Re: Night lights again

[Clive Warren <Clive.Warren@xxxxxxxxxxxxx>]

At 1:15 pm +0100 4/10/99, Willem-Jan Markerink wrote:

>On  4 Oct 99 at 10:05, Clive Warren wrote:
Snippety snip snip snippety
>>
>> Willem-Jan,
>>
>> You have mentioned your problems with manufacturers previously.  Agree with
>> you that such "out of spec." filters would be unacceptable.
>>
>> I would be happy to supply you with professional quality CoCam Infrared
>> filters in Cokin "P" size if your suppliers are unable to provide
>> consistent products :-)
>
>You better check yours too by comparing them with Wratten
>filters....the inconsistency itself wouldn't be that bad, if the
>manufacturer acknowledged there was a problem, and also informed
>previous customers of this problem. I felt, and still feel, like talking
>into the desert....any manufacturer claiming 'better than Wratten
>accuracy' should take such a problem a lot more seriously, including
>information to previous customers.
>
>So there are probably dozens, if not hundreds of these filters
>circulating among other photographers/scientists, bought previously
>and afterwards (two very different batches of off-spec filters delivered
>to me only can't be exceptions....I suspect off-spec colors every
>other batch, if they do spectral checks inbetween at all)....without
>them knowing about this problem. And from an academic/photographic
>standpoint, that stinks the most. IR gives enough erratic results as
>it is....8-))
>
>So I hope you have a set of Wratten originals in your posession, and
>a tungsten/halogen lamp to compare....never trust manufacturers....;-))
>
>Btw, I did get correct-spec #87 and #87C from them in the past....so
>I haven't given up yet....also because they claim they can do #87B
>and #87A....
>
>--
>Bye,
>
>Willem-Jan Markerink


Willem-Jan,

Sound advice and I do indeed have Kodak Wratten gel filters to use as a
simple coarse comparitive measure.  However the best test is a spectral
analysis of the filters themselves as you say.  The filters I supply are
tested using this method on a spectrophotometer at the manufacturers'
factory.

For a substantial additional fee I can supply a colour printout of the
spectral curves of the filters in a particular batch.  This is really
overkill though as the filters are manufactured to Wratten specifications.




All the best,

             Clive   http://www.cocam.co.uk
                     Photographic Services, Filters and Equipment
                            http://clive.bel-epa.com
                            Adventures in Cyberspace - Digital Art and Photos


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