Re: (Fwd) Re: Color UV?

[infrared@xxxxxxxxx]

pjohnso@xxxxxxx (Zoe Paddy Johnson CIRT CSOS) wrote:

> Our 1968 Wratten Handbook shows 3 filters labeled 47, 47A and 47B.

I have in my homepage similar info which was put on-line by someone else.
See 
        http://www.mat.uc.pt/~rps/photos/other-filters.html
It seems to be somewhat different from yours. Can you check if the
differences are only missing data in mine or if numbers for the same
wavelenght are different ?

> The 47 is called dark blue and has the same description Russ gives.  The 
> filter transmits light from 350nm thru 530nm, so it is getting much more 
> blue than uv.  The old number was C5.

> The 47A is called light blue.  It transmits over a broad multi-lobed 
> curve from 290 thru 560, with another lobe that extends into the IR 
> starting at 680nm.  No old number.

> The 47B is again called dark blue.  It transmits from 380 nm thru 500nm.
> No old number.

The info I have for these 3 filters only extends from 400 to 700nm.
Other filters on the file have more info.

Of the 3 filters only the 47A has some transmitivity near 700nm (less
than 1%). The narrowest (or bluest ?) filter is the 47B: 16% at 400nm,
(I suppose this means some transmitivity at shorter wavelenghts), peak
(50%) at 430nm, and cut-off at 500nm (at 480 it only transmits 4.5%).

The 47 has the peak at 440nm (50%), and extends to 520nm (10% at 500nm).
On the short side it transmits 9.7%, so I would guess that it doesn't
extend very far to the UV side.

The 47A has an higher peak at 440nm (63%) and extends to 560nm (12% at
520nm). At 400nm it still passes 26.4%.

In the list I have, the only filter with data for UV is:
  18A       nm    %     density
  AAA      300    --      --
           310   0.40    2.40
           320   8.00    1.10
           330  20.00    0.70
           340  42.00    0.38
           350  52.00    0.28
           360  63.00    0.20
           370  50.00    0.30
           380  31.40    0.50
           390  10.00    1.00

with some transmissivity on the near infrared (6.3% at 740nm).

I hope this helps more than confuses.

BTW, which film(s) are people using ? I have read somewhere that modern
colour films include an UV-blocking layer (this was presented as the
reason why UV filters are not needed anymore except for protection).

Where does the sensitivity of a typical film (say Kodak Gold or Fuji
Super G) begins ?

-- 
http://www.mat.uc.pt/~rps/photos/       an ex-tifoso since 95/11/13

.pt is Portugal| `Whom the gods love die young'-Menander (342-292 BC)
        Europe |    Villeneuve 50-82, Toivonen 56-86, Senna 60-94

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