Forum - Basic FAQ for Optics

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[#1]

Here is the basic optics for our system. Please use this forum to discuss any questions related to Optics!

Cross section of scope. Excitation path is in blue. Emission path is in green.

The optical path of the miniature microscope is very similar to a tabletop wide-field fluorescence microscope. The main difference is the size of the optical elements and the use of a GRIN lens as an objective. A more detailed discussion on GRIN lenses can be found here.

The optics in the miniscope use off the shelf lenses and diced commercial filters. Excitation light generated by an LED passes through a half-ball lens to help collimate the light which is then bandpassed through an excitation filter and reflected using a dichroic mirror.

Emission light exits the objective GRIN lens in roughly a parallel orientation, passes through the dichroic mirror and then bandpassed through an emission filter. The light is then focused onto the CMOS imaging sensor using an achromatic lens.

Posted by Tristanshuman (administrator) on 2 December 2015 at 19:57.
Edited by Tristanshuman (administrator) on 14 January 2016 at 16:37.

A few questions

a.Have you tried using a 1mm GRIN lens? Would it work without any modifications with the system? If so, what is the expected reduction in the FoV?

b. After the baseplating procedure, is it possible to modify the FoV by somehow moving the miniscope in relation to the baseplate (similar to the way done in the Inscopix if I understand correctly). Also, what is the utility of the sliding part for the excitation LED/lens?

c. In the base plate, there are 3 small holes, that much the 3 small holes on the miniscope. Are they for the magnets?

Posted by Nikolas on 26 March 2016 at 13:58.

Hi Nikolas, 

a.Have you tried using a 1mm GRIN lens? Would it work without any modifications with the system? If so, what is the expected reduction in the FoV?

Yes we have recently begun using 1mm GRIN lenses with much success. There is a small modification that must be made to the scope and I am in the process of righting up a description of the modification on our wiki. It takes a total of about 5 minutes to do and is reversible if you ever want to go back to just using larger GRIN lenses. The overall lens/optical setup will look similar to Inscopix's system. You will need a 1.8mm or 2mm diameter GRIN lens mounted in the base of the scope and you will implant a 1mm or 0.5 mm diameter relay GRIN lens into the brain. This recent Nature Protocols Paper does a great job in outlining the procedure needed to use small GRIN lenses. The FOV from a 1mm diameter GRIN lens still fills our entire imaging sensor. Anything small and the FOV will start to decrease. 

b. After the baseplating procedure, is it possible to modify the FoV by somehow moving the miniscope in relation to the baseplate (similar to the way done in the Inscopix if I understand correctly). Also, what is the utility of the sliding part for the excitation LED/lens?

Yes it is possible. You can both adjust the relative angle of the scope to GRIN lens as well as use translational adjustment to shift the FOV. There is no sliding part on the excitation LED but there is a sliding mechanism for the CMOS imaging sensor. Sliding the imaging sensor up or down will shift the focal plane in the brain from around 0um to over 200um. 

c. In the base plate, there are 3 small holes, that much the 3 small holes on the miniscope. Are they for the magnets?

Yes they are for magnets. The 3 magnets in the baseplate and 3 magnets in the base of the scope help with the initial attachment of the scope.

Posted by DAharoni (administrator) on 26 March 2016 at 15:01.
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