I have a hobbit of picking up stuff that I think they might be useful in the future, if not at the moment. The extension tubes, filters, old lenses etc., that I picked up many years ago are now finding use in my DIY lenses. Of course it has the bad side effect of having too much junk in the house, but let's not talk about that :)
Just a bit more on the helicoids that I used, and I don't think I mentioned that in my last post, is that the Vivitar 2x macro teleconverter helicoid has a 55mm thread, and my Yeenon 18-33mm has a 52mm thread. This means I need tubes in both sizes. But I don't normally use the 18-33mm helicoid for long lenses, so we will just concentrate on the 55mm tubes.
Tubes of various sizes
In the hay days of Point & Shoot cameras, manufacturers, and third parties made a lot of accessories for them, and the "Lens Tube" was one of the most popular ones. Basically it's a metal tube that replaced the tube on the existing camera and provides a 52mm or 55mm thread for the filters. I have a few of these from Fuji, Nikon, Olympus, etc. Some of them have non-standard threads on the camera side, but some are standard 55mm, so they are essentially 55mm extension tubes, which is very useful for my purposes. Most of these tubes are around 4 cm to 5 cm in length
If you don't have any extension tubes lying around, and you must buy them, I suggest a search on NEX extension tubes on eBay. You can buy a 3-section tube, with a length of about 50mm, and it comes with an E-Mount for about $8. I bought three sets of these and you can stack them when you remove the E-mount. Unfortunately, the mount is terrible and they don't fit well. Too much play which is very annoying. Another annoying thing is that the thread on these tubes is non-standard. It's just shy of 58mm. This means you can't use filter rings to add spacing in smaller steps. What I ended up doing was to get rid of the sections with mounts, and use only the tubes. For the tubes, I glued a 58mm filter ring to the female thread side, and put on a 55-58mm step-up ring, so that it would accept 55mm filter rings. On the male thread side, I glued a 62mm filter ring on it, and then screwed a 55mm-62mm step-up ring to make both ends 55mm.
Extension tubes from eBay converted to 55mm female/62mm male threads.
For those of you who use a M42-M42 helicoid, you can get a 62mm to M42 conversion ring; this allows you to mount the tubes to your M42 helicoid. More on this below.
In the beginning, when I was experimenting with adapting lenses without focusing to digital cameras, I used a lot of filter rings to make tubes, because I have so many (at least a couple hundred in various sizes). They work great, except they look really weird with all sorts of brand names on them. These filter rings are necessary because the extension tubes tend to be very thick, with the thinnest at about 10 mm. This is not good enough for infinity adjustments. If the spacing is longer than necessary, close focus distance will increase. In most cases, I use a combination of extension tubes with filter rings to get infinity focus or just slightly beyond. Sometimes, I bring a couple of them with me, in case I wanted to focus closer, I would just screw on the filter rings between the tube and the lens. Most filter rims are made of aluminum. Rare ones are made of plastic, and the best ones are made of brass, by B+W. B+W are my filter ring of choice.
Filter rings of various sizes.
Step-Up and step-down Rings
Step-up rings are conversion rings that the male thread size is smaller than the female thread size. For example, if you have a lens with a 49mm filter size, but you only have a 52mm size filter, you will need a 49mm-52mm step up ring. The reverse is true. A step-down ring has a larger male thread size than female thread size. These conversion rings come in amazing number of sizes and are usually quite inexpensive. Another useful conversion ring is the L39 to M42. Many enlarging lenses have a 39mm thread size and with the L39 to M42 converter, you can mount the enlarging lenses on the M42 helicoid. They are one of the most useful accessories to have, for those of us who do not have access to metal lathe or NC tools to make our own adapters.
Step-up/down rings of various sizes
In Part V, we will talk about the importance of lens hoods.