UV sensitivity of lens....explanation, please

Archived from groups: rec.photo.digital (More info?)

Bob Salomon, bob_salomon@mindspring.com writes:
>There are special filters made which appear to be opaque that
transmit >either only UV of a specified band width

Yes, I bought a B+W 093 UV pass filter, but I wanted to know
how to compare the UV sensitivity of my Oly C-2020's lens with
the double-coated lenses of other cameras.

Dale Bricker

Archived from groups: rec.photo.digital (More info?)

"Dale Bricker" <dbricker@cyburban.com> wrote in message
news:41ddab44$0$9380$45beb828@newscene.com...
> I have read that the lens of a certain older Olympus digital
> camera, the C-2020z, is "UV-sensitive", relatively speaking.
> I understand that this is intended to mean relative to other
> cameras with double-coated lenses, but I don't understand
> what the following numbers mean in the specifications for
> this particular cameram, as compared to other cameras:
> "6.5 - 19.5mm, F2.0 - 2.8.8 elements in 6 groups (equivalent
> to 35 -105 mm lens on 35mm camera)".
An element is an individual piece of glass. Sometimes elements are cemented
together to form a group. In this case, the lens has 8 individual pieces of
glass which are combined into 6 groups (i.e. some groups have only one
element). The zoom lens itself has a focal length which can be set to any
length between 6.7 mm and 19.5 mm. It has the same angles of view as a
35-105 zoom has on a 35mm camera.
>
> For example, how does that compare to the following: "Helios
> 58/2 has 6/4, Canon 28-80 has 10/10, and 75-300 has 13/9".
Well, the Helios 58mm f2 lens has 6 elements in 4 groups, etc.
>
> For me, the more UV permeability of the lens, the better,
> as I want to attempt UV photography.
None of these descriptions tell you much about the UV permeability.
Jim

Archived from groups: rec.photo.digital (More info?)

In article <LbiDd.11887$wi2.7214@newssvr11.news.prodigy.com>,
"Jim" <j.n@nospam.com> wrote:

> as I want to attempt UV photography

There are special filters made which appear to be opaque that transmit
either only UV of a specified band width or only IR of a specified
bandwidth.

the UV versions would normally be used with long or short wave UV light
sources.

Is this what you want to do or are you looking to shoot items that and
change color using a combination of normal and UV light?

--
To reply no_ HPMarketing Corp.

Archived from groups: rec.photo.digital (More info?)

You might want to look at Robert Monaghan's page:
<http://medfmt.8k.com/mf/uv.html&gt;

Dale Bricker <dbricker@cyburban.com> wrote:
> I have read that the lens of a certain older Olympus digital
> camera, the C-2020z, is "UV-sensitive", relatively speaking.
> I understand that this is intended to mean relative to other
> cameras with double-coated lenses,

I think lens coating has very little to do with whether
or not a lens passes UV. When Pentax announced their
"Super Multi-Coated" lenses they pointed out that their
new lenses incorporated UV filtering, but this doesn't
seem to be inherent to multicoated lenses: some multicoated
Nikkors appear to work quite well in the near-UV.

UV photography with a digital camera has the special problem
that most UV-pass filters (B+W 403, Tiffen 18A) also pass
near-infrared and that the sensors on digital cameras tend
to be more sensitive to the near-IR than the near-UV. You
can tell if you are getting more UV effect or IR effect by
taking a picture of white clouds against a blue sky: on
a UV photograph the sky will be blank or with very little
contrast between sky and clouds, the clouds may even
be slightly darker than the very light sky. If you are getting
mostly IR then the clouds will be light and the sky will
be dark with much contrast between sky and clouds.


> but I don't understand
> what the following numbers mean in the specifications for
> this particular cameram, as compared to other cameras:
> "6.5 - 19.5mm, F2.0 - 2.8.8 elements in 6 groups (equivalent
> to 35 -105 mm lens on 35mm camera)".

That tells you a very little about the optical formula of
the lens and is not useful for telling how well the lens
will pass UV.

Glass is an effective filter of the far-ultraviolet (anything
shorter than arround 330nm. There are special and expensive
lenses made of quartz and fluorite which will pass wavelengths
much shorter than this. Regular B&W film (provided it does
not incorporate a UV barrier layer) shows good sensitivity
to UV as short as 230nm and some sensitivity to UV as short
as 190nm: shorter wavelengths are stopped by the gelatine
in the emulsion.

Many modern lenses have built in UV filtering which cuts
more of the near-UV than the inherent filtering of the
glass. Both SMC Takumar/Pentax lenses, and Leitz/Leica
lenses made after 1965 are claimed by their manufacturers
to have fairly effective UV filtering built-in.

Even if a lens passes near-UV there can be problems from
some types of optical glass and some types of lens cement
which can fluoresce under UV. The lens may also not
be well corrected for UV, but this is often not a problem
if the lens is stopped down a bit. One good thing about
UV photography is that diffraction is much less of a
problem: diffraction at f/22 with near-UV light is no
worse than yellow/green light produces at f/16.

EL-Nikkor enlarging lenses are claimed to be very well
corrected for the 350-400 nm UV region as well as for
visible light. So if you were looking for a lens for near-UV
using an El-Nikkor on a bellows with a SLR could be
a good idea. The 105mm or longer lenses should provide
infinity focus with a bellows for a 35mm camera.
You could just try a number of different lenses and
see what works.

Peter.
--
pirwin@ktb.net

Archived from groups: rec.photo.digital (More info?)

The lens is not the only problem. Silicon CCD chips are not nearly as
sensitive to UV as film is, so you'd be better off using film. On the
other hand, these chips ARE better at recording near-IR, though some
cameras have filters to reduce the overall IR response.

There are UV sensitive imaging chips made of materials other than
silicon, but these are quite expensive for consumer use. They are used
by military and astronomy folks.

Archived from groups: rec.photo.digital (More info?)

Dale Bricker wrote:
> I have read that the lens of a certain older Olympus digital
> camera, the C-2020z, is "UV-sensitive", relatively speaking.
> I understand that this is intended to mean relative to other
> cameras with double-coated lenses, but I don't understand
> what the following numbers mean in the specifications for
> this particular cameram, as compared to other cameras:
> "6.5 - 19.5mm, F2.0 - 2.8.8 elements in 6 groups (equivalent
> to 35 -105 mm lens on 35mm camera)".
>
> For example, how does that compare to the following: "Helios
> 58/2 has 6/4, Canon 28-80 has 10/10, and 75-300 has 13/9".
>
> For me, the more UV permeability of the lens, the better,
> as I want to attempt UV photography.
>
> Thanks for an explanation, or suggestion where to go online
> to find a good explanation.
>
> Dale Bricker

The capacity of a lens to pass UV light depends on the materials in the lens, which may be a glass or a plastic, or both in
different lens elements. Camera makers usually block UV light, because it can create unwanted color effects.

When Polaroid first made color film (actually, Kodak made it for them initially), it was tested on a prototype camera with
glass lenses that didn't transmit UV light. When they put the film for the first time in a production Polaroid camera for
color film, the colors were off because the plastic lens in the camera passed some UV. I don't remember whether they
reformulated the film to work with the camera, or modified the lens to block UV.

Archived from groups: rec.photo.digital (More info?)

On 6 Jan 2005 15:21:07 -0600, Dale Bricker <dbricker@cyburban.com>
wrote:

>I have read that the lens of a certain older Olympus digital
>camera, the C-2020z, is "UV-sensitive", relatively speaking.
>I understand that this is intended to mean relative to other
>cameras with double-coated lenses, but I don't understand
>what the following numbers mean in the specifications for
>this particular cameram, as compared to other cameras:
>"6.5 - 19.5mm, F2.0 - 2.8.8 elements in 6 groups (equivalent
>to 35 -105 mm lens on 35mm camera)".
>
>For example, how does that compare to the following: "Helios
>58/2 has 6/4, Canon 28-80 has 10/10, and 75-300 has 13/9".
>
>For me, the more UV permeability of the lens, the better,
>as I want to attempt UV photography.
>
>Thanks for an explanation, or suggestion where to go online
>to find a good explanation.
>
>Dale Bricker

If you are interested in UV photography you're best off with a DSLR so
that specialized lenses can be used. Certain enlarging lenses are
excellent for near-UV work, and can often be easily adapted to bellows
units. I have found the Nikon D100 to be moderately sensitive to near
UV, enough at least to shoot flowers and such under noonday sun, using
a Rolyn U-360 pass filter. With a two-piece 58mm filter holder, these
filters can be easily adapted to most cameras. For best results these
filters usually need to be stacked with a hot mirror IR cut filter,
since most UV pass filters also have a small response bump in the IR
range that tends to spoil the effect. Have you checked out Bjorn
Rorslett's page?
http://www.naturfotograf.com/uvstart.html
-kBob