Wista loupe: how adjustable the focus is, and "duct" type loupe alternatives.

Good morning! I am considering buying a Wista duct-type loupe (picture below), which I believe should be high 12-15 cm approximately. I wonder (and ask) if its focus is *widely* and by *widely* I mean *widely* adjustable, even through the extra thickness of the fresnel lens, and for both near and far sighted people?

I ask because I have previously bought a Gaoersi duct-type loupe, which is besically a tube a dozen centimeters high. When I received it I thought I had struck gold, it was so easy to handle, but very quickly I came to realize that it's dark, doesn't magnify very much, but most of all can't really focus through the fresnel lens as its focus is "adjustable" only in the wrong direction.

Before buying the unusable Gaoersi, I've always used a very simple linen (thread counter) approximately 10X, and it has always worked wonderfully, it is much brighter than the multi-lens Gaoersi, except that it's a tiny object and it's uncomfortable to fit (it, as well as my head) inside the leather flaps of the finder of my Linhof. I am really frustrated, I wonder how is it possible that a few bucks linen can be so much better than a complicated multi-lens loupe.

Are there other alternatives? Once again: I'm looking for a tall, duct-type loupe, in the 8X or better 10X range. In general I'm not interested in flat stuff hard to handle inside the flaps, or as big and heavy as a prime 50mm lens. Thank you!

Attachment 210837