MicrobeHunter.com Microscopy Forum

I got an Oly BX40CY for parts. The brochure from Olympus states that the -CY lowers the nosepiece and stage to make the scope more ergonomic since the stage is closer to the table.

The revolving nosepiece appears to be mounted on a spacer to lower it. But, it’s not an empty tube; rather, it has a very thick (about 20mm) lens in it. It doesn’t appear to have any optical power. It reminds me of the optical assembly above the revolving nosepiece in a BTHU.

Does anyone know the purpose of this optical element? I can’t see why, if the point of the -CY model was to lower the height of the revolving nosepiece and stage, that the spacer on which the revolving nosepiece is mounted wouldn’t just be a hollow tube.

Is this to reduce vignetting since the tube lens will be farther away from the objective back focal plane? Is it for better flat field correction? I think this optical element is a single piece of glass.

Thanks!

Photos

Odd. Theoretically no glass should be needed.

It's a puzzle to me as well.

Perhaps a subtle reference tube length change (just plain glass can do this) so that all the usual BX intermediate accessories can stack without reduced field???

A permanent mag changer?

Somehow putting the tube lens lower to reduce height?

In a quick check it looks like most of the BX40CY scopes come with a tilting ergo head - so the eyeppoint can get pretty low even without the 30mm or so drop in stand height.

You could try pulling it out and see what happens with just a clear parallel path to the head.

Normally, an increase in the length of the infinity portion of the tube can be accomodated. That's one of the major perks of an infinity system. However, one would assume that there are limits to how much length can be added and that the diameter and thus collector surface of the telan lens, designed so that diagonal ray bundles emanating from the periphery of the object are collected , would beyond a certain length be too small. If the length is too long, then some peripheral rays would be lost, lowering resolution, brightness and causing internal reflection. Was the CY idea an afterthought, and had to be fit into an existing optical tube design?
In the Balplan for instance, designed in the 60's and never intended to achieve a 26mm f.o.v. like a BX 40, they put a very wide telan lens, certainly wider than other 20mm f.o.v. infinity systems I have looked at from that point of view. The reason might be because it too has an about 2" extension that can be installed between the nosepiece and limb to allow for reversal of the nosepiece. It's in the infinity space but there are no optics involved, so would cause diagonal ray bundles to miss a smaller telan lens
Maybe Olympus just put a corrector plate in, to shorten the infinity space back to spec.because the telan lens was too narrow to accomodate that extra length.

Explanatory diagram.

Easy to understand diagram

The infinitely distant objective must be matched with a matching (refractive) tube lens for the final image.

This differs from the BHT turret lens which increases the focal length of the objective lens.

The salient point related to the poster's query is that all rays emanating from an infinity corrected objective are in parallel bundles but the bundles are not necessarily parallel to each other. Peripheral rays can be lost and scattered due to the lengthening of the infinity space.