 1.35 volt mercury battery. It is calibrated for that voltage, and using higher voltage battery causes underexposure. It doesn't take a lot of voltage discrepancy to make a large error, so even though there is only a .2 volt difference between the now-banned mercury battery and the silver-oxide battery you will see a large error in exposure, more than a stop.

 

[halfaninchawater]

Is there an adjustment mechanism on the Canonet that will allow you to correct the meter for the voltage discrepancy or must you add a Schottky diode into the meter circuit to adjust the silver oxide battery's 1.5 volts down to 1.35 volts?

 

[Chriscrawfordphoto]

Is there an adjustment mechanism on the Canonet that will allow you to correct the meter for the voltage discrepancy or must you add a Schottky diode into the meter circuit to adjust the silver oxide battery's 1.5 volts down to 1.35 volts?

You have to use a diode. The meter won't be linear just adjusting the meter.

 

[eli griggs]

There is a good bit of info on this site and online, including YouTube, on installing the correct diode for using silver cell batteries.

If you can no attempt this yourself, there are others here that may do the job for a reasonable sum.