I recently remembered that I had a few photos left in my polaroid spectra. I have a model that has the self timer and contrast features. I couldn't remember exactly how/when the photo came out after taking a picture using the self-timer and I accidentally figured out how to do multiple exposures!
The picture doesn't come out right away if you use the self timer so all you need to do is push down the lever that opens the door to the place that the film is stored after the first photo has been taken. MAKE SURE you are holding your hand over the door while you push the lever. It will open just a tinch and then you should close it again. You'll feel a little click.
Set up the camera to take another photo using the self timer. You should also try to make this photo a little darker using the contrast switch. After it has taken the photo move the self timer switch and the photo will come out. Viola!
This is an example of what the images look like before doing anything to them: 
Very light, right? It looks cool but it's hard to make out the details.
To make them look better I scanned the images and messed with them in Photoshop as they originally came out pretty over exposed. I used the "apply image" setting, you can mess around with the overlay settings within that feature to see which one looks best to you. I Then fiddled with the brightness/contrast settings and levels until the image was more visable.
I just found this page that has information about this very process! Their directions are probably easier to follow than mine- however, they are for a spectra without a self timer.
