9.06.2020 Kowa TSN-884 1.25" astro eyepiece adapters & binoviewer.

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I purchased the astronomical eyepiece adapters at the same time as the telescope. I have inverted one of them for the photograph to show the details but they are essentially identical. Which seems rather pointless. The thumbscrews make it impossible to screw in the adapter!

The one with the hidden grub screws means that the eyepiece has to be fixed into the adapter first, and the grub screws tightened, before insertion into the telescope. The zoom eyepiece having been removed first to expose the internal thread.

I mention this early in my description of the telescope system because I want to try binoviewing with the superb Kowa optics. Which meant using one of the adapters to hold the binoviewer spigot firmly in place.

These images show how I tested the basic concept using an old, no-name 20mm eyepiece and one of the adapters. I was easily able to reach focus [and well beyond.] While the resulting image was superbly sharp and bright. Providing a power of 25x to match the lowest zoom magnification.


The images on the right right show the result of removing the ring which protects the large male thread intended for digiscoping and also to accept the 1.6x Kowa Extender.

The Extender is a sophisticated form of negative lens [Barlow lens] used to amplify the original telescope [zoom] powers from 25-60x up to 40-96x! Which suggests it may well have astronomical uses as well as to bring in very distant wildlife subjects. More on this subject later when I have had a chance to try it more thoroughly.

Well that was disappointing! Despite using a full compensation [2.6x105mm] T-S, Glass Path Corrector on the nose of the Telescope-Service binoviewers I could not reach distant focus in the Kowa. I screwed the adapter in first and then pushed the binoviewer gently in as far as it wanted to go. It still could not focus much beyond 30'. I was at the full range of the '884s focusing knobs. Odd. I thought it might work. The ordinary astro eyepieces have plenty of inward travel to find distant focus.

Mystery solved: Despite the dealer's claims, the 2.6x GPC is not fully compensating for the binoviewer. I checked on another telescope with lots of room to focus inwards. The T-S GPC is 20mm short of full compensation. Since the binoviewer cannot be physically pushed 20mm inside the Kowa telescope it cannot possibly reach distant focus. The magnification is rather high anyway with the 2.6x GPC.

In late sunshine I had a look at a Blackbird perched on the ridge of a distant roof, at 175 yards, at 96x. Every detail of his glistening plumage was clearly visible. As were the details of his eyes. That is a truly remarkable, optical performance from the Kowa!

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