Argh!

[DeanC]

I discovered this afternoon that one of the 120 inserts for my Mamiya 645 Super doesn't work with the dark slide/shutter interlock in the back I had it installed in. Unfortunately I didn't notice I hadn't pulled the dark slide until I'd shot a whole roll of my 3 year old and two other kids devouring my wife's Dove Bar at a picnic we were at...

Can anyone tell me if:
a) Am I the only idiot who's ever blown a roll and a fantastic photo op on something like this?
and
b) Can I get the insert fixed and is it worth it or should I just junk it and send KEH another ~$40?

Thanks,
Dean

 

[egdinger]

Well I can't say that I have done the same thing, in medium format. But I have missed out because my dark slide was in and I couldn't figure out why the shutter wasn't firing.

Now large format...

 

[Greg_E]

The problem isn't the dark slide or the insert, it is either the camera or the film back. When the dark slide is inserted, and operates a small switch which either opens or closes two of the contacts on the back. I'm not sure which two contacts, or the state of those contacts, but I could probably find out. Chances are good that when the dark slide is in it closes the contact, since the camera operates fine with the back removed (all contacts are then open). You can (carefully) get to the switch by removing the 9 screws and lifting the "plate" off. Be carefull as there are some small parts that will be loose (depending on whether you have the old or new style back). I've only had one of mine apart, so my memory is a little foggy. Mine has a winding problem where the gears jam when moving fast. I have a feeling that it has been used to death. i use that back with a pinhole camera that I made since it winds fine by hand.

Now if the problem happens to be with your camera, you are really out of luck! Might as well drill a hole in the dark slide plastic and tie a large bright ribbon to the end to remind you to remove it!

Is this the newer or older style back? The newer style uses a small pin to on the mounting surface to release the dark slide. The older style has a lever in the bottom mount that gets pressed to release the slide. The newer often has a red slide, the older a blue slide. The slides are exactly the same except for the color of the plastic.

 

[DeanC]

Thanks Greg, but it really does appear to be the insert. When I swap a different insert into that same back (it's one of the older ones with the bottom lever and the blue slide) the interlock starts working again and I can't trip the shutter with the slide in place. I'll try the suspect insert in my newer back once I finish off the half-shot roll that's in it.

 

[haris]

Don't know. I have two backs for my Mamiya RB67proS. One works perfectly. On other double shot proventing doesn/t work, and dark slide don't lock when inserted, that. BUt since I know those faults, I just think about that when using that back, and have no problems with it.

For 40$ I would in that situation probably buy another one insert, or whole back, or few more, fixing I belive would cost that much or very near that price...

Then again, today I shot some frames with my rangefinder and only after noticed I left lens cap on lens. Talking about idiotism...

 

[Roger Hicks]

Dear Dean,

The exact nature of the mistakes/screw-up varies, but we all make them, even after 40 years of taking pictures in my case.

Can't help with the backs, though.

Cheers,

Roger (www.rogerandfrances.com)

 

[JBrunner]

I don't screw up much any more, but at some time or another I have made about every mistake, stupid, or subtle, that there is to make. (except for the ones I have yet to discover, or lessons that I might forget over time)

So don't feel bad. My mistakes happen when I am in a hurry, distracted, or over confident in my abilities.

 

[Greg_E]

Well that is really strange. In looking at the only back that I have at home, I can't find any interaction between the insert and the dark slide switch. You might want to check each screw to make sure it is tight as the other insert may be flexing the back just enough to make the switch work. I would probably pull the plate off the back and check underneath, on the older backs I don't think anything small comes loose just by removing that cover. You should be able to leave the metal mount attached to the back.

If you have a multimeter, here's what the electrical contacts do:
. . . .
1234

#1 (the farthest from the edge) and #2 are the dark slide switch. They are shorted when the slide is in and open when the slide is out.
#3 and #4 (closest to the edge) are for the film speed and the resistance varies with the indicated speed from around 500 ohms at 25 ISO to around 10K ohms at 6400 ISO.

 

[DeanC]

If you have a multimeter, here's what the electrical contacts do:
. . . .
1234

#1 (the farthest from the edge) and #2 are the dark slide switch. They are shorted when the slide is in and open when the slide is out.
#3 and #4 (closest to the edge) are for the film speed and the resistance varies with the indicated speed from around 500 ohms at 25 ISO to around 10K ohms at 6400 ISO.

Outstanding! Thanks! I'll try the 6 back/insert combos I've got and see what I can see.

 

[rpsawin]

It have made labels for each back that reads "REMOVE DARK SLIDE". Let's just say this has eliminated the problem.

Bob

 

[MattKing]

I have had a similar problem.

I have two M645 Super bodies and one M645 Pro body. I also have three backs, and several inserts.

When I use one of my inserts, the dark slide interlock lets me release the shutter. If I move the back to a different body, I get the same result. If I try the same insert in a different back, I get the same result. If I switch inserts, the problem disappears.

I think it is the insert.

Matt