This thread topic may defy conventional forum categories...
Ok, I'm dabbling with an idea for a do-it-myself lens construction. Like so many projects, once I start making a list of all the obstacles and/or necessary parts I begin to feel the thing is hopeless because I don't even know where to begin. In this case, I'm struggling to figure out an effective way of holding lens elements in place. I'm hoping someone can suggest a viable solution in the form of either a pre-existing product or a re-purposed lens.
What I'm hoping to do more or less equates to a moderate telephoto lens in the realm of 100mm. The optical formula is relatively simple - at most, three elements in two groups, or possibly two achromats at opposing ends of the lens. Ideally, I would be using the three-element solution. The fact remains that no matter how many or few elements I'm using I still need a way to
- Secure the elements
- Allow for changing distances between elements to fine-tune the arrangement
- Allow for a focusing method, possibly with the help of a helicoid mechanism
- Have a way of inserting some kind of aperture, either through mechanical means or simple discs (paper, washers, etc.)
There are empty lens tubes available from certain companies (Thor Labs, for one) but these can be rather narrow because they are primarily meant for laser applications. It's tempting to go with one of these empty tubes because the companies also manufacture irises and aperture mechanisms with threading on both sides. This means two tubes can be combined with the aperture in the middle. Nevertheless, these things are all expensive just for the sake of an experiment, and it doesn't even take into account purchasing the glass itself (likely from Surplus Shed).
And speaking of Surplus Shed, I've scoured their site hoping for some kind of turn-key solution without much luck. I've considered trying to acquire a junk lens - the criteria for focusing and an aperture would be satisfied - however it would mean knowing how to properly disassemble the lens. I've taken a few apart and depending on brand, vintage, and seven other variables it's easy to mess up the aperture control or put the lens into an almost permanent state of tinker's parts. Another issue with the junk lens route is that it seems all lenses have elements of diminishing diameters as the construction gets closer to the camera mount. This isn't the end of the world, but for my experiment I'm trying to keep things consistent with elements of the same diameter. I'm actually trying to preserve certain kinds of optical defects, and with my scant knowledge of optics I haven't yet determined how differing element diameters impact the design.
Lastly, I am aware of a gentleman who runs the site JohnnyOptic.com - a relatively small site, but still useful in that he deftly summarizes some optical principals. The majority of his projects involve making lenses for the purposes of macro work. Most of these devices are a cobbling together of things through the use of empty filter rings. I may be forced to follow this path - convenient that the parts are readily available and plentiful - but it would involve creating a cylinder of many smal pieces. I've considered materials like PVC, but I have yet to find a method of successfully installing elements. Staying within the boundaries of photographic materials is useful because it means matching threads sizes, not needing to paint things black to avoid reflections, etc.
Any thoughts? Sorry to make it go on and on. Like I said, there's a lot to consider and I don't want to leave anything out that could later rule out an otherwise sound suggestion.