How to test an in-camera (OM-1) light meter?

[jdk01]

I am trying to test an OM-1 light meter. The light source is an ‘day-light emitting’ professional Aputure Amaran 200d lamp. I have a device to measure the actual LUX being emitted from the 200d as well as a modern sekonic analogue meter. Can I shine light directly into the camera lens? Or do I need to use my 45 degree 18% grey board? My experience is that the sekonic and LUX meter agree with the range of light levels being received directly from the 200d lamp. However the OM-1 shows different readings - 2 stops out. Is this a potential problem with the OM-1 or with the technique of not using the grey card? Your advice is appreciated.

 

[MattKing]

Use the grey card at a 20 degree angle, as per the grey card instructions.
The OM-1 meter is a reflected light meter, not an incident light meter.
The sekonic meter should also be used in incident mode, unless it has a special mode for LUX readings.

 

[jdk01]

Thank you... I have now introduced a Sony digital camera into the scenario ... it seems that the OM/1 is 1-2 stops out.,, so, with the light source and Sony camera pointing towards the grey card from an equal distance and the sekonic and Lux meter pointing from the grey card back towards the light source, I am getting consistent readings between Sony, Luca meter and sekonic . When I substitute the Sony camera for the OM-1 then the OM-1 is 1-2 stops out...

 

[MattKing]

Are you using the correct battery in the OM-1?
It was designed for a 1.3 volt 625 mercury battery.
Zinc air batteries - both hearing aid type and batteries adapted to fit in the 625 slot are close enough to that to work.
Some OM-1s have been adapted for use with a 1.5 volt silver oxide battery.
Some people buy diode equipped adapters that allow use of smaller silver oxide batteries in the adapter in the battery compartment.
I'm not sure whether the OM-1 can take some of the very last focusing screens that required exposure adjustment.

 

[wiltw]

I am trying to test an OM-1 light meter. The light source is an ‘day-light emitting’ professional Aputure Amaran 200d lamp. I have a device to measure the actual LUX being emitted from the 200d as well as a modern sekonic analogue meter. Can I shine light directly into the camera lens? Or do I need to use my 45 degree 18% grey board? My experience is that the sekonic and LUX meter agree with the range of light levels being received directly from the 200d lamp. However the OM-1 shows different readings - 2 stops out. Is this a potential problem with the OM-1 or with the technique of not using the grey card? Your advice is appreciated.

First of all, what battery are you using?! The OM-1 is known to be VARIABLY in error, depending upon the intensity of ambient light being measured when you put in a PX625 alkaline battery!

 

[jdk01]

Are you using the correct battery in the OM-1?
It was designed for a 1.3 volt 625 mercury battery.
Zinc air batteries - both hearing aid type and batteries adapted to fit in the 625 slot are close enough to that to work.
Some OM-1s have been adapted for use with a 1.5 volt silver oxide battery.
Some people buy diode equipped adapters that allow use of smaller silver oxide batteries in the adapter in the battery compartment.
I'm not sure whether the OM-1 can take some of the very last focusing screens that required exposure adjustment.

Hi, I am using a new Wein battery. I will also try to obtain a 357 silver oxide. Thank you.

 

[jdk01]

First of all, what battery are you using?! The OM-1 is known to be VARIABLY in error, depending upon the intensity of ambient light being measured when you put in a PX625 alkaline battery!

Hi, I am using a new Wein battery. I will also try to obtain a 357 silver oxide. Thank you.

 

[wiltw]

Hi, I am using a new Wein battery. I will also try to obtain a 357 silver oxide. Thank you.

Do not bother with the 357 unless you KNOW your body was modified to regulate 1.5v down to 1.35v

An alternative is to buy yourself an MR-9 adapter, which takes a silver oxide battery and physically adapts the battery to fit in the space of a PX625 mercuric oxide cell AND regulates the voltage down from 1.5v to the needed 1.35v

BEWARE!: There are some pseudo MR-9 being sold, which simply force you to buy and insert expensive 1.35v air cells, which deteriorate even with zero usage, if the air seal has been removed.

 

[jdk01]

Do not bother with the 357 unless you KNOW your body was modified to regulate 1.5v down to 1.35v

An alternative is to buy yourself an MR-9 adapter, which takes a silver oxide battery and physically adapts the battery to fit in the space of a PX625 mercuric oxide cell AND regulates the voltage down from 1.5v to the needed 1.35v

BEWARE!: There are some pseudo MR-9 being sold, which simply force you to buy and insert expensive 1.35v air cells, which deteriorate even with zero usage, if the air seal has been removed.

Thank you for your advice. I may have discovered a problem? The movement of the needle appears sensitive and unpredictable to gentle pressure to the casing of the galvanometer or to the nearby camera casing. A short?

 

[beemermark]

Go point at a cloudless blue sky about 45 deg above the horizon. Should be F16 at shutter speed = film speed. Assuming your shooting B&W or Color don;t get too hung up on the meter accuracy. More important is knowing how to meter.

 

[jdk01]

Thank you ... will do so after I try to identify potential electrical problem with meter...

 

[ic-racer]

Personally I'd do the test outdoors in bright shade using two reflected meters.No need for a calibrated gray card white or black or any shade in between will do. One meter is the one in the camera and the other would be a hand-held meter. Ideally a hand-held view-meter.

 

[jdk01]

Personally I'd do the test outdoors in bright shade using two reflected meters.No need for a calibrated gray card white or black or any shade in between will do. One meter is the one in the camera and the other would be a hand-held meter. Ideally a hand-held view-meter.

View attachment 269521

Thank you...