How to use your GL/XM2 as your ULTIMATE LIGHTMETER!

[Igor Trajkovski]

Edited by Rob Lohman: split this up into two posts. Part 1
is the preperation and part 2 is how to use this while shooting!


Today was a great day.An idea came to me.

How to properly and accurately expose with my XM2. How to
keep continuity in lighting levels and ratios.

How to make sure that "that white surface" still has detail in it,
and the shadows are still with some texture.

And all without a lightmeter. And all without a gray card.

I hope you will find my "system" helpful in your daily GL/XM2
use and abuse.

In short:

Make a picture with grayscale zones in the bottom.

Black, -2, -1, 0, +1, +2 White.
Upper part is transparent.

Use this picture as TITLE MIX.

Compare if the tonal value of critical subject/scene part is equal
with the desired zone. Correct the exposure so the part and the
zone have same tonal value.

PROCEDURE:

Flatly lit a white or gray surface. Mount your cam on a tripod.

Zoom almost to the max into the surface. If you go max, you
won’t be able to set aperture to 2.0. Manually defocus so you get
a solid textureless surface in your finder or LCD.

Turn your camera custom preset off. This way you make sure that
any black level setting won’t affect the gamma/blackness of your picture.

Manually whitebalance. Now the shooting.

Go to manual exposure. Keep the dB to 0. Adjust the shutter and
aperture so the meter indicator is in the middle. The picture you
see now is middle gray.

Ideally set your aperture to 4.0 and then set the shutter till the
meter indicator sets down to the middle. 4.0 is halfway in the
aperture scale so you can easily go from there up to 2.8 and 2.0
and later down to 5.6 and 8.0. Or in another words, +1 and +2
overexpose and -1 and -2 stops underexpose.

If it is to bright and you have trouble of going into the range of
-+2 f/stops reduce light with your build ND filter, or if artificial
lightsource is used dim it or move it further away from the surface
you are shooting.

All set, lets "shoot" somebody. I did my first shooting in CARD
mode. I shot all the zones as JPEG’s in the memory.

Now I decided to do it in TAPE mode. Reason? I am always in
FRAME movie mode, and I like to have the light response of that
mode. I noticed when I switch back and forth between TAPE
FRAME mode and CARD(interlaced) mode there is a difference in
picture appearance.

It seems like the FRAME mode "adds" some green/yellowish tint
to the picture. It is pleasing to me, of course. Probably the effect
of the green pixel shift or something happening in FRAME mode.
So while there is some shift in hue, I guess there might be some
shift in luminance also.

Anyway…

Press the photo button so you record a photo shot of the middle
gray surface on the tape. 6 sec long will be the recorded picture
on the tape.

Now, set the exposure one f/stop brighter. If you were at f4.0 go
to 2.8. If you started with a different value do 4 clicks up with
your exposure dial. It equals 1 f/stop.

Shoot again by pressing the photo button. Now set the exposure
2 f/stops brighter than the middle. If the start value was 4.0 now
should be 2.0. Shoot. Now, if you like, take another shoot of
overexposure by 2.5 stops.

Let’s go down.

Go 1 stop down under middle gray. From 4.0 to 5.6. Or 4 clicks
down from your actual middle value. Shoot. Go down for 2 stop
and shoot.

Same as above, if you like do a -2.5 shoot. It’s a wrap!

THE COMPUTER THING

Capture your just recorded footage or upload the JPEG’s if you
shot in CARD mode. From your NLE or After Effects export frames
of every exposure.

You should have at least 5 tones of the grayscale. Name them for
example Gray 0, Gray +1, Gray +2, Gray -1, Gray -2 accordingly.
This is the case without the -+2.5 exposures taken.

Go to Photoshop or your similar picture editing prog. Open all
frame grabs. Now we want to make a tonal scale of 7 blocks at
the bottom ¼ of the frame.

Why seven? We will include also white (255,255,255) and black
(3,3,3). Black (0,0,0) is transparent! I did it by using the grids, set
to 25% and subdivide 2. I created a new 640x480 pixels document.

Made the grids visible and activated snap to grid. This is for easily
selecting the area where to paste into. Go to the middle gray
document, make the grid visible and make an rectangular
selection somewhere in the middle. It should be 1 grid square
wide and 2 grid squares high. The snap to grid will make it easy
to do the precise selection.

Copy it (ctrl + c). Go back to your new document and make the
same size selection. Place it approximately in the middle
horizontally and starting from the bottom vertically.

Paste the gray copy into it. Now copy and paste the rest of
your grayscale samples into the new document by arranging
the +1 gray left to the middle 0 gray. +2 left to the +1.
Same with the darker parts.

If you are in Photoshop and all the grays are in different layers,
link them all together and MERGE linked.

Center this new layer containing the scale so the middle gray is
in the middle horizontally.

Make a selection in the left end touching the -2 zone and fill it
with black (3,3,3). Make a selection in the right end of the scale,
touching the +2 zone and fill it with white (255,255,255).

Now let’s define the transparent "lookthru" surface. With the
grids and snap active select the top ¾ space of the frame.
Fill it with pure black (0,0,0). Save the document as JPG.
I let the quality setting to 9.

Copy it into your XM2 memory card in the title folder. I had only
two title files inside before, so I rename the new one in
USER00003. Rename yours accordingly.

[Rob Lohman]

Edited by Rob Lohman: this is Part 2 of Igor's post even if it
is under my name.


HOW TO USE

Put the card into your camera. In the title mix setting select your
new JPEG as title. Open the cover on the handle and press Title
Mix to show the grayscale superimposed in the lower ¼ of the
frame. It would be less here. Overscanning, remember?

So you would say great, but it is gray! I am taping in color!

No prob. Next step is to choose and activate the B/W Effect.
You see now a gray tonal rendition of you scene. Now is
comparison time.

You decide the skintone of the bright side of your actors face to
be always +1 stop brighter than middle gray. Zoom in if
necessary to the bright side of actors face, place the +1 gray
square beneath it and adjust the exposure by comparing
them till they become the same. The skintone patch should
blend "into" your +1 square. Voila! Your have mail! Sorry, I mean
you have adjusted face to +1 gray.

Turn off B/W effect by pressing the effect on/off button.
Turn off title mix.

If the surface you want to compare/measure is texturized or not
that even, then defocus. Make it a blurred patch.

After setting exposure, zoom out, compose the shot, focus,
call "action" or what ever you do. Don’t forget to press the record
button before the "action" thing!

Ratio(nal) thing.

Expose for your subjects light side as above explained. Compare
your subjects dark side with your scale. Is it equal with -2? Or -1?
Or black? Adjust fill light so you got the dark side in the desired
zone.

Do another light setup and you can easily place your fill levels in
the ratio you you did in your previous shot. I made the extremes
of the scale black and white. No detail at all in there.

Another variant to do is to find and shoot the exposure for
the minimal black level where detail can still be seen, same for
the white thing. Grab those frames and paste them into your title
jpg at the end of the scale, next to -+2 accordingly.

This will indicate the surface where still some detail in shadows
and highlights will remain. For the highlights this won’t be
necessery. You could use the zebras instead. Off course set to
the %-tage where detail still available is.

FINAL WORDS

You can put the scale on top of your frame if you like. Or on the
left border, or right, or on all four sides. A variation could be a
scale with skin tones exposure zones.

Find some likable skin hue. Example somebody’s forehead. Zoom
in, light flatly, expose for middle value. Shoot. You got your
Zone 0 hue/tone square.

Under and overexpose -+1 and -+2 stops. Maybe -+2.5 also.

Arrange those new hues in Photoshop. I would suggest you
combine them: The skin hue scale on top, the gray scale on
bottom.

So this is the idea that came to me today in the early evening.
I did it and wanted to share it with the rest of the XM2 users.

I hope it will help you in better using your GL/XM2 babe.
Any comments and suggestions are welcome!

PS: I did now new zone shots.

Interesting thing that appeared was the vigneting occuring on
wide open apperture that was discused here in some thread. In
my previous shots of the white surface it was not there. Now one
shot was so obvious.

My first scale was Black, -2, -1, 0, 1, 2, White
I made now a 8 zone scale: -3 -2.5 -2 -1 0 +1 +2 +2.5
+2 and +2.5 look the same in the EVF and LCD.

All best, Igor.