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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 12 Jul 2018 (Thursday) 01:19
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Light metering question for New York guys

 
ZoranC
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Jul 12, 2018 01:19 |  #1

If this week you go out on completely clear and sunny day at the time sun is at its strongest, go to spot where nothing casts a shade, pull out your lightmeter, set it at F2.8 ISO 100 and meter what is the shutter speed you would get?

I am trying to see how many stops approximately difference in latitude between Los Angeles and New York results in.




  
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Jul 12, 2018 07:39 |  #2

0.0 difference

<<< not from NYC


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Post edited 4 months ago by Wilt. (2 edits in all)
     
Jul 12, 2018 08:34 |  #3

ZoranC wrote in post #18661044 (external link)
I am trying to see how many stops approximately difference in latitude between Los Angeles and New York results in.

The realistic answer is, "It depends upon how smoggy it is in LA at the time of the measurement" and what time of year it is.


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Jul 12, 2018 08:55 |  #4

Wilt wrote in post #18661176 (external link)
The realistic answer is, "It depends upon how smoggy it is in LA at the time of the measurement" and what time of year it is.

Not to mention how much smoke from wildfires is present, but I will anyway. ; )


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Jul 12, 2018 09:23 |  #5

Just read that Lambert's Law applies to the situation: Lambert's cosine law says that the radiant intensity or luminous intensity observed from an ideal diffusely reflecting surface or ideal diffuse radiator is directly proportional to the cosine of the angle θ between the direction of the incident light and the surface normal.

Difference in lattitude between LA and NYC is just under 7 degrees latitude, but the sun declination angle is not the same as the latitude difference. Someone much more knowledgeable about celestial navigation please jump in, but when at about Vernal Equinox (when daylight=night duration) there is only about 1.7 degrees difference in declination angle at the two locations (based upon latitudes of LA and NYC), which would mean the intensity difference would be 'too small to matter, practically speaking' with a Cosine angle difference of 1.7 degrees (way less than 0.33EV)


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Jul 12, 2018 10:36 |  #6

ZoranC wrote in post #18661044 (external link)
If this week you go out on completely clear and sunny day at the time sun is at its strongest, go to spot where nothing casts a shade, pull out your lightmeter, set it at F2.8 ISO 100 and meter what is the shutter speed you would get?

What color is the surface you're pointing at?


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Jul 12, 2018 10:39 |  #7

1/2500 for skin, if there's something white in the frame I might knock it to 1/3200

I'm not in NY by the way, but ISO100 1/1250 f4 is always my starting point for full sun.


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John ­ Sheehy
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Jul 12, 2018 11:11 |  #8

daisan wrote in post #18661242 (external link)
1/2500 for skin, if there's something white in the frame I might knock it to 1/3200

I'm not in NY by the way, but ISO100 1/1250 f4 is always my starting point for full sun.

Of course, if you use a flexible converter and shoot RAW, the actual saturation-based ISO across cameras is around two stops. One camera might be 113 at "ISO 100" and another, 29.

It would be a shame for a person to expose "ISO 100" for 100 and lament not having ISO 32, when in fact, they can actually shoot at ISO 32 with "ISO 100". Just no room for specular highlights, but that is not even an issue in many scenes. Again, your converter has to flexible enough with your camera.

Try it; set your camera to its lowest ISO, and shoot a color-checker at sunny f/16 for a range of low ISOs, and see where the white patch actually clips or where your converter can't be tweaked to get color right. In most cases, you can drop to at least 80, and possibly much lower with some cameras.

This is less dangerous than TTL metering, because darker things on the weighted part of the meter do not cause over-exposure of the base-ISO RAW.




  
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Jul 12, 2018 11:12 |  #9

THis (external link) tool is fun to play with. It's for solar panels but does show the difference between locations.


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ZoranC
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Jul 13, 2018 00:13 |  #10

OhLook wrote in post #18661238 (external link)
What color is the surface you're pointing at?

We are not talking reflective metering.




  
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ZoranC
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Jul 13, 2018 00:17 |  #11

gjl711 wrote in post #18661250 (external link)
THis (external link) tool is fun to play with. It's for solar panels but does show the difference between locations.

That tool is showing total amount of energy that is depending on total number of sunny hours.




  
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ZoranC
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Jul 13, 2018 00:17 |  #12

So nobody with an actual light meter?




  
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Wilt
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Post edited 4 months ago by Wilt. (3 edits in all)
     
Jul 13, 2018 11:50 |  #13

ZoranC wrote in post #18661620 (external link)
So nobody with an actual light meter?

Pointless! Unless you measure at the same time of year, there can be variances. And on a given day, there may be more/less water vapor or smoke in the air to dispell light. And unless you use the SAME meter in both places, you cannot account for differences in individual meter calibration!

Look at what the post 9 web page says:

Solar Irradiance figures
New York City

Average Solar Insolation figures
Measured in kWh/m2/day onto a horizontal surface:
Jan Feb Mar Apr May Ju​n
1.96 2.79 3.89 4.80 5.51 6.04

Jul Aug Sep Oct Nov De​c
5.77 5.24 4.30 3.23 2.12 1.72

Solar Irradiance figures
Los Angeles

Average Solar Insolation figures
Measured in kWh/m2/day onto a horizontal surface:
Jan Feb Mar Apr May Ju​n
2.93 3.62 5.12 6.60 7.49 7.83

Jul Aug Sep Oct Nov De​c
7.54 6.87 5.70 4.45 3.34 2.73

yes, the irradiance calculator will then show monthly figures showing the average kWh per square meter per day for energy at your location, but you at least get an idea of the relative amount of light (although you have no idea of the number of minutes of light at each location).


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Jul 13, 2018 12:34 |  #14

I get 1/5000 sec. @ 50° 26' N.


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Post edited 4 months ago by Wilt. (2 edits in all)
     
Jul 13, 2018 15:30 |  #15

Alveric wrote in post #18661970 (external link)
I get 1/5000 sec. @ 50° 26' N.

1/4000, f/2.0 + 0.9EV @ 13:30hr PDT, Latitude 37° 31' N measured with Minolta Autometer Vf with flat disk


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Light metering question for New York guys
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