Edmund Optics article on Reflective Objectives

[Lou Jost]

No idea what it means in this context, I'd guess something like the default position, the calibrated position, the position from which adjustments are made from etc.

Thanks Chris. Maybe you focus it by moving the objective, and then flatten the field with this ring? Similar to a Mamiya 6x7 lens with manually controlled floating elements?

[ray_parkhurst]

I pulled out the Beck 36x and quickly remembered why I have not used it...WD is only a few mm, far too short for my purposes. Talk above about long working distances must be relating to a completely different type of reflecting objective.

[Macro_Cosmos]

(the ring says "Nullpunkt", what's a nullpoint in this context?).

Nullpunkt in german is usually a point where you start at.
No idea what it means in this context, I'd guess something like the default position, the calibrated position, the position from which adjustments are made from etc.

This makes me think "correction collar" (Korr), but that objective Lou was holding was obviously designed to be used without a coverslip, indicated by the "0" mark.
Pretty interesting.

Just some general comments regarding the many posts here, did not expect this to garner so much interest!
- Yes, the benefit of such reflective objectives is price and broadband chromatic correction. Resolution is lacklustre.
- I own one of the EO TechSpec 15x objectives, NA of 0.28, and the image quality was odd. I assumed ZS did not handle the doughnut out of focus blobs well? Perhaps with slabbing, I can get better results.
(https://www.photomacrography.net/forum/ ... 25&t=40833)
- As for the type of microscopes that use this, I have only seen FTIR microscopes and perhaps one was an IR Ramen Spectroscopy microscope with such objectives installed.

[jmc]

Just to add to the general comments, and perhaps explain some of my earlier ones.

Working distance is of course less of an issue now with the advent of high quality long working distance glass based objectives. As such mirror objectives have less of an advantage with regards to that. Back when these started to be used though they offered a distinct advantage in that regard.

They do offer a very wide range of usability in terms of wavelength - Beck for instance say 200nm to over 10 microns for theirs, which glass based optics cannot match. Another quote which expands on that, this time from a 1952 article “Spiegelobjektive für Mikroskope” (English translation: Mirror objectives for microscopes) by Dr Hans Gehne, Carl Zeiss Jena 1952, which myself and my wife translated into English last year (original paper was published as Gehne, H. (1952), Spiegelobjektive für Mikroskope. Phys. Bl., 8: 453-460. https://doi.org/10.1002/phbl.19520081004). The article stated "...one should always remember despite all criticism that catoptric systems today are not at all utilised for visual usage, i.e. for the visible spectrum, but were built for important investigations in the ultraviolet and infrared.".

[Lou Jost]

Did the article explain why the visual results were poor? Maybe just because users of these didn't care about that? As we know, in deep-space astrophotography, reflective systems are the norm and achieve remarkable results.

[jmc]

Did the article explain why the visual results were poor? Maybe just because users of these didn't care about that? As we know, in deep-space astrophotography, reflective systems are the norm and achieve remarkable results.

It's mainly because there are fewer elements with which to be able to do corrections (compared to a multi element refractive objective with different glasses), and in the early days the difficulty with reliably making small aspheric or complex shaped mirrors.

[Perl]

Its a Objective for Micro Hardness Tester

https://www.ebay.com/itm/324323767119

Regards
Pär