Tutorial for Sekonic L-758DR: How to create a custom profile
NOTE: This tutorial was created using the original calibration target and version 1 of the Sekonic Data Transfer software. Since writing this, the new Calibration Target II and version 2 of the Sekonic Data Transfer software have been released. You can still use this procedure with version 1 or you can download the new software and use either the original target or the new Target II.
I’m posting this how-to in an attempt to clarify the horrible manual that accompanies the data transfer software and to demystify the process. There is no doubt that doing a full custom profile is time consuming and does leave a lot of room for human error but after having spoken to the L-758DR project manager and performing the procedure several times I have a grasp on the process and can perhaps shed some light on this topic.
I think that for most people, if you already own an L-758DR you’ve got one of the finest meters out there so to think that the custom profile is a must just isn’t so. For those that want to be as accurate as possible and are working with 1/10 stops rather than 1/3 or 1/2 stops then there are some benefits and I have explained some of them in this post from another thread.
The first thing that most owners of this meter learn quickly if they want to create a custom profile is that on top of the cost of the meter you have to buy the Sekonic Calibration Target, which has an 18% gray card on one side and a series of grayscale patches on the other.
If your computer is one of the newer Intel based Macs then you can view and create a profile on your computer but you can’t transfer the profile to the meter. This is a problem that is being corrected and should be in the updated software due out in August.
I’m going to outline the procedure for a Flash/Incident profile since that is the most common use of a light meter. The procedure for Flash/Reflected is identical. I’ll use ISO 100 as an example and I’m shooting RAW. If you shoot JPG then it’s very important that you change all color, saturation, contrast and brightness settings to a zero value so no processing is being applied.
- Select the lens you want to use. Pick a lens that you use often and one that has a 7 stop range. For example, an aperture range of f/2.8 to f/22 would work well. This is based on having a lens where you can find a middle exposure and have the ability to move 3 stops in either direction. Typically this is going to mean that f/8 is the middle exposure and the 7 stop range is f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22. If you have a lens that has f/4 as its largest aperture then you would make f/11 your middle exposure and the range would be from f/4 to f/32, assuming you could stop down to f/32.
- Set up the target and camera (see images #1 and #2 below). You’ll need the ‘B’ side (gray card) first. The target should be set up so it’s perpendicular to the floor and parallel to the background. Make sure that you don’t have any light or colored backgrounds and that there are no light sources returning light to the target. Normally small amounts of light or color cast would be acceptable but since this is actually a calibration you should do everything you can to keep things precise in the procedure, as these things could easily throw off the results.
Setup the camera at whatever distance needed from the target so the entire frame is filled with the target. With my 85mm lens I’m not quite 4 feet from the target to have it fill the frame. Manually focus on the target (I find it easiest to focus on the white text below the gray area before you frame the shot). If you’re lens is not in focus it could adversely affect the results. Set your shutter speed for the sync speed you use with your strobes and camera. I use 1/125s with Alien Bees strobes. Also set your ISO for the first one (or only one) you want to have in the profile. So let’s use ISO 100.
- Set up the lights (see images #1 and #2 below). Depending on the lens used and power of your strobes you’ll end up with a slightly different setup and power level settings will vary. You’ll need 2 lights on light stands.
Ideally, you want your strobes at 45 degree angles from the center of the target and the easiest way to find that angle is to take the distance of the camera from the target and measure that same distance to the side of the camera, staying parallel to the background. That point should be 45 degrees off axis. Do this for the left and right light. Make sure the lights are set at the same power levels. Adjust the height of the lights so the center of the light is on the vertical axis of the lens. Then check your settings by taking an incident reading (lumisphere extended) from the center of the target with your meter at target position and find the power level setting that gives you that middle value of f/8. Measure across the target taking a far left and far right reading, making sure that there isn’t more than 1/10 stop variation. If there is then fine tune the angle of the light(s) so you have even lighting from left to right.
If you find that you're working in the bottom end of the power slider (1/16 or below) on your strobes to get your middle exposure of f/8 then you should move your lights further away, making sure to keep them the same distance from the target and at 45 degree angles.
- Set Custom White Balance. Since you’ve already set up and metered for f/8 you can take your gray card shot and set a Custom White Balance on your camera.
- Take pictures for calibration. Turn the target over to the ‘A’ side, maintaining the same position so it’s centered in frame. Take a series of 7 images. I always do mine with the middle exposure first, then I open the aperture and then close it, so my final series of images is f/8, f/5.6, f/4, f/2.8, f/11, f/16, f/22 (see image #3 below). Some people find it makes more sense if they shoot them as f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22. I figure I might as well take the f/8 first since I was already there from the gray card shot and because it’s the first image I’m going to use once I go into Photoshop to find and generate the results.
If you’re going to move on to the other ISO’s then you’d now change the ISO in your camera and on your meter (moving one stop up from ISO 100 to ISO 200), and readjust the power levels so you are back at your starting point of f/8. Then you do your gray card shot for custom white balance at the new ISO and repeat the process of taking the 7 test shots with apertures from f/2.8 to f/22. Repeat for as many ISO’s as you want or for the whole range of ISO 100, 200, 400, 800, 1600. The software gives you the option of only using 2 ISO settings and it will figure out the rest but I did this and then did a full profile and found that I came up with different numbers than the software did on those other ISO’s. I think if you’re going to the trouble of creating a custom profile then you might as well do the whole thing, get it over with and then it’s done.
- Interpreting the results. You now have 7 images for each ISO setting you shot. Since our example is using ISO 100 that’s what I’ll use for the next steps. You perform this next procedure for each ISO.
Open the 7 images in Photoshop. Then open the Info Window. If you haven’t changed the defaults you’ll find it right in between the Navigator and Histogram tabs. In the Info tab you’ll see 4 sections. Look at the top left section and you should see an eyedropper dropdown menu and RGB values. Make sure the eyedropper dropdown is set to Actual Color. We’re only going to be looking at the Green (G) value to obtain the correct information. Now, using the eyedropper tool (not the dropdown menu you just used), move the eyedropper over the 7 grayscale patches on the image shot at f/8 (middle exposure) and find the one where you get a value of 118 (± 2). Ideally, it should be the center patch but it’s fine it isn’t. I’ve done this a few times and never seen as narrow a deviation as ± 2. Usually there is devation within a small area of as much as ± 5. You’ll find that the neighboring patches will have very similar values and at times you have to really be careful as to which patch you select. This is where the human error comes in so be careful. This process gets more difficult as the ISO is increased because it becomes harder to differentiate the pixels with the noise from those without.
Now that you know which patch is giving you a Green value of 118 you need to open the Sekonic Data Transfer Software. This is where the manual is not only difficult to understand but it is incorrect and useless. Using the Camera 1 setting, click on the Flash/Incident button. This will open up the table that will ultimately be filled in with values. The far left column is ISO. Scroll down to ISO 100. The column to the right of ISO is Compensation Value. Double click in that field to open the Compensation Value calculation window. (Getting the impression this is tedious? It gets worse).
For Light Meter Measurement you need to enter the settings from your meter. In this case it’s 125 for the shutter speed and an aperture of f/8. For Camera Exposure Data fill in exactly the same information as you did for Light Meter Measurement. Next click on the patch that you found the 118 value from, and finally click the Calculation button. Click OK to close that window and return to the data table.
Back to the Photoshop images. Now we need to get the –Clipping Point and –Dynamic Range. To do this, find the image and the patch that gives you a value of 20 for the –Clipping Range and the image and patch that gives you a value of 35 for the –Dynamic Range. Now take the apertures of the images and the patches that gave you the correct value for both these parameters and go back to the Sekonic software.
The next two columns in the data table to the right of Compensation Value are the –Clipping Point and –Dynamic Range. Double click on either of those values in the ISO 100 row to open the Calculation window. Enter the Light Meter Measurement Data just as you did before. This is something that they senselessly have you re-enter each time. So you enter 125 and f/8. Then for Camera Exposure Data you’re going to enter the values you came up with, starting with the –Dynamic Range. Shutter speed remains the same and that is another thing that you’ll be entering every time. The exposure for the image that you found the value of 35 is what you want to enter for F Stop (in the software it’s called FNo.). In my case I found 35 in the image shot at f/16 and it was the patch just to the right of center. Enter the value and click on the patch. Then do the exact same thing on the right side of that calculation window, entering the data for –Clipping Point. Once you’re done click OK and return to the data table. None of the values filled in mean anything until you complete the +Clipping Point and +Dynmaic Range.
To get these values you go back to Photoshop one more time and now you’re looking for the images and patches that give you 245 for the +Clipping Point and 230 for the +Dynamic Range. Make a note of the ones you found.
Go back to the Sekonic software. The next 2 columns to the right in the ISO 100 row are the +Clipping Point and +Dynamic Range fields. Double click either of these to open the Calculation window. Enter the values for +Clipping Point and +Dynamic Range just as you did for the negative values. Click OK. This time when you return to the data table you’ll see values filled in across the ISO 100 row and you’ll be able to see the dynamic range and clipping points for your camera/sensor.
That’s the process for one ISO setting. Now you can either select another ISO, perform the same procedure, have the software interpolate and plug in the numbers for the other ISO’s or you can manually complete the process for any and all ISO’s you would like.
The manual does explain how to save and open profiles as well as how to transfer them to and from the meter.
I hope this tutorial helps those that have not been able to figure this out or were confused by the manual.