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Parfocal Length Extenders for Microscope Objectives
35 mm, Internal and External
15 mm, Internal and External
Objective with 45 mm Parfocal Length
Parfocal Length Extender
Click to Enlarge
As shown here, the parfocal length is the distance from the shoulder of the objective to the focal plane.
Thorlabs' parfocal length extenders increase the parfocal length of an infinity-corrected objective by a fixed amount. The parfocal length is the distance from the shoulder of the objective to the focal plane. Parfocal length varies between manufacturers and between different objectives; for common standards, see the table below and to the right. Using a parfocal length extender to match parfocal lengths when switching between various microscope objectives minimizes the refocusing required. When using parfocal length extenders, take care to not exceed the maximum recommended distance from the objective to the tube lens; otherwise, vignetting may occur.
We offer 15 mm and 35 mm extenders with RMS (0.800"-36) threading or M25 x 0.75 internal threading to accommodate industry standards (refer to the tables to the right for details). By stacking two matched 15 mm adapters together, the user can also extend an objective with a parfocal length of 45 mm to one with a parfocal length of 75 mm. The 35 mm adapter can be used to adapt our TL4X-SAP Super Apochromatic Objective with a 60 mm parfocal length to match the 95 mm parfocal length of our TL2X-SAP Super Apochromatic Objective. For objectives or objective holders with different threading, we offer a wide selection of thread adapters; note that the use of an adapter could increase the parfocal length.
The PLE152 RMS-Threaded Extender is directly compatible with our OT1 Objective Lens Turret, which is RMS-threaded and enables easy manual switching between four objectives.