Relay lens spacing

[Nikolas]

It seems that the necessary spacing between the relay and imaging lens is ~50-100 um.
This corresponds to an air gap, that practically is a major hurdle to optimize and maintain.

If I understand correctly the optics behind this, changes in this distance can be compensated by changing the focus using the slider mechanism.
If that is correct, I was thinking about the possibility of creating an "adapter"/"sleeve" that fits the two lenses and maintains a constant ~75um air gap between the two lenses. Then the perfect focus would be adjusted with the slider.

Do you think this is a valid approach?

[Daniel Aharoni]

Hi Nikolas,
Sorry for the slow response.

The spacing between the relay and objective GRIN lenses in the dual lens setup will generally be around 300um. Optically, changing this gap length will shift your imaging plane in the brain. Roughly speaking, a shift up or down of 10um in the gap length will shift the imaging plane up or down by 10um. Our preferred approach is to lock the focus slider of the Miniscope about mid way while baseplating. We then watch the live video stream as we lower the scope down until cells become in focus. At that point we hold the scope and baseplate in place and cement the baseplate to the skull. The result of this approach is we can hit about the right focal plane just by picking the right gap length between the two lenses and still give us +/-100um of focal plane adjustment by using the focus slider.

If you make a sleeve/adapter to fix the gap between the lenses then you lose one degree of freedom when baseplating the animal.