Be sure to crop the photo so nothing but the gray card is showing. If you don't it will not be accurate.Yes, take a photo of an 18% grey target using the (manual) exposure indicated by your L358 and then open it in PS. Using the color sampler tool determine the level of the target image. Since the target is neutral grey it should indicate a nominal value of 128. It won't be perfect but as long as it's within about 8 or so it's ok. If more than that, the camera is overexposing. If much less, it's underexposing.
In order to correct the difference between what the L358 indicates as the correct exposure (which you set in the camera) and what your camera actually does using that exposure you can calibrate the L358 in 1/10 stops using its calibrate feature as follows, per the L358 user manual...
"1. To enter the calibration setting of the meter it must first be turned off.
Press the power button on while holding down the ISO 1 and ISO 2 buttons simultaneously; the screen will display CAL 0.0 (for calibration).
2. The calibration setting can be changed by rotating the Jog Wheel while pressing and holding down the ISO 1 and ISO 2 button simultaneously. A range of +/- 1.0 EV in 1/10 stop increments is possible for calibration. The calibration setting is not displayed on the main screen once it is set."
In this way you can calibrate the L358 in order to compensate for what your camera is doing verses what the L358 indicates as the correct exposure. For example, if your camera is underexposing you can add positive compensation using the L358 calibration feature. Thereafter, when setting the L358 exposure in your camera the target image will sample close to 128 which indicates you have the correct exposure.
I hope that makes sense. :smile:
It won't help. :smile: I do agree with 12% (Sekonic, Nikon and Canon do use K=12.5 for reflected meters). Kodak did say if metering their 18% card, to open 1/2 stop for average scenes. But it seems good to involve the obvious facts into the discussion.So anyone know where I can get a 12% grey card :smile:
That is the page I quoted, in part. However, it's not describing how to calibrate the meter to a camera. Thus, there is no reference to a grey card or any other calibration target. The instructons are simply on how to use the meters calibration feature.WayneF said:Page 26 of the 358 manual covers it. And here is a article from Sekonic about how to calibrate the light meter. They do not mention gray cards.
At the risk of an appeal to authority argument, what I detailed is according to both the MAC Group and Sekonic Corporation. And using an 18% grey reference target is what they suggest when using the Sekonic calibration feature to match it to a specific camera.WayneF said:Modifying our light meters calibration so that a 18% gray card is at 50% on the histogram has been a false tale for years. But for entirely unrelated reasons, it is a coincidentally a small error. It can be then be compensated, so that it does not shut us down. But it is still certainly the wrong idea - no science behind it. Absolutely nothing says 18% ought to be midpoint of our gamma histograms. My bet is on Sekonic, they surely know much more about it than that.
Yes, I believe that is what he was asking when he asked how to use the Sekonic calibration feature. And is what the calibration feature is for, using the method I described. The Sekonic manual simply describes how to use the calibration feature, not why you would want to or how.Tony W said:In the OP’s case I think the most important factor is to match the Sekonic meter response to that of the camera so he can just “set my camera to match what is on the meter?”
The method you described (although I have no experience of the Sekonic) seems to me quite logical and correct. The only thing I am a little uncomfortable with is the differences that may exist between Photoshop histogram generation vs Nikon.Yes, I believe that is what he was asking when he asked how to use the Sekonic calibration feature. And is what the calibration feature is for, using the method I described.
It has nothing to do with the cameras reflected meter. I say that since reflected meters keep coming up in the discussion and can confuse the issue.
You said this twice, it seems the heart of your system, but this was the specific part that cannot be right. For reasons explained, there simply is no possible relationship between an 18% gray card and 128 at the center of a histogram.The idea is to sample the reference target which should be as close to 128 as possible if your camera is exposing properly using the exposure indicated by the L358.
We do agree that there certainly is no mention of gray cards in the Sekonic meter calibration procedure.That is the page I quoted, in part. However, it's not describing how to calibrate the meter to a camera. Thus, there is no reference to a grey card or any other calibration target.
That part seems OK, except histogram 128 is certainly not the determination of correct exposure of an 18% gray card. We would need some reason why that could be true, and all the facts show there is no possible relationship.If we presume the L358/L758DR indicates the correct exposure then we set the camera to that exposure while using manual exposure mode. We then take a photo of a known reference source. The camera should then correctly expose that target using the Sekonic's exposure settings. If it does not, then the camera is either over or underexposing when compared to the exposure the L358 or L758DR indicates.
We agree on many things, on each of your several points, except more qualification could help this one.My suspicion is that there is value in metering in camera a known value be it 18% or ideally 12% (as this is what the camera averages to?) and then this value should probably appear around the centre point of the camera histogram. If this is not the case then it may indicate the need for exposure compensation in camera.
Right, there are samples of each method shown at http://www.scantips.com/lights/gamma.html (in the yellow box along the right hand side). When the camera is showing its one single luminance value, it is showing theoretical computed grayscale luminosity values, which have their own meaning. The camera can however also show the three actual individual RGB curves, which Adobe typically shows overlaid in place.As I believe that Photoshop uses a different method of generating histograms than those of the camera manufacturer I do not think this would be the best way to go.
Wayne, it isn't 'my system'. It's one many people use and as I said is the method MAC Group/Sekonic USA suggest using. Including the 128 RGB value with a tolerance of +/- 8, , when calibrating the meter.WayneF said:That part seems OK, except histogram 128 is certainly not the determination of correct exposure of an 18% gray card. We would need some reason why that could be true, and all the facts show there is no possible relationship.