OM1n is battery converted already?

TomOM1n · Feb 3, 2017

Hello
This is my first post, i hope in posting in the right place!
I just dusted off my om 1n to start using it again. I went to replace the battery as the meter wasn't working and ordered a d357h/sr44 battery (silver oxide 1.5v) the same as what was in the camera.
I then read about the original mercury batteries being 1.35v so bought a Wein cell mrb 625 as well.
It turns out that the Wein cell doesn't fit (diameter is too big) but the d357h is a perfect fit. I looks like I could take the washer thing off the Wein cell and it would fit.

So... My question is, do you think my camera has been adapted to fit newer d357h batteries? Im guessing It has and the voltage has been adjusted with diode. Or is it normal to use the Wein cell without the washer?

I've included an image of Wein cell that won't sit inside what looks like a plastic holder for the battery.

Thanks for your knowledge!
Tom

MattKing · Feb 3, 2017

Welcome to APUG.
That looks to me like a collar has been inserted into the battery compartment. So the camera may have been adapted for use with the SR44 battery. I say "may" because there is no way to tell if the necessary circuit change has also been done.
Some times an adapted camera will have a sticker inside the film compartment confirming the adaptation.
The problem with using silver oxide cells in an un-adapted OM-1 is that the error arising from the voltage difference isn't linear.
In my case, I've got other meters that I could check the in camera meter against. I'd look around for someone who could do the same for you.
There are a lot of UK APUG people. Where roughly in the UK are you - you might be able to arrange a meet?

TomOM1n · Feb 3, 2017

Hi Matt, thanks for replying so fast!
Thanks for the external meter idea, i'm in Bedfordshire
I thought the silver oxide produced a steady voltage but alkaline decreases over time?
I don't see a sticker unfortunately.
Thanks,
Tom

Ricardo Miranda · Feb 3, 2017

Did you put the battery with the + side (holes side) on the top facing the cap?

MattKing · Feb 3, 2017

TomOM1n said:
I thought the silver oxide produced a steady voltage but alkaline decreases over time?

That is correct, but the metering circuit in the OM-1 is only accurate and linear in its response if the voltage supplied is both consistent and at or near the voltage of a mercury cell - 1.35 volts.
If the adaptation is complete, a diode will have been inserted to drop the 1.5 volts supplied by the silver oxide cell to 1.35 volts.

Ap507b · Feb 3, 2017

Might be worth taking the bottom cover off to have a look to see if one has been fitted? Only a few screws. YouTube video here on doing the diode mod

TomOM1n · Feb 3, 2017

Thanks for making that clear matt!
Ricardo - the holes up towards the +side (screw cap) and the foil pointy bit directed into the camera.
Thanks

TomOM1n · Feb 3, 2017

Good idea Ap, thanks for posting that video. I've had a look inside and there doesn't appear to be a diode. If it's got a separate sleeve inserted its a very good fit!
So is it best to use the Wein cell without the washer?

Ricardo Miranda · Feb 3, 2017

Unless the diode was fitted on the top and I have been told some would have done so, you are best served with a zinc-air ZA675 that you can get in packs of 5 at Boots.
The ZA675 is exactly the same size as a SR44 but its voltage is 1,4V. And that would be a perfect fit for that chamber.

flavio81 · Feb 3, 2017

MattKing said:
That is correct, but the metering circuit in the OM-1 is only accurate and linear in its response if the voltage supplied is both consistent and at or near the voltage of a mercury cell - 1.35 volts.
If the adaptation is complete, a diode will have been inserted to drop the 1.5 volts supplied by the silver oxide cell to 1.35 volts.

I never understood the reason of bothering with voltage conversion diodes, when a #675 zinc-air battery can be easily made to fit into the same compartment, gives steady 1.35V, and is far, far, far cheaper than a silver oxide battery. Here i can get a six-pack of #675 batteries for the price of one silver oxide SR44 battery, and each cell will last me at least 3 months.

Ricardo Miranda · Feb 3, 2017

flavio81 said:
Here i can get a six-pack of #675 batteries for the price of one silver oxide SR44 battery, and each cell will last me at least 3 months.

About the same as here in the UK.
I've made a mistake ion my previous answer as it is a six-pack and not 5 as I stated.

TomOM1n · Feb 3, 2017

Excellent, thanks!
I think I'll use the inside of the wein cell, even though it was £5. It looks like the inside part is essentially a 675 zinc air but with less holes in.
So im assuming it will work.
Then I'll buy some 675s from boots for when it dies.
Do you guys use om1s?

Ricardo Miranda · Feb 3, 2017

TomOM1n said:
It looks like the inside part is essentially a 675 zinc air but with less holes in.

That's about right.

Yes, I use a few OM-1.

MattKing · Feb 3, 2017

TomOM1n said:
Excellent, thanks!
I think I'll use the inside of the wein cell, even though it was £5. It looks like the inside part is essentially a 675 zinc air but with less holes in.
So im assuming it will work.
Then I'll buy some 675s from boots for when it dies.
Do you guys use om1s?

It will work fine, unless there is a diode inserted into the circuit. In which case it won't work .
Good luck.
I don't have an OM-1 currently, but I've lots of experience with them, having bought new an OM-1 (pre MD) back in 1974 and used it a lot for years.
I've got four OM bodies currently: OM-G, OM-2s, OM-2n and an OM-4T.

klownshed · Feb 3, 2017

I have an OM-1 (and 2 and 4!).

The OMs are my all time favourites. I use mine with the Duracell hearing aid zinc airs too. I cut up one of my wife's hair bobbles (don't tell her!) which I ran around the inside of the battery compartment and that keeps the battery nice and snug.

When I first bought the batteries I got them from Amazon. i started receiving junk mail trying to sell me hearing aids before the batteries even arrived! It wasn't until I moved that I stopped getting the junk mail.

Now I just buy the batteries in Superdrug. ;-)

TomOM1n · Feb 3, 2017

I've just got one, that will do for now. Im excited to get back into film!
I've got some expired films from 10 years ago that I might try to figure out what to do with, and some fresh hp5 to get started!

TomOM1n · Feb 3, 2017

Haha! I'll get off the sofa and down to boots then!

darkroommike · Feb 3, 2017

flavio81 said:
I never understood the reason of bothering with voltage conversion diodes, when a #675 zinc-air battery can be easily made to fit into the same compartment, gives steady 1.35V, and is far, far, far cheaper than a silver oxide battery. Here i can get a six-pack of #675 batteries for the price of one silver oxide SR44 battery, and each cell will last me at least 3 months.

One silver oxide battery will last longer than a 6 pack of zinc oxide batteries.

John Koehrer · Feb 3, 2017

FWIW, and that's not much.that's a slick battery compartment and it looks factory made. I'd
suspect if someone had that/those made the camera's been modified.......Oh well.

TomOM1n · Feb 4, 2017

So I tried the wein cell without the washer ring, it fits perfectly but not powering the meter. I then used the 1.5v silver oxide battery and it is operating as usual. Although don't know if it's accurate!
I guess it has been given a diode somewhere, so I'll try shooting a film at normal metering and see what happens. And try to get hold of a light meter.

Ap507b · Feb 4, 2017

If you have an android/iPhone you might be able to put a free light meter app on your phone?

Chan Tran · Feb 4, 2017

Just put the silver oxide battery in there and use it. For sure it won't damage the camera. Just check it out and see if it's accurate. Even if the camera has all the original batteries I would still have to check it out for accuracy. I don't trust camera meter of that vintage.

pentaxuser · Feb 4, 2017

klownshed said:
When I first bought the batteries I got them from Amazon. i started receiving junk mail trying to sell me hearing aids before the batteries even arrived! It wasn't until I moved that I stopped getting the junk mail.-)

One day soon, Jeff will even know what you had for breakfast so that the right cereals can be offered to you before the milk is poured on. Said only partly in jest.

pentaxuser

thuggins · Feb 4, 2017

MattKing said:
The problem with using silver oxide cells in an un-adapted OM-1 is that the error arising from the voltage difference isn't linear.

Both the silver and mercury cells have an essentially constant voltage over their life. The problem with using a silver cell in an unmodified camera is that the voltage is just plain wrong and the meter reading will be inaccurate, but the error will be consistent. Alkaline cells produce varying voltage over their life and need a bridge circuit to compensate for that. Neither the diode fix nor the MR9 adapter are a bridge circuit; they just add resistance to the circuit to drop the ~1.5V of the silver cell to match the ~1.35V of the mercury cell.

Given that the cell compartment has been modified with a spacer, the circuit has most likely been modified. But I have various cameras that were modified with no physical indication. It becomes a real pain to have a mix of "updated" vs not, especially since the MR9 adapter is the perfect solution, providing both the correct voltage and the correct physical size. There are two ways to know for sure; run a roll of slide film thru it and see if it comes back properly exposed or compare it to a known meter.

flavio81 · Feb 6, 2017

thuggins said:
Both the silver and mercury cells have an essentially constant voltage over their life

And zinc-air cells too.

OM1n is battery converted already?

TomOM1n

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