| Author |
Message |
    
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 169
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, December 14, 2011 - 07:48 am: | 
|
I have a Nikon F with a 1st generation non-TTL Photomic head -- the one with the semaphore used to turn the meter on and off. It takes one 1.35v 625 mercury battery. I've been using 1.4v 675 hearing aid batteries in it, but it's a hassle using them. In another thread on the Canon EF, Rick Oleson mentioned to me that the EF wasn't so sensitive to voltage and that a regular 1.5v 625 alkaline could be used. I know this is also the case with a few others, like Pentax.
So I'm wondering if the old non-TTL F Photomic head might also not be so sensitive to voltage differences? I don't at this moment have a 625 alkaline cell to try it out with, otherwise I wouldn't bother with this post. |
Brcamera
Tinkerer
Username: Brcamera
Post Number: 134
Registered: 08-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, December 14, 2011 - 12:23 pm: |
|
The Nikon F metered finders are sensitive to battery voltage. They depend on the 1.35v constant discharge curve of the mercury cell together with the VR ring and the photocell to give accurate readings. Pentax used a "balanced bridge" type of circuit in the Spotmatics so voltage is not critical. As for the Canon EF, like most electronically controlled cameras, the battery voltage is fed to a voltage regulator and the camera uses this regulated voltage for its functions, so there is a leeway in battery voltage input...
Bill |
M_currie
Tinkerer
Username: M_currie
Post Number: 279
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, December 14, 2011 - 07:11 pm: |
|
I don't know how the innards of the old Photomics work, but the later FTn finder was not terribly hard to recalibrate for higher voltage. It might be worthwhile either finding a repair person willing to try it, or hunting further for info on this, if you intend to use the meter regularly. For occasional use I might see how much offset of the ASA dial will put it right, and leave it at that. If it's under two stops, you probably won't have any problems just fudging the film speed. |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 170
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, December 15, 2011 - 11:01 am: |
|
Thanks for the replies. That old Photomic head requires re-positioning of the ASA dial depending upon what the maximum aperture of the lens is -- so if I can refine accuracy by tweaking ASA, maybe that would be the way to go.
The old Photomic's innards are just about as basic as you can get. I had it apart once and as I recall there just wasn't much of anything inside there beyond a few resistors and capacitors. |
