Checking objectives

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Munich
Posts: 28
Joined: Mon Jun 16, 2014 5:36 am

Checking objectives

Post by Munich »

I have to sell a considerable amount of objectives and am looking for a reliable and hopefully fast way to check for defects, i.e. fungus, delamination etc. On the web, I saw procedures of shining lasers through the lenses and inspecting them with measurement eyepieces and am curious what people here are doing.
And, how would you go about doing basic performance and alignment tests for Mitutoyos and alike? I have no possibility for comparison as I don’t own multiple copies of one lens.

Scarodactyl
Posts: 1617
Joined: Sat Apr 14, 2018 10:26 am

Re: Checking objectives

Post by Scarodactyl »

If it's a high value objective it's worth taking the time to do test pictures and present them with the listing.
Even if you can't do a comparison you can show whether anything is seriously wrong, and it's hard to complain if exact performance is illustrated. Otherwise a phase telescope can help sweep through internal lens surfaces.

RobertOToole
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Joined: Thu Jan 17, 2013 9:34 pm
Location: United States
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Re: Checking objectives

Post by RobertOToole »

Munich wrote:
Tue Dec 13, 2022 6:48 pm
I have to sell a considerable amount of objectives and am looking for a reliable and hopefully fast way to check for defects, i.e. fungus, delamination etc. On the web, I saw procedures of shining lasers through the lenses and inspecting them with measurement eyepieces and am curious what people here are doing.
And, how would you go about doing basic performance and alignment tests for Mitutoyos and alike? I have no possibility for comparison as I don’t own multiple copies of one lens.

A simple flashlight test works wonders. Aim a light into the opposite end and carefully observed from the other end, against a dark background, and will give you a good idea of the condition of the glass and it takes a few seconds. If you can light the lens from the right angle you can easily avoid looking into the direct (bright) light.
Anything non-glass will stand out back lit against the dark field. Fungus is very easy to spot this way.

I've returned a few Mitutoyo objectives that had what looked like a haze on an inner element was tiny fine bubbles, or tiny pricks or dots when examined with a loupe. The objectives looked like new and came in the original box.

BR

Robert

Munich
Posts: 28
Joined: Mon Jun 16, 2014 5:36 am

Re: Checking objectives

Post by Munich »

Hello Scarodactyl, Hello Robert,
Thank you for your insights!

blekenbleu
Posts: 146
Joined: Sat May 10, 2008 5:37 pm
Location: U.S.
Contact:

Re: Checking objectives

Post by blekenbleu »

For quick initial check of objectives up to 60x, I point them close to an LCD monitor and check for crisp bright RGB subpixels.
High values objects are usually expected to be parfocal and parcentric..
Metaphot, Optiphot 1, 66; AO 10, 120, and EPIStar 2571
https://blekenbleu.github.io/microscope

patta
Posts: 86
Joined: Mon Apr 20, 2020 9:51 am
Location: Stavanger Norge
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Re: Checking objectives

Post by patta »

Two a bit more laborious methods:
- You can mount the objective in front of a camera macro lens, then focus the macro inside the objective; it is the same as "phase telescope" but the view is a bit better. To do that I usually mount macro lens + camera in the camera port of the microscope, then focus the macro on the surfaces inside the objective. It is very useful to understand exactly what surface is affected.
- To check alignment and aberrations, there is the "star test": you manufacture a microscope slide, black with some tiny holes (painting a glass slide with a black marker may work). Then look at those holes, they're like stars, and if they're small enough the aberrations are well visible. If the diffraction pattern in the center of the field is off-center, well, some element got knocked off-center. This is a common method to re-center an objective after disassembly. Working with reflected light, tiny dust particles over a black background can work as stars.

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