Re: opaque filter inside slr

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

On 18 Jan 00 at 11:02, ADavidhazy wrote:

> > 3. where can I find that kind of filter, is it expensive?
> 
> WJMarkerink the owner of this list offers the less expensive variety. 

It's not so much cheaper, but more robust than the usual Wratten 
gelatine. Especially the 0.4mm thick polyester #87C is a nice 
solution, as it would never bend far enough to interfere with the 
shutter.
Add the risk of moisture, scratches and fingerprints during 
darkloading, and gelatine becomes a less than ideal solution for this 
kind of application.

> Or, you
> can buy gelatin Wratten filters from most professional camera supply stores
> although they may have to special order them. Most large on-line camera stores
> such as Cambridge, Porter's, Ritz, etc. may also carry the IR filers such as
> the 70, 87, 88, 87C, etc. If you are just a beginner you have a lot of
> information to accumulate. The Wratten filter are expensive IMO - maybe
> something like $20-25 for a 3" square filter.

The only applications left for gelatine are the darker colors #87B 
and #87A....haven't found those an polyester alternative yet, but I 
can supply them in a different brand, which also appears to be a tad 
less moisture sensitive when touching them with bare fingers.
This was also inspired by (first) rumours and confirmation from Kodak 
that they didn't make those darker colors anymore. Yet recently 
someone told me they still did....old stock, or changed policy?
 
> Many photographers just use a deep red filter over the camera lens and this
> works for their purposes. A filter such as the Wratten 25 or 29.

Even in IR-strange environments like snow-covered Alpine mountains, I 
feel there is something lacking with those lighter filters....perhaps 
it is the intensity of the halo's, relatively stronger in IR than in 
partial visible light.
However, a counter-argument might be the extreme contrast that is 
generated between shadow and highlight area's....this winter, I found 
fabulous snow covered trees in the shadow, but none of the brackets 
could cover both highlighted mountains and shadow in exposure.
Perhaps a lighter filter *could* have tackled that extreme contrast, 
but might have lacked IR-effects in other ways.

Anyone ever done some semi-scientifical tests involving this
density-range? The non-scienfical variable messing up such a test is
of course the IR-reflective nature of the subjects....one would have
to measure it with an IR-lightmeter.








 

--                 
Bye,

Willem-Jan Markerink


      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


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