[rollei_list] Re: OT: Selenium Meters

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <rollei_list@xxxxxxxxxxxxx>
  • Date: Fri, 21 Apr 2006 14:27:44 -0700


----- Original Message ----- From: "Carlos Manuel Freaza" <cmfreaza@xxxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Friday, April 21, 2006 12:09 PM
Subject: [rollei_list] Re: OT: Selenium Meters


--- Jan Decher <jan.decher@xxxxxxx> escribió:

To bring this around to Rollei: How good is the tiny
(Gossen?) Selenium
meter that is attached/hinged to the Rolleiflex (Bay
II?) lens hood?
Anyone here using one, or have one for sale?


That is the Rolleilux made by Gossen and then it must
be good. It's attached on a special Bay I lens hood
that has an also special ring that can turn 180º to
fix the Rolleilux on  Rolleiflexes, Rolleicords and
4x4 with bayonet size 1 but different design, it
allows reflected and incident light readings (using
the dedicated diffusor).
The problem with selenium meters is that the cells
lose sensitivity along the years due to exposure to
light and dust becoming dead finally, the quation is
not if they'll die, the question is when, however
there are old selenium meters in good condition tilll
today, i.e. my 3.5F lightmeter is in good condition
yet.
You can see a nice Rolleilux for sale here:
http://www.collectcamera.com/bladenrollei/rolleiacc/rolleilux.htm

All the best
Carlos

Its not exposure to light but moisture leaking into the cell or exposure to high temperatures. Both cause chemical changes to the cell. The usual symptom is compression of values for bright light, i.e., the meter reads low for high brightness. Most Selenium meters have an overlap between the high and low range. One can generally get a reading in this overlap region which will be on the low end of the meter scale on one range and on the high end on the other. The two should be the same or at least very close. If the cell is damaged the reading on the high end of the meter will be lower by about 1 stop, sometimes more.
Selenium meters can also suffer from poor contact with the cell and, of course, from wiring or meter problems. Some contact problems are easy to fix others not. On Weston or Sangamo-Weston meters the contact problem can result in low or intermittant readings. Often putting some pressure of the cell face and turning it a bit will fix the problem.
I can't comment on Gossen meters because I've not seen enough of them but Weston's seem to be the most rugged of the lot, General Electric DW- series not so good, often having damaged cells, the PR-1 and PR-2 being somewhere inbetween. The idea is to check any meter as I have described above. Selenium meters do not generaly have any calibration adjustments other than mechanical meter centering. If the cell is good the meter will read right. Electronic meters, like Cds meters, can have adjustments. One must have some sort of standard to adjust them.
Low light performance of Selenium meters is not very good. The Selenium cell is a generator which drives the meter. If one has a large cell and sensitive meter movement the low light sensitivity will be decent (Weston meter), small cells or poorer meters will limit low light readings. The response of the cell for low light will be about the same as at high light, they do not have the low light lag of electronic meters. Also, while a "memory" effect has been described for Selenium, none of the many Selenium meters I've used showed any practical effect from this.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx




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