These are instructions for making an inexpensive protective case for a camera lens. It features a low-friction inner lining, a durable outer covering, and a securely fastened lid.
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Step 1: Assemble Supplies and Tools
The case is constructed of urethane packing foam, polyethylene (as from a bottle), a Tyvek envelope, Velcro, gaffer tape for the cover, and clear packing tape and plastic mending tape to hold things during assembly. We will also need a cylinder of the proper diameter to serve as a mandrel, and measuring, marking, and cutting tools. You will likely want to put masking tape on the foam so you can see your marks and cut accurately. Don't use duct tape - the gaffer tape is more durable, and its adhesive does not dry out over time.
Step 2: Measure
Carefully measure the lens. Before deciding on the length, consider whether you want to add a UV filter to protect the lens, or a tether for the lens cap using a self-adhesive button. You will likely want a rear lens cap. For each of my lenses, I actually use two rear caps taped back to back. This simplifies switching lenses. The mandrel for this lens is a PVC pipe shimmed out to the proper diameter (about 1/16" larger than the lens).
Step 3: Sketch
Draw a sketch with your dimensions. I suggest foam one half inch thick, but you can adjust that depending on how much space you have and how much protection you think you need. The length of the foam needed to wrap around the lens depends on the effective circumference. I suggest cutting the foam a little extra long and trimming it as shown in the next figure. The extra length (a bit more than the thickness of the foam) accounts for two effects: First, in the final cylinder the whole inner surface of the foam is under compression, whereas for this wrapped shape, part of the foam is straight, and for that part the inner surface is relaxed. Second, you are applying pressure to get the foam to conform to the mandrel, whereas we want the final cylinder to just touch it without applying any pressure. You may want to cut a narrow trial strip (for a one inch long "tube") and check that it just slips over the Tyvek lining. The lining needs to be about three inches wider and a half inch longer than the foam.
Step 4: Inside Lining
Wrap the lining around the mandrel, with the printed side out, and fasten it with transparent mending tape first on the inside then on the outside.
Step 5: Cut the Foam
Cut the foam to the chosen thickness. I'm using a bread knife with half inch thick guides. You can also use a saw, which would allow a longer tube, but leaves many foam crumbs to clean up.
Step 6: Wrap and Tape the Foam
Wrap the foam around the lining and tape it.
Step 7: Test Fit
Pull the foam and lining off the mandrel and test that the lens fits easily.
Step 8: Cut Tripod Foot Relief
If your lens has a tripod mounting foot, then at this point in the assembly, you can cut a relief slot in the lining and foam, then tape a polyethylene patch on the outside where you can fasten the lid. (This case has a simple lid that I have not yet upgraded to the more recent design.
Step 9: Secure Lining
Cut the lining into pointed tabs. Wrap each point around the outside of the tube and stick it down with a bit of tape. Leave enough of the foam exposed for the gaffer tape to stick to.
Step 10: Add Bottom
Cover the bottom similarly. Insert it into the tube, positioning it on the mandrel for support.
Step 11: Cover With Gaffer Tape
Cover the outside with lengthwise strips of gaffer tape.
The gaffer tape adhesive is strong. You can use this technique to ease unrolling the tape.
Cut the bottom end of each strip into three tabs. Make one of them long enough to reach to the center, but trim the other two into shorter triangles. Stick down the short triangles first, then the wider tab. The aim is to cover the entire bottom without creating a thick mound in the center.
At the top, cut each strip into three tabs that do not quite reach the inner surface of the tube.
You may finish with a narrow strip.
Step 12: Cut Top Plate
Cut a circular paper pattern for the top plate, 1/4" smaller than the outer diameter of the tube. Tape the pattern to one side of a sheet of polyethylene. Apply two strips of gaffer tape to the other side, with a gap of 1/2" or so between them. Cut out the plate and the two pieces of gaffer tape at the same time. Peel off the semicircular pieces of tape for use later.
Step 13: Assemble Top
Line the top with two more strips of gaffer tape, again with a gap between them.
Cut the overhanging tape into tabs.
If the polyethylene is curved, take advantage of it - put the convex side up, and orient it so the hinge and closure will be at high points. That way the curvature will help hold the lid closed on both sides.
Fold each tab around the foam and around the edge of the top plate, then apply the large semi-circles cut earlier.
Step 14: Attach Top
Put the top on, then apply the single strip of gaffer tape that fastens the top to the tube and also forms the hinge and Velcro closure. Note its folding path at the top of the sketch.
Finish by sticking the end of the tape to the lining.
Step 15: Add Velcro Closure
Apply a patch of Velcro loops to the side, and a matching patch of hooks to the tab.