Minox 35GT - battery test readout is off with PX27G Alkaline 6V battery

albireo · Dec 10, 2021

Just chanced on a Minox 35GT. Came with an old, long exhausted Duracell 5.6V mercury battery so I couldn't do a battery test and had to order replacement batteries online before getting to know whether the camera works or not.

In terms of batteries, the simplest option where I live seemed to be a PX27G alkaline 6V replacement. Based on what I had read online, the voltage difference shouldn't produce a metering error.

The good news is that the battery fits and the shutter and exposure meter appear to be operational (open back - set to f/16 - cock and trip the shutter in a dark room - observe the shutter clicking open and closed; viewfinder needle swings about as expected following aperture variation).

The so-so news comes from the battery test button: when I perform a battery test as indicated in the manual, the needle readout in the viewfinder says 1/500, whereas the manual suggests it should give a '1/125 or beyond' readout.

I test metered the same scene with the Minox set at 400IS0 and an SLR +50mm prime set on centre-weighted metering and set at 400ISO. The scene was the same, but I cannot exclude metering variations induced by a) different centre-weighted metering distribution across cameras 3) different angle across lenses. Having said this, I repeatedly found that to get, on the Minox, the readout I was getting on the SLR I had to move the film sensitivity wheel on the Minox down to 160-200EI from 400ISO.

Does the above suggest the 6V alkaline battery might be leading to systematic underexposure? What are people's experiences wrt this?

Nitroplait · Dec 10, 2021

albireo said:
Does the above suggest the 6V alkaline battery might be leading to systematic ~1EV overexposure? What are people's experiences wrt this?

FWIW: I have my 35EL set to 200 ISO for use with 400ISO film otherwise the 6V battery will result in underexposure (not overexposure as you write).
The battery check readout in my 35EL finder goes to 1/250 but the 35EL manual states that the needle should be on 1/125 or above.
I don't know if the meter variation is linear or not, but compensating one stop through the ISO setting works fine for me.

albireo · Dec 10, 2021

Thank you Nitro - apologies - two typos/imprecisions on my side, both fixed. Having double checked the manual, it says '1/125 or beyond' so it seems that going by the battery check alone the battery should be within specs.

However it does seem like using box speed on the selector might results in systematic underexposure. This is solvable with 400ISO film but it means I won't be able to expose 100ISO film correctly.

Nitroplait said:
FWIW: I have my 35EL set to 200 ISO for use with 400ISO film otherwise the 6V battery will result in underexposure (not overexposure as you write).
The battery check readout in my 35EL finder goes to 1/250 but the 35EL manual states that the needle should be on 1/125 or above.
I don't know if the meter variation is linear or not, but compensating one stop through the ISO setting works fine for me.

Nitroplait · Dec 10, 2021

albireo said:
However it does seem like using box speed on the selector might results in systematic underexposure. This is solvable with 400ISO film but it means I won't be able to expose 100ISO film correctly.

If 100ISO is your lowest setting, correct.
My 35EL goes from 25 to 400ISO which in theory allows me to use 50-800 iso film. I only use 100, 200 and 400 ISO and there seems to be reasonable linearity when compensation is done as outlined above with these values, so I am fine.

AgX · Dec 10, 2021

As a general remark, without knowing the circuit in question:

If a camera has got a voltage regulator, one can use batteries of slightly different nominal voltages.

In designing the circuit for such camera, with the standard battery in mind, it makes more sense to place the sub-circuit for the battery voltage (battery check) before such regulator. In such case employing a fresh battery of different nominal voltage will result in a metering off the mark for the standard battery.

Nitroplait · Dec 10, 2021

I just checked with Kanto Camera. They sell both regulated and unregulated adaptors (for use with 4x SR43) they recommend the unregulated version for all Minox 35 models. SR (silver oxide) actually have a higer voltage than LR (alkaline) thus the recommended adaptor would supply 6.2V. No mention of a need for compensating ISO setting.

Is it possible that the need to compensate is due to other factors than voltage - ageing CdS cell perhaps? -but I would think that would lead to decreased sensitivity not increased as we see in this case.

albireo · Dec 10, 2021

Nitroplait said:
If 100ISO is your lowest setting, correct.
My 35EL goes from 25 to 400ISO which in theory allows me to use 50-800 iso film. I only use 100, 200 and 400 ISO and there seems to be reasonable linearity when compensation is done as outlined above with these values, so I am fine.

I have just checked the ISO selector at the bottom of the camera. There is an extremely faded sticker but I can just make out the ticks for '30/800' and '15/2...' . I had missed these before. If as I hope15 stands for 15 DIN then the selector goes down all the way to 25 ASA as is the case with your camera, which means I should be alright exposing 100ISO film (I don't use any film less than 100ISO box speed). Many thanks for all the provided hints so far.

runswithsizzers · Dec 10, 2021

I think you are on the right track. If you can adjust your camera's ASA dial until the camera meter reading matches the reading from a known reliable meter, that should work. But if you are using batteries of a different voltage than intended, I'm not sure how much you can trust the camera's battery check function.

It might be helpful if it can be established whether your camera has a voltage regulation circuit - or not. When researching battery options for my Konica Autoreflex T4 (which does not have voltage regulation), many of the references I read suggested using silver oxide batteries - and not using alkaline - because the voltage is more constant over the life span of a silver oxide batteries. That is, the voltage from alkaline batteries decreases more as they are used, compared to silver oxide. If you use an alkaline battery, it might be necessary to periodically keep checking the camera reading against a known source multiple times as the alkaline battery becomes weaker due to use.

If your camera has a built-in voltage regulator, then it may be able to compensate for the incorrect battery voltage, making these concerns moot.

benjiboy · Dec 10, 2021

I use 2 Duracell CR 1/3N 3volt Lithium batteries in My Minox 35 GT I buy from Amazon, and have no problems.

albireo · Dec 10, 2021

benjiboy said:
I use 2 Duracell CR 1/3N 3volt Lithium batteries in My Minox 35 GT I buy from Amazon, and have no problems.

Thanks - by 'no problems' do you mean the exposure readout at box speed matches the one you get from another camera you have?

benjiboy · Dec 10, 2021

albireo said:
Thanks - by 'no problems' do you mean the exposure readout at box speed matches the one you get from another camera you have?

Yes.

benjiboy · Dec 10, 2021

albireo said:
Thanks - by 'no problems' do you mean the exposure readout at box speed matches the one you get from another camera you have?

Yes, and a Sekonic digital light meter.

Nitroplait · Dec 10, 2021

benjiboy said:
I use 2 Duracell CR 1/3N 3volt Lithium batteries in My Minox 35 GT I buy from Amazon, and have no problems.

CR 1/3N are narrower and two are slightly longer than S27PX, but if they fit I would much prefer lithium to silver oxide or alkaline. They have much longer shelf life and rarely leak - and CR 1/3N can be used in all those cameras that normally take 2x SR44 (LR44) - which means all mine except for one - that would be a great relief!

MattKing · Dec 10, 2021

It isn't just the initial voltage. Unless there is a regulator, the voltage consistency is important. Alkaline batteries have voltages that change over time.

benjiboy · Dec 11, 2021

Nitroplait said:
CR 1/3N are narrower and two are slightly longer than S27PX, but if they fit I would much prefer lithium to silver oxide or alkaline. They have much longer shelf life and rarely leak - and CR 1/3N can be used in all those cameras that normally take 2x SR44 (LR44) - which means all mine except for one - that would be a great relief!

I can assure you that they do fit in my Minox 35 G.T.

Patrick Robert James · Dec 11, 2021

I use four 357/sr44 batteries in my Minox EL. I put a paper insulator around the battery compartment so I can just drop the batteries right in. I do drop the ISO. Not sure if there isn't a circuit for the voltage difference or not but it works fine that way. They are fantastic cameras. I really aught to use mine more.

Huss · Dec 11, 2021

Forget the batteries, I’m just amazed u lot have working Minoxes! Have not yet found one w a functioning shutter.

benjiboy · Dec 11, 2021

Huss said:
Forget the batteries, I’m just amazed u lot have working Minoxes! Have not yet found one w a functioning shutter.

It might surprise you to learn I've had my Minox about 25: years and have never had any problems with it, although I bought it second hand.

albireo · Dec 11, 2021

Just done developing an exposed test roll. Kentmere 400 in Xtol stock. Negatives are hanging to dry. The ISO selector on the Minox was set to 200. Negatives look a bit thin at first glance, but they're still wet and the lighting is poor - will check tomorrow. On the plus side, all 37 frames are exposed. Also no frame overlap and no light leaks, suggesting that the shutter operates consistently across frames, the film advancement works and the camera is light tight. Quite happy though I'm sure things might still fail in the future. Let's see.

Huss · Dec 11, 2021

benjiboy said:
It might surprise you to learn I've had my Minox about 25: years and have never had any problems with it, although I bought it second hand.

I am indeed.

albireo · Dec 15, 2021

Quick update on my attempts to find suitable power for this Minox 35GT.

The results of my first roll were noticeably underexposed, even though I had set the ISO to half box speed (200 in this case). This using the alkaline PX27G 6V battery.

I then purchased a pair of CR1/3N lithium batteries branded 'Varta'. As Nitro suggested, two stacked CR1/3N are a good 2mm longer and a little narrower than the alkaline I was using:

I dropped them in to check they'd fit in the compartment. They do fit and the cap screws in ok as far as I can see (there is perhaps a little added pressure on the + contact in the battery cap). However, the battery test wouldn't work. The needle would just flicker about 1/30 and go back to resting position. I took the batteries out.

Assuming the test failure could be related to spurious contact between the sides of the batteries and any metallic areas in the battery compartment, I wrapped two lengths of electric wire around the batteries.

Dropped them in, and repeated the test. No luck again. The meter needle moves a little around the 1/30th mark then goes back to rest.

Then I noticed my rookie mistake. I didn't check the polarity and had inserted the 2x lithium upside down: whereas on the PX27 the little 'bump' is the +, on the lithium ones the bump is on the '-'.

The batteries work with the electrical tape insulating them and when inserted with correct polarity. The battery check readout is again hitting 1/500 but I will run a new test roll to see if underexposure at 200EI persists or if these batteries perform better.

albireo · Dec 21, 2021

Quick update. I have developed a test roll which was exposed using the lithium batteries as above. I hae tested the in camera meter again against my SLR using these batteries and found the readout to match almost perfectly. I exposed a Kentmere 400 roll at 320EI and got *much* better negatives than I had gotten using the alkaline batteries.

So many thanks everyone for all suggestions and special thanks @benjiboy for the lithium cell recommendation. It really is night and day difference ime.

Now to my next question. Lens sharpness. What are people's experiences with focus guestimation using this camera? I have to admit the results I got were pretty underwhelming in terms of nailed focus. I'm not exactly a newbie with distance guessing (I have and use an Agfa Isolette and Agfa Record folders, all without rangefinders and am used to estimating distances).

My idea with the test roll was to go with f/11 (where possible) and place the focus ring so that the indicated usable DOF is 2m < dof < infinity. I mostly took pictures of subjects in the 3m < subject < 15m range.

As stated this gave me pretty poor results. Is the DOF scale on the Minotar lens a tad optimistic perhaps? Might I have a misaligned sample and if so, any idea on how to disassemble and recalibrate?

polka · Dec 21, 2021

I have a Minox35EL since 1979, and used it a lot more than my other 35mm cameras (because it's so small and so streamlined that you may have it with you all the time in your pocket. A few remarks :
1/ I used alkaline batteries when the mercure batteries were forbidden and I did even color slides with no film sensitivity corrections ; because by principle, the electronic shutter computes the charging time of a capacitor through the CdS photoresistor by comparison with fixed resistors on the same battery voltage. You should test it with a slide film (more sensitive to exposure errors), and no correction of the film sensitivity. if it's not good, it's not because of the battery (maybe because of aging of the electronics ?).
2/ To test if distance setting is all right, you should take a landscape at infinity at several aperture settings (full open to full closed) and compare the sharpness of the backgrounds. If it's OK at infinity, it's OK anywhere.
3/ My method for guestimating the distances (with the Minox35) : as the Minotar focal is 35mm and the width of the negative is also almost 35mm, if you can imagine that on the plane where you want to focus your subject is full framed 1m wide (of tall), you set the distance to 1m ; if you see it 2m wide (of tall), set it to 2m ; etc.

benjiboy · Dec 21, 2021

albireo said:
Quick update. I have developed a test roll which was exposed using the lithium batteries as above. I hae tested the in camera meter again against my SLR using these batteries and found the readout to match almost perfectly. I exposed a Kentmere 400 roll at 320EI and got *much* better negatives than I had gotten using the alkaline batteries.

So many thanks everyone for all suggestions and special thanks @benjiboy for the lithium cell recommendation. It really is night and day difference ime.

Now to my next question. Lens sharpness. What are people's experiences with focus guestimation using this camera? I have to admit the results I got were pretty underwhelming in terms of nailed focus. I'm not exactly a newbie with distance guessing (I have and use an Agfa Isolette and Agfa Record folders, all without rangefinders and am used to estimating distances).

My idea with the test roll was to go with f/11 (where possible) and place the focus ring so that the indicated usable DOF is 2m < dof < infinity. I mostly took pictures of subjects in the 3m < subject < 15m range.

As stated this gave me pretty poor results. Is the DOF scale on the Minotar lens a tad optimistic perhaps? Might I have a misaligned sample and if so, any idea on how to disassemble and recalibrate?

Regarding the focusing on the Minox Minotar lens, the reason I bought the camera in the first place is that I was looking for a compact camera that would go in my shirt pocket with a good lens, and I read in a test report in a U.K camera magazine that said "the Minotar lens would put the standard lens on most S.L.Rs to shame" so I bought it. I'm currently using the camera with an old clip-on Voigtlander rangefinder I keep it in my pocket and set the focus at the indicated distance on the rangefinder I get sharp results every time at that distance whatever aperture I set.
I have owned this camera for about thirty-two years and found that the magazines claim about the lens sharpness is true.

albireo · Dec 21, 2021

benjiboy said:
I have owned this camera for about thirty-two years and found that the magazines claim about the lens sharpness is true.

I do not doubt it's potentially a good lens - I'm saying that something seems to be off with my sample. It's perhaps due to errors on my side, but there's probably more.

I have been pixel-peeping the focus on a test shot I did - camera on tripod, f/8, self-timer. This shot has good centre sharpness, and good sharpness towards the right side of the frame. However, sharpness around the left side of the frame is noticeably off. I suspect some sort of misalignment, to do with lens assembly or focus plane or both. The pressure plate seems to be in good condition. I wonder if the camera was badly handled which might have misaligned the lens. Visually, the camera is in truly spectacular condition, and bears no obvious signs of mishandling.

Either way, as it is the pictures are not satisfactory. Pity because I got 38 well exposed shots on my second test roll, suggesting the shutter is doing well for the time being. I might try my luck with another sample as it does seem to have a good form factor, and I can see myself carrying one of these in my pocket at all times.

Minox 35GT - battery test readout is off with PX27G Alkaline 6V battery

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