How To Use In-Camera Blend Modes For Multiple Exposure Photography (Pt II: Additive Mode)

In my last post, which focused on the use of the Average blend mode in multiple exposure photography, I mentioned that the Average and Additive modes give results that are most like what people think of when they imagine what a multiple exposure photograph looks like. That is to say that they look very similar to what a multiple exposure from a film camera would look like. If you haven’t had a chance to read that post, you can read it here.

So let’s delve into Additive mode and see how that works. If you recall, when using the Average blend mode the camera does some fancy calculations for you, freeing you up to be creative. More specifically, the camera calculates the exposure for each component image of the multiple exposure so that they are all given equal weight and so that the final image is correctly exposed. The specifics are in that last post.

Now imagine that you are in Average mode and that you could tell the camera to just take a little break and not do those calculations. And that, my friends, is Additive mode. It is just Average mode without the camera doing those calculations to help you out.

“But wait,” you say. “Why would I want the camera to not do those calculations? I hate math and want to focus on the image I’m creating. So I’ll never use the Additive blend mode. Let’s get rid of it.” OK. I see your point. But here’s the thing, remember I said that when using the Average mode the camera does calculations to give each of the images that make up the exposure equal weight? There is something in that statement that you could potentially use creatively. What if you don’t want to give each of the component images equal weight? What if you want one (or more) of the images to make up more of the final result than some of the others?

Here are a couple of examples. Let’s say you are photographing a flower. Might it be interesting to combine a wide open aperture image of the flower with very limited depth of field with one at a small aperture that renders most of the flower in focus? Might it be fun to photograph the flower completely unfocused and combine it with an in-focus image? And then what if you could weigh the final image either towards the exposure with a deep depth of field (or the in-focus one) or towards the one with the shallow depth of field (or the out-of-focus image)? You can in Additive mode.

What if you wanted to make a multiple exposure image and, as part of that final image, photograph something that serves as a textured background? Couldn’t you do some creative things by weighing the final result towards or away from that background. Yup, you can do that with Additive mode. I think you get the idea.

So now that you have the gist of the mode, how do you actually use it? The first step is to understand how to use it to emulate Average mode. You wouldn’t necessarily want to do that since you could just use Average mode and be done, but understanding how to give each component image equal weight is the first step to understanding how to give any of the component images unequal weight. So let’s dive in.

If Additive mode is like Average mode, but with you doing the exposure compensation to weigh each shot equally, how do you figure out the compensation. Without going into equations, here is the answer (which depends on how many shots are in the multiple exposure, since each shot lets in more light). To emulate Average mode while using Additive mode use this table:

• For 2 exposures decrease the exposure for each shot by 1 stop (exposure compensation -1)

• For 3 exposures decrease the exposure for each shot by 1.5 stops

• For 4 exposures decrease the exposure for each shot by 2 stops

• For 5 exposures decrease the exposure for each shot by 2 1/3 stop

• For 6 or 7 exposures decrease the exposure for each shot by 2 2/3

• For 8 exposures decrease the exposure for each shot by 3 stops

So let’s see a real life example using this tacky wedding cake ornament. This is a single shot at f8 straight out of camera and converted to a jpg.

Single in-focus exposure.

© Howard Grill

The next photo is a 4-shot multiple exposure using Average mode, with three of the exposures thrown out of focus and one of the exposures in-focus. All 4 shots were made using no exposure compensation. You can see how the one in-focus exposure appears to be weighted equally with the other exposures in terms of brightness

Average mode 4 shot multiple exposure as described above.

© Howard Grill

Now let’s look at the exact same results using the Additive mode, but, since there are 4 exposures, I will underexpose each of the 4 by 2 stops, just as the table tells me to do (I am hand-holding so the degree of movement between each exposure will be different, but I believe the point will still be made). As you can see, the results in terms of the prominence of the in-focus photo is essentially the same as in the Average mode, which we have now successfully emulated by manually equally reducing the exposure for each photo.

Additive mode emulating Average mode as described above.

© Howard Grill

But, as I said, the benefit of using Additive mode is that you, the photographer, can use your creativity to change the image weighting any way you would like. So let’s say I want to make the in-focus shot more prominent (which would make more sense if this were, say, flower photography). In the following 4 shot multiple exposure, I underexposed the three out-of-focus images by 2/3 of a stop more than the 2 stops I was supposed to in order to achieve equal weighting. That means I need to make up 6/3 of a stop (2/3 stop x3), or 2 stops. So instead of underexposing the in-focus photo by 2 stops, I gave it 0 exposure compensation (making up the 2 stops of light that I had lost). This ‘overweights’ the in-focus image, and the result is seen below. You can see how I achieved approximately the same exposure (there is always going to be a little difference depending on how much dark background I included in the photo since I am handholding), but that now the in-focus image is far more prominent.

Using Additive mode to make one of the four component images of the multiple exposure more prominent than the others.

© Howard Grill

What happens if I try to do the same thing in Average mode, by taking three exposures and then adding +2 exposure compensation to the in-focus image? I get this, and while it overweights the in-focus shot it has also overexposed the photo.

Using Average, instead of Additive, mode to overweight a component image has led to overexposure of the multiple exposure.

© Howard Grill

I know, this all seems complicated. But the bottom line is this. If you want a multiple exposure that emulates film with equal weighting to each of the images, then use the Average blend mode. If you want to be a bit more creative, you can use the Additive mode to give one or more of the images prominence over the others.

In my next post, we can stop worrying about the math and start to get super creative, making mind-boggling and unexpected multiple exposures using the Light (Bright) or Dark modes. Unlike using the Average and Additive modes, the Light and Dark modes yield results that were simply not possible using film cameras. I’m going to show you how, and this will be where the fun really begins.

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