on 10/05/2005 19:44, Carlos J. Santisteban Salinas at cjss@xxxxxxxxxxxxx,
wrote:
Hi Carlos,
Welcome back, seems you're enjoying some kind of holiday these days :^)
>
>> on 9/05/2005 07:32, Andrew Fildes at afildes@xxxxxxxxxxxxxx, wrote:
>>> Never sure what the KR means but a KR3 is much 'warmer.'
>
> Dear colleague ;-), I think that K stands for 'correction' (in German
> spelling!) and R for 'red' -- there's another line of bluish KB filters.
> The number is the correction strength in deca-MIREDs; a KR 1.5 then
> corrects colour 'temperature' by +15 MIRED.
deca-mired units, go figure !!
>
> BTW, 'MIRED' means 'MIcro REciprocal Degrees' -- that's a more 'natural'
> measure of colour 'temperature'. For instance, the typical 5600 K daylight
> would equal to:
>
> 1000000 / 5600 = 180 MIRED (approx.)
>
> But the typical 3200 K tungsten light would be:
>
> 1000000 / 3200 = 310 MIRED (approx.)
>
> The odd thing of the Kelvin scale is that a *warmer* ('more' temp.) light
> has a *lower* (?) temperature -- unlike MIRED, which results in a *higher*
> figure.
Yes indeed, the chart at:
<http://www.schneideroptics.com/images/filters/filters_for_still_photography
/temperature_chart/chart.gif>
goes along with this logic. It makes life ssssooooo easy :^)
>> From: Fernando Gonzalez Gentile <fgnzalez@xxxxxxxxxxxxx>
>> Just did a little googling and to my surprise, the KR 1.5 corrects
>> temperature from 3400 to 3200 K,
>
> 3400 K => 295 MIRED. If we add +15 MIRED (the KR 1.5)... voilà! we've got
> 295+15 = 310 MIRED => 3200 K (remember previous paragraph?). MIRED makes
> life so easy... :-)
>
>> which would be a Sky 1A equivalent.
>
> I don't think so... the 1A has a pinkish tone, instead of the pale brown of
> the KR series -- but you already knew that!
>
>> But the 81a seems to correct from 3400 to 3200 too !!
>
> Then KR 1.5 <=> 81A.
>
>> Looking at it, it looks quite brownish - and my Hoya Sky 1a looks rather
>> pink, with green relections due to multicoating.
>
> Sure...
>
>> Looking through it, it seems to warm up much more noticeable than the Hoya.
>
> That's right -- and the 1A needs *no* exposure compensation, not even the
> slight x1.1 of the KR 1.5 / 81A (something like 1/6th of a stop, according
> to my calculations)
>
>> That's why I thought it was a 81a - but the table at the link above lists KR
>> filters as different to the 81a & 81b.
>
> I beg your pardon? If the same correction is made, that should be the very
> same filter -- only danomination (B+W vs. Kodak Wratten) is different.
I've followed your reasoning so far, but WHY ON EARTH do they publish a
table on which there's a filter whose name is KR 1.5 and another filter on
the same table whose name is 81a, both correcting colour temperature from
3400 to 3200 K.
Take a look at, while feeling my surprise (besides, ignore many sites which
state that Sky 1a = KR 1.5):
<http://www.schneideroptics.com/filters/filters_for_still_photography/uv_&_w
arming/more_information/>
Thanks a lot,
Fernando
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