the Leica III in the UV

[heqm]

<p>When I presented my <a href="/classic-cameras-forum/00dVFy">Leica III</a>, I mentioned that my motivation (justification) to buy it was a project shooting in the ultraviolet, where a coated lens would actually reduce the amount of light going through. Here are some results. The difference between the UV and visible is generally pretty subtle. First, the John Douglas Brown house here in Alexandria, which was built before Alexandria was a town.</p><div></div>

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<p>And for comparison, the sames scene in the visible.</p><div></div>

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<p>Now a garden door in the Carlyle House, built after Alexandria was founded, but not long.</p><div></div>

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<p>And again in the visible.</p><div></div>

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<p>Now the garden itself:</p><div></div>

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<p>And in the visible:</p><div></div>

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<p>For a final scene, the corner of King and Union, in the heart of the tourist district. Note that you can't read the signs!</p><div></div>

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<p>And again, in the visible:</p><div></div>

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<p>And of course I have to show the camera itself.</p><div></div>

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<p>This should give you a taste of what the UV looks like. Thanks for looking.</p>

[SCL]

<p>Alan - Sweet looking package! What film/filter combination were you using?</p>

[heqm]

<p><strong>Stephen</strong>, the first two shots were on Pan-F+, the rest on FP-4+; developed in D76 1+1. I was testing the films for their UV sensitivity. I don't recommend Pan-F for this project: not only is it slow to start with, it's proportionately less sensitive to UV than FP-4 or Tri-X. Tri-X is the most useful of all I've tried. Rule of thumb: take a light reading through a blue (47B) filter, and <em>add three stops</em> of exposure.<br>

I use a B+W 403 filter, visually opaque, ordered from B&H, improvised mounting (originally, taped to the end of the lens). Of course what's normally called a UV filter is exactly what I didn't want! </p>

[winfried_buechsenschuetz1]

<p>Transmission of UV-light of a camera lens is not (only) a question of coating. <br>

It is true that coatings are optimized for the visible light range and will not reduce reflections in UV light very efficiently. Anyhow, the rate of reflection per uncoated glass surface is about 5 p.c. and so the losses in the UV range would be in the range of 30...40% for a multi-element lens. <br>

The transmission of the glass itself is more important. There are types of glass which will block UV more efficiently than others. So it is not possible to predict the transmission of UV light for a certain lens. I remember a camera test decades ago where they checked the standard lenses for UV transmission, too (all lenses were in the f/1.7 .... f/2.0 range and 50...55mm focal length and probably all 6- or 7-element lenses). The results were quite different between lenses. </p>

 

[heqm]

<p><strong>Winfried</strong>, you're right, of course. There are a lot of factors going into this, and the thickness (and type) of glass is probably more important than just the coating. But lens designs before coatings had fewer elements, because of the reflections at each surface (as you mention) which cause flare and loss of light, and so the total thickness of glass will generally be smaller. I've only tested four or five lenses (on different cameras) but the uncoated lenses do pass more UV. </p>