The subject of my experiment is the Sekonic L258D incident/reflective light meter. The meter was recently purchased from the Harry’s Pro Shop in Toronto, Ontario.
There seems to be a difference, sometimes considerable of the light meter reading compare to the reading of the camera in manual mode. I used a new grey card (DGC-100 Robin Myers). This card appears to be lighter in color than my old Kodak gray card. The card was setup under an array of daylight florescent lights. Using a Canon 40D and a 24-70mm f/4 lens with custom white balance adjusted to the grey card.
I made a series of exposures with asa of 200, ranging from 5*1/3 stops under and over the given light meter reading in incident mode of 1/160 f/8. Upon examination of the images in camera raw, I found the correct exposure was 1/200 f/8 (a value of 116 in the green channel) 1/3 stop under exposure. On the meter I made a correction of -.4 stops. I then switched to the reflective mode and found the meter required a correction of +.7 stops, to have the meter agreed with the reading in incident mode that gave me the correct exposure of 1/200 f/8.
The zone scale that Ansel Adams created has the 10 zones spread evenly over an 8 bit digital scale of 0 (total black) to 255 (total white). Each step is approximately 25.6. His scale used a value of 128 as zone V
With this Zone scale in mind I made a scale representing the Sekonic Profile card. There is approximately 25 points between 4 to 5 and 5 to 6. Zero represents 118 (Green channel), the next higher step is - 1/6 EV (1/6*25 = 4) a value of 122. The next higher is -1/3EV (1/3*25 = 8) a value of 126 etc. The +- 2 1/3 values I think are the clipping range that is referred to throughout there manuals. The value is 20 and 245
This image show the positions of different EV values. #1 is +2 1/3, #2 is -1/2 EV, #3 is -1/3 EV, #4 is -1/6 EV, #5 is 0, #6 is +1/6 EV, #7 is +1/3 EV, #8 is +1/2EV and #9 is -2 1/3 EV. The position #5 has a value of 118(Green channel) as compared to Zone Scale with a zone 5 value of 128. These positions # are used with the included software to create a camera profile. The values that I have used to make up this profile chart are at best just a guess. My intent was to get something reasonably close to use as a practice tool to create the profiles. To that end they seem to work quite well.
The next step was to make a variety of images outside using the L-758D incident meter reading. It became rapidly noticeable that the correction that I had made on the light meter of -.4 stops was not helping to produce a good image. I quickly made 10 exposures in all light directions. I then examined them with camera raw only to find out that nearly all the exposures were underexposed by about -1 full stop. I made a correction of +1.0 full stops in the meter and waited for the weather to improve.
With the weather, bright and sunny. I started my test with the Sekonic in incident mode and +1 compensation. I exposed 26 images. Before taking them into the raw converter I set the preference in Bridge to Auto Tones. The reason was to see what the raw converter though my exposure required in the way correction. From 0 to +.5 stop correction there were 4 imges. From +.5 to +.9 were 6 images. These correction particularily the higher ones were images of dark texture and looked better without the raw correction. With this consideration I'm was pleased with the exposure, they were quite consistant
The next part of the test was to set the meter to reflective mode with a correction of +1 stop based on only a few images. After making 27 exposure and with raw set up as for the incident mode. There was only 5 images with corrections from +.5 to +.7 and those were images that I wanted as dark with detail. Again with this part of the test I was very pleased with all the images as view in a group
During the process of the two tests, I also used the gray card as describe above. I will have to do some experimenting with this card. The slightest of tilt or twist in the wrong direction would either lighten or darken the reflective reading. On serveral occasions the reading were off by as much as +- 2 full stops.
My conclusion with requard to these two test were very positve. On several images I used the Average/Delta EV button to average out the exposure on others I used the mid point button to shift specific light values to a designated position. Both of these procedures made very well exposed images.
I still have difficulty with the range of correction for the gray card under florescent lighting and the corrections that I have used outside.
Thanks for visiting this page, if you have any questions please send E-Mail to dbardell@cyberbeach.netReturn to Cyberbeach's Home Page.