Luna-Pro simple question

[336v]

Gossen Luna-Pro users, when you change upper to lower scale with side rocker switch while meter remains in the same position and no object lighting changed, do readings on both scales have to match? Like if it reads 12 on last tick of upper scale, is it suppose to also read 12 on the first tick of the lower scale (since no light input changed)? My meter reads different numbers on top and bottom, like 11 on top scale and 14 when switched on the bottom scale - is it malfunction, out-of-calibration, or normal? If normal, which scale then to use for actual correct exposure? 3-4 stops difference for identical lighting just after switching scales (ranges?) does not seem to be normal meter behavior - unless I'm missing something obvious. Battery is good. Any thoughts? Thanks!

 

[Disconnekt]

The manual for it will have more info on metering for it, here's a site for the pdf for it if you dont have it:

Gossen Luna-Pro instruction manual, user manual, camera manual

Gossen Luna-Pro, Gossen Luna Pro Electronic, instruction manual

www.butkus.org

 

[grain elevator]

Yes, the scales are supposed to match. What kind of battery are you using? If it's an alkaline that's no good, if silver oxide the meter needs to be calibrated for the higher voltage or something to drop the voltage installed. A zinc-air cell may or may not be close enough to the original mercury battery to give correct readings.

 

[Chan Tran]

I think there could be a small difference but as you said 2 stops is way too much.

 

[chuckroast]

Gossen Luna-Pro users, when you change upper to lower scale with side rocker switch while meter remains in the same position and no object lighting changed, do readings on both scales have to match? Like if it reads 12 on last tick of upper scale, is it suppose to also read 12 on the first tick of the lower scale (since no light input changed)? My meter reads different numbers on top and bottom, like 11 on top scale and 14 when switched on the bottom scale - is it malfunction, out-of-calibration, or normal? If normal, which scale then to use for actual correct exposure? 3-4 stops difference for identical lighting just after switching scales (ranges?) does not seem to be normal meter behavior - unless I'm missing something obvious. Battery is good. Any thoughts? Thanks!

There is noticeable nonlinearity between the top of the low scale and the bottom of the high scale. Inside the meter, there are actually different calibration adjustments for each range.

Somewhat over a full stop of difference isn't unheard of, particularly as these meters are old, their internal adjustments are oxidized, and the CdS cells do age. It's possible to take them apart and fiddle with the adjustments, but I do not recommend this unless you are a very capable electronics tech - the guts are
really touchy.

Here's the important thing - is the difference consistent. If it is, you can take it into a account when metering and adjust accordingly.

 

[BrianShaw]

Before blaming the meter, it might be best to rule out confound from possible metering technique issues. The CdS sensor does not have a particularly fast response. Flipping quickly between hi-low scales will yield poor readings. Allow each reading to “settle” before locking them. Count “one-Mississippi, two-Mississippi” and maybe “three-Mississippi” with the measurement button held.

 

[Marcelo Paniagua]

Agree with battery type. I had this same scenario (with a MR-09 adapter in place) with alkaline batteries. Readings was pretty inconsistent between upper/lower scale, as well.

Issue was fixed when I installed silver oxide batteries (again, with 2 MR-09 adapters) and issue was fixed (at least for me).


Again, like BrianShaw said, it could be a thousand other things. Just sharing my experience.

Regards

 

[Marcelo Paniagua]

Now, if you want to get mercury batteries and you are environment unfriendly, there are certain places that you can get those

 

[F4U]

This is a good meter. I use mine constantly, but it MUST be used with 357 silver batteries only, and recalibrated for them. No alkaline, ever. And it needs to be known if the CdS cell itself has lost linearity because of age. This can best be checked at home by comparison with a known good meter. If the Luna Pro can give an accurate reading in both bright daylight and also in a low-light situation and both are accurate, then the cell is deemed calibratable. (is that a word?). When I say low light, I don't mean indoors at night under tungsten light, as the spectral response of the cell will void the result. I mean bright light and low light when the light source is the same color temperature (more or less). If the meter can give an accurate reading in one situation but is off by an f stop or more under the other, then the cell has gotten week and can never be calibrated with any accuracy. Many of these Luna Pros 50 years later are still good. Many are not.

 

[Sirius Glass]

Welcome to Photrio!

If you can find a calibration laboratory that can check the calibration with a standard light source and make the linear and non linear adjustments, then your concerns would be addressed and any adjustment would be made. You may not be charged for the initial test, depending on the calibration laboratory.

 

[Chan Tran]

I would get another meter like the Luna Pro SBC if you like that type of meters. But the SBC doesn't operate quite the same way right?

 

[Dan Fromm]

BATTERY ADAPTER SET | Gossen

gossen-photo.de

 

[BrianShaw]

I would get another meter like the Luna Pro SBC if you like that type of meters. But the SBC doesn't operate quite the same way right?

I was reluctant to suggest this , so thanks @Chan Tran . The LunaPro SBC is a much better meter. I transitioned from the old Luna Pro to the SBC and find it a lot faster to measure light and a lot faster to use thanks to the nulling capability. The 9v battery is fool-proof. The only drawbacks are that it is a bigger meter and when using the multi-angle attachment there is greater chance of user error since the offsets must be put manually on the calculator dial. But it really was an improvement when introduced and remains quite usable today.

 

[BrianShaw]

BATTERY ADAPTER SET | Gossen

gossen-photo.de

Yup! $30 at B&H if buyer is US-based. Well worth it even though other adapter options work too.
Important to note is the sepcification for SR-43 (386) silver-oxide battery. It is just a tad shorter than the SR-44 (357) battery and fits the battery compartment better.

 

[Sirius Glass]

I was reluctant to suggest this , so thanks @Chan Tran . The LunaPro SBC is a much better meter. I transitioned from the old Luna Pro to the SBC and find it a lot faster to measure light and a lot faster to use thanks to the nulling capability. The 9v battery is fool-proof. The only drawbacks are that it is a bigger meter and when using the multi-angle attachment there is greater chance of user error since the offsets must be put manually on the calculator dial. But it really was an improvement when introduced and remains quite usable today.

That is my experience too.

 

[Marcelo Paniagua]

I would get another meter like the Luna Pro SBC if you like that type of meters. But the SBC doesn't operate quite the same way right?

It work in a similar way but it lack upper/lower lighting switch. It just one dial/reading from EV -8 to 24.

I have both the Luna Pro and the Luna Pro SBC (actually the SBC is sitting in front of me at the moment) but to be honest, I prefer the Luna Pro. Ergonomics are quite good.

On the other hand SBC is newer and have better technology.

Marcelo

 

[Marcelo Paniagua]

BATTERY ADAPTER SET | Gossen

gossen-photo.de

Yes, that's a good adapter. Really recommended. I use the MR-09 adapters only because I had bought them already for other cameras that uses Mercury batteries.

 

[Chan Tran]

It work in a similar way but it lack upper/lower lighting switch. It just one dial/reading from EV -8 to 24.

I have both the Luna Pro and the Luna Pro SBC (actually the SBC is sitting in front of me at the moment) but to be honest, I prefer the Luna Pro. Ergonomics are quite good.

On the other hand SBC is newer and have better technology.

Marcelo

I think it works in a different way. With the older Luna Pro you make the measurement and see which LV number it indicates. Then you set that on the dial to figure out your aperture/shutter speed etc.. With the SBC you turn the dial until the meter null then you read on the dial. It's one operation instead of 2. I like the Minolta Auto Meter is that it works similar to the SBC but by just pushing the button the dial turns by itself instead you have to turn it to get the null reading.

 

[336v]

Thanks all who replied; all answers are appreciated, though most were not to the question at hand. I was just asking if the top and bottom scales are suppose to match or not. The answer consensus seems to be yes. Logically, if the light intensity hitting the meter is so many LUX, it must show identical number on whichever scale you choose, so you set [the same] exposure based on whichever scale you choose. Not the case with my meter.
I wasn't asking if occurring mismatch between readings is due to the wrong battery or whatever else the reason might be. All I wanted to know if mismatch is by design or something is not right.
My understanding is that since top scale ends with 12 and bottom scale just starts with 12, you switch to bottom one only if pointer on top scale overshoots beyond12, e.g. it's too bright for that. Similarly, if for low light the needle on top scale shows *anything* below 12 (like 11), the bottom scale must show dead zero since it starts from 12 on, and the light intensity is only 11, so it's not suppose to register ANY movement on the bottom scale. Do I understand this right? However, it is not really possible to make top scale over-range. When the light is very intense such that it shows near 22 on the bottom scale, it is *barely* beyond 12 on the top scale, which is full 10 stops off! I think there is a movement limit implemented restricting over-range and slamming pointer to the right when top scale is chosen and the light is too bright, but it starts way too close to 12, like "soft saturation" and non-linearity starts beyond 10 on top scale. Basically, sensitivity between 10 and 12 is so compressed, that it cannot be trusted. 10 on top corresponds to 11.5 on bottom, 11 on top - 13-1/2 on bottom, and near 12 on top is anywhere between 16 and 20 on bottom; as i said I can't quite reach 12 on top no matter how bright the light is, as if a Zener diode limits galvanometer movement beyond 12. My question was if that's by design or my unit settings got drifted that far and this can be fixed by (re)calibration. And yes, 'course I don't switch between scales in one second and make a judgement, I waited long enough to settle (up to 15 sec for top scale). The battery I use is two 357 Silver Oxide button cells with a Si diode in series dropping total voltage to exact 2.7V value, which makes battery test pointing smack in the middle of the red mark (see my cells above the meter on the attached photo - the diode is soldered electrically between them). But being an electrical engineer, I've also tested the meter with variable power supply, dialing above and below 2.7V and see how far I can deviate and whether voltage value makes a difference when changing scales. For my particular meter the pointer is at the beginning of red zone (17) at 2.64V and at the end of it (17-2/3) at 2.95V, so this must be acceptable spread of the battery voltage. There is no internal voltage stabilization circuit, so these 2/3 of the stop "length" will be your nominal error when the battery is within "normal" red limits. This also tells me that the internal circuit is purely passive one. Another firm conclusion is you can use ANY chemistry battery (alkaline included) AS LONG AS you manage to keep its voltage within 2.95V...2.64V limits while it's being discharged. As with any analog multimeter, the voltage affects the top scale the most. Changing it from 2.7 to 3.3V changes readings just half-stop (12 to 12-1/2), but at the top with light intensity resulting in 10 at 2.7V it will read 11 at 3V (full stop difference) and 12 at 3.3V (two stops difference), but that's consistent, and otherwise no adverse effects on the meter whatsoever. Meaning you can feed it with two 1.5V cells in series, no problems, the battery test points just to the end of red mark at that voltage. A single 3.3V lithium cell would not be a problem as well if you're willing to make mental adjustments - it reads 1 stop higher at the mid scale and 2 stops at the end, sort of "expanded" scale, but that's all. The point of my long rant is that the battery voltage being 2.700 V sharp is not critical at all, and those who think otherwise unnessesarily restrict themselves in choices of alternative power sources for their meters.