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02-25-2013, 09:33 PM   #1
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Light Meter Differences

I ran the following light meters at the same controlled source (tungsten kitchen scene at night) and got varying results:

All had the ISO set to 400:

K1000 with 50mm @ f 2 says to shoot at 1/60
Super Program with 50mm @ f 2 says to shoot at 1/60
A3000 with 50mm @ f 2 says to shoot at 1/60
K-01 (apc crop) with 35mm @ f 2 says to shoot at 1/20
iPhone light meter apps (two different ones) both said to shoot at 1/30

I took pictures with the k-01 at all three suggested times, and liked the 1/30 the best.

There is a 1.5 stop difference between the k-01 and the film cameras. This makes me nervous :-) A full stop difference from film to iphone.

On digital you want to avoid overexposing, but on film you want to never underexpose, right?

My workflow is local pro lab developing and then I scan on my Epson V500.

I am new to film (on my third roll now) and many of my pictures have more grain than they should because I think I am underexposing. I have a ME super arriving this week then I will decide which 2 film cameras to keep. I know the super program is staying.

Thanks for any advice or tips anyone has for me on the metering!

Jamey

02-25-2013, 09:58 PM   #2
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The best way to check exposure is a gray card with a constant light source. Make sure all you can see through the camera is the gray card.

If you are shooting with typical C41, you will have so much latitude - particularly on the highlight side, that a 1 - 3 stop overexposure will typically be rendered the same by most scanners in autoexpose mode. So you have a lot of latitude to overexpose. Keep in mind this is not the same as don't underexpose. You should feel free to over or under expose intentionally as you like. However, know your camera's metering as well as your film's characteristics to get the results you want.
02-25-2013, 10:33 PM   #3
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QuoteOriginally posted by LesDMess Quote
The best way to check exposure is a gray card with a constant light source.
What he said....sort of. A gray card will give you a measure of incident light and has the same reflectance (18% gray) as the standard that light meters are calibrated against. That being the case, the gray card is an excellent way to compare meters and a very decent way to gauge light for difficult subjects.

As for rules of thumb (under vs. over exposure for film/digital), there is a lot to this subject. I would recommend a good book on exposure theory. I know it sounds dry, but once the light comes on in your head, you will never approach the camera's metering system the same. What the meter "sees" is one thing. How the film/sensor behaves is quite another. The exposure you choose all depends on what photograph you want to take.


Steve

BTW...your phone app is probably the least accurate meter in your mix.
02-25-2013, 10:52 PM   #4
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QuoteOriginally posted by stevebrot Quote
What he said....sort of. A gray card will give you a measure of incident light and has the same reflectance (18% gray) as the standard that light meters are calibrated against. That being the case, the gray card is an excellent way to compare meters and a very decent way to gauge light for difficult subjects.
Sorry but that simply isnt true.
The ANSI standard is closer to 12%, read more about it here Richard L. Hess Web Pages - Why 18% is not the right reflectance
18% gray is middle gray and that is used in the printing world.

But like you say it's good to meter from a standard source to compare differnces.

02-26-2013, 08:05 AM   #5
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IMHO f/2 1/60 with a 50 sounds about right.
I don't know about your lighting, but printing a gray card to use as target will help
02-26-2013, 08:28 AM   #6
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QuoteOriginally posted by Jamey777 Quote
I ran the following light meters at the same controlled source (tungsten kitchen scene at night) and got varying results:

All had the ISO set to 400:

K1000 with 50mm @ f 2 says to shoot at 1/60
Super Program with 50mm @ f 2 says to shoot at 1/60
A3000 with 50mm @ f 2 says to shoot at 1/60
K-01 (apc crop) with 35mm @ f 2 says to shoot at 1/20
iPhone light meter apps (two different ones) both said to shoot at 1/30
The first thing I noticed Jamey is where you used the same lens, you got the same recommendations. It was only when you changed the lens used by your meters did the results change. I'd like to make two points to this:
#1- different field of view (FOV) What we don't know is how even the scene is lighted or how uniform the reflectance was in your scene. While 50mm on a full frame is close to 35mm on APS-C, there is still a minor difference in FOV.
#2- f/stop variation between lenses. While this should be very minor, there is still some variability.
02-26-2013, 10:26 AM   #7
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QuoteOriginally posted by JimJohnson Quote
The first thing I noticed Jamey is where you used the same lens, you got the same recommendations. It was only when you changed the lens used by your meters did the results change. I'd like to make two points to this:
#1- different field of view (FOV) What we don't know is how even the scene is lighted or how uniform the reflectance was in your scene. While 50mm on a full frame is close to 35mm on APS-C, there is still a minor difference in FOV.
#2- f/stop variation between lenses. While this should be very minor, there is still some variability.
Good points. I need to do some controlled experiments once I settle on the two film bodies. Thanks for the advice.
02-26-2013, 10:46 AM   #8
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QuoteOriginally posted by Jamey777 Quote
I am new to film (on my third roll now) and many of my pictures have more grain than they should because I think I am underexposing. I have a ME super arriving this week then I will decide which 2 film cameras to keep. I know the super program is staying.

Thanks for any advice or tips anyone has for me on the metering!
the super program use a center weighted metering. make sure your iphone and you K01 were using the same settings. i think it could explain most part of the difference.

02-26-2013, 10:56 AM   #9
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Comparing meters between cameras using reflected readings needs to be done carefully due to metering patterns, differences between lenses etc. And that's assuming the meters are adjusted properly in the first place. The light meters are normally calibrated using a controlled light source ideally on an optical bench. You would probably get a more accurate comparison using an incident meter (white) lens cap.

The rule of thumb is when shooting negatives expose for shadows. WIth positive (slide and digital) expose for the highlights.
02-26-2013, 10:19 PM   #10
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QuoteOriginally posted by Anvh Quote
Sorry but that simply isnt true.
You are correct that meters are calibrated against a standardized light source, but the value used for reflectance meters may be calculated to about 18% reflectance (or a little less). The 12% value is derived from the calibration standard for incident light meters with hemispheric diffusers and is promoted by a few people on the Web as the "true" value for a reflectance meter target based on the notion that the world is not flat.

I have always found the 18% card to work well when doing film speed testing for establishing baseline at box speed for new film/developer combos (funny thing). If a person wants to try 12%, I suppose you could buy a "more correct" 12% gray card (available from some sources) or simply dial in +1/2 stop exposure compensation. You may be able to see a difference or perhaps not.

For a concise discussion about the ISO standards involved (ANSI is U.S. only) and how the calibration is done for reflected, incident, and in-camera meters (yes, they are all treated differently), I would direct you to (ta! da!) the wikipedia:

Light meter - Wikipedia, the free encyclopedia


Steve

BTW...I just took an incident reading with my Sekonic (hemispheric diffuser) followed immediately by a reflectance measurement from an 18% gray card...same result. I would take that as pretty good evidence that the 18% card is acceptable for metering incident light. OTOH, my Sekonic is supposed to have been calibrated to a value of K=12.5 and C=340 which would yield 11.5%. Go figure. It's only 1/2 a stop.

Last edited by stevebrot; 02-26-2013 at 10:49 PM.
02-26-2013, 11:00 PM   #11
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QuoteOriginally posted by aurele Quote
the super program use a center weighted metering
Ditto for the A3000. And the K 1000 has an averaging meter. The K-01 supports matrix, center-weighted and spot. The phone cam apps, on the other hand, extrapolate exposure from whatever setting the camera used for a particular subject. I have found the Android versions to be uniformly inaccurate.

That is why a gray card was suggested, though any uniformly lit surface will do, even a blank white wall in indirect light should yield the same reading regardless of metering system used.


Steve
02-27-2013, 12:56 AM   #12
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QuoteOriginally posted by JimJohnson Quote
The first thing I noticed Jamey is where you used the same lens, you got the same recommendations. It was only when you changed the lens used by your meters did the results change. I'd like to make two points to this:
#1- different field of view (FOV) What we don't know is how even the scene is lighted or how uniform the reflectance was in your scene. While 50mm on a full frame is close to 35mm on APS-C, there is still a minor difference in FOV.
#2- f/stop variation between lenses. While this should be very minor, there is still some variability.
Well spotted, not only that but the T-stops are also different.
02-27-2013, 01:04 AM   #13
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QuoteOriginally posted by stevebrot Quote
BTW...I just took an incident reading with my Sekonic (hemispheric diffuser) followed immediately by a reflectance measurement from an 18% gray card...same result. I would take that as pretty good evidence that the 18% card is acceptable for metering incident light. OTOH, my Sekonic is supposed to have been calibrated to a value of K=12.5 and C=340 which would yield 11.5%. Go figure. It's only 1/2 a stop.
Sure but saying that 18% is a standard while it actually isn't is something else, there is no standard out there for light metering that use 18% gray.
Also the angle at which you hold the card matters you know, because you're metering the reflective light.

Anyway i always use the histogram since i expose to the right so it doesnt matter for me if you;re concerned about that
02-27-2013, 08:54 AM   #14
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Shooting film

On your third roll already!!!

Come back and add to this discussion after you have a little experience with film; say 1000 rolls or so.

40 years ago I was shooting and processing sometimes 100 rolls of slides a day. That, of course, was followed by several days over a light table culling!
02-27-2013, 09:59 AM   #15
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QuoteOriginally posted by Anvh Quote
Sure but saying that 18% is a standard while it actually isn't is something else, there is no standard out there for light metering that use 18% gray.
I guess that explains the plethora of 12% gray cards on the market. What am wondering is why my hand-held meters (both of them) provide the same value for both incident light and reflected off the 18% card. (And yes, I am aware that the angle is important...been doing this a lonnnng time.)

QuoteOriginally posted by Anvh Quote
Anyway i always use the histogram since i expose to the right so it doesnt matter for me if you;re concerned about that
An excellent solution for someone shooting digital (you did notice that this thread is in the film slr section)


Steve

Last edited by stevebrot; 02-27-2013 at 10:06 AM.
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