Re: 18a filter

["R. C. Lacovara" <lacovara@xxxxxxxxxxx>]

Ordinary lenses are not very transparent to UV. See 
http://www.photo.net/photo/edscott/cf000010.htm and 
http://www.photo.net/photo/edscott/uv000010.htm

To take advantage of HIE's UV sensitivity, it is necessary to use quartz 
lenses (hardly practical for most folk) or use another lens which does pass 
UV: a pinhole.

For folks interested in UV, there are some filters available from Edmund's 
Scientific which pass UV only. They are a bit pricey (I think I paid $25 or 
so for a 1 cm lens) but you don't need a 52mm filter to cover a pinhole.

Curiously, a monochrome CCD camera has some UV sensitivity. I have used 
these with the Edmund's filters. Considering that these cameras are 
sensitive to UV, visible, and IR, I find that they are handy in "looking" 
at things in various spectral ranges.

For the interest of the group:

The retroreflector on the space station is used when the Space Shuttle is 
docking. The ranging "light" is from an IR laser in the 880 nm region. 
Curiously, the return from the retro reflector is becoming weaker... some 
contamination is suspected. NASA is thinking about getting a camera out 
there to have a look. I am trying to convince them to "look" in the IR, 
where the degradation is occurring. If I finally get any IR views of the 
Station, I'll post them, at least, if they are of any visual interest.

Bob

At 08:52 AM 1/19/01 -0500, you wrote:

>I've shot a few frames of HIE using this filter. In my opinion, there is
>not much use for this filter other than for UV photography. It's
>expensive and if you want to shoot IR only, you're better off with the
>regular IR filters. I shot HIE with this filter to see what effects I
>might get by photographing UV and IR light together, but nothing
>remarkable happened. HIE happens to be quite a bit more sensitive to UV
>than to IR, so it could make a nice (expensive) UV film. You'd have to
>filter out the IR though. One problem with trying to record UV and IR on
>the same frame is that the lens cannot focus both at the same time, so
>you get a blurry image. You could try double exposing and refocusing in
>between.
>
>Anyway, you should still try it out - and tell us what you get!
>
>Dave
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