How to set up a 4f relay?

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DevonianSea
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Joined: Sun Aug 22, 2021 1:07 am

How to set up a 4f relay?

#1 Post by DevonianSea » Tue Sep 21, 2021 5:18 pm

I've read about 4f relays and how they allow the externalization/projection of the objective back focal plane. It's a fascinating concept and I certainly see some potential (future) use, which led me to investigate how to actually set one up. Although the concept is pretty easy to grasp, I'm slightly confused about some of the technicalities:

- Can any pair of relay lenses with the same focal lengths (f) be used as long as they are aligned with the BFP, in which f is the distance from the first lens to the objective focal point? Are they required to be aspherical and/or achromatic to prevent visual aberrations?

- How would one integrate such relay in a finite 160mm tube length microscope? I assume designing (and perhaps 3D-printing) some kind of intermediate tube in which the relay lenses can be placed?

- How would you know the distance from the objective BFP to the top of the stand/nosepiece (where an intermediate tube or head would be inserted)?

- Would the process of setting up a 4f relay differ between finite tube length and infinity corrected microscopes?

Thanks in advance!

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patta
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Location: Stavanger Norway
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Re: How to set up a 4f relay?

#2 Post by patta » Wed Jan 12, 2022 12:06 pm

So many questions... "Po prostu to zrób!"

Here the newest "4f"; I've assembled it today with two 58mm camera objectives as relay; over a finite (and sturdy) microscope.
The disk in the middle is in aperture space, can host a filter, a phase ring, an iris, those stuff. In the photo, it is a fixed aperture stop. Maybe next time, a convenient slider to change the filter there, now it needs to be unscrewed each time. Two lenses, the aperture stop, and the rest is just spacers and mechanical adapters.
The whole relay is built exactly as the "double standard" published one month ago, just this time it is mounted over the microscope intermediate image. https://patta107285337.wordpress.com/20 ... -standard/

Answs: Relay whatever lens Yes; Achromatic Yes; Aspheric No; 3D print yes; BFP measure or create it; Spacings need some care; Objective compensation No; infinite, maybe next week.

The purpose of this patchwork was bi-telecentric imaging at high NA, which is almost unprecedented because notoriously pointless.
The last photo is just a joke, "4F" is also the main sportswear brand in Poland.
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