Odd/Interesting Mamiya 7 low-battery behavior

[Steve Goldstein]

Yesterday I had a new-to-me experience that I thought I'd post for posterity and comments.

It had been a while since I'd used my Mamiya 7 (not II) backup body so I decided to take it out for a spin. I took the battery from my "daily driver" Mamiya 7 and popped it in the backup, operated the shutter a couple of dozen times (seemed OK), loaded a roll of Kentmere, and headed outside. All was well for the first 8 shots, all shot in manual-exposure mode so I could cycle through the speeds, but I noticed an unusual sound on the last two shots (one at 1/250, one at 1/500) as if the shutter was running really slow. After I finished the roll and unloaded the camera I fired the shutter a few times - all speeds seemed fine except the two fastest, both of which behaved like maybe 2 seconds. I also noticed the blinking warning light in the lower left of the finder, which according to the manual indicates a low battery.

I put in my "new" lithium battery spare and everything worked normally. The old alkaline battery went into the trash, the lithium cell moved into the daily driver, and the backup went back onto the shelf. I would have put the dd on the shelf and switched to the backup but the dd is loaded with a partially used roll.

The Mamiya 7 (and II) manuals don't say anything about slow/hanging shutter speeds with a low battery, at least not that I could find. I guess when the battery voltage is low enough all manner of weird things can happen.

I've also posted this on RFF to get the word out.

 

[MARTIE]

Hi, I'm just curious if you've processed the film and seen the resulting negs?

 

[Steve Goldstein]

I plan to process it in the next few days and will report the results.

One thing I neglected to mention is that I used my Pentax digital spot meter to determine exposure and didn’t pay attention to the internal meter so I don’t know what it was doing or how the reading compared to that of the handheld meter.

 

[grahamp]

It happens with the Mamiya 6 as well. I don't recall any exposure issues on the one time it happened to me, but I have no evidence either way.

 

[Steve Goldstein]

Just a followup - all the exposures except the ones where the shutter was audibly slow were fine. Again, exposures were determined using a spot meter and I didn’t pay any attention to the internal meter readings.

 

[Mamiya_Repair]

On the Mamiya 7, when the 6 volt battery drops to 4.3 volts under load, a release inhibit signal is sent to the control board to prevent the shutter from releasing since at this voltage, the shutter may act erratically. In this case, it seems like the release inhibit signal is not being sent due to a possible calibration issue or electrical fault. Next time the camera is being serviced, mention this to the technician so that it can be checked.