Re: hoya R72 Filter

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On 21 Aug 96 at 5:23, joe b. wrote:

> In message <199608202340.AAA24091@xxxxxxxxxx>, Willem-Jan Markerink
> <w.j.markerink@xxxxx> writes
> >The Hoya R72 is definately *not* visually opaque. 
> >It equals a Wratten #89B. Even the much darker 88A can be looked 
> >through with some effort.
> >This 89B color is also known as Schott RG695, which is used as normal 
> >IR filter for both Heliopan, B+W (092) and Rollei.
> 
> There seems to be a slight difference when I compare directly between a
> couple of these that I have. Holding them in front of one eye just now,
> through the B+W 092 I can clearly see the light bulb above me and I can
> also the detail of the moulding on the ceiling around the light fairly
> clearly. When I try this with the Hoya R72 I can see the lightbulb, but
> to see the moulding takes some effort. It is visible, but only just. I
> wonder whether this is just variation between samples, or whether the
> Hoya R72 is actually a (slightly) different filter. I have known a B+W
> filter to have the wrong glass in the mount- ie not what it says on the
> filter rim, but a closely related filter instead; only once though, but
> it shows it can happen. But this 092 is definitely  a real 092, as it is
> the same as a couple of 092 filters I've got in other sizes.

Apart from the difference, the big question is: did you test it 
indoors or outdoors? I can't see much through either filter 
indoors....;-))
Further note that 5 or 10nm is not much technically, but has a large
effect on the human eye (either as color difference in normal
filters, or darkness differences on the visible limit of infrared. 
Even different batches of Schott glass (used by B+W, Heliopan,
Rollei etc) can show this difference. Actually, even (Wratten)
gelatine, know as the tightest spec filter, had a margin of 10%. 

--
Bye,

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The difference 
between men and boys
is the price of their toys

<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]

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Topic No. 2