In my case I own a set of Cokin "P" series of B&W filters, and a P series ring to fit 58mm threaded lenses. My other film camera is a Mamiya 645 medium format, and while it shoots great pictures it doesn't do wide format landscape. My family purchased the new Holga 120Pan, which shoots 6x12. I was so excited to get it for Fathers Day this year! They ordered it from Freestyle Photo, which is a great resource for analog photography.
When I received my new Holga, Freestyle was kind enough to include a book with the history of the Holga. There was also a lot of info on accessories, where it stated you can "Firmly twist the step-up ring into the pliable plastic lens of the Holga." (quoted from page 33). I prefer not to do this because it is far too easy to get the ring on crooked, or not on firmly enough and have your expensive filters fall to the ground. My process involves removing plastic from the inside the front of the lens (about 1/2 a millimeter) in order to press fit the step-up ring into it.
The steps below will take you through gathering your tools and supplies, disassembly of your Holga (the steps will also work for a standard Holga), fitting the step-up ring, and re-assembly. I highly recommend removing the lens to avoid breakage or scratching.
P.S. Hooray for my first instructable! I hope you enjoy it!
Added June 27th, 2012:
IMPORTANT! : I just received my Holga Shutter Release for long exposures and found out that it won't fit over my step-up ring... OOPS! Not a real big issue, though. If you go to put yours on and it won't fit, just take the lens off and put the Shutter Release on, then re-install the lens.
P.S. I just shot part of my first roll of film with the camera and used my polarizing filter. I'll post a few scans after I finish the roll, which won't be until Friday the 29th.
Step 1: Gather Your Tools and Supplies
1. A small screw driver
2. Thick tape (I used Gorilla Tape - available at Lowes or Home Depot)
3. An RX bottle (mine was a T-20 size - located on the bottom of the bottle), or a similarly sized strait sided cylinder. It must fit close inside the Holga's lens
4. Sandpaper - 220 grit will work the best
5. A hobby knife
6. A flat surface
7. A clean towel - not shown
8. A can of compressed air
9. A step-up ring to fit your filters.
10. Epoxy of your choice (if you intend to attach the step-up ring permanently) - not shown - 5 to 20 minute cure times recommended
11. Mineral Spirits (if you will be using epoxy)
12. Paper towels (again, if you will be using epoxy)
Step 2: Remove Your Holga's Lens
2. Locate the two screws that hold the shutter assembly onto the front of the camera and remove them.
3. Carefully remove the shutter assembly and lens from the camera body. There are two wires attached to fire a slave flash. Be careful not to pull on them.
4. Unscrew the Lens Stop Screw. You do not need to remove it completely, and I do not recommend that you do.
5. Unscrew the lens from the shutter assembly and remove it.
IMPORTANT : Do not bump or remove any of the springs. Also, the shutter release lever may fall out of the shutter assembly. Don't panic... you can put it back in right before you re-attach the shutter assembly. It falls out easily.
Step 3: Prepare the Lens and RX Bottle
2.Tape the front of the lens with blue painters tape. Cut around the outside of the lens ring with your hobby knife and remove the excess.
3. Wrap a single layer of your tape (more if yours is thin) around the RX bottle. Be sure to keep it even at the bottom. Overlap the tape and cut through both layers to get a perfect seam.
NOTE: Most RX bottles have a slight taper to them. The bottom has a smaller diameter then the top. Stretch your tape to keep it even on the bottle.
4. Tape on a piece of your 220 grit sandpaper that goes between 1/3 and 1/2 the way around the bottle. Keep the sandpaper even at the bottom... use your flat working surface to make this easier. This is important so that you can sand all the way inside the Lens. Also, keep the tape holding the sandpaper on at least 3mm above the bottom.
Step 4: Sanding and Fitting the Ring
2. Place the RX bottle inside the front of the lens.
3. Begin sanding by rotating the lens around the RX bottle. You will need to apply light pressure to the RX bottle to keep the sandpaper in contact with the lens body.
NOTE: You will have to clean off the sandpaper regularly to keep it from clogging. I used my can of compressed air to dust off the sandpaper every 2 or 3 rotations of the Lens.
When you notice that the RX bottle is fitting a lot looser inside the front of the lens add another layer of tape and continue sanding. Don't forget to check the fit of your step-up ring every so often. You want it to fit very snugly inside the front of the lens, especially if you don't want to epoxy it in place.
Once the step-up ring is fitting snugly inside the front of the lens you are done sanding. If you want to permanently attach the ring you may move onto Step 5. If not, you are done!
Step 5: Epoxying the Ring (Optional)
1. Make sure the tape on the outside of the lens will not be anywhere near the front edge of the lens. You don't want to epoxy the tape to your lens!
2. Mix your epoxy in the proper proportions, and mix it thoroughly. I used a tooth pick with the end cut off and flattened.
KEEP YOUR WORKING TIME IN MIND! Once the epoxy is thoroughly mixed you will have roughly 2/3 of its working time to get the ring in place AND clean up any excess!
3. Coat the threads of your step-up ring with enough epoxy to fill the threads with very little extra. Do not get epoxy on the bottom of the threads as any extra will squeeze out while pressing it in place. It will be very difficult to clean any excess epoxy from inside the lens!
4. Clean up any excess epoxy with a paper towel and mineral spirits. Use the mineral spirits lightly.
5. Wait for the epoxy to cure thoroughly before moving onto the final step.
Step 6: Re-Assemble Your Holga
Don't forget to : 1) Remove the tape from the back of the lens, and 2) make sure the shutter release lever is in place.
Remove the blue painters tape last.
NOTE: If you have opted to attach the step-up ring permanently, you will need to get a new lens cap to fit it. You can get one from your local camera shop, or online.
Enjoy using your already purchased filters with your Holga!