140-200mm variable length eyepiece tube for a microscope

This eyepiece tube has an adjustable mechanical length. This compensates for different back focal lengths of objectives.

Tube length range is from 140mm to 200mm, the scale value is 1mm.

Originally, the RMS standard tube length was 160mm. But different manufacturers presented objectives purposed for different tube length.

You can still get a focused image if the objective purposed tube length and actual microscope rube length differs, but this may increase image distortion and chromatic aberrations.

That is where the variable tube comes useful to achieve a better image quality.

The variable tube consists of the two parts:

1. The body with a 41.4mm dovetail mount (unfortunately, I don't know which exactly microscope it was purposed for). The flange diameter is 52mm.
2. The inner sliding tube that has RMS female thread at the bottom end, and can accept common eyepieces with 23mm diameter on the top end.

This inner tube has 111.5mm length, and can be used separately as a simple handheld microscope if you add some low-power objective and eyepiece to it.

The image quality will be not the best possible, but enough for fun or quick initial research.

This tube seems to be a rare thing, and it can have a collector's value as well.

Unfortunately, manufacturer is not specified