Newbie question - Eye to eyepiece distance

[The Sparrow]

I've googled all over for this but not many clear answers.
Should my eyes be really close to the eyepieces?
I'm getting some eyestrain as my head movement causes misalignment and the black outer limits of the viewing area to move around.
My ##### eyelashes get in the way a lot too.

can any of you experienced folks teach me a bit.
I have a binocular scope. I wear glasses but have been removing them.
I can get nice viewing, but my eyes are really really close to the eyepieces.
Does that sound right?

[rjlittlefield]

The proper head position depends on what you have for eyepieces.

If you hold a piece of tracing paper above the eyepiece, you can see that the light coming out of the eyepiece forms a sort of double cone: broad right next to the eyepiece, then getting narrower, then getting wide again. The location where the cone is narrowest is called the "exit pupil" of the eyepiece. Your head should be positioned so that the pupils of your eyes coincide with the exit pupils of the eyepieces.

Eyepieces that are designed for use with eyeglasses have exit pupils that are located relatively far from the eyepiece, a so-called "high eyepoint position". It sounds to me like your eyepieces are not of this type, so that your eyes have to be close.

I'm getting some eyestrain as my head movement causes misalignment and the black outer limits of the viewing area to move around.
My ##### eyelashes get in the way a lot too.

These are all common problems. I do not know any magic for eliminating them. Really the only controls that you have are 1) separation between the eyepieces (so that the distance between their exit pupils matches separation between your eye pupils), and 2) how far back you position your head.

The problem of "black outer limits...move around" happens because the pupil of your eyes shifts sideways when you redirect your view to a different place in the field. If the shift is enough, then the light from the eyepiece may actually miss your pupil after your eye moves, in which case the view suddenly dims or becomes black. This problem may be helped by working in dim light, so that the pupils of your eyes become larger.

You used the word "misalignment", which might describe several different effects. Can you describe in more detail exactly what you see?

--Rik

[The Sparrow]

...
You used the word "misalignment", which might describe several different effects. Can you describe in more detail exactly what you see?

--Rik

I think you nailed it in your response, but yes it is the sense that my eye is no longer centered over the image exiting the eyepieces. Keeping close and looking at the center of the field, while moving around the stage, works better than "trying to look all around the image".

[rjlittlefield]

..."misalignment"...
...is the sense that my eye is no longer centered over the image exiting the eyepieces.

That sense is completely correct. The way our eyes work, the pupil inevitably moves sideways whenever the angle of view changes. The only way to keep your pupils lined up with the eyepiece is to move your head in compensation. As you've noticed, tutorials on "how to use a microscope" often don't mention this aspect. All I can guess is that those tutorials are written by people who have spent so much time looking through eyepieces that they now just automatically move their head as needed, and have somehow forgotten to mention that that's part of the process in many circumstances!

Keeping close and looking at the center of the field, while moving around the stage, works better than "trying to look all around the image".

This approach is a good one in any case, because except for high end scopes, the image quality is noticeably higher in the center of the field.

--Rik

[The Sparrow]

Thanks for the feedback.

I learn! I learn!

[Pau]

Rik has provided a very nice explanation of eyepieces and their eyepoint.
If your microscope is the one linked by ChrisR with the same 10X eyepieces, they are pretty comfortable, some scopes at my school's lab have the very same ones. In principle avoid the 20X, they are much less convenient both for ease of use and image quality

Just to add one point: eye strain often is due to inadequate distance between eyepieces and/or to trying to focus with the eyes like in their normal use. To be comfortable the vision must be relaxed without forcing the eyes to follow the image both about convergence and focus (your eyes must focused to infinite)

The method I teach to my students (with variable degree of success )
0- Put a slide with a thin subject with recognizable details and good contrast. Set the light intensity to a comfortable level with the condenser aperture not much closed
1- Focus* with the microscope focus to a small well defined point at the center of field with the eye whose eyetube has no regulation of if both have it with your best eye setting the diopter graduation to zero**
2- Focus to the same point with the other eye only by means of the eyepice diopter adjustment.
3- Open both eyes and relaxing the view regulate the eyepiece distance up to be sure that you see only one image circle
4- Refocus if needed, some binoculars change the focus point when you change the interpupilary distance, very likely to happen if your microscope is the one linked by ChrisR
5- If not convinced repeat all steps avoiding doing it when tired

* Always focus (and perform any other regulation) forward and backward of the focused point to get the optimal setting
** or to your actual graduation if needed