Exposure compensation for non mercury batteries?

[Patrick]

I have one of those super 8 cameras that accepts the little discontinued mercury battery. I have heard that the replacement battery does not provide accurate light meter readings. For those of you who have used these replacement batteries, would you recommend opening or closing the aperture to compensate - and by how much? The camera in question is a Cosina (can't recall the model name as I don't have it with me now.) There may be a + and - compensation on this camera but I wouldnt know exactly how much of a compensation would be given - half a stop or full stop.

[Actor]

I have one of those super 8 cameras that accepts the little discontinued mercury battery. I have heard that the replacement battery does not provide accurate light meter readings. For those of you who have used these replacement batteries, would you recommend opening or closing the aperture to compensate - and by how much? The camera in question is a Cosina (can't recall the model name as I don't have it with me now.) There may be a + and - compensation on this camera but I wouldnt know exactly how much of a compensation would be given - half a stop or full stop.

Personally I'd shoot a test catridge, 10 feet opened up one stop, 10 feet opened up a half stop, 10 feet nominal, 10 feet closed a half stop and 10 feet closed a full stop. All of the same subject under the same lighting.

[Steve P.]

Which replacement battery? The zinc-air or the 1.5 alkaline?

Personally I'd shoot a test catridge … of the same subject under the same lighting.

Agree with test shot, but the response is not linear over light levels. If it’s not linear, you can’t easily infer exposure equivalents by using any one aperture (or ASA, or shutter speed) as a base. You also need to factor for focal length.

You didn’t ask for it, but my advice would be to consider the diode adapter. It just seems the easiest, most-convenient method to replace the mercury PX 625.

[Patrick]

Thanks for the tips. Unfortunately a test film is out of the question. I have lent the camera to my father who has gone interstate to attend a wedding. Foolishly, I didnt realise at the time that this camera required the special battery for the light meter...not until he arrived. I bought the camera over a year ago but I have never ran film through it...but I do recall that it ran on AAs with no problems when I first checked it out.

[lastcoyote]

When I shoot my Nizo 801M, I'm using the PX625 as well, the camera ask for 2 X 1.35V button cells. But I replace with 2 X 1.5V button cells. It ends up okay. I am okay with that.

[oneatatime]

Patrick:

Go down to your local chemist and buy some zinc-air hearing aid cells of the correct physical size and use foil and a little tape to fit them into the cell holder. There is also a mail order bunch online in NSW where you can get them even cheaper and I also believe hearing aid batteries are GST free :o))

I have use them with great success in old Nikon S8 cameras and the difference between the Hg cells at 1.35V and 1.4V for the Zn-air is tiny. K40 was always exposed spot on for me.

Cheers

[Guy Bennett]

Sorry to flog yet again this long dead horse but non-mercury PX625 1.35v batteries are available from Du-All Camera, Super 8 Stuff, and Wittner Kinotech, and they're cheap -- $US 5-8. Why use anything else?