Check of Eyepieces and Filters with an UV Lamp

[j.gardavsky]

Hello all,

a UV lamp is helpful to check the optics on the unwanted fluorescence, which may reduce the contrast of visible details on the bright objects, like the Moon and the bright planets.
The first picture shows two Abbe ortho eyepieces illuminated by an LED fluorescence lamp, as used for checking the banknotes or gemstones,

JG

The eyepiece at left shows practically no fluorescence in its interior behind the singlet eye lens. The reflections are on the multicoatings of the lenses.
The eyepiece at right is another Abbe ortho, showing a bright fluorescence glow on the cement in the triplet.

The second picture shows the fluorescence of the yellow astronomy filters, against no fluorescence on the professional grade color filters, as used in the old Leitz microscopes. The upper row is with the UV lamp switched off, the lower row is with the UV lamp switched on,

The amount of the yellow fluorescence on the astronomy filters is bad enough to reduce the contrast of the details on Moon, as I have noticed when using these filters.
Best,
JG

[notFritzArgelander]

Excellent idea!

[EAGLE 5]

That is clever.

[j.gardavsky]

That is clever.

I know.

Thank you Eagle,
JG

[Bigzmey]

That's a neat trick JG, thanks!

[Michael131313]

Thanks JG. I did not know this. Very good.

[Don Quixote]

Excellent share, JG.
Thank you...again.

I happen to have this lamp in my tool kit. It is used to find refrigerant leaks with a die introduced to the refrigerant system.

Now I have another use.

[j.gardavsky]

Thanks for the nice comments!

I have made these tests already 9 months ago, but had no time to post them.

Best,
JG

[yobbo89]

awesome test!, i think i need to understand more on how and what is fluorescences and how it affects optics/filters.

[notFritzArgelander]

awesome test!, i think i need to understand more on how and what is fluorescences and how it affects optics/filters.

Well simply put your telescope collects ultraviolet light which may be invisible. If the coatings convert the ultraviolet light into visible light as done in this demonstration your contrast will be destroyed.

[j.gardavsky]

awesome test!, i think i need to understand more on how and what is fluorescences and how it affects optics/filters.

The optical color filters (Wratten), like those used in the classic photography, are glass doped with selected transition metal ions, which build up the color centers in the otherwise clear glass matrix.

These color centers absorb light on the short wavelengths (visible UV, blue), and the absorbed enrgy of UV/blue light is after some loss to the heat/vibrations in the glass matrix, emitted again in the form of light photons, but at the smaller energy and hence longer wavelength. And this is called the green, yellow, ... fluorescence.
The longer wavelengths of light are passed through the filter, and hence these filters are called the Long Pass Filters.

So, in the worst case scenario, the visible UV and blue light is turned into the yellow fluorescence, which is passed by the filter together with the other yellow transmitted light into the eyepiece.

The Canada Balzam, popular for cementing the doublet and triplet lenses, is an organic transparent resin, with its own brigt fluorescence.

Best,
JG

[j.gardavsky]

Fluorescence of color filters, continued

Here is an article in depth on the problem,
https://www.researchgate.net/publicatio ... ce_Filters

Best,
JG

[Apollo69s]

That was smart.maybe some posts showing up so a comparsion between different eyepieces can be done..