How to recalibrate m6 ttl door

MingMingPhoto

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hey guys,

Is it easy/ does anyone know the process for changing callibrating the iso number to the the meter on the m6ttl back door?




so I own an MP and learned recently I can put an m6ttl back door on it.

I tired it and it seemed to have consistent results (though I did have to move the dial out of its intended marked position - so to meter for 400 I had to put the dial to 50 to get the correct results for example)

my MP back door is a bit janky. the iso numbers fell off and it's impossible to turn the dial by hand. I thank fully have 400 scratched into position so I can just count the notches to change but I have to use a compass to change the dial speed.

I'd like to switch to the m6ttl back door as I learned those used to be the doors they'd use on these cameras. and I prefer to use that back door as it's better built and easier to use.
 

koraks

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Could you perhaps simply supplant the circuitry (supposedly some kind of resistor divider) from the original MP door to the replacement?
 
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MingMingPhoto

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koraks said:
Could you perhaps simply supplant the circuitry (supposedly some kind of resistor divider) from the original MP door to the replacement?
Click to expand...

what’s the circuitry? you mean something independent from the actual dial? becisse the main thing i’m looking for is the dial itself to be replaced with the m6 ttl dial
 

koraks

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Then swap out the dial. Either way, I'd start by looking for some documentation on the back door; a construction drawing or an exploded view from a service manual would be nice. Lacking that, start prying around with some appropriate tools.

Or do the obvious and send it out to a repairman.
 
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MingMingPhoto

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totally. i tried taking it apart but at some point i got to a point where if i went further i raked breaking the door.

since it still technically works, and it gives INCREDIBLY accurate readings i don’t want to mess it up.

i’ve contacted this one guy and he said he’s order the last but quickly stopped responding.

contacted leica directly and they told me they are not willing to sell any parts to someone who is not one of line three of their “verified repair ppl” (something like that). i’d have to send my camera in and even then they’d only replace/repair with intended parts.

so this is why i’m asking around trying to see what ppl know about doing by hand
 

koraks

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Do you want me to change the thread title to "How to replace ISO dial on Leica MP back door"? Because it sounds like that's the main question you're facing. It's not really about calibration.
 
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MingMingPhoto

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i’m really asking about the back door calibration because i need to learn that so i can be confident putting all this work into getting an m6 back door will not be done in vain. i’m sure i can find some kind of loop hole / trick them into giving me a m6 ttl back door. or i can but a broken m6 ttl i guess and use that. but i need to figure out how to re calibrate (move the numbers so they match my own cameras sensitivities)
 

koraks

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My guess is that the dial on the back door switches a resistor divider network, which the camera 'reads out' using only two or three contacts to determine ISO setting. If this is the case, calibration is nothing more than ensuring the correct resistor network is in place. That's not a process of calibration; it's a process of swapping out parts. Mind you, that's a guess from my end on how it might be done.

If it's a simple matter of 'moving the numbers', why not meter a controlled scene (like an evenly lit wall), determine which position is which speed, and then write that on a sticker and paste it across the back? Sounds rather simple, doesn't it? The main problem I see with this approach is that you may end up realizing your ISO range turns out to be restricted to e.g. 200-12800 instead of a more sensible range. Or the steps between the ISOs you measure turn out to not be spaced in a logical way (e.g. 1-1/3 stop or 2/3 stop between each click instead of a logical 1 or 1/2 stop). Anyway, you can find this out pretty easily by just doing some measurements. You don't even have to take apart either of the back doors. Just put the camera up on a tripod facing an evenly lit wall and take a second light meter to compare the Leica's readings against.
 
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MingMingPhoto

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would you mind explain the first bit in more detail?


also yes i’ve done this. i got another persons camera and asked them to let me use it for 20 min. swapped back doors and read the same scenes with my lens and it does work. and yea i lost the range. i had togo down to like iso 50 for 400. which is fine i only shoot 400, 100, 160, 800.so truthfully i’ll just do this if it turns to be too hard to recalibrate.

so you think if i take apart my back door and send you photos you can tell what the process would be like?
 

250swb

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The M6 TTL door and ISO dial is indeed the same as the early production MP style of door and dial. But it hasn't any circuitry other than a ribbon cable ending in pins that connect to the body when the door is closed, so fitting the 'new' door should work, so I suspect something else is going on. Has the OP cleaned the contacts between door and body for example?
 
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MingMingPhoto

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it “works” but it is not calibrated. so the ISO value is not correct for the ISO shown
 

koraks

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MingMingPhoto said:
would you mind explain the first bit in more detail?
Click to expand...

No, but as @250swb indicates above, it's moot. Apparently they use a different kind of network that relies on more contacts. The switch/dial apparently encodes ISO across that array of contacts.
The net result would still be the same: you'd have to keep the MP's switching circuitry when you swap out the dial. How this is implemented physically I don't know.
 
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MingMingPhoto

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i don’t think this is true (the way the iso functions)
i took part my iso dial one level in. so the numbers are removed and i can see that the iso dial is physically rotated till it sits in accordance with accuracy - then from there the label is placed on top and the whole assembly is rotated to match the same position as all other MPs

also i read somewhere the m6 ttl used to come with the MP. so idk i think it’s not too complicated - but maybe someone out am there has taken apart the m6 ttl dial and can say more
 

koraks

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Sorry, I can't make sense of your description. Consider posting a couple of photos.

Anyway, I clearly can't help you, so good luck with your project.
 

250swb

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MingMingPhoto said:
also i read somewhere the m6 ttl used to come with the MP. so idk i think it’s not too complicated - but maybe someone out am there has taken apart the m6 ttl dial and can say more
Click to expand...

That is what I said, the early production MP's came with the same M6TTL/M6 dial, I have one on my own MP so I know it works.

Nevertheless there are two further things that come to mind, the M6TTL shutter speed dial rotates in the opposite direction compared with all other Leica M's, including the MP. So for the sake of argument perhaps the M6TTL ISO dial also has it's ribbon circuitry 'reversed' to match this? However I would have thought anything like that would be done in the camera's circuitry given it's a standard M6 rear door. More complicated is that the meter of the M6TTL is not the same as the MP or M6. So while the M6 and MP both have TTL metering the distinction back in the day of naming it an M6TTL was because it had TTL flash metering, but again I don't think this should make any difference.

With a multimeter you should be able to test the circuit on the rear door to make sure it's complete, but it's a simple track so there is nothing to calibrate inside the dial. Perhaps the M6TTL rear door is faulty anyway?
 
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