A fresh wiencell @ 1.4 V will introduce atleast a half stop error.
John
HI100@xxxxxxx wrote:
>
> Hi Oly Repairers,
> Still more comments relating to my previous post
> and
> some follow up comments on the thread in general.
>
> John lind wrote:
> >>
> There are three off-the-shelf solutions I know about. The following URL's
> go straight to their sites: ...
> <<
>
> Unfortunately John, the 1.4V of the zinc-air cells still leads to errors as
> the charts at the end of my last post indicated. Also the MR9 adapter will
> give
> errors as **estimated** in my post (since I don't own one)
> and apparently verified by Gary Reese (see Below.)
> For zinc-air, I have reformatted data from my last post and
> interpolated to 1.4V in a few cases:
> approx error:
> EV3 0 stop
> EV6 -0.1 stop
> EV 7 -0.6 stop
> EV 16 -0.6 stop
> This is *much* better than nothing but still a bit too loose for my liking
> ===============
>
> Gary Reese wrote:
> >>
> I just tested 4 OM-1 's on an exposure meter tester and I got non-liner
> errors in all four using a MR-9 adapter in each. The situation is personally
> disgusting since the errors are major. I refuse to sell a camera that I know
> is out of specs (ex. for shutters at 1/1000 and above, which is to be
> expected in an aged camera). To me, it makes no financial sense to have a
> commercial overhaul of an OM-1 since overhaul costs eliminate any reasonable
> profit. I guess I'll have to learn to adjust them myself.
> I'm planning on retesting the meters with a mercury cell just to see what
> error is attributable to the MR-9 adapter.
> <<
>
> Gary,
> were the errors mainly at high EV as my test suggests is likely
> with an MR9 type adapter? What was the largest error?
> A general comment: if the errors are at low EV's it is likely that it is the
> photocell as the Cadmium sulphide or cadmium selenide cells used
> in most cameras of that vintage do drift over time and the camera is
> generally insensitive to battery voltage at low EV. Interestingly the meter
> response really gets sluggish at low light when going quickly from light to
> dark conditions. Be careful when you test.
> =======
> Wayne Shumaker commented about using a Linear tech
> i.c ,switched capacitor voltage regultar which draws 18uA and would use
> a pair of thin Lithium batteries. At 6V input this would have a
> much higher power consumption than a simple linear design
> with a similar parts count. On the other hand the batteries will probably
> have more energy to start with, as the Lithium batteries have higher
> energy density.
> Wayne reposted later saying he might find a single cell to fit (3V)
> but that in rereading the i.c.spec sheet he found it had a standing
> current of 150uA rather than 18uA. Better than
> a shunt regulator but still rather high for forgetful photographers.
> ===========
>
> John Maynard commented:
> >>Tim ... I'd like to try this. What do you plan to use, specifically?
> Perhaps a PCB
> can be designed with surface mount components and made inexpensively; while,
> as you say, this might be beyond the average home repairman, it might be
> simple enough to be duplicated by folks with experience in the area.
> <<
>
> John,
> I have a "back of the envelope" 3 transistor design using 5
> resistors.
> I may need a cap for stability as the parts get rather slow at low current.
> The current drain should be about 11uA. The static current is determined
> largely by the requirements (min gain) of the series pass transistor
> near saturation. I may have to tweak this depending on my junk parts
> availability. I will keep you informed if this works out well in test for
> me, when I get round to building it!
> Surface Mount ?? There is no reason that this should not be built with
> sot23's
> and chip resistors for surface mount but I am hoping I can find enough space
> in an used corner for regular parts,1/8W resitors and perf. Or even
> (horror) a spider in epoxy!
> Maybe I am too optimistic on size.
>
> Tim Hughes
> Hi100@xxxxxxx
>
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