[Alt-photo] Re: Digital Negative Correction Curve using a spectrophotometer.

[Loris Medici]

Hi Martin,

I think if you calibrate based on the L values of the test print you'll get
a darker than intended image. I tried that before (with a scanner) and it
didn't work well for me, especially with cyanotypes. (Maybe processes that
produce neutral prints would be much more compatible with this method...)

Making the black and white point adjustment is necessary, because the
calibration is based on relative values instead of absolute values. I'm not
sure about Ron's method because I use Mark's method myself, but if Ron does
it that way you'd better stick to his work flow; this is a pretty critical
modification.

Does your spectophotometer allow you to make readings in %, by zeroing the
paper white?

Regards,
Loris.



2014-02-25 15:22 GMT+02:00 Martin Herrera <tinchohs at martinhsphoto.com>:

> Hi, I am creating digital negatives to print platinum using the technique
> of Ron Reeder.  In his book he scans the Step Tablet using an Epson Scanner
> V700 with Silverfast AI to measure the input | output values to then derive
> the correction curve.
>
> I don’t have a scanner, but I do have an spectrophotometer.  My
> understanding would be that the L value (from the LAB spot metering) would
> be in fact a very precise measure of tone for each of the patches from the
> Step Tablet.
>
> Yet, in his process he also uses the Histogram tool in the Silverfast AI
> software to move the white and black points just outside the limits of the
> histogram.  My understanding is that this would in fact re-distribute the
> tones.  This part, and I’m not sure how critical it is, is what I don’t
> know how to do with the Color Munki or i1 spectrophotometer.
>
> Anyone using these tools that can help me shed some light on the topic?
>  Thanks so much.  m.
>
> [Also posted in Digital BW, The Print].
>
> Martin Herrera Soler | tinchohs at martinhsphoto.com |www.martinhsphoto.com| +1
> (310) 592-3474 | +598 (94) 143-978
>
>
>
>
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