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UltravioletPhotography

UV through glass


Lee Kelly

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I am very new to this UV world and really excited to try some thing, which I will post soon.

I am waiting for a lens and a camera to be modified but in the meantime maybe someone can answer a quick question?

 

If I was photographing a flower or similar, through glass or a window or similar, will this lessen the effect of UV light reflecting off my subject to the lens? My limited understanding is that a significant amount of UV light will be blocked by glass. Are there specific types of glass that is available to everyday people that will allow this reflected UV light through?

 

I wanted to try something that involves shooting through glass, but not sure itll work.

 

What about mirrors? Does this enhance the UV or reduce it?

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All glass is different, although any glass with visible tinting will probably block UV heavily. With glass that is not chosen for optical performance (e.g. bottles or windowpanes) it is something of a crap shoot--I have seen beverage bottles that transmitted down to 320nm, and window glass that did not transmit much below 360. Just try it and see. Thin glass, all other things being equal, will be better than thick glass.

 

With mirrors, first-surface mirrors and polished metal mirrors generally perform excellently. Second-surface mirrors are as good as the glass substrate, which light must traverse twice: once inbound and again outbound. Again, just try it.

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In my neck of the woods we use double glazing and there is not much UV that pass through. Compared to the outside, less than 1/10 of the UV registers inside. Plus there is even more efficient attentuation of the shorter wavelengths, so you get a skewed balance as well.

 

Indoor UV is the domain of UV flash only.

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Lee,

 

Simple window panes can be thought of as longpass filters, aka short wavelength sharp UV cut-off filters, analogous to the Schott WG & GG types of optical filter glass. Depending on the thickness and purity of the glass the cut off wavelength can vary as can the sharpness, or slope, of the cut-off.

 

Uncoated colorless, water clear, glass windows can have have cutoffs ranging from ~320-360 nm similar to the WG filters. The thicker tempered commercial glass, slightly green tinted when viewed on edge, will have longer wavelength cut off more similar to the GG filters.

 

Double glazed windows, as Bjørn has indicated, should be expected to transmit much less UV as will windows with tints or coatings to attenuate solar radiation or insulate energy loss. Laminated safety glass, such as that used in automobile windshields, often contains highly UV absorbing adhesives and usually transmit almost no UV, appearing opaque in UV photos.

 

If you are considering UV photography underwater you might consider a uv transparent (UVT) acrylic, polymethyl methacrylate (PMMA) commonly known a Plexiglas. Some PMMA sheets are doped with UV absorbers so be sure to get UVT grade.

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All very interesting.

My gear is still on its way so i have no way of testing just yet but excited to see what will work.

I get the feeling it may be harder to get the best UV images, that I have seen from you guys, through glass. Baby steps. Ill try and get my head around what works in sunlight with simple setups and work from there.

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