Olympus OM-1n exposure meter conversion

[Chan Tran]

I have never own an OM-1 so I can't say much. But I have many cameras with similar meter design. Even with the correct power (that is you supply it with a rock solid external power supply at 1.35V) I have not seen one that is even accurate to 1/3 stop. It can be adjusted to be right on at 1 brightness level but not over a range say from EV5 to EV14 for example. That is why I don't really care for the meter on these type of cameras. I can simply estimate exposure.

 

[Chris Douglas]

no help

I apologize to the web master for waisting space here. I think this is a valuable service you provide, but not one of the 26 responses addressed my question. I suppose the only people who know how to calibrate an OM1n are the professionals who market their skills at a price. This is just a hobby for me, I'm surprised there isn't another hobbyist with more experience than I have out there somewhere. No matter, perhaps I'll attempt it on my own. Thanks everyone.

 

[paul ron]

You're right Chris. Just open the bottom plate of the OM and install the diode, there is plenty of room for it. OTHERWISE.. get a hand held meter, you'll never have to deal this question again.

 

[wblynch]

I bought 25 Schottky diodes on ebay fir $6. I put one in one of my junker OM-1 bodies. It was difficult soldering to the stainless battery contact but it works great. The meter has not been calibrated and the camera has not been serviced, so who knows how in-accurate it is, but the pictures came out fine. Cost about 25 cents. Does anyone really need to build an exotic voltage regulator or a grip with AA batteries?

 

[paul ron]

NO. But if you have 25 of em, I'd be interested to take a couple of em off your hands?

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[ic-racer]

I apologize to the web master for waisting space here. I think this is a valuable service you provide, but not one of the 26 responses addressed my question. I suppose the only people who know how to calibrate an OM1n are the professionals who market their skills at a price.

Why ignore 26 responses of useful information.

My personal (amateur) recommendation is to use a zinc cell.

If you want what a "preofessional who markets thier skill at a price" take heed of the recommendation above for a Shottky.

Quote from Chamtech photo services website:
BTW, my OM-1/1N (Pen FT, 35RC, 35RD, 35SP etc.) overhaul builds equivalent MR9 schotkey diode into the meter circuit.

If that is not enough I'd suggest trying that micro 1.3V regulator, TPS79913DDCR, as it cost only about a buck.

If you want to tread new ground and re-calibrate the resistors yourself, here is the OM-1 meter schematic. Resistors R1 and R4 control the LOW end and resistors R2 and R3 control the BRIGHT end of the response.

 

[paul ron]

So when adjusting a meter, what exactly are the lows n highs you are adjusting to? Is it total dark vs blinding white?

I've never had any luck with those adjustments n would rather live with the inconsistancies by compensating my exposures using film development n printing standardisation, I get more conssitnat results that way regardless of waht batteries I am using.

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[ic-racer]

Here is the adjustment procedure from the OM1 manual:

BV = Brightness Value (EV?)
S.S = Shutter speed
MS 5014 = 50mm 1.4 lens
"...it returns to the state of the order (1)" = go back to (1) and to through the sequence again

 

[paul ron]

Thanks for the tables. I'm sure that will a great help to anyone calibrating the camera.

Aren't those resistors pots?

 

[ic-racer]

Thanks for the tables. I'm sure that will a great help to anyone calibrating the camera.

Aren't those resistors pots?

All are fixed resistors. From the blurry pictures I have seen, it looks like they may be 2% (red tolerance band), thus, when tweaking resistor values one can follow the E 48 Series of values.

 

[Chris Douglas]

Eureka

IC,

Thank you for the procedure, it will be fun to experiment and see how difficult calibration is. I suspect the four resistors are "selected" values that were chosen for each particular camera per a factory procedure. Hopefully there is no difference between the procedure for the OM1, and the OM1n. Thanks again.

 

[paul ron]

Just a sugestion to make fine adjustments easy... temporarily wire in a pots and make your adjustments. Then after all is done, measure the pots then use fixed resistors in their place.

Substituting as you go will make it almost imposable to get anything right plus you'll need a full compliment of resistors to solder in n out each time you need to bring her in. Heat frying your wires n a the mess of solder will just make your life miserable even if you are just tacking em in.

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[John Hermanson]

It will pretty funny to watch as someone tries changing one single resistor in the darlington network of an OM-1 meter. IF YOU CHANGE ONE RESISTOR, THEN ALL HAVE TO BE CHANGED. My success with the schotkey diode speaks for itself. I am not trying to sell my service on this. If I was I would not have mentioned 1N-6263 as the diode you would use. You can probably buy the diode for $1. That's all the information you need for the do-it-yourselfer. John

 

[E. von Hoegh]

It will pretty funny to watch as someone tries changing one single resistor in the darlington network of an OM-1 meter. IF YOU CHANGE ONE RESISTOR, THEN ALL HAVE TO BE CHANGED. My success with the schotkey diode speaks for itself. I am not trying to sell my service on this. If I was I would not have mentioned 1N-6263 as the diode you would use. You can probably buy the diode for $1. That's all the information you need for the do-it-yourselfer. John

"Darlington network"? What is that? FYI, there are no transistors in that meter circuit. Could you perhaps be talking about the bridge circuit?

 

[paul ron]

You do have a point about using the $1 diode, it is the simplest solution n I am sure will serve just as reliably but it has no educational value that way. Understanding how n why it works is key.

So for the sake of sharing technical information, in depth, this thread is priceless since it has explored all the latest technology n even managed a schematic n reapir info of the circuit as printed by the manufacturer. Now it is on record, searchable for anyone needing this info in the future.

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[wblynch]

Has anyone ever heard of a cost-benefit ratio?

 

[paul ron]

Whaz dat?

The education is priceless, so what do you think is better than that for free?

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[wblynch]

The point being that all this is a waste of time. There is no education here since there is no practicality to this exercise of trying to make a super meter in an OM-1.

Use a hearing aid battery, or use a diode to convert for a 1.5v battery, or use a CHRIS/MR9 adapter, or just use a 1.5 volt battery and compensate, or just turn the meter off and use your senses.

cost (high) / benefit(low) = bad ratio

 

[paul ron]

Ah the lessons...
Why your 1.5V battery doesn't work in this OM1 meter circuit
How a diode can remedy the situation
The technology advances of voltage regulators
Wheatstone bridges... did you know that is what this is called?
A darlington circuit?... ever hear of that?
An actual circuit diagram of the OM1 meter
The factory calibration manual for the OM1 meter
Learn anything about resistors n how they effect a meter circuit?
Explored all the possible ways we can repair this meter?

AND yes, last n foremost advice of the year... cost-benefit ratio

But nothing here was a waste, otherwise you can say APUG in general is a waste; since most of all we spend lots n lots of time looking into the technology of photography... in all it;s boring detailed depth complete with checmial formulai n equations.. which is generally not very fashionable anymore in today's ADDH world of duming everything down to mind numbing over simplification. Perhaps if this were offered in sound bites of 15 seconds or less it might be more enticing? I doubt it.

Just my 2¢, so if you'd like a refund, present your receipt at the front desk.

So come on, sit back n have some fun? I'll bet the OP used a hearing aid battery anyway, everything we discussed is not for the average user but more for postarity n future reference.

This is for you my grandchildren that find my old junker cameras in a big box in the garage when I'm gone. At least they'll know how to reapir the meter in my OM1.


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[John Hermanson]

The point being that all this is a waste of time. There is no education here since there is no practicality to this exercise of trying to make a super meter in an OM-1.

Use a hearing aid battery, or use a diode to convert for a 1.5v battery, or use a CHRIS/MR9 adapter, or just use a 1.5 volt battery and compensate, or just turn the meter off and use your senses.

cost (high) / benefit(low) = bad ratio

You said it brother, amen. John

 

[JohnPaul]

I apologize to the web master for waisting space here. I think this is a valuable service you provide, but not one of the 26 responses addressed my question. I suppose the only people who know how to calibrate an OM1n are the professionals who market their skills at a price. This is just a hobby for me, I'm surprised there isn't another hobbyist with more experience than I have out there somewhere. No matter, perhaps I'll attempt it on my own. Thanks everyone.

Just go over to eBay and get one of the "new" MR-9 battery adapters for $22.50. Just type in the search phrase... MR-9 battery adapter.

I went this route because I don't like jacking around. I want the light meter in my Olympus OM-1n to work like it originally did at 1.35v...but that's just me.

 

[BetterSense]

I solve the OM1 meter/battery problem by leaving the switch set to 'off'.

I actually wish they made an OM1 with no meter at all; it's a sexy camera but if there was no ISO dial cluttering up the top cover, and no meter needle cluttering up the viewfinder, it would be truly awesome.

 

[Chan Tran]

I solve the OM1 meter/battery problem by leaving the switch set to 'off'.

I actually wish they made an OM1 with no meter at all; it's a sexy camera but if there was no ISO dial cluttering up the top cover, and no meter needle cluttering up the viewfinder, it would be truly awesome.

I totally agree with you but if back then Olympus made the OM-1 without a meter they could not sell it. Although there were many people back then who could shoot without a meter but back then the built in meter made the camera much more valuable to people. Today I think the number of people who rely on meter is greater than in the old days but meterless camera is more appealling. Uhm! an oxymoron?

 

[GRHazelton]

Bridge circuits don't care about mercury cells, I think.

While my ancient Praktica LTL wants mercury cells, since it is a bridge circuit - usually identifiable by a meter needle "wanting" to be centered in a fixed circle or whatever, actual voltage is not critical, except perhaps in terms of ultimate low light sensativity. Finding a silver oxide of the appropriate size is the problem.

It is amazing how long mercury cells last! I have an ancient LaFayette Radio (anyone else remember them?) CdS meter. I may have replaced the mercury cell once after buying it to replace a dead Sekonic Microlite meter sometime in the mid '70s I think. The cell still hits the BC mark. Gotta be perhaps 30 years old?

I've often wondered if a solution to the mercury contamination problem would have been a huge deposit on the purchase of a mercury cell, at least partially refunded when the cell was turned in for reprocessing. The huge deposit would cover the cost of the exchange program. Thus my Bulova Accutron series 214 Spaceview could be completely authentic.

 

[BMbikerider]

There is a small company trading under the name of 'The Small Battery Company' based in London who sell an insert the same size as a PX625 which will take a SR44 silver oxide. They don't make them so there has to be a manufacturer out there somewhere. They sell here for around £20 (around $23). They seem to work well, and I have never heard any problems with them