Such a long name for a simple device. Good thing is: the name itself is pretty self-explanatory. It served only one simple purpose: to protect a reversely mounted lens's rear optics/base from dust. It's meant to be used along with a reverse adapter ring, which holds the lens to the camera body via its lens filter thread.
Nikon has a BR-3 widely available for this, while Pentax (I am not sure about other manufacturers) doesn't have such offering. The only option for me is to make one from scratch. Spyglass from the PentaxWorld forum suggested that I could drill a hole on a rear lens cap as mini-hood, thus came the idea to add a step-up ring to it and make an equivalent of BR-3.
Below is my steps in making the bayonet mount adapter ring. I'd suggest one to buy if available, as the drilling step could be dangerous, and it might be much economical in total. BTW, these steps are generic to all SLR lens mount.
Materials & Tools
A bayonet mount type rear lens cap. You'll need either the after market type (top) or the original (left, with extra flange). Avoid those cheap soft plastic push-in rear lens cap (right, mine came with the smc P-DA 18-55mm F3.5-5.6 AL II, aka kit lens), they are not fit for the purpose.- A 49-52mm step-up ring. Larger size step-up ring might be too large to be glue onto the rear lens cap.
A high speed power drill, with a cutter for rigid plastic. Spyglass recommended this, while I used what I managed to borrow from my friend - a high speed tile cutter.- An 8" half-round file.
- Transparent/non-coloured fast-dry epoxy glue (AB-glue). Avoid Superglue at all cost! Superglue will leaves white marks when dried.
That's all you'll need for making the adapter ring. Generic steps as followed. I assumed that you posses the required knowledge and skills on using the tools mentioned, i.e. how to use a power drill, how to file, and most important of all - keep yourself safe!
Steps
1. Remove the center piece of the rear lens cap.
1.1. Use the power drill to make a series of holes. Few things worth taking note:
- Even an after market rear lens caps is made of rigid plastic - they are really hard.
- You might want to begin with doing some test drilling on the middle part of the cap.
- When start making hole, drill the cap with its logo facing DOWN, as shown in the test drilling photo.
- When you are trying to enlarge the holes made (to connect them), flip the cap over and drill it slowly and carefully, especially if you are using your hand to hold the cap.
1.2. Use a half-round file to worn-away the horn-like remaining. The aim is to make a perfect round - as close as possible. You can leave some small space next to the cap's perimeters. The file is very effective tool, be careful not to overdone it.
2. Clean and wash the rear lens cap with clean waters. Dry it.
3. Mix the epoxy glue. The instructions of the fast-dry epoxy glue that I used said it will dried in 5 minutes, so I have only 3-4 minutes of working time.
4. Apply the mixed epoxy glue onto the top of the cap's perimeters. The aim is to have enough glue to hold the step-up ring to the cap's perimeters. Excessive glue are not necessary helpful and can be ugly.5. Align and glue the step-up ring to the cap, with the 49mm (male filter threads) contacting the cap's top.
6. Done! Let the new adapter ring for about 16-hour (the epoxy glue that I used needs 16-hour to be fully hardened).
A finished product should like like following. One should be able to screw any matched filter to the glued step-up ring.
Here's how the whole setup (a reversely mounted lens onto the DSLR body using a reverse adapter, while the rear lens mount is covered by the newly made bayonet mount adapter ring with an UV filter) looks like.
If you read until this line, you deserved to make one yourself. Have fun! ;)
