Pentax Spot Meter - quick check?
I made a post late yesterday but it didn't seem to make it to the Forum.
The costs of recalibrating the meter are not "inconsequential", at least not until I can find a local shop who can do the work. The cost of sending the meter across the border and back by courier would come close to what I paid for the meter.
I am glad you had a good laugh Robert ;-)
All of the exposure meters that I have worked on in my 35 years in photography and in the electronics service and design field have been resistive bridges where the only active (non-linear) component is the photocell. A well designed bridge is largely immune to fluctuations in battery voltage. Also, resistors have excellent long-term stability and do not change much with age, temperature, humidity, etc. (unlike active components). A resistive bridge is also absolutely linear - if you have calibrated the zero point and the full-scale point, every point in between will also be calibrated.
Although I do not have a schematic yet for the Pentax spot meter, it appears (from the internal components) that the Pentax is also a resistive bridge - actually TWO resistive bridges, one low range, one high range - with some additional circuitry to provide the battery check function.
The first problem I had was with the range switch being dirty which caused the full-scale sensitivity to change because the switch resistance changed from one operation to the next. To clean the switch properly, I dismounted the PCB, which disturbed a cold solder joint and caused the meter to become intermittent (on/off) on the high range. Repairing the multiple cold solder joints alleviated that problem.
Now, since I had not replaced any components and was still using the same active component (photocell), making an approximation test for full-scale DOES ensure that the meter readings will be the same as they were before the switch started causing problems and before I disturbed the cold solder joints.
There you go! Another post to give you a good laugh!
Pentax Spot Meter - quick check?
Ohhh CJ... Please do not eviscerate the mythic light meter for all to see!
Ahhh, too late... The magic is gone and the mythical beast has turned out to be a simple device.... What will we vernarate now????
:-()
Pentax Spot Meter - quick check?
BTW, I think I saw a brand new pentax spotmeter V in a local store for about cdn$175.00 (I may be wrong... may have misread as I wasn't really looking for it) what do they go for these days?
Pentax Spot Meter - quick check?
I sold one last week on Ebay for USD 57.-
Pentax Spot Meter - quick check?
CJ: As someone already noted, the palm of your hand is Zone VI. What I find rather nifty is that it does not matter what skin colour a person is -- the palm of *everyone's* hand is Zone VI. And, you're less likely to lose it than a grey card, too.
Something tells me that ordinary lawn grass is Zone V, but I wouldn't swear to that.
Cheers from the sunny skies of B.C.
donw
Pentax Spot Meter - quick check?
BTW: The meter's working fine now - good negatives.
Thanks all!