I should mention that this is not quite accurate statement - the forward voltage drop on any diode, Schottky or plain, is not fixed - it can be 0.21V only for certain current flowing through it (let alone only at certain temperature), e.g. this voltage is highly current dependent. In case of usage in Luna Pro - meaning this drop will be different depending on which scale you're taking the reading at: the meter draws ~10...300uA on low scale, ~50...500uA on high scale and ~200uA during "Batt Check". So the diode voltage drop will vary depending on what you're doing; the diode will not only introduce non-linearity, but inconsistent one. Small, but noticeable. For most users it's just small enough not to matter, but it's there. The right way to deal with this is to make a proper voltage regulator with fixed 2.7V output.
I don't want meter with 1/2 stop EV error.
Well so you say since you can't get your film to behave you don't need good meter? I would shoot film without a meter any day but I don't use a meter that is not accurate. I have a good number of camera that takes mercury battery for the meter I simply just use them without meter. Besides an exposure meter I don't know any kind of measuring instrument that a 25% off is good enough accuracy.To truly evaluate exposure effectiveness I’d plot curves and check resulting subject negative densities.
Very often I find my densities so far up the straight line that I question what I was thinking when I planned the exposure. That’s in usual day-to-day picture taking.
I’ll try to come up with another example again sometime. I have done the testing carefully in the past. Last time it was a picture of my dog and a gray card and the result was 1/6 stop away from what I expected.
Just acquired a Lunasix 3 Gossen and then realized it uses mercury batteries (1,35V). I put PX 625 (1,5V) in the battery chamber. I could compare the reading with another lightmeter but I would like to have your opinion on this. Is the difference in voltage significant?
I have several cameras that have no meter. My dad has a Lentar meter that he bought in Germany in the late 50s. It takes the unobtainium Mercury battery 1.35v. Im not sure how accurate this meter is especially in low light. In these modern times, is there any cheap and accurate hand held light meter I can buy? Please advise.
Thanks.
The same thing happened to me with my Olympus OM-1. Of all the cameras in my collection, I think it’s the most sensitive to the absence of mercury cells. I actually use a voltage converter so I can use alkaline ones.I tested a mercury cell vs. an alkaline cell in an Olympus OM-1n. I found that
Some meter designs can tolerate the difference (mercuric oxide vs. alkaline cell Voltage), some cannot. The 'newer' meter designs are not so dependent upon 'constant' Voltage characteristics typical of mercuric oxide cells.
- the amount of error in meter reading was significant
- the degree of error would change in low light vs bright light conditions
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