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I have recently purchased a binocular microscope (Saxon Researcher Compact Biological Microscope 40x-1600x), and have had difficulty getting the two circles of light that I'm seeing through the eyepieces to merge. I've focused the microscope without much difficulty, but when I look through I still see the two circles. Researching this problem told me to bring the eyepieces closer together until the circles merge, however when I do this, I just stop seeing through one of the eyepieces (I close one eye, nothing changes, I close the other - and I just see black in the eyepiece. Also when I move my head slightly I can see through the other eyepiece, but as soon as it's adjusted so I can see through both there's the two circles ). Does anybody have any suggestions as to how I could fix this?

Additionally in my research I saw that you eyes should be 1.5-2cm from the eyepieces, but I cannot see anything but a small dot in the centre until my eyes are almost pressed up against the lenses, is this wrong?

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  • $\begingroup$ One problem seems to be a small "exit pupal" typical of inexpensive equipment. It is the size of the circle you see in the eyepiece. $\endgroup$ Oct 23, 2021 at 0:57

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Your best bet is to measure your inter-pupillary distance and use this to set the lenses at the correct distance on the scale on the centre piece between the eyepieces. The black indicates that you have something mis-aligned, probably the eye-pieces are raised or lowered with respect to each other, rather than equally adjusted about a central point. It may also be that you have the dioptre incorrectly adjusted so one lens is a lot closer to you than the other.

To measure your inter-pupillary distance you need a ruler (marked in mm preferably, as this is the standard for most microscope inter-pupillary distance scales) and a mirror (or alternatively someone to do the measurement for you). Stand about 15-20 cm (6-8") from the mirror. Close one eye. Align the 0 mark on the mirror with the centre of one pupil, look straight ahead, close the open eye and open the closed eye, and measure the distance to the centre of the now opened pupil.

Now, you should be able to set this on the microscope. Once you have done this, test to see if you can see with both eyes. If now, adjust BOTH eyepieces equally in small amounts.

As for the viewing distance. To be honest I had never measured how far away my eyes are when using a microscope, but having checked, mine are about the width of my index finger away from the lenses. This would be about 1.5 cm, but not much further than that. In your case I would put my eyes close to the lens and slowly move away to a point that feels comfortable and that the light almost fills your field-of-vision.

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