Spot meter readings vary

[Ron Smith]

I did a some tests today and here is what I found with my Sekonic meter.

I have not calibrated my meter to the RED MX and am using the factory defaults on the light meter.

To get accurate middle grey readings on the RED MX camera - I am using the spot meter option on the RED camera as well as my Sekonic 758 cine.

I am having to put my ISO on the Sekonic at the following ratings in order to get to brightness 50 on the RED MX spot meter. The camera set on shutter speed 180, 4K 2:1, Redcode 36, most recent build.

Under kitchen flourescent lighting at 3600K with green tinge. Camera WB 3200K.
ISO 800 on MX - ISO 400 on Sekonic.
ISO 500 on MX - ISO 250 on Sekonic.
ISO 320 on MX - between ISO 125 and ISO 160 on Sekonic.

Under incandescent lighting at 2500L. Camera WB 3200K.

Iso 800 on MX - ISO 320 on Sekonic.
ISO 500 on MX - Between ISO 250 and ISO 200 on the Sekonic.
ISO 320 on MX - ISO 125 on Sekonic.

Why is there so much variation between the color temperatures?

Also, something very interesting. Under daylight 5600K camera wb to 5600K. I found a red towel on the ground to be consistently darker than what my meter would give me as a readout. It would be about half a stop darker than what my Sekonic would give me. Does the Red camera absorb less red or does it render red objects less bright? The other colors (non red) were exposed normally.

 

[Alexander Ibrahim]

I did a some tests today and here is what I found with my Sekonic meter.

I have not calibrated my meter to the RED MX and am using the factory defaults on the light meter.

To get accurate middle grey readings on the RED MX camera - I am using the spot meter option on the RED camera as well as my Sekonic 758 cine.

I am having to put my ISO on the Sekonic at the following ratings in order to get to brightness 50 on the RED MX spot meter. The camera set on shutter speed 180, 4K 2:1, Redcode 36, most recent build.

Under kitchen flourescent lighting at 3600K with green tinge. Camera WB 3200K.
ISO 800 on MX - ISO 400 on Sekonic.
ISO 500 on MX - ISO 250 on Sekonic.
ISO 320 on MX - between ISO 125 and ISO 160 on Sekonic.

Under incandescent lighting at 2500L. Camera WB 3200K.

Iso 800 on MX - ISO 320 on Sekonic.
ISO 500 on MX - Between ISO 250 and ISO 200 on the Sekonic.
ISO 320 on MX - ISO 125 on Sekonic.

Why is there so much variation between the color temperatures?

Also, something very interesting. Under daylight 5600K camera wb to 5600K. I found a red towel on the ground to be consistently darker than what my meter would give me as a readout. It would be about half a stop darker than what my Sekonic would give me. Does the Red camera absorb less red or does it render red objects less bright? The other colors (non red) were exposed normally.

Are you sure you are using the Sekonics defaults and that it is working properly? Are you set for the right frame rate and shutter angle?

Also how are you measuring color temp, and how are you evaluating what you set the camera up for?

I've found color temp to be consistent on Red One, M or MX.

I've found MX and Epic to be much closer than you report on ISO with my Sekonic set to defaults. (758Cine)

 

[Ron Smith]

Yes, my Sekonic is set to factory defaults. I have been the only owner of this unit and it is working consistently from when I bought it. I have kept it in good condition and it has not been subjected to any harsh conditions. Even with the regular RED (non MX) I was metering in camera 320 iso with 125 on the meter to get accurate results.

The meter was set to 24 fps, shutter angle 180.

I am measuring color temperature with a Sekonic C500 color meter.

Are you seeing exposure ifferences between daylight color temperatures and tungsten? Or household flo and tungsten?

 

[Ron Smith]

I don't really care too much about my meter showing a different ISO than the camera. However, it becomes quite confusing for me when under different lighting (tungsten vs daylight vs flourescent vs house hold bulbs) conditions I get different results.

 

[Ron Smith]

Has anybody else had this kind of weird effect happen to their meter and MX?

I am going to rent another spot meter and see if I see the same thing happen.

 

[Richard Goodwin]

Using this method of reading it's hard to be sure exactly how far apart the two metering methods are (esp as the Sekonic does not show precise values for ISO). You would be better off fixing ISO and shutter speed and comparing the resulting F stop values, where the meter will give you a much more precise reading. I say that because the readings above to not show a clear pattern of variance between the two meters. More accurate readings along a larger range of light values would help. (You could vary it more by adding various ND filters in front of both meters to test a larger luminance range).

Also, the sekonic is not calibrated for 18% grey out of the factory, not sure if the RED is calibrated to 18% or not. But, the point is the two meters might not calibrated to the same percent grey (standard luminance value). Which would account for the spread between them.

 

[Alexander Ibrahim]

Are you seeing exposure ifferences between daylight color temperatures and tungsten? Or household flo and tungsten?

No. My 758Cine reads the same exposure variance under different lighting conditions.

FWIW I get a variance of some sort with my 7D as well. (Stills and motion) And the XL-1, and the EX1, and in my short time with Epic-M #0008. (Thanks Ketch!) Oh, and Kodak Velvia and Portra stills film.

That's why there is a calibration something or other on the thing, which I never use. I test the heck out of my camera/stock instead and get a mental map of the variance.

Babble babble.

My point is that there may be something wrong with either your camera or your meter. I read that you are getting another meter, so that's good. Meter another camera- any camera really. You should be getting closer results than you are reporting.

 

[Dan Hudgins]

12% Gray?

12% Gray?

See this,

http://www.bythom.com/graycards.htm

RED has said they use "about 46%" for midtone.

SD encode is gamma 2.20 (Rec 601) about 45.8%

HD encode is gamma 2.22 (Red 709) about 46.2%

ITU Monitor standard is gamma 2.4 now(?)

So its hard to get anything to match, and the EI/ISO curves in the camera shift the values above and under mid-tone, so moving the lens 1 stop does not always equal 1 stop of change in the DPX file as 90 points. You just need to reset the ISO on your meter to what works in the camera.

Some meters are red bias, so do not track the green exposure well, some may even pick up IR so the reading is only rough, or in your case the light may lack IR so reads low.

 

[Ron Smith]

Update: The problem was with the light meter. It was sent into Sekonic and came back working perfectly.