old mercuty battery cameras and exposure

[peter_kim2]

I went ad bought myself a minolta hi-matic F. One of those 70's

rangefinders. Its pretty nice and all black, looks like a Minolta

CLE.

 

But it uses those infamous mercury batteries. I got it work using

1.5 volt alkalyne batteries but I hear that it does not expose

right. Some people have said to set the ASA to 200 to get correct

exposure for a 400 speed film. Does this mean that the 1.5 volt

battery 'fools' the camera into underexposing a stop?

 

So say I use a 400 speed film and set the ASA to 400...assumeing the

meter is off...would this mean that the camera is effectively

exposing at 800 speed?

[al_kaplan1]

Yes it would if the 2 to 1 ratio is accurate. Best to shoot a test roll, bracketing your exposures, and then see what works best. The alky cells tend to lose voltage with use so you need to change them more often than the merc batteries.

[lex_jenkins]

Alkaline replacement cells will only *appear* to be accurate for a short time during the life of those batteries when used with incompatible cameras.

 

The best replacement for the old size 625 mercury cell is a size 675 zinc air hearing aid battery. Cheap, reliable, with output characteristics that very closely follow the mercury batteries.

 

Been using 'em for years in various cameras designed for mercury cells. Accurate enough to get good exposures even with Velvia and Kodachrome.

[charles_stobbs2]

I second the nomination of 675 zinc/air cells. Once you make up your own adapter (an O-Ring or a thin strip of foam rubber wrapped around the cell) you are all set. They are cheap enough (compared to the film and processing) that you can replace the cells away every 2 or 3 rolls of film and they give you the correct voltage.

[douglas_greenberg]

There is no way to know in the abstract exactly how far off the meter will read with a battery of different voltage. The easiest thing to do is to take a light reading with your Minolta using the 1.5 volt alkaline (or silver oxide) battery, then also use a second camera that you know meters correctly to take a light reading of exactly the same image (or better still, use something like a grey card). Do this a few times until you get an idea of how far "off" the meter using the 1.5 volt battery reads. You can then adjust the ISO setting on your camera accordingly.

 

With my old Nikon Ftn metering head I finally had the thing recalibrated to read "correctly" with 1.5 volt batteries, as part of an overall overhaul that included cleaning the ring resistor, etc.

[charles_stobbs2]

I also advise the use of 675 zinc/air cells. Once you make up your own adapter (an O-Ring or a thin strip of foam rubber wrapped around the cell) you are all set. They are cheap enough (compared to the film and processing) that you can replace the cells away every 2 or 3 rolls of film and they give you the correct voltage.

[Ken Katz]

With an Alkalyne battery, I would calibrate the meter against a meter (or built in meter in a camera), which you have confidence in, and adjust the ASA on the Minolta so that the aperture/shutter combination matches the camera/meter you are using to calibrate. Dropping the ASA in half is consistent with the results calibrating my Canonet (black body) against an EOS 3.

 

The zinc air are better, but the method outlined above works well enough to shoot print film. As often as I use the Canonet, I would need to replace a zinc air everytime I used the camera.

[walter_degroot]

the trouble with alkalines despite what the manufacturers say:

they have a sloping discharge, the exposuer will be off and then on and then off in the other direction as the battery discharges.

this is slow so POSSIBLY you can recalibrate every week

silver oxide have the right charateristics but a 1.6v not 1.35v.

 

the zinc air at 75 cents and the wein air cells costing $5.00 are at 1.4v ( close enough ) my wal-mart-hearing aid 675 cells still seem ok after 5 months. I put nail polish on 2 of the 4 holes.( tiny dab)

 

the zinc-air cells ( hearing aid) act like mercury batteries, when they DIE they die and you know it's time. just like mercury batteries.

there are some old cameras that don't care. I believe these cameras use a bridge circuit rather than a series resistor circuit.

possibly some of the pentax cameras. this circuit compares voltage

and is not as dependent on an excact 1.35v source.

 

there is a pdf files somewhere that explins all this and more.

[richard_oleson]

The Zinc/Air recommendations are spot on.

 

Adjusting the ISO setting on your camera will not work, no matter how carefully you check it against a known meter.... even if your batteries didn't have the sloping-discharge-curve problem. The reason for this is that the amount of error caused by the incorrect voltage varies with the light level: if you change the ISO setting to make your meter read accurately at a particular light level, it will be accurate ONLY at that light level, and will be off in brighter or dimmer light.

 

The second-best solution to the problem is a silver cell with either the CRIS adapter or an in-camera modification (installing a diode) to drop the voltage. This is more accurate than adjusting the ISO, but less accurate than the zinc/air cell.

 

:)=

[douglas_greenberg]

Here is the URL of a battery-related discussion by Robert Decker, who recalibrated my Nikon Ftn meter.

 

http://hometown.aol.com/drwyn/myhomepage/webdoc4.htm

 

Apparently the use of 1.5 volt batteries is just fine in the old Nikon metering heads; maybe it's not the case for other in-camera light meters.

 

He doesn't think much of the C.R.I.S. voltage regulator.

[peter_kim2]

Thank you for all the suggestions! I think I'll try getting a zinc-air battery and shimmying it to fit in the slot. Since its a PX 640 battery originially its a little thick...

 

Also I think I am begining to understand the metering.

Am I right when I saw that when I set the ASA to 200 the camera (using the new 1.5 batteries) it will meter as if it was 400? So for instance if my handheld meter gives me a reading of say 1/60 at 5.6 then setting the camera at 200 will give me a similar reading in the camera? I was mistaken before thinking I would lose a stop by 'pulling' (even though Im not really) the film to 200 from 400...

[richard_oleson]

That is not a safe assumption, Peter. If that's the way it responds when you compare it against a good meter, then you can work that way at similar light levels, but you need to check it (which is hardly worth the effort, if you have to carry a handheld meter to check your camera, you might as well just use the handheld meter). Different meters will respond differently to the voltage error.

<br><br>

<a href="http://members.tripod.com/rick_oleson/index-111.html">(Here's my battery-substitution page)</a>

<br><br>

rick :)=

[peter_kim2]

Wow rick, thats a cool little page, thank you. Thats an even better idea. But yeah...the camera I have a Minolta Himatic F is actually a fully automatic camera. But I like taking some lower light pictures so I wanted to make sure I can hand hold it when it starts to get darker, but not totally night time of course, without a flash. Setting it from 400-200 I thought (I think mistakenly, that I would lose a stop).

 

The funny thing is I shot a test roll with the ASA set at 50, 100, 200, 400 and 500...To my suprise there wasent that mush difference in exposure. The settings at 50 and 100 were obvioiusly overexposed but still showed good detail, the 200 seemed good and 400 and 500 seemed 'slightly' underexposed but not by much. I guess I can chalk it up to the great exposure latitude of Tri-X!

 

Pete

[ron c sunshine coast,qld,a]

walter is right,the discharge slope of alkalines is gradual meaning they will give different readings over their usefull life.