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| Impact of Coverslip Thickness on Image Quality |
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New High Performance Coverslips Offered by Carl Zeiss
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Coverslip #1.5 - ~ 170nm Thickness
Axio Observer, Plan Apo 40x/0.95
Indian Muntjac fibroblasts stained with Alexa Fluor 488 conjugated to phalloidin | Coverslip #2 - ~ 200nm Thickness
Compliments of Dr. Michael Davidson/FSU |
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One of those most overlooked influences to image quality is the coverslip thickness. Most objectives designed for use in high resolution biological imaging are calculated for a coverslip thickness of 170nm. In the objective design, the coverslip is included as the final part of the “imaging lens” contributing significantly to the image quality in brightfield and fluorescence applications.
A varying thickness of the coverslip and different optical characteristics of the glass (other material than borosilicate-glass) alter the optical performance of the objective lens system. These changes in the beampath result in an increase of spherical aberration. The severity of this aberration depends on the numerical aperture of the objective.
Visible effects in the image are:
- Optical Aberrations, primarily spherical
- Decreased Image
Contrast
- Loss of Signal
- Degraded Point Spread Function
- Limited the Optical Resolution
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Cover glass matches design thickness 0.17mm
- all rays meet at object point (at lower surface of the cover glass)
| Cover glass is too thin
- Focal plane get shifted
- Paraxial and marginal rays do not meet at object point anymore (sperical aberration)
- This effect mainly depends on ray angle / numerical aperture and immersion medium
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Commercially available coverslips are coded for thickness and typically offer a range of coverslip thickness within one code. For high end imaging applications, coverslips can be hand selected for the required 170nm thickness to optimize image quality.
To avoid this tedious process and to ensure consistent and reproducible image quality, Carl Zeiss now offers high performance coverslips with the correct thickness.
Number | Ideal Thickness | Typical Range |
# 0 | 100 μm | 80-130 μm |
# 1 | 150 μm | 130-170 μm |
# 1.5 | 170 μm | 160-190 μm |
ZEISS # 1.5 | 170 μm | 170 +/-0.005 mm |
# 2 | 220 μm | 190-250 μm |
Detailed technical Information for Carl Zeiss High performance cover slips (Part # 474030-9000):
- Size 18x18 mm˛
- Type 1 1/2 H as per ISO 8255-1 with restricted
- thickness-related tolerance
- D=0.17 mm +/- 0.005 mm
- Refractive index = 1.5255 +/- 0.00015,
- Abbe number = 56 +/- 2
- box with 1000 Individual Cover Glasses
A sample of 100 coverslips is included with every high performance Objective delivered by Carl Zeiss. | |
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