Lightweight Triplet Super-Apochromat Refractor

The Russian Lomo 80mm f/6 and f/7.5 OK4 triplet apochromats are considered by many to be among the finest 80mm refractors in the world. However, they are also known for being built like tanks. My APM Lomo 80mm f/6 in a William-Optics tube and with a Feathertouch focuser weighs 4.26 kg (9.4 lb) all in, which is heavy for an 80mm refractor.

Here we see the weight with a typical 18mm AstroTech Paradigm ED eyepiece, 2" diagonal, tube rings, and small Vixen dovetail:

On the other hand, the modular Borg refractors are well-known for being supremely portable and lightweight. However, they have been less known for being at the pinnacle of optical performance.

So I wondered, what if you could marry the best traits of the Lomo OK4 triplet and the Borg refractors?

Behold - the Lomoborg:

It is constructed from the 7803 80mm diameter x 205mm long Borg tube and the 7835 helical focuser. The tube ring is from a Takahashi FS-60. This setup was for my Borg 76ED, which has a 500mm focal length. The OTA is a little too long for the Lomo 80mm f/6 which is a 480mm focal length, so some eyepieces won't reach focus (the 18mm AstroTech Paradigm ED eyepiece barely reaches focus with a 2" diagonal, with about 2mm of in-travel left).

All-up weight is 2.9 kg (6.4 lb) which is a win!

In comparison, the Borg OTA with the 76ED objective weighs 2.46 kg (5.4 lb) so the Lomo objective adds 1 lb of weight.

The Lomo lens was adapted to the Borg tube using a 3D-printed adapter, which is secured to both the lens cell and the Borg tube using 3mm grub screws - not an ideal arrangement. For an actual production setup, the adapter would need to be made of aluminum and with threaded ends. Also, some sort of dew shield would be necessary.

3D Printer Use Case: Repairing a Dented Lens Filter Ring

I dropped this ancient Schneider-Kreuznach Retina lens on the floor, dinging the filter ring:

To repair it, I 3D-printed two plastic pieces (in HIPS with 100% infill) one matching the inner diameter of the filter ring, and the other matching the outside diameter:
Some ugly use of a C-clamp (the clamp's thread managed to put some marks on the opposite side of the lens filter ring, d'oh!):
And the result: leaves something to be desired, but still an improvement over the original damaged filter ring.