I had a first encounter with the Kowa 1.6x Extender on a Kowa 883 & 25-60x wide zoom today.
Briefly, it is excellent and just as good as could be hoped for.
- Very little additional light loss. When viewing through just the extender alone, against a brightly lit white glass shelf very much like a light table, there is barely perceptible darkening through the lens, almost none. So little that if the alternative would be a dedicated eyepiece with a 40-96 range, I doubt I could see a difference to the zoom-extender combo. Coatings look very good.
- Image quality looks just the same as with the eyepiece without extender at corresponding magnifications. I had limited time so did not check fields of view.
- Sharpness, contrast and illumination is limited by the scope, not the eyepiece-extender combo. And the scope is very good indeed and can easily take magnifications up to the 154x I tried (will get to that in a minute).
- Just as without the extender, the image is sharp from edge to edge, with exceptionally low levels of lateral CA. Of course, as magnification goes up, the later CA there is becomes easier to see, but there is so little that it does not become objectionable.
- The extender is very compact, and adds less than an inch to the overall length of the eyepiece. It mounts very solidly and inspires confidence. It threads onto the male thread at the base of the eyepiece bayonet, the same thread that Kowa's digiscoping adapter threads to. In order to facilitate the digiscoping adapter, there's another identical male thread on the extender, under a plastic cover ring that screws off. The eyepiece bayonets on the extender, and there's a small metal safety pin/latch to prevent accidental eyepiece removal. For intentional eyepiece removal, the knobby needs to be pushed towards the scope body, not pressed down, while turning the eyepiece. There's a white arrow on the extender body to indicate the direction of movement, but for those who do not read instruction or look for these kinds of things, there's a risk of breaking the pin by incorrect operation and excessive force.
- The big surprise for me is that these extenders can be stacked. Since there's that digiscoping adapter mounting thread, on it, you can mount a second adapter onto the first just the same as the first to the scope body, and can keep adding if you wish. I tried it with two, which gives a range of 64-154x magnifications, and the results were just as good as could be expected with a high-quality 88mm scope at those magnifications. It will take much more rigorous testing to evaluate how much useful resolving power one gets in daylight viewing with the 100x + magnifications, but for birders who wish to use their spotter for astro use the 883 with a double extender at 154x would be an excellent planetary viewing scope.
I'll do a detailed review later, with comparisons to my ATX 95, but I think I can already say that for those who have a good 883/4 and do serious birding, the extender is a no-brainer. I would personally also choose this combo over the Swaro ATX 85. Compared to the ATX 95, these two have slightly different strengths, so if I could afford it I may wish to have both. As it is, I will most likely stick to my superb ATX, but if I were coming into premium scopes from something less spectacular, I might have to think about the choice a bit.
Kimmo
