Spotmatic light meter batteries
Posted 05/05/2005 - 18:15
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The Wein MRB400 cell is a zinc-air battery that is an exact equivalent that delivers the correct 1.35v
When you get one of these, peel off the sealing strip and leave it for about 30 minutes to activate, then it should be fine.
Some users put 1.5v silver oxide cells in their Spotmatics, but personally I do not think this is a good idea. The different voltage may alter the meter reading by up to 2 stops, and there is always the chance that the circuitry could be damaged by the higher voltage.
My advice is to use the correct Wein cell.
When you get one of these, peel off the sealing strip and leave it for about 30 minutes to activate, then it should be fine.
Some users put 1.5v silver oxide cells in their Spotmatics, but personally I do not think this is a good idea. The different voltage may alter the meter reading by up to 2 stops, and there is always the chance that the circuitry could be damaged by the higher voltage.
My advice is to use the correct Wein cell.
Best regards, John
Posted 05/05/2005 - 18:25
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Hi,
I don't like to disagree with John but the meter circuits in the Spotmatic are based on a balanced bridge circuit. As the battery supplies both sides of the bridge, a small change in voltage will not affect the accuracy of the meter at it's null or correct exposure. The wein cells are expensive and short lived. The silver cells work just as well. You can get a a PX400 equivalent but these are no more than a than a 394, AG7 or SR45 with a collar round them. If you use these the important thing to remember is that the + side needs to go in first. The original PX400 were made the other way round to most batteries and the case is - rather than the stud.
Kim
I don't like to disagree with John but the meter circuits in the Spotmatic are based on a balanced bridge circuit. As the battery supplies both sides of the bridge, a small change in voltage will not affect the accuracy of the meter at it's null or correct exposure. The wein cells are expensive and short lived. The silver cells work just as well. You can get a a PX400 equivalent but these are no more than a than a 394, AG7 or SR45 with a collar round them. If you use these the important thing to remember is that the + side needs to go in first. The original PX400 were made the other way round to most batteries and the case is - rather than the stud.
Kim
Posted 05/05/2005 - 23:16
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Feel free to disagree!
The 2 stop difference is relatively well documented, so there is a discrepancy in our information, but I don't doubt for a moment Kim's info. so I wonder if there is more than one design of meter circuit in the Spotmatics?
The 2 stop difference is relatively well documented, so there is a discrepancy in our information, but I don't doubt for a moment Kim's info. so I wonder if there is more than one design of meter circuit in the Spotmatics?
Best regards, John
Posted 05/05/2005 - 23:57
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Hi John,
Having seen several versions of the Spot service manual, I don't think there were different circuits and the manual shows a variation on the standard balanced bridge circuit. The older clip on meters don't seem to be mercurey dependant either. I have a toal of 8 Spots in various guises and 2 SPFs. Although this is a relatively small sample, I have found no difference in any of then between a mercury, silver or wein cell when measuring the "correct" exposure. I have found differences between separate bodies using the same lens and interestingly, I found differences in changing the lens on the same body! There is one minor difference, which is what one would expect, in that the meter becomes slightly more sensitive to readings away from the correct position. So the needle will move further away from the null position for each stop or half stop of over or under exposure.
I have also found several references to the battery voltage being critical but I have found many more from those I trust more saying the bridge circuit is quite happy with silver cells. These include the general opinion on the Spotmatic user's group, the AOHC and others. It is also generally quoted that the meter circuit for the K1000 and KM is the same as the SPF and these use the LR/SR44s. The major difference between the SP and SPF circuits is that the SPF has an extra LDR to "switch" the meter circuit on.
Kim
Having seen several versions of the Spot service manual, I don't think there were different circuits and the manual shows a variation on the standard balanced bridge circuit. The older clip on meters don't seem to be mercurey dependant either. I have a toal of 8 Spots in various guises and 2 SPFs. Although this is a relatively small sample, I have found no difference in any of then between a mercury, silver or wein cell when measuring the "correct" exposure. I have found differences between separate bodies using the same lens and interestingly, I found differences in changing the lens on the same body! There is one minor difference, which is what one would expect, in that the meter becomes slightly more sensitive to readings away from the correct position. So the needle will move further away from the null position for each stop or half stop of over or under exposure.
I have also found several references to the battery voltage being critical but I have found many more from those I trust more saying the bridge circuit is quite happy with silver cells. These include the general opinion on the Spotmatic user's group, the AOHC and others. It is also generally quoted that the meter circuit for the K1000 and KM is the same as the SPF and these use the LR/SR44s. The major difference between the SP and SPF circuits is that the SPF has an extra LDR to "switch" the meter circuit on.
Kim
Posted 06/05/2005 - 20:26
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John,
The fact that Wein cells work is not disputed. The claim that silver cells cause an error, however, is rubbish. Just because a myth is reported in the forums of DPReview doesn't magically make it fact.
As Kim says, all authoritative sources agree that silver cells work, and unless you have real evidence to the contrary, it is surely best not to give these spurious claims further credence by repeating them on here.
George
The fact that Wein cells work is not disputed. The claim that silver cells cause an error, however, is rubbish. Just because a myth is reported in the forums of DPReview doesn't magically make it fact.
As Kim says, all authoritative sources agree that silver cells work, and unless you have real evidence to the contrary, it is surely best not to give these spurious claims further credence by repeating them on here.
George
Posted 06/05/2005 - 21:27
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Hi George
I agree that spurious information should not be repeated.
I think you'll find that in my original comment I did mention that there were two sides to this argument, and concluded with a personal opinion.
This really boils down to, in general, me being happy to follow the instructions unless there is a real imperative to find an alternative. In this instance, as I have access to 1.35v cells, there is no imperative for me to use something outside the normal parameters. When the Wein cells become unavailable I will perform my own tests to establish what I need to do.
In the meantime, I think we have opened an interesting debate and information exchange, and the choice is there!
Has anyone reading this done a series of comparative tests?
I agree that spurious information should not be repeated.
I think you'll find that in my original comment I did mention that there were two sides to this argument, and concluded with a personal opinion.
This really boils down to, in general, me being happy to follow the instructions unless there is a real imperative to find an alternative. In this instance, as I have access to 1.35v cells, there is no imperative for me to use something outside the normal parameters. When the Wein cells become unavailable I will perform my own tests to establish what I need to do.
In the meantime, I think we have opened an interesting debate and information exchange, and the choice is there!
Has anyone reading this done a series of comparative tests?
Best regards, John
Posted 06/05/2005 - 22:20
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Hi John,
If you read my post above, you will see that I have run some tests albeit I only had 8 Spots and 2 SPFs to compare I have also done some extensive research into the circuit design.
Whilst I am all for following instructions, I don't like to waste money and I believe that in some cases rules are for the guidance of wise men and the obedience of fools. You may use the "recommended" battery but do you always use the exposure it recommends? Wein cells are typically £5 and last for about 6 months. You can prolong this if you take them out, block the holes and then then reopen them before re inserting them. The silver cells cost about 60p and last 3 times as long with no fiddling. A Wein cell for the SPF costs the same. I could use a silver 625 but find that the SR44s work just as well and I can get those for about 50p. What's more, they are the same as nearly all the MF Pentax's so I only have to keep one set of batteries.
In your original post you also suggested that silver cells could damage the camera. IMHO Wein cells are more likely to do this. Whilst they have a long self life until activated, they work by unblocking the holes to allow air to contact the chemicals. As long as they are removed when they are discharged, there is little danger. However, if they are left inadvertantly in the camera, there is a strong possibility that they will leak. This is far less likely with silver cells which are sealed and have a very long shelf life even when partially used. I have lost track of the number of people looking for replacement bottoms or selling cameras with corroded battery compartments for this very cause.
Kim
If you read my post above, you will see that I have run some tests albeit I only had 8 Spots and 2 SPFs to compare I have also done some extensive research into the circuit design.
Whilst I am all for following instructions, I don't like to waste money and I believe that in some cases rules are for the guidance of wise men and the obedience of fools. You may use the "recommended" battery but do you always use the exposure it recommends? Wein cells are typically £5 and last for about 6 months. You can prolong this if you take them out, block the holes and then then reopen them before re inserting them. The silver cells cost about 60p and last 3 times as long with no fiddling. A Wein cell for the SPF costs the same. I could use a silver 625 but find that the SR44s work just as well and I can get those for about 50p. What's more, they are the same as nearly all the MF Pentax's so I only have to keep one set of batteries.
In your original post you also suggested that silver cells could damage the camera. IMHO Wein cells are more likely to do this. Whilst they have a long self life until activated, they work by unblocking the holes to allow air to contact the chemicals. As long as they are removed when they are discharged, there is little danger. However, if they are left inadvertantly in the camera, there is a strong possibility that they will leak. This is far less likely with silver cells which are sealed and have a very long shelf life even when partially used. I have lost track of the number of people looking for replacement bottoms or selling cameras with corroded battery compartments for this very cause.
Kim
Posted 06/05/2005 - 23:54
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For sure, batteries left in cameras can cause immense damage.
Taking your comment about light readings - do I always use the meter reading? There's a subject in itself! What I actually do is to use a very simple technique loosely based on the Zone System. Before anyone cringes in horror at the words Zone System, it's not as bad as it sounds.
Assuming that we are talking about negative film for a moment, let's take a caucasian skin tone, which I reckon is on Zone 6, slightly lighter by one stop than mid-grey. So we take the exposure measurement, which would place the skin tone on Zone 5 or 18% grey, and increase the exposure by one stop to move the tone to Zone 6. So in a sense, yes I do always use the exposure measurement of the camera, but then modify it. If it were a white wall I would increase the exposure by three stops to place the wall on Zone 8, almost white but retaining a hint of texture.
That's one reason I like simple meters like the Spotmatic one, or the MX one, because you know what you are measuring.
That's my thought for the day....
Taking your comment about light readings - do I always use the meter reading? There's a subject in itself! What I actually do is to use a very simple technique loosely based on the Zone System. Before anyone cringes in horror at the words Zone System, it's not as bad as it sounds.
Assuming that we are talking about negative film for a moment, let's take a caucasian skin tone, which I reckon is on Zone 6, slightly lighter by one stop than mid-grey. So we take the exposure measurement, which would place the skin tone on Zone 5 or 18% grey, and increase the exposure by one stop to move the tone to Zone 6. So in a sense, yes I do always use the exposure measurement of the camera, but then modify it. If it were a white wall I would increase the exposure by three stops to place the wall on Zone 8, almost white but retaining a hint of texture.
That's one reason I like simple meters like the Spotmatic one, or the MX one, because you know what you are measuring.
That's my thought for the day....
Best regards, John
Posted 04/06/2005 - 06:47
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Let me immediately confess that I'm no techie, merely a guy who has hung around Spotmatics since 1968. The Wein cells, I have found, work OK, once you figure out that you have to peel off the covering and let them sit around for up to a half hour as they are essentially much like hearing aid batteries.
Not knowing this initially - as the packet said nothing about it - I bought several that "didn't work." After I figured out that you had to let them sit about before installation, they worked just fine, but lasted far less than six months, frustrating to me as the old mercury batteries had seemed to last forever.
Recently I learned about the theory of the bridge circuit on other forums and took the risk of buying silver batteries. I think I bought 392's and they seem to work fine. However, to get them to fit - as they are smaller - I had to take the little felt collars off the equally small Weins and fit them onto the 392's, but that meant I had to put them in the reverse of the Weins. I immediately checked the Spotmatic meter readings with 392's against my Gossen meter and readings were basically either the same, or within a half-stop of each other. Using the same meter with a number of my other cameras (Bessa R, Bessa L, Yashica GSN, Olympus XA) I have found that the half-stop variant is not uncommon.
And, of course, the silvers are much cheaper.
Ted
Not knowing this initially - as the packet said nothing about it - I bought several that "didn't work." After I figured out that you had to let them sit about before installation, they worked just fine, but lasted far less than six months, frustrating to me as the old mercury batteries had seemed to last forever.
Recently I learned about the theory of the bridge circuit on other forums and took the risk of buying silver batteries. I think I bought 392's and they seem to work fine. However, to get them to fit - as they are smaller - I had to take the little felt collars off the equally small Weins and fit them onto the 392's, but that meant I had to put them in the reverse of the Weins. I immediately checked the Spotmatic meter readings with 392's against my Gossen meter and readings were basically either the same, or within a half-stop of each other. Using the same meter with a number of my other cameras (Bessa R, Bessa L, Yashica GSN, Olympus XA) I have found that the half-stop variant is not uncommon.
And, of course, the silvers are much cheaper.
Ted
Posted 15/06/2005 - 03:10
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Interesting while this light meter converstaion is, can we get back to wht actual battery replaces a Px-400. I opened a camera I got recently and found some unmarked battery with a collar on it. so 1.35 or 1.5v + base would be a WHAT??? and where do you get the collars?
Posted 15/06/2005 - 05:32
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I can only tell you where I got my collars.
From the Wein Cells (MRB400) which come with little felt black collars that act as spacers, I suppose. I merely removed them from the dead Weins and fitted them onto the 392's. As both batteries have a small side and a large side, the collar fits on the small side, but in the case of the 392's, the + side was opposite of the Weins.
My suggestion would be to buy some MRB400's and when they wear out in 4 to six months, pull the collars off and use them on whatever batteries you can find that will work. The collars look to be reusable indefinitely.
I am assuming you can get the Weins in the UK.
Regards,
Ted
From the Wein Cells (MRB400) which come with little felt black collars that act as spacers, I suppose. I merely removed them from the dead Weins and fitted them onto the 392's. As both batteries have a small side and a large side, the collar fits on the small side, but in the case of the 392's, the + side was opposite of the Weins.
My suggestion would be to buy some MRB400's and when they wear out in 4 to six months, pull the collars off and use them on whatever batteries you can find that will work. The collars look to be reusable indefinitely.
I am assuming you can get the Weins in the UK.
Regards,
Ted
Posted 15/06/2005 - 07:14
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You can get Wein cells in the UK from Jessops and other sources such as The Small Battery Company.
Best regards, John
Posted 15/06/2005 - 11:02
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Hi,
The silver equivalent is the S400PX. Details here http://www.smallbattery.company.org.uk/index.htm?http://www.smallbattery.company...
These come with the collar attached. You can then remove the collar and use the normal silver cells which are more readily available and cheaper. Having said that, I find it no problem using the cell without the collar.
Regards
Kim
The silver equivalent is the S400PX. Details here http://www.smallbattery.company.org.uk/index.htm?http://www.smallbattery.company...
These come with the collar attached. You can then remove the collar and use the normal silver cells which are more readily available and cheaper. Having said that, I find it no problem using the cell without the collar.
Regards
Kim
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