Help me figure out what's wrong with my light meter?

[BrianShaw]

There's any number of alternatives, both light/exposure meters and cameras. This thread is about a specific Gossen Luna Pro F, which the user is just getting to know. So far, though, the meter hasn't been proven to be faulty or inaccurate... yet, at least. I'm betting that the meter is fine. That's a rather well-built meter. It's about noon in New Mexico so I'm hoping the meter gets out for a lunch break so we can see if the meter works as it should or not.

 

[MattKing]

dcy,
You appear to be on the defensive. What many of us posted were pointing out cautions about very common assumptions that people can make in photography, which can often be proven to be wrong rather than universally true. Awareness that these are not always true...

1. Sunny 16
2. blue sky brightness follows Sunny 16
3. cell phone meters are accurate (or even consistent with each other, once installed but used without calibration adjustment)

So that you have eyes wide open about the potential wrong conclusions in continued blind belief about the 'rules', not to accuse you of anything (thereby putting you on the defensive). That, and pointing out techniques to neutralize individual things that can mislead one.

What he said - not a "don't do what you did".
A "watch out for this tendency" instead.
And my reference to the benefits of experience was to inform about where I and others were coming from, not a criticism of you.
As said in my earlier post - "well done" in what you have done so far.

 

[GregY]

Get a real camera and a reliable meter. Use the Pentax 17 as it was intended for kids to take snaps to post on the web.

Looking down on someone's equipment choices isn't really that helpful.....

 

[aconbere]

Get a real camera and a reliable meter. Use the Pentax 17 as it was intended for kids to take snaps to post on the web.

This isn’t helpful

 

[ic-racer]

Buying a used meter without a warranty is taking a chance.
If the meter doesn’t let you expose easily printed negatives, see if you can get your money back.

 

[GregY]

Buying a used meter without a warranty is taking a chance.
If the meter doesn’t let you expose easily printed negatives, see if you can get your money back.

....if properly used.....
a meter isn't as automatic exposure device and requires some skill to both test & use.....

 

[mshchem]

I'm sorry

 

[dcy]

dcy,
You appear to be on the defensive.

I was bewildered by Matt's post. I am still 100% confused by it. He said that

"Our words of caution were prompted by your reaction after you figured out how to switch the ambient/flash switch, and then attempted to draw a conclusion about the much smaller discrepancy between the metering app results and the Gossen reading."


I feel like somehow I stepped into a parallel universe where there was some other conversation that I am not aware of. I honestly haven't the faintest clue what reaction or what conclusion Matt is referring to.


The rest of my post was a response to this:

"Which is a backhanded way of saying I wouldn't have needed to check the clearly wrong initial reading against a cel phone app - I would have known it was wrong immediately."


Perhaps this is the part where you feel I got defensive. Perhaps I could have written a little more eloquently. But there are only so many ways you can explain to someone that the inference they made is incorrect. The bulk of my response was the reason for the app was clear communication --- to make a thorough report that would maximize the chance of a productive conversation.

Just like I went into some details about the batteries, or what I had done to check calibration. These are good things to include. It is meant to explain clearly what I did, under what conditions, and what the result was.

 

[dcy]

I for one don't trust the phone but since the OP tested under sunny 16 condition and although the scene has influence the error was too large. That's why I thought about the flash and ambient mode.

+1

Yeah. I waited a day so I could test & report from sunny 16 conditions.

 

[dcy]

Nice meter, and a great price. Congratulations!

One of the things to remember when testing/using handheld meters, especially when comparing readings between different meters, is that the specific angle of view and coverage pattern may not be the same. In fact, it's often an unknown. That's why sone folks suggest using a blank neutral wall or a gray card to do the testing... to mitigate that unknown. Another time-honored way to both test and use is to point the meter down a bit to exclude the sky. Generally that gives more consistent readings, albeit possibly a tiny bit skewed.

Enjoy the experience of learning a new photographic tool. BTW, when I looked at your first post, my initial reaction is that your phone's meter knows what it is measuring. Your light is very similar to mine.

Thanks!

 

[MattKing]

I cannot test the same conditions anymore (sun has gone down) but I tested again on the hallway, and now the Gossen meter is just over 1 stop away from the camera's light meter. The Gossen meter says to shoot at F/8 and 1/15" for ISO 200, while the app on my phone says to shoot at F/8 and 1/6". Hopefully the 1.3 stop difference can be explained by the two meters weighing the scene differently.

Emphasis added - that is where we see you concluding that the cel phone app is a reliable standard of reference.
That is where caution is advisable, because the app may or may not be.
The same applies to the Gossen.
In each case, until some experience with them/testing tells you otherwise.

 

[dcy]

Get a real camera and a reliable meter. Use the Pentax 17 as it was intended for kids to take snaps to post on the web.

As others have said, disparaging comments about my equipment aren't helpful. But let me also point out just how gratuitous the comment about my camera is. My camera was at home and was not involved in my attempt to diagnose my light meter.

If instead of owning a Pentax 17, I owned a large format camera, which doesn't even have a light meter, would you have written a similar comment?

 

[abruzzi]

It's about noon in New Mexico so I'm hoping the meter gets out for a lunch break so we can see if the meter works as it should or not.

We've had a surpising amount of cloudy days with rain over the last few weeks in southern NM (not sure where dcy is), but today was beautifully sunny, like we normally have.

 

[MattKing]

As others have said, disparaging comments about my equipment aren't helpful. But let me also point out just how gratuitous the comment about my camera is. My camera was at home and was not involved in my attempt to diagnose my light meter.

If instead of owning a Pentax 17, I owned a large format camera, which doesn't even have a light meter, would you have written a similar comment?

Moderator hat on:
This might be necessary if @mshchem's post had not already been roundly criticized and had he had not apologized for it. But as that has been the response to it, you didn't need to add to the response.
It was those criticism and that apology that made it unnecessary for us moderators to deal with it.

 

[BrianShaw]

Emphasis added - that is where we see you concluding that the cel phone app is a reliable standard of reference.
That is where caution is advisable, because the app may or may not be.
The same applies to the Gossen.
In each case, until some experience with them/testing tells you otherwise.

Hi Matt. Your point is understandable but a bit moot. EV 14 1/2 (200) is actually very reasonable for the scene depicted and measured. A decent negative is quite possible in that situation using that exposure recommendation.

 

[mshchem]

There's absolutely nothing wrong with the Pentax 17. Great modern haf frame camera And a lot easier to fit in your pocket than a Nikon F5.

Again I apologize. I didn't mean to offend.

 

[mshchem]

I am always amazed at the quality of the pictures from my 5 year old Samsung mobile phone.

Maybe these metering apps tap into the camera data??? Amazing how accurate they are.

 

[MattKing]

Hi Matt. Your point is understandable but a bit moot. EV 14 (200) is actually very reasonable for the scene depicted and measured. A decent negative is quite possible in that situation using that exposure recommendation.

Absolutely Brian - but we know that, whereas those new to using meters don't have the same reservoir of experience.
I'm trying to help @dcy and anyone else in a similar position realize where the uncertainties might lie.

 

[dcy]

Hopefully the 1.3 stop difference can be explained by the two meters weighing the scene differently.

Emphasis added - that is where we see you concluding that the cel phone app is a reliable standard of reference.

I guess I can kind-of sort-of see why you feel that way, but your inference is wrong.

First, this was a bit of a throw-away comment that was not meant to be hyper-analyzed. Second, it does not say which meter, if any, is supposed to be the reliable one. What I was thinking at the time I wrote this is that if you have two light meters of uncertain reliability and different origin, it is a good thing if they agree with each other. That would increase confidence in both. Failing at that, it is a good thing if the discrepancy is explained by them weighing the scene differently. That also would increase confidence in both and would help you interpret their results. If you knew that the difference can be explained because one is more center-weighted than the other, that would be a good thing, and better than not knowing why they don't agree.

 

[BrianShaw]

Hi dcy… whenever you can would you please re-do your post #1 measures and re-verify that your phone meter reasonably measures the scene and determine how close the LunaPro F is when used in the correct mode. Sooner than later would be nice as the arguments can easily be resolved with just a couple of minutes of effort.

 

[cowanw]

What I was thinking at the time I wrote this is that if you have two light meters of uncertain reliability and different origin, it is a good thing if they agree with each other. That would increase confidence in both. Failing at that, it is a good thing if the discrepancy is explained by them weighing the scene differently. That also would increase confidence in both and would help you interpret their results. If you knew that the difference can be explained because one is more center-weighted than the other, that would be a good thing, and better than not knowing why they don't agree.

This is very astute and the reason I suggested a single toned subject like "the roadway" to see if the meters agree without having to worry about how much sky or whatever field of view is used.

 

[GregY]

This is very astute and the reason I suggested a single toned subject like "the roadway" to see if the meters agree without having to worry about how much sky or whatever field of view is used.

Exactly..... that's why we often meter a substitute....a hand for skin tones.... or use an incident reading.

 

[Bill Burk]

Note that you can easily get the Luna Pro F meter to recommend different exposures amounting to a stop or more even with itself when used correctly.

Here’s how: Incident mode vs. Reflected light mode vs. Zone System technique.

a) Incident reading from the subject position aimed at the camera. For this in sunny 16, choose an ordinarily lighted subject (not backlit).

b) Reflected light metering, from camera point meter at subject. Here the tones of the subject influence the recommended exposure.

c) Zone System technique. Meter a specific tone in the subject and assign it a Zone. Example put the palm of your hand in the subject’s light and meter it. “Place” the reading on Zone VI by noting one stop greater exposure than meter says at null. Another example: meter a dark part of the subject influence- the darkest important tone. And “Place” that on Zone III by noting two stops decrease in exposure.

Having taken all these readings, see how different they are. Expect there to be differences. What you might feel is that any of them could be “right”.

 

[wiltw]

Emphasis added - that is where we see you concluding that the cel phone app is a reliable standard of reference.
That is where caution is advisable, because the app may or may not be.
The same applies to the Gossen.
In each case, until some experience with them/testing tells you otherwise.

!
I extract a portion of what I posted not long ago, to retain only the pertint parts:

One ASSumes that the light meter application is 'accurate'. Not necessarily true! I have to use the adjustment feature of the light meter app in my phone in order to get its reading to agree with a known-accurate spotmeter with 0.1EV precision and with the mid-histogram reading (which matches the spotmeter) obtained with my digital camera.​

1. The same app installed on 2 phones from the same manufacturer (succesive models) does not agree with each other, if unadjusted reading, 1+ EV difference in reading
2. If unadjusted, neither phone agrees with my Minolta Spotmeter F.

phone 1: 1/6 f/2.8 ISO250​

phone 2: 1/10 f/2.8 ISO250​

spotmeter: 1/15 f/2.8 +0.2EV ISO250 (about 1/20 f/2.8 ISO250)​

TWO phone app readings (same program on two phones) do not even agree with each other, much less agree with a known-good exposure meter (or a histogram-proven digital camera exposure)! Why I noted the need for proving (either of your meters) against film exposure before coming to any conclusion.

 

[mshchem]

I wonder if I installed the same app on my phone in 3 places, (same phone just 3 copies of the same app) if all 3 would read the same? I don't know how I could measure simultaneously. Temporal distortion?

I use an incident meter for slide film, still I bracket.

For black and white I use sunny 16, meter or just guess.

Way over thinking for my meager brain.