Re: Re:Stouffer wedge (was VDB is "Brownprint" process?)

----- Original Message -----
From: "Judy Seigel" <jseigel@panix.com>
To: <alt-photo-process-l@sask.usask.ca>
Cc: <alt-photo-process-l@usask.ca>
Sent: Thursday, February 23, 2006 11:42 AM
Subject: Re:Stouffer wedge (was VDB is "Brownprint"
process?)

>
>> At 05:16 AM 2/23/06 -0800, Susan Huber wrote:
>>
>>> BTW; does one need a 21 step wedge for alternative
>>> processes and how does one use it?
>>> I went into the store yesterday and found out the Kodak
>>> step wedge costs $144. US and the Stouffer wedge costs
>>> $5.80 US- a big difference in price, any difference in
>>> quality?
>
> Kodak has (or had) a less expensive step tablet, about $18
> in the US. The $144 tablet, whatever it costs in the US,
> is probaably *calibrated.* That is, minor variations in
> actual density, either from batch to batch or even from
> strip to strip, occur in the making. My understanding is
> that "calibrated" step tablets have actual density of each
> step read & recorded.
>
> AFAIK this matters in rocket science (possibly).
>
> J.
>
   The calibration is NIST tracable and certified. That
means each step is measured using a densitometer which has
in turn been calibrated using tracible standard or has
itself been calibrated by NIST. The exact values are given
for each step of the calibrated wedge along with the limits
of the measurement. This is hand work and expensive. If the
manufacturing process for the step wedges or tablets is well
controlled the values on an uncalibrated sample should be
very close to the "nominal" value. The tracible calibration
is probably needed only if one is doing very precise work or
if one needs the tracible calibration for some reason.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com