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

GregY · Friday at 11:07 AM

wiltw said:
Just for reference...another rule of thumb to keep in mind: The palm is -- generally speaking -- about +1EV compared to an 18% gray card.
My own palm has measured up to +1.3EV compared to an 18% gray card, but today it is +0.8EV brighter...IOW it too is somewhat variable.

And the reading with an incident meter also can be somewhat variable...it can measure somewhat differently at different times and depart from the Sunny 16 approximation 'rule of thumb' even with the meter facing the sun directly (which is not the way to use it). It should be held horizontally and facing where the lens of the camera will be -- and that specific horizontal angle will vary the incident meter reading as you rotate about 360 degrees.

Many things about photography are not absolute.

"Many things about photography are not absolute."

Bill Burk · Friday at 11:13 AM

Here’s a sketch I made for myself about the relationship between C and K and percent gray.

marhalloweenvt · Friday at 11:18 AM

As I recalled, Sekonic/Canon/Nikon meters, K is typically 12.5; Minolta/Pentax is 14 (Correct me if I'm wrong)|

wiltw · Friday at 11:28 AM

marhalloweenvt said:
As I recalled, Sekonic/Canon/Nikon meters, K is typically 12.5; Minolta/Pentax is 14 (Correct me if I'm wrong)|

Taken from Wikipedia (for convenience)

ISO 2720:1974 recommends a range for K

of 10.6 to 13.4 with luminance in cd/m2. Two values for K

are in common use: 12.5 (Canon, Nikon, and Sekonic [15]) and 14 (Minolta,[16] Kenko,[16] and Pentax); the difference between the two values is approximately 1⁄6 EV.

Each manufacturer choses its own standard value for both K and for C, which is why one brand's readings might not exactly match a different brand's readings...but they should be within 1⁄6 EV!

Chan Tran · Friday at 1:29 PM

wiltw said:
Taken from Wikipedia (for convenience)

ISO 2720:1974 recommends a range for K

of 10.6 to 13.4 with luminance in cd/m2. Two values for K

are in common use: 12.5 (Canon, Nikon, and Sekonic [15]) and 14 (Minolta,[16] Kenko,[16] and Pentax); the difference between the two values is approximately 1⁄6 EV.

Each manufacturer choses its own standard value for both K and for C, which is why one brand's readings might not exactly match a different brand's readings...but they should be within 1⁄6 EV!

Minolta uses K14 as specified in Minolta manual. K250 for flat diffuser and K330 for the dome.

Chan Tran · Friday at 1:39 PM

BrianShaw said:
Oh, joy… you bring K and C into the discussion. This should be interesting discussion!

Exposure meter manufactuers have the liberty of calibrating their meter in lots different standards. When they specified a C or K value that ties their meter to a definite scientific measurement. A incident meter with a C250 meanss that it will indicates EV0@ISO1 for an illuminance of 250 Lux. A refective meter with a K14 means that it will indicate 0EV@ISO1 for the luminance of 14 Candela per squared meter or Nit.

BrianShaw · Friday at 1:51 PM

Interesting but probably not going to really help @dcy figure out if his meter is wonky or not… or if his phone app is accurate or not.

GregY · Friday at 1:58 PM

Dcy...if you do return the meter.....perhaps have a look at some other models that are smaller than your camera.....

Bill Burk · Friday at 2:03 PM

I recall a meter manufacturer wrote, in response to a question about their choice of K, that they picked a value that made photographers’ pictures come out right. (Highly paraphrased but something like that). I was trying to track down the last sixth of a stop I couldn’t confirm.

Chan Tran · Friday at 2:13 PM

BrianShaw said:
Interesting but probably not going to really help @dcy figure out if his meter is wonky or not… or if his phone app is accurate or not.

I would want to see dcy do a sunny 16 condition measurement in incident mode that would tell me if his meter is OK. For now I think it's OK.

jeffreyg · Friday at 2:21 PM

I must be lucky. Just photographed some flowers indoors with a skylight providing the illumination. My Pentax Zone VI modified off a gray card matched exactly my old Gossen Luna Pro incident reading and my phone app pocket meter was a half second different. Film is Delta 400 120. Of course we’ll know when I finish the roll and develop the film.

Chan Tran · Friday at 2:29 PM

GregY said:
Dcy...if you do return the meter.....perhaps have a look at some other models that are smaller than your camera.....

There is no problem using a meter larger than a camera. Which camera does he use?

GregY · Friday at 2:43 PM

Chan Tran said:
There is no problem using a meter larger than a camera. Which camera does he use?

Pentax half frame 17.....
CT....it depends if you want to carry a bigger bag or wear cargo pants

i'm not suggesting there's a problem.... but it is less convenient...& somewhat counterproductive.
Luna pros /Luna sixes were great meters designed for the pro market....nowadays there are much smaller fully functional smaller meters.
I carried one for years along with motordriven F2s & F3s.....
I'd take a Sekonic 308 in a heartbeat let alone the diminutive Digisix or one of the tiny hotshoe mount meters.

Bill Burk · Friday at 3:09 PM

@dcy

Try comparing the Luna Pro incident mode (aim dome at camera from subject) to the digital in Digital ESP Metering mode (aimed at subject).

Reflected light metering always requires some evaluation of “what you’re aiming at” vs “what tone the subject is supposed to be”. ESP will try to evaluate that, and incident ignores tone of the subject and evaluates how much light is falling on the scene.

If the meter is working and the camera guesses the scene right, you should get comparable results. Pick a typical scene, not gray pavement or bright wall.

dcy · Friday at 3:18 PM

BrianShaw said:
Interesting but probably not going to really help @dcy figure out if his meter is wonky or not… or if his phone app is accurate or not.

Ha ha. Yeah, that whole discussion about C & K just made me think of Calvin Klein underwear. I've mentally filed that into a part of my brain labeled "things to think about later."

New Light Meter Test:

Today I did a new test using my Olympus OMD mirrorless camera as the reference light meter. This time I was also careful to point at subjects that look gray-ish, as opposed to the very white sidewalk that might have introduced an additional source of error. With these changes, the Luna Pro F light meter seems to line up with the Olympus one quite well --- better than I expected.

Today the conditions were not quite ideal. It was a bright sunny day, but the uneven cloud cover caused the lighting to vary visibly. I made an effort to take the meter reading and the digital camera shot at the same time, but looking back, I could've done a better job at that.

I am not able to get the images from the digital camera because I'm a dummy and forgot to bring my SD card adapter. I went back and took photos with my phone so at least you can see more or less what the scenes looked like, but it won't be exact.

The Olympus OMD's meter was set to "center-weighted".
The Luna Pro F's meter was set to "reflected light".

Test 1: Pavement.

Olympus ---> 1/125" F16 ISO 200
Luna Pro ---> 1/125" F16 ISO 200 (same!)

Test 2: Sun-Lit Beige Wall.

The light was changing rapidly. I ended up taking two measurements with each device.

Olympus ---> 1/400" or 1/500" F16 ISO 200
Luna Pro ---> 1/300" or 1/400" F16 ISO 200

Test 3: Shaded Wall.

At this point my finger must've slipped and changed the OMD's aperture to F14. I will report the value in the EXIF data and the equivalent at F16.

Olympus ---> 1/60" F14 = 1/46" F16 ISO 200
Luna Pro ---> 1/38" F16 ISO 200

Test 4: Normal Scene.

OMD still set to F14...

Olympus ---> 1/80" F14 = 1/61" F16 ISO 200
Luna Pro ---> 1/86" F16 ISO 200

BrianShaw · Friday at 3:36 PM

Well that looks promising…

Perhaps there was some user “error” in the earlier measures where the Luna Pro showed “bad” readings. It really would be nice if there’s no problem as it may be big but it’s a fast and versatile meter to use.

(Im still not convinced that light meter app cannot be trusted since it was giving quite credible readings in your initial comparison. But that’s neither here nor there.)

GregY · Friday at 3:39 PM

Hallelujah..... the first job with a new tool is to learn how to use it..... non?

dcy · Friday at 4:09 PM

Bill Burk said:
@dcy

Try comparing the Luna Pro incident mode (aim dome at camera from subject) to the digital in Digital ESP Metering mode (aimed at subject).

Reflected light metering always requires some evaluation of “what you’re aiming at” vs “what tone the subject is supposed to be”. ESP will try to evaluate that, and incident ignores tone of the subject and evaluates how much light is falling on the scene.

If the meter is working and the camera guesses the scene right, you should get comparable results. Pick a typical scene, not gray pavement or bright wall.

I can do that!

Light Meter Test:

Olympus OMD metering set to "Digital ESP Metering".
Luna Pro metering set to "incident" mode.

I chose smaller human-scale subjects so I could walk up to the subject and hold the Luna Pro right at the subject (dome pointed in the direction from where I took the shot with the camera, away from the subject).

Scene 1: Flowers --- Direct sunlight

Olympus ---> 1/160" F16 ISO 200
Luna Pro ---> 1/177" F16 ISO 200

Scene 2: Fire Hydrant --- Direct sunlight

Olympus ---> 1/160" F16 ISO 200
Luna Pro ---> 1/125" F16 ISO 200

Scene 3: Bench --- Direct sunlight

Olympus ---> 1/200" F16 ISO 200
Luna Pro ---> 1/226" F16 ISO 200

Seeing how well the Luna Pro was performing under ideal conditions, I decided to give it a more tricky scene.

Scene 4: Bench --- Tree in the shade, with a brighter background.

Olympus ---> 1/40" F16 ISO 200
Luna Pro ---> 1/14" F16 ISO 200 --- I think this just shows it was indeed a tricky scene.

Then finally...

Scene 5: Shelf --- Indoors.

Olympus ---> 1.3" F16 ISO 200
Luna Pro ---> 1.1" F16 ISO 200

Not bad.

BrianShaw · Friday at 4:23 PM

I don’t want to incite another purchase, but now you need a spot meter for scene 4.

Bill Burk · Friday at 4:27 PM

That's great, lots of 1/6 stop difference in readings! I'd say Luna-Pro F is good.

MattKing · Friday at 4:48 PM

Bill Burk said:
That's great, lots of 1/6 stop difference in readings! I'd say Luna-Pro F is good.

+1
And as for the discussion about K and the like, that sort of analysis is much more likely to resemble @dcy 's day job than he probably ever wants to get into when out with a camera.
If you like to learn how the metering sausage is made - and I'm recommending that you do or suggesting you don't - the posts of several Photrio members like @Bill Burk and in particular @Stephen Benskin are recommended.

Chan Tran · Friday at 6:13 PM

GregY said:
Pentax half frame 17.....
CT....it depends if you want to carry a bigger bag or wear cargo pants

i'm not suggesting there's a problem.... but it is less convenient...& somewhat counterproductive.
Luna pros /Luna sixes were great meters designed for the pro market....nowadays there are much smaller fully functional smaller meters.
I carried one for years along with motordriven F2s & F3s.....
I'd take a Sekonic 308 in a heartbeat let alone the diminutive Digisix or one of the tiny hotshoe mount meters.

I asked because there is a problem using any meter with the Pentax 17. The 17 doesn't have any manual exposure controls except the exposure compensation but... To use the exposure compensation you have to know what the settings the camera has chosen so that you know how much to compensate. The 17 doesn't display the aperture or shutter speed it chooses.

MartinCrabtree · Friday at 6:16 PM

I have a Weston Master II that was refurbished by George Milton of Quality Light Metric. It took me awhile to begin to use it easily. Never tested it against anything else 'cause the photos I get when utilizing it are what I want...so far. I use it both reflected and incident with an Invercone. Learning to use a tool is key to success.

dcy · Friday at 6:40 PM

BrianShaw said:
I don’t want to incite another purchase, but now you need a spot meter for scene 4.

Ha ha.

Bill Burk said:
That's great, lots of 1/6 stop difference in readings! I'd say Luna-Pro F is good.

Yay! Thanks for the help! Really appreciate it.

MattKing said:
+1
And as for the discussion about K and the like, that sort of analysis is much more likely to resemble @dcy 's day job than he probably ever wants to get into when out with a camera.

Yeah. I was very intentional when I decided to aim for a laid-back experience with film. It's not that I'm scared of math or details; quite the contrary, my impulse is to obsess over details. I'm trying to get my brain to unplug, and use my hands and feet more.

Chan Tran · Friday at 6:43 PM

Out of curiousity I wonder initially the OP got bad reading because he had it in flash mode. However, I think if you interprete it correctly you can get the right reading even with the meter in flash mode. I know I can do that with the Minolta flashmeter.

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

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