A classic Rolleiflex with a modern meter (2013)
This is an old dream, a classic Rolleiflex with a modern meter. Admittedly, there is not much wrong with the original meter, if it works. But this meter takes its signal from a selenium cell, and most of these have meanwhile given up working properly. Typically, the element characteristics change such hat they indicate too low at higher light levels, so that (if you stick to the meter),exposure may still be correct at lower light levels, but the pictures will come out overexposed when it is bright.
Technically, this is down to the sealing of the selenium cells by some kind of laquer, that starts to fail and that lets the performance of the cell degrade. Contrary to what you can read sometimes, the reason is not the amount of light that the cells had to absorb over time. A Selenium meter can lie in the sun for decades, with the needle at max as long as the cell is “tight”, this will not do harm.
After the end of serial production, Rollei and the meter manufacturer have supplied spare parts for a couple of years, but when this ended, there was indeed a kind of run for the few selenium cells that were still available, and without which the meters of the classic and much loved Rolleiflex cameras just didn’t work. I remember that I spoke to a person from Gossen (at around 1995) who admitted that they were constantly getting inquiries from serious Rollei users, whom they would love to help, but whom they were – since they had abandoned (and scrapped) the entire selenium technology – just unable to help.
And even if one had finally got hold of a working (old) selenium cell, this could itself become bad a week later. On the very camera that this chapter is about, I have had the cell replaced with a new one – a repair that lasted for about six months….
This is now all water under the bridge. Every now and then, new (old) selenium cells turn up on Ebay, sold “as is”, for still significant money. And the remaining lovers of the late Rollei TLRs now use a hand held meter – of have bought a GX.
Which is a pity, because the iconic Rollei TLR is characterised by this row of humps in front of the meter cell, over which I ran my fingers when I was a child. Also, the handling of the “F” is unsurpassed, this is ergonomics at its best. The GX is a fine camera, but only second best, and when I see a F with a handheld meter, I feel sad, somehow.
Well, after my own 3,5F was back to a “laggy” meter again, and I couldn’t bring myself to investing into yet another new cell, I remember a discussion in the “RUG”, the Rollei User Group, that circled around the possibility to replace the selenium thing with some more modern technology, but that led nowhere and the project disappeared in some drawer for around 15 years.
Until I just recently read somebody’s report on the internet, who claimed to have replaced the selenium cell (of a Russian Zenit) with the solar cell of an old calculator. I had an old calculator and indeed the needle moved – however far from the correct amount.
Still the idea was back on my mind, and I also got the nevessary help in my favourite photo forum.
Thanks a lot Jürgen, for your guidance to stop messing with solar cells, and for your patience and your help. Without you, this project would not have been completed.
As said, the idea was to replace the original selenium cell with a modern photo diode (BPW21) and to operate the camera instrument with it, via suitable electronics, so that the match-needle metering concept of the camera remained intact and the camera itself stayed unchanged, at last optically. Aside from the diode, the camera would have to house the electronics board somewhere, together with a battery and a switch to start the meter (and some cables).
The electronic circuitry is from the data sheet of the IC LM10, but not exactly. To enable a full scale deflection of the instrument, some resistor values had to be changed.
The board layout nearly drove me crazy. My first tries needed multiple additional wires, the last version only needs three:
Before version 1.0, which now sits inside the camera, I had to make four prototypes. Number one did work, but was unable to produce that full scale deflection, and was much too high for the space I had planned to fit it into. Number two and three did not work at all, for whatever reason. Number four worked well, but was still too high, so that the focusing screen image was obscured a little.
I learned a lot about soldering…
Selecting transistors was a funny exercise. I had to do this after I had ruined the (expensive) LM394 “supermatch” pair of transistors. Two transistors of identical amplification had to be selected, glued together and fitted under a common cork “cap”.
Now, the electronics sit in the mirror box, in the space kindly provided by Franke & Heidecke, to the right of the reflex mirror, the battery to the left below the lever that actuates the parallax mask.
The numerous cables are all under the mirror – and I hope they stay there.
The photo diode is where the selenium cell used to be, if one looks closely it can be spotted there, this could not be avoided.
This left me with the problem of how to switch on the meter. Other than with the selenium cell, which lives on sunshine alone, electronics need a battery and also a switch (or rather a push button thing, because on/off switches are so easily forgotten).
Unfortunately, the circuitry does not lend itself to fit a timer that would keep the meter on for a couple of seconds, after switched on once. On the other hand, the classic way of handling a Rolleiflex is with both hands, where the camera rests in the hands and aperture and speed are adjusted with the thumbs, and where the index fingers are free to e.g. operate a meter switch.
I eventually decided against the initial idea to somehow switch the meter on via the shutter release button. For once, there is not much space to easily fit a switch, and I was also reluctant to make the butter smooth shutter release any harder to press. This soft shutter is one contributor to the fact that shutter speeds as slow as 1/15 can often be used hand-held on a Rolleiflex. And (at least on my camera) I am sure I would have often released the shutter accidentally, when all I wanted was to activate the meter.
So I sacrificed the P/C (flash) socket. This is a sacrilege for sure and it does permanently modify the camera (something had said I would avoid). On the other hand I will not use the camera with a flash (I don’t like flash photography anyway) and this is a perfect place for a button. Where the P/C socket once was, the left index finger starts the meter, the thumbs adjust speed and apertuire to match the needle, and the right index finger stays free to wait for that decisive moment.
So the final camera is almost unchanged from the outside. The meter works well, as if it was never out of order. To adjust the meter to the correct exposure was a piece of cake, eventually, and – all in all – I do not feel I have ruined that classic camera at all. Had Rollei stayed in the business after 1981, they might have done something similar, they already had prototypes (to be found in Prochnow’s books)
One word of caution, should somebody now plan to also do this modification, after being fed up with the lame meter of his beloved “F”. As much as I am delighted if somebody draws inspiration from my tinkering, this particular one wasn’t simple, even if it now looks so inconspicuous. I am happy to help, but this is not a “plug and Play” solution…