Parfocal Length Extenders for Microscope Objectives

Add 15 mm or 35 mm to the Parfocal Length of an Objective
Versions Compatible with RMS or M25 x 0.75 Objectives
Stackable for Compatibility with Industry-Standard Parfocal Lengths

PLE351

35 mm, Internal and External
M25 x 0.75 Threading

PLE152

15 mm, Internal and External
RMS (0.800"-36) Threading

Application Idea

Objective with 45 mm Parfocal Length
Using PLE153 Extender to Match
60 mm Parfocal Length Objective
(Shown Mounted on CSN200 Nosepiece)

Parfocal Length Extender

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Overview
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Specifications
Item #	PLE152	PLE153	PLE151	PLE351	PLE352
Extension	15 mm			35 mm
External Threading	RMS^a	M25 x 0.75	M25 x 0.75	M25 x 0.75	M26 x 0.706
Internal Threading	RMS^a	M25 x 0.75	RMS^a	M25 x 0.75	M25 x 0.75
Diagram

RMS (0.800"-36) Threading

Click to Enlarge
As shown here, the parfocal length is the distance from the shoulder of the objective to the focal plane.

Common Objective Standards
Parfocal Length		45 mm	60 mm	75 mm	95 mm
Manufacturer/ Thread	Thorlabs	-	M25	-	M25
	Olympus	RMS^a	-	M25	-
	Nikon	-	M25^b	M32	-
	Mitutoyo	-	-	-	M26

Dry & Oil Immersion Microscope Objectives
Dry & Oil Immersion Microscope Objectives; Physiology Objectives; Phase Contrast Objectives.

Features

Threaded Spacers Increase an Objective's Parfocal Length
Stackable Design Matches Multiple Industry-Standard Parfocal Lengths
Versions Available with RMS (0.800"-36) or M25 x 0.75 Internal Threads
Anti-Reflective Interior Coating Minimizes Stray Reflections
Solid Brass Construction with Anti-Reflective Interior Coating

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.

Posted Comments:

james.parker (posted 2017-03-29 09:21:42.637)

It would be useful if you offered similar parfocal length extenders to use with your LMU-series UV objectives. The 40x and 20x do not conform to the usual parfocal length standards. I haven't looked at the rest. I'm currently having made M25 to RMS extenders for the 40x and 20x for my own use.

tfrisch (posted 2017-03-31 01:57:48.0)

Hello, thank you for contacting Thorlabs. I have posted your feedback in our internal engineering forum. I will reach out to you directly about your needs for a custom parfocal extender.

chris.percival (posted 2016-06-17 13:51:17.427)

Could i get a quote for a custom PL15M25, but 50mm long? I suppose that would then be a PL50M25

besembeson (posted 2016-06-21 02:09:58.0)

Response from Bweh at Thorlabs USA: We can provide this as a special item. You could also consider a combination of components such as an SM1A18, SM1L10, SM1V05, and SM1A17. I will follow-up with you to understand your application as most microscope objective parfocal distances are 60mm, 45mm or 75mm.

aoki (posted 2014-11-22 11:47:57.983)

I would appreciate 15 mm Parfocal Length Extender with outer RMS and internal M25 threads to fit an Olympus objective to a Nikon lens mount.

cdaly (posted 2014-11-25 02:02:32.0)

Response from Chris at Thorlabs: Thank you for your suggestion. This is now something we are look internally into introducing.

cbrideau (posted 2014-03-06 13:26:01.59)

Any plans for making this in the more modern M25 thread?

cdaly (posted 2014-03-11 01:59:33.0)

Response from Chris at Thorlabs: Thank you for your feedback. We can likely offer an M25-threaded version as a custom. We will contact you directly to discuss this option.

View All »Matching Part Numbers

Parfocal Length Extenders for Microscope Objectives

Features

15 mm Parfocal Length Extenders

35 mm Parfocal Length Extenders