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

[BobUK]

What is the name of the meter app you have on your phone?
I thought it would be interesting for me to read the instructions, and any write ups about the app.

 

[BrianShaw]

What is the name of the meter app you have on your phone?
I thought it would be interesting for me to read the instructions, and any write ups about the app.

Light Meter - By WBPhoto

A light meter app for iOS and Android with reflected and incident (Android-only) metering for photography and cinematography. Also includes an exposure calculator and a white balance meter.

www.lightmeter.dev

Android "Light Meter" App Review

Taking a step away from photo taking and tackling one of the most important questions - light metering. Light meter within a phone is the most convenient option for me. Read the review of "Light Meter" light meter app and decide whether it's something you need as well.

50mmf2.com

 

[BobUK]

Thanks Brian .

It's not that I am to lazy to read all of the posts. I have lost my reading glasses, and trying to use a rubbish hand held magnifier at the moment.
I've not been out all day so they are here in the house someplace.

Thanks again.

 

[wiltw]

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.

1. Three copies of same app on same phone (if it were even possible) would result in same reading...the hardware (sensor) in the phone has a fixed output in response to a fixed amount of light.
2. My installing same app on two (different models from same manufacturer) tested the (probable) use of different sensors in different generations of phone from same manufacturer...different response from (likely) different sensors, seems to show that all sensors are not identical in their response to a fixed amount of light.
3. Inability to measure 'simultaneously' is resolved simply by using a not-variably illuminated scene...an indoor artificially illuminated blank featurelesss wall accomplishes that.

No need to overthink, apart from recognizing and neutralize any variables in a test circumstance...keeps things simple for the simple mind, or simply meets 'scientific' test criteria.

Bracketing even using incident meter simply illustrates why pros shooting for clients will bracket even artifically illuminated shots...what one finds to be 'most pleasing' rendition can subjectively depart from 'ideal exposure'. And 'ideal' for offset print often is different from 'ideal' for projection...different 'ideal' for different uses.

 

[Chan Tran]

1. Three copies of same app on same phone (if it were even possible) would result in same reading...the hardware (sensor) in the phone has a fixed output in response to a fixed amount of light.
2. My installing same app on two (different models from same manufacturer) tested the (probable) use of different sensors in different generations of phone from same manufacturer...different response from (likely) different sensors, seems to show that all sensors are not identical in their response to a fixed amount of light.
3. Inability to measure 'simultaneously' is resolved simply by using a not-variably illuminated scene...an indoor artificially illuminated blank featurelesss wall accomplishes that.

No need to overthink, apart from recognizing and neutralize any variables in a test circumstance...keeps things simple for the simple mind, or simply meets 'scientific' test criteria.

Bracketing even using incident meter simply illustrates why pros shooting for clients will bracket even artifically illuminated shots...what one finds to be 'most pleasing' rendition can subjectively depart from 'ideal exposure'. And 'ideal' for offset print often is different from 'ideal' for projection...different 'ideal' for different uses.

I think even 2 phones of same make and model woudn't have the same reading. I believe when they build meter or even cameras they have to calibrate each one and can not count on that the hardware are the same.

 

[wiltw]

I think even 2 phones of same make and model woudn't have the same reading. I believe when they build meter or even cameras they have to calibrate each one and can not count on that the hardware are the same.

If it were an analog device, I would tend to agree. But the sensor is a digital device, the phone manufacturer does not need to calibrate each and every phone individually in order to use the built-in camera app that is included with each phone...right?
Once the sensor is chosen for a model, the O/S for the phone can be 'calibrated' once with a value specific to that MODEL, but not for each unit of that phone.

 

[Chan Tran]

If it were an analog device, I would tend to agree. But the sensor is a digital device, the phone manufacturer does not need to calibrate each and every phone individually in order to use the built-in camera app that is included with each phone...right?
Once the sensor is chosen for a model, the O/S for the phone can be 'calibrated' once with a value specific to that MODEL, but not for each unit of that phone.

I don't think phone manufacturer calibrate and so if someone has 2 of the same phone would want to do a test? I suspect that they will read different. Digital or analog I don't think you can make hardware that are exactly the same.

 

[dcy]

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.

Yeah. Sorry it took so long to get to this, but I've now completed a test with several different scenes.

Summary:

• On "normal" scenes with some amount of complexity, the Luna Pro F meters about +1 stop brighter than the phone.
• On mostly uniform scenes, the Luna Pro F meters about +2 stops brighter than the phone.

For most of the uniform scenes, I don't have a good intuition for what the correct exposure should be, but one of them is pointing straight at the cloud-free blue sky (see "Uniform Scene #4" below). The sky should be brighter than Sunny 16, right? The phone is telling me to expose the sky as if it's 1 stop darker than Sunny 16, and the Luna Pro is telling me to expose it as if it's 1.3 stops brighter than Sunny 16. So it looks to me like the Luna Pro is right and the phone is going wonky on uniform scenes.

Full Results:

For every test, I am keeping the aperture at F/16 and the ISO at 200, so we can just compare the shutter speed.

Normal Scene #1: Outdoors, in a bright sunny day with clear sky at noon.

Phone = 1/250" vs Luna Pro = 1/400"-ish ---> 2/3 stop difference.

Normal Scene #2: Indoors -- a shelf in my office.

Phone = 1/1.5" vs Luna Pro = 1/3"-ish ---> 1 stop difference.

Uniform Scene #1: Outdoors, pointing at the sidewalk.

Phone = 1/180" vs Luna Pro = 1/1000" ---> 2.5 stop difference.

Uniform Scene #2: Outdoors, pointing at a beige wall in the shade.

Phone = 1/13" vs Luna Pro = 1/60" ---> 2.2 stop difference.

Uniform Scene #3: Outdoors, pointing at the sidewalk.

Phone = 1/250" vs Luna Pro = 1/1000" ---> 2.0 stop difference.

Uniform Scene #4: Outdoors, pointing up at the blue mostly cloud-free sky.

Phone = 1/125" vs Luna Pro = 1/500" ---> 2.0 stop difference.

Uniform Scene #5: Indoors, pointing at a whiteboard in my office.

Phone = 1/1.6" vs Luna Pro = 1/8" ---> 2.3 stop difference.

 

[dcy]

What is the name of the meter app you have on your phone?
I thought it would be interesting for me to read the instructions, and any write ups about the app.

In his infinite wisdom, the developer decided to call it "Light Meter"... Yeah, there are at least 3 apps with exactly that name. The one I have is this one:

Light Meter - Lite - Apps on Google Play

A reflected light meter with spot metering and incident light metering.

play.google.com

 

[dcy]

Hmmm....

I have a mirrorless (digital) camera. That has light meter that should be accurate. It's at home right now, but I could grab it and bring it tomorrow to work and see what it says.

I don't know how well one can compare ISO settings for digital vs film. My understanding is that digital ISO is more or less a made up number from the manufacturer. But presumably it's close enough to film ISO to prove that the Luna Pro F knows what the sky looks like better than my phone's light meter app.

 

[mshchem]

1. Three copies of same app on same phone (if it were even possible) would result in same reading...the hardware (sensor) in the phone has a fixed output in response to a fixed amount of light.
2. My installing same app on two (different models from same manufacturer) tested the (probable) use of different sensors in different generations of phone from same manufacturer...different response from (likely) different sensors, seems to show that all sensors are not identical in their response to a fixed amount of light.
3. Inability to measure 'simultaneously' is resolved simply by using a not-variably illuminated scene...an indoor artificially illuminated blank featurelesss wall accomplishes that.

No need to overthink, apart from recognizing and neutralize any variables in a test circumstance...keeps things simple for the simple mind, or simply meets 'scientific' test criteria.

Bracketing even using incident meter simply illustrates why pros shooting for clients will bracket even artifically illuminated shots...what one finds to be 'most pleasing' rendition can subjectively depart from 'ideal exposure'. And 'ideal' for offset print often is different from 'ideal' for projection...different 'ideal' for different uses.

Bracketing also insures against the inherent variables in processing. Especially color films.

 

[Chan Tran]

Hmmm....

I have a mirrorless (digital) camera. That has light meter that should be accurate. It's at home right now, but I could grab it and bring it tomorrow to work and see what it says.

I don't know how well one can compare ISO settings for digital vs film. My understanding is that digital ISO is more or less a made up number from the manufacturer. But presumably it's close enough to film ISO to prove that the Luna Pro F knows what the sky looks like better than my phone's light meter app.

If you could, under sunny 16 condition use the Luna Pro F in incident mode and see what you get.

 

[BrianShaw]

Well that’s sad. The Light Meter readings continue to be realistic and the Luna Pro F are high. Very sad. Perhaps that is why it was offered at a bargain price. If it was advertised as working correctly you might want to file a “not as advertised “ claim and return it for a refund. I always contact the seller first to coordinate the return/refund. Sorry to learn this as it’s a really good meter.

 

[mshchem]

Also make sure you keep "boogers" off the lenses of your cell phone

 

[dcy]

If you could, under sunny 16 condition use the Luna Pro F in incident mode and see what you get.

Conditions are no longer Sunny 16, but I decided to try anyway. It's 5:20 pm here and there's some cloud cover.

Summary: Phone vs Luna Pro F in incident-light mode.

• On a normal scene outside, there is a 2/3 stop difference.
• Testing again with my whiteboard as a uniform scene, the Luna Pro F now gives the same answer as the phone.

Full Results:

Normal Scene in Incident Mode:

Phone = 1/15" vs Luna Pro = 1/25"-ish at F/16 ---> 2/3 stop difference.

Uniform Scene in Incident Mode: The whiteboard in my office.

Phone = 1" vs Luna Pro = 1"-ish at F/16 ---> same.

 

[Kino]

The app is measuring reflected light, which is sampled from the circle.

The Luna Pro is measuring Incident light, which is measured from the dome integrator.

The white board is also acting much like the dome integrator, so the readings are the same.

Apples and oranges. Nothing needs fixing.

 

[wiltw]

Hmmm....

I have a mirrorless (digital) camera. That has light meter that should be accurate. It's at home right now, but I could grab it and bring it tomorrow to work and see what it says.

I don't know how well one can compare ISO settings for digital vs film. My understanding is that digital ISO is more or less a made up number from the manufacturer. But presumably it's close enough to film ISO to prove that the Luna Pro F knows what the sky looks like better than my phone's light meter app.

The ISO for film = ISO for digital, period. There is not an ISO standard distinction. My 'for film' lightmeter matches exactly the result I get with my digital camera, it puts the peak in the histogram exactly in the middle, shooting a target with a black +18% + white tritone.

the target

representative histogram (not necessarily from above shot)

 

[dcy]

The app is measuring reflected light, which is sampled from the circle.

The Luna Pro is measuring Incident light, which is measured from the dome integrator.

The white board is also acting much like the dome integrator, so the readings are the same.

Apples and oranges. Nothing needs fixing.

That's a relief, but out of an abundance of caution, I'd like to ask @BrianShaw if your comments change his opinion, or if he still thinks I should return the meter and request a refund. I feel fairly confident that if I report that the meter does not work as advertised and request a refund, I will get the refund.

@Kino Do you think my other attempts at metering a uniform scene (e.g. a wall, the sky) are also equivalent to adding a dome integrator?

 

[MattKing]

A whiteboard would only be an appropriate subject if you are using both light measuring tools as reflective light "meters".
A better target closer would be something that reflects 18% of the light, but the whiteboard will di in a pinch.

 

[Kino]

I feel you are over thinking this. If the reflected grey card readings match your phone light meter, or even within a1/2 a stop, you are good to go.

It's more about interpreting a scene while keeping in mind what form of metering you are doing. When in doubt and in a hurry, a quick incident light reading will be your best bet with negative film.

With slide film, you need to be more discerning in how you interpret your scene, because the latitude for reversal film is no where near as forgiving as negative.

Just chose a meter or two meters to work with and learn how to interpret the results. You can only do this if you take accurate notes and review them with the results.

Otherwise, you will endlessly try and discard meters looking for the "perfect" meter. That is the long and the short of what I can advise you.

 

[mshchem]

Another thing, most of the old school Kodak cards are 18% on one side and 90% on the other. Both sides are not shiny, i.e. as flat as is feasible. Any kind of specular artifact will make meters bounce around.

I have a real preference for incident metering. My Minolta has a little pocket in the case for the flat diffuser to help setting lighting for portrait and product work. Setting ratios are faster (for me) with a flat diffuser and incident mode.

Spot meters are awesome for black and white work, even here I still, usually, make incident work

MHOFWIW YMMV

 

[dcy]

A whiteboard would only be an appropriate subject if you are using both light measuring tools as reflective light "meters".
A better target closer would be something that reflects 18% of the light, but the whiteboard will di in a pinch.

I don't have a gray card. As an imperfect substitute, I held my hand (Caucasian skin tone) 2 inches from the light meters (hoping to cover the entire field of view), trying to keep the same angle relative to the ceiling light in my office. In that setting, the Luna Pro F meter in reflected-light mode and the phone light meter gave identical answers, within the margin of error: The phone app flickered between 1s and 2s exposure, while the Luna Pro F gave me a reading of 1.5s ---- all at F/16, ISO 200.

 

[BrianShaw]

That's a relief, but out of an abundance of caution, I'd like to ask @BrianShaw if your comments change his opinion, or if he still thinks I should return the meter and request a refund. I feel fairly confident that if I report that the meter does not work as advertised and request a refund, I will get the refund.

@Kino Do you think my other attempts at metering a uniform scene (e.g. a wall, the sky) are also equivalent to adding a dome integrator?

In post 58 your testing seems correct, with the Luna Pro measuring reflected light and the comparison is valid. My reading of the Luna Pro is that it is high for the lighting situation depicted and the phone app is much more in line with what should be expected. The real way to tell is to expose some film using boht readings and decide which negative is most correct. For that , you'd need that mythical $100 manual camera. I would not consider the Luna Pro to be giving reasonable reflected measures in normal daylight.

In post 65 Kino is correct that the Luna Pro is in the incident configuration and the comparison is not valid. I didn't look at those results until just now.

But whoever wrote that there is too much over-thinking is correct. Unfortunately this has become much more complicated and convoluted than I feel it needs to be. But that's just me...

 

[GregY]

D, the Luna Pro series were a great meter..... but they haven't been made since the mid '80s. Your example may well have been dropped....(or not).....so any expectation of calibration or accuracy may be wishful thinking.
If i were in a similar situation.... i'd compare it with one of my other known meters. In your case i'd shoot a roll of transparency film (with both reflected and incident readings) and have it processed. If it needs service try Richard Ritter.

 

[MattKing]

I don't have a gray card. As an imperfect substitute, I held my hand (Caucasian skin tone) 2 inches from the light meters (hoping to cover the entire field of view), trying to keep the same angle relative to the ceiling light in my office. In that setting, the Luna Pro F meter in reflected-light mode and the phone light meter gave identical answers, within the margin of error: The phone app flickered between 1s and 2s exposure, while the Luna Pro F gave me a reading of 1.5s ---- all at F/16, ISO 200.

There isn't anything particularly magical about a grey card for your purposes, it is just that a good one will be a consistent target near to the reflectance for which exposure systems are calibrated.
Hands are great, because you always have yours with you - they are always "at hand" one might say.
They can be challenging to keep still and as such difficult to keep facing the light in a consistent way.
For that reason, if a grey card isn't nearby, I grab something like a book or a piece of cardboard or a piece of coloured paper - anything reasonably close to a mid-tone.
All meant as a "tricks and tips" suggestion, not a criticism.