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hardware:objectives [2022/10/07 11:25]
Jon Daniels [Magnification] |
hardware:objectives [2022/11/10 01:39]
Jon Daniels [Mechanical Angle] |
| ==== Mechanical Angle ==== | ==== Mechanical Angle ==== |
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| For traditional light sheet microscopy with two orthogonal objective lenses, the objectives have to be able to co-focus before they mechanically bump ((For low-NA illumination you can sometimes extend the working distance a bit of the illumination objective by introducing diverging rays into its back aperture, but this is usually only a small win.)). Regardless of working distance, the most important/fundamental factor in whether or not two objectives can be co-focused orthogonally is simply whether the sum of their mechanical half-angles is less than 90° ((However if the working distance of one is very long then perhaps they can co-focus with only use of the optical angle.)). For any objective lens, the mechanical angle must be at least as big as the optical angle, i.e. it must be at least big enough to capture the cone of rays corresponding to its numerical aperture (NA) across the entire field of view. The mechanical angle is computed as arctan(dia/2/WD) where dia is the diameter of the first surface (assuming the rest of the objective lens fall inside the line from the focal plane to this first surface as is usually the case). The optical (half) angle is computed as arcsin(NA/RI) where RI is the medium refractive index. Some objective lenses have mechanical angles only barely larger than the lower bound optical angle, but others are much less efficient in a mechanical/bulkiness sense. | For traditional light sheet microscopy with two orthogonal objective lenses, the objectives have to be able to co-focus before they mechanically bump ((For low-NA illumination you can sometimes extend the working distance a bit of the illumination objective by introducing diverging rays into its back aperture, but this is usually only a small win.)). The question of whether or not two objectives can be co-focused orthogonally can usually be simplified to whether the sum of their mechanical half-angles is less than 90°((if the working distance of one is very long then perhaps they can co-focus with only use of the optical angle.)). For any objective lens, the mechanical angle must be at least as large as the optical angle, i.e. it must be big enough to capture the cone of rays corresponding to its numerical aperture (NA) across the entire field of view. The mechanical angle is computed as arctan(dia/2/WD) where dia is the diameter of the first surface (assuming the rest of the objective lens fall inside the line from the focal plane to this first surface as is usually the case). The optical half-angle is computed as arcsin(NA/RI) where RI is the medium refractive index. Some objective lenses have mechanical angles only barely larger than the lower bound optical angle, but others are much less efficient in a mechanical/bulkiness sense. |
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| A detailed overview and helpful table of many (more) objective lenses can be found in Supplementary Note 6 in the Power/Huisken review paper ([[https://media.nature.com/original/nature-assets/nmeth/journal/v14/n4/extref/nmeth.4224-S1.pdf|link to supplemental]]). | A detailed overview and helpful table of many (more) objective lenses can be found in Supplementary Note 6 in the Power/Huisken review paper ([[https://media.nature.com/original/nature-assets/nmeth/journal/v14/n4/extref/nmeth.4224-S1.pdf|link to supplemental]]). |
