The first thing you need to do is figure out the focal length of your Holga. Your focal length (distance from the lens to the film when focus is at infinity) equals the image distance for a far away subject. The Holga’s focal length at infinity is 60mm and sources vary as to the actual f-stop but most agree it’s either f/8 or f/11.
A diopter is basically a magnifying glass that you can attach to the end of your lens. They come in various strengths ( +1, +2, +5, +10…) and can be stacked together to achieve super-close-up capabilities. The diopter strength is basically the inverse of your focal length.
To use the diopter on your Holga first secure it to your lens. You can either use tape like I did in this picture. My +10 diopter is a 49mm and it is exactly the same size as my Holga lens so if you got a 48 1/2 mm size, it would probably work. You can also use the Cokin filter system.
When using diopters set your Holga to infinity (the mountain symbol). Because you can’t preview your images in a Holga you have to guess how close you can get to your subject. There’s a really scientific close-up lens calcualtor from Schneider optics that is available to save as an Excel file. The Schneider chart can be a little overwhelming to use when you first start out but fortunately there’s a more basic chart (re-posted below) available from the flickr Macro Holga group. Check them out for some superb examples of macro Holga shots and pick their brains for great advice:
+1 diopter = 1 meter (3′ 3″)
+2 diopter = 0.5 meter (19.5″)
+3 diopter = 0.333 meter (13″)
+4 diopter = 0.25 meter (9 7/8″)
+5 diopter = 0.20 meter (7 7/8″)
+10 diopter = 0.10 meter (3 15/16″)
This gives you a good place to start but in order to get really precise and truly focused images you need to do a little experimentation. With the +10 diopter attached to my Holga, set at infinity, I set up some toy blocks at staggered distances of 3″, 6″, 9″, 12″ and 18″. I carefully measured the distance from the lens to the block and checked my results using my Holgaroid back.
As you can see from this picture, the block all the way to the left at the bottom of the picture is the most in focus. If I recall that block was indeed almost 4 inches from my camera lens. Now, how was I to replicate this in the real world? There are a couple methods. One, take a string and cut it to the size of your focal length so that when stretched from lens to subject one end will be at your camera lens and the other end at your subject. Two, you can use your body, which is what I do. It’s not as accurate as the string but it’s a little more convienient. The distance between my wristwatch and the tip of my thumb was about the correct length and I’ve achieved some pretty nice results using my “rule of thumb” (pun intended).
So that’s it. I’ve used the same process when experimenting with macro Lubitel shots but because I don’t have the instant feedback of the Holgaroid my process takes much longer and is a little less exact. You can figure out your focal length without the Polaroid back on your Holga but I recommend that for each frame of film you document exactly what you did so that all your hardwork makes sense when it comes back from the photolab. I hope this helps some of you aspiring macro photographers!