No1.5 vs No2 Fused Quartz Coverslips: Which Thickness?
By UQG Optics | Published: 2026-10-13
Category: Comparisons
Compare No1.5 (0.17 mm) and No2 (0.20 mm) fused quartz coverslips on thickness, dimensions, and working distance so you can choose the right one for your setup.
Quick answer
Choose No1.5 (0.17 mm) when your objective is corrected for 0.17 mm and you need the highest resolution, especially for high-NA or UV imaging. Choose No2 (0.20 mm) only when your setup is already calibrated for 0.20 mm, or when a slightly thicker, more robust coverslip is acceptable and your working distance and correction collar can compensate.
What the thickness number actually changes
The difference between No1.5 and No2 is 0.03 mm, which sounds negligible until you consider how microscope objectives are corrected. Most high-NA objectives are designed to look through a 0.17 mm coverslip. Adding 0.03 mm of glass shifts the point of best focus and introduces spherical aberration, which softens the image and reduces contrast. That is why a No1.5 coverslip is the default for critical imaging and a No2 coverslip is usually reserved for setups that are already built around 0.20 mm.
Dimensions and formats available in fused quartz
Thickness is only half of the selection. Fused quartz coverslips come in different footprints, and the right one depends on your stage, holder, and sample size. UQG Optics lists both round and rectangular formats, so you can match the coverslip to your existing workflow rather than adapting the workflow to the coverslip.
When fused quartz is worth it over borosilicate
Fused quartz transmits deeper into the UV and has a lower thermal expansion coefficient than borosilicate glass. If your work involves UV excitation, high-temperature steps, or thermal cycling, quartz helps avoid the fluorescence and expansion issues that can appear with standard glass. If you are doing routine brightfield imaging in the visible range, borosilicate is often sufficient and less expensive, so weigh the application before paying the quartz premium.
Trade-offs at a glance
- Optical correction: No1.5 matches the 0.17 mm design of most high-NA objectives; No2 adds 0.03 mm that those objectives are not corrected for, which can reduce contrast and resolution. If image quality is the priority, No1.5 is the safer choice.
- Working distance: A thicker coverslip consumes more of the objective's working distance, so short-working-distance or high-magnification setups may not reach focus with No2. Check your objective's working distance and correction collar before choosing No2.
- Mechanical robustness: No2 is slightly thicker and can tolerate more handling, which may matter in repeated or automated workflows where coverslips are touched often. If robustness matters more than optical perfection, No2 can be a reasonable compromise.
Product facts
- Fused Quartz Coverslip #No1.5: Fused Quartz Coverslip #No1.5, thickness 0.17 mm, round 24 mm diameter, part CFQ2417. The 0.17 mm thickness matches standard high-NA objectives, and the 24 mm round format fits common multiwell plates and round sample holders.
- Fused Quartz Coverslip #No2: Fused Quartz Coverslip #No2, thickness 0.20 mm, round 15 mm diameter, part CFQ1520. The 0.20 mm thickness suits setups calibrated for No2, and the smaller 15 mm diameter is useful when you need a coverslip that fits inside a limited well or chamber.
- Fused Quartz Coverslip #No1.5: Fused Quartz Coverslip #No1.5, thickness 0.17 mm, rectangular 25 x 50 mm, part CFQ2550. The 25 x 50 mm rectangle covers larger samples or multiple sections at once while keeping the 0.17 mm thickness that high-resolution objectives expect.
- Fused Quartz Coverslip #No1.5: Fused Quartz Coverslip #No1.5, thickness 0.17 mm, square 25 x 25 mm, part CFQ2559. The 25 x 25 mm square is a practical middle size for standard slides and many inverted microscope stages, again with the 0.17 mm thickness for optical correction.
Which thickness fits your setup?
Best for
- High-NA and UV microscopy where 0.17 mm correction is required
- Researchers who need fused quartz for UV transmission or thermal stability
- Users who want a choice of round, square, or rectangular formats in 0.17 mm
Not for
- Setups already calibrated for 0.20 mm coverslips, where No1.5 would be the mismatch
- Routine visible-light work where borosilicate glass is sufficient and lower cost
- Applications where a 15 mm round format is too small for the sample
