rolleiflex 3.5f -- light meter issue

unfortunately, it appears the light meter on my much beloved rolleiflex 3.5F is on the fritz. my guess is that its the selenium cell. but maybe its the meter needle module in the focusing knob... or maybe something else.

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after not using the rolleiflex for quite a while, i put 5 rolls through it last month. all of them came out over-exposed to some degree. the most over-exposed frames were in difficult, bright light conditions (snow, overcast with thin clouds)... so i figured it was just user error in making adjustments for those conditions.

well, i took the rolleiflex out again last week -- along with a spot meter and rangefinder with a TTL meter to double check exposure. when metering i discovered that the rolleiflex meter was over-exposing in strong light conditions by as much as 2 and 3 stops!!

so, yesterday i did a more "scientific" test to try and understand the problem. using a grey wall outside i metered the rolleiflex, rangefinder and spot meter -- along with a nikkormat SLR and a weston euro-master handheld meter. i did this a number of times throughout the day to get a range of light levels. note: using the spot meter and an 18% grey card, the wall fell in zone-6.

then, using the reading taken with the spot meter as the "baseline" i compared the readings from all other sources. basically, all other meters were within a 1/3 or 1/2 stop of the spot meter... except the rolleiflex which was off by as much as 2 2/3 stops for higher EV light conditions. the error in the rolleiflex readings definitely increases with EV.
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anyone else have a similar experience with their rolleiflex? what are the possible avenues for repair? can the selenium cell be replaced / repaired if that is the problem? ...thanks!!!!

You didn't accidentally set the filter compensation wheel up to 3?

dpurdy said:

You didn't accidentally set the filter compensation wheel up to 3?

Click to expand...

nope -- i checked that and everything else i could think of.

that would have been "nice"

I had light meter problem with mine and did the cleaning of the contacts thing at the light receptor and meter needle end without much change but then noticed a cold solder joint at a connection to the selenium cell. After re soldering this it has been working fine.

richyd said:

did the cleaning of the contacts thing at the light receptor and meter needle end without much change

Click to expand...

just gave that a try with no change in performance -- still over-exposing / under-metering by 2+ stops in bright light. the contacts were in pretty good shape but cleaned them off anyway. thanks for the suggestion.

circuitry seems good -- my multi-meter shows ~0.35 mV when the selenium sensor is ~6" away from a 60 watt light bulb. so, must be either the light cell or meter module which is faulty... unless there is something else i am missing.

Get a can of http://www.homedepot.com/p/CRC-11-oz-QD-Electronic-Cleaner-05103/205021975 . Remove knobs, covers as needed to access the exposure compensation and ASA dials. Spray the dial contacts liberally and operate the full range while wet with the contact cleaner.
Reassemble and try again. Other brands of contact cleaner do not work as well. Its sold at many retailers including auto parts stores.
A Rolleiflex TLR service manual is available at http://www.kyphoto.com/classics/repairmanuals.html
be sure to follow the download instructions at the top of the page. The pdf looks fuzzy until you increase the zoom to 200% or higher then it becomes very sharp.

Maybe a stupid question on my part...

Isn't this the typical reduction in sensitivity that ultimately happens to selenium meters? That is, they give a lower EV reading than they should, causing you to overexpose the scene.

I've heard that low-light sensitivity is first to start failing, but it seems that in your case brighter conditions are the problem - which is odd.

I wonder if there's an issue with the ISO setting mechanism (probably just a variable resistor).

Theo Sulphate said:

I wonder if there's an issue with the ISO setting mechanism (probably just a variable resistor).

Click to expand...

No ISO on these. ASA
Selenium cell connects directly to the galvometer. Mechanism is all mechanical. A wonder at that too!

Selenium cells are nearly impossible to find working replacements for them these days. I have one that I would like to have refurbished or replaced and no one has them.

The over exposure is typical when selenium cells start to fail, they produce less current at full light level, causing the meter to under read, leading to over exposures.

There is a lot of misconceptions about selenium cells, so I'll take this opportunity to mention a few things. The failure mode for these cells is corrosion due to moisture. The doped selenium is a solid state material, which does not degrade appreciably with electrical or optical use. Selenium oxidized easily, so the cell is sealed with a lacquer layer to keep moisture out. When this layer is breached, the cell will start to corrode and fail. Scratching the surface when handling it will cause this. The other most common issue is the break down of the lacquer with UV exposure (hence the common thought that UV degrades the selenium). You will find a lot of Gossen selenium meters still working after 50+ years, because they used a high quality lacquer. Covering the selenium cell when not in use also extends the life of the lacquer.

Silicon has replaced selenium because it have no corrosion issues, and a larger output that can be incorporated into a amplification circuit for lower light level sensitivity. However, it is more sensitive to IR and Red light, so most cells have a blue filter to compensate. I only mention this because you can replace the selenium cell (they are very hard to get now) with a silicon version, as long as you compensate for the higher output and sensitivity to red.

PDF page 6 shows the DIN/ASA setting and the filter factor setting (exposure compensation) setting. http://www.butkus.org/chinon/rollei/rolleiflex_35-28/rolleiflex_35-28.pdf
There is a procedure for resetting the meter on PDF pages 16 and 17.
The ASA and filter factor settings are variable resistors. Variable resistors are usually a thin carbon disk with a brass wiper arm but can be wire wound. The wiper arm contact can tarnish and cause a higher resistance than selected resulting in erroneous readings.

shutterfinger said:

PDF page 6 shows the DIN/ASA setting and the filter factor setting (exposure compensation) setting. http://www.butkus.org/chinon/rollei/rolleiflex_35-28/rolleiflex_35-28.pdf
There is a procedure for resetting the meter on PDF pages 16 and 17.
The ASA and filter factor settings are variable resistors. Variable resistors are usually a thin carbon disk with a brass wiper arm but can be wire wound. The wiper arm contact can tarnish and cause a higher resistance than selected resulting in erroneous readings.

Click to expand...

Selenium cell connects directly to the galvometer. Mechanism is all mechanical, (including the galvometer zero screw, exposure compensation, ASA, shutter speed and aperture compensation). Calibration is actually listed on page 2.02.0220 of the service manual, and it is only the mechanical "follow arm" that can be adjusted. The selenium cell connects directly to the galvometer and the needle moves only in response to light, unaffected by any controls on the camera.

Oh! its a dinosaur, only the scale is moved.

itsdoable said:

The over exposure is typical when selenium cells start to fail, they produce less current at full light level, causing the meter to under read, leading to over exposures.

Click to expand...

this definitely the symptoms my rolleiflex is experiencing. i was hoping it was something else but that is looking less and less likely. guess i will keep an eye out for a non-working rolleiflex being sold for parts in the hopes of picking up a functioning selenium cell. in the meantime i can carry an external meter.

any recommendations for a service shop here in the US that might be able to help?