Wow! That sounds a little scary. doesn’t it! I think so, or rather I did until I started playing around with it! The technique is basically just as it says. It’s a multiple exposure image done in camera. While you’re still composing the images and selecting the settings there are still things you can’t do that you could do if you were creating a multiple exposure in post processing. You can mask out part of an image or most of an image. You can edit the image before using it. When doing it in-camera though, those options aren’t exactly readily available.
You’ll have to check your camera manual to see what options you have available to you. Many of the newer mirrorless models have a lot of options but the older you camera the more limited your options are, most likely. You might be able to do two images or nine. You might have the option of a few blending modes or two.
As usual I didn’t do a whole lot of research. I just jumped in and started playing. I didn’t have a lot of keepers or any if I’m being honest! But I had my camera in my hands and was trying to understand what all the fuss was about! From my disorganized way of experimenting I realized two things right off the bat. Trying for a double exposure first was going to be the easiest. And using my camera’s option of average mode was also going to make my life a bit easier. When using average your camera will average the exposures out. You see I tried “add” first and wondered why all my images were over exposed. This is why your camera manufacturer gives you a manual. I’m learning too!
I haven’t mentioned lenses yet and for good reason. I’ve had a little success with every lens I’ve tried so far. I haven’t tried a long zoom yet though, but that doesn’t mean I won’t try it. Who knows. I might like it! I have tried using one lens for the first image and different lens for the second image though. This is not possible with all cameras so check your manual but think of the fun if your gear allows! I have used my kit 24-70 f/4 Nikon Z lens, but only once. The rest of the time I’ve played with the Lensbaby Double Glass ii and the Velvet 56. I plan to explore with the Edge series though….think of possibilities using that sliver of focus!
There are several ways to do multiple exposures. Some people use the darker areas as a window if you will. Think of a silhouette of a person where another images shows up in what would have been the darkened area of a person. Some people like to do one in focus and one out of focus image. Some like to line them up next to each as I have done above with this four image multiple exposure! There’s no right or wrong. There’s what makes you happy. While it’s easy to teach this technique it’s not always so easy to teach what images work well together because while it might work for me, it might not work for you. And vice versa! So what’s my advice to you? Just play with it. But start by bringing a lighter subject in through a darker area of a different subject! Then go from there!