Re: self masking and POP

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From: Richard Urmonas (rurmonas@senet.com.au)
Date: 02/04/03-02:47:00 PM Z


I may be misunderstanding the situation, but I thought self masking was
relatively easy to test. Simply use a step wedge and overexpose.
A self masking process will give a series of low contrast
steps at the "shadow" end of the scale.

I have observed this with salted paper, where during my exposure
calibration tests, I obtained a print of a 21 step with 12 dark steps,
with the steps just discernable from each other and above these
the well seperated steps in the "straight line" part of the curve.

If the process gives well seperated steps with a distinct Dmax
then it is not self masking.

Richard

---
Richard Urmonas
rurmonas@senet.com.au
>> As for "self masking" -- from what you say it's impossible to test 
>> that so
>> we can say anything we please.  Well, I shall say that there is no 
>> self
>> masking and how will you prove that there is?
> 
>  I actually tried to figure a way to do this with carbon some weeks 
> ago because Dick Sullivan offered the opinion, perhaps on another 
> list,  that the print-out image that results from conversion of 
> dichromate to chromate, even in the absence of pigment, should lead 
> to some self-masking in carbon. I don't believe that is correct 
> because of the almost linear response of a carbon curve that you see, 
> in practice. However, to this point I have not been able to figure 
> out a good test for self-masking in carbon.
> 
> 
>>   After all, you can't simply
>> compare it to another process, because every process has a different
>> contrast range.  And also and therefore the range of every process
>> (including and especially every paper combo with a particular 
>> procedure
>> and chemistry) has to be tested separately.  So what is the meaning 
>> in
>> this context of any *theory* at all?  Suppose, if we must have 
>> theory, that
>> I have a theory that cyanotype makes you more beautiful than 
>> otherwise.
>> There are all kinds of reasons for that but it's now 4:21 AM & my 
>> bedtime.
> 
> 
> Yes, it is true that every process has a certain contrast range, 
> although this can usually be modified significantly. However, from a 
> practical perspective we know that certain things are true of DOP 
> processes as opposed to POP processes. With a  DOP process you will 
> loose either the highlights or the shadows, depending on amount of 
> exposure, unless the contrast of the negative is carefully matched to 
> the exposure scale of the paper. Assume, for example, that you try to 
> print with a negative that has a higher density range than the ES of 
> the paper. If you print for good shadow detail the highlights will 
> have no texture, whereas if you print for good highlight details the 
> shadows will block up completely and go completely black. And of 
> course I mean a straight print, with no dodging, burning. With a POP 
> process you can print the entire tonal scale of the negative, even 
> when the density range of the negative is much longer than the 
> exposure scale of the process, *but* by the time you managed to get 
> good detail in the highlights you will start to lose contrast in the 
> shadows because of self-masking, and the overall contrast of the 
> print will be significantly reduced. The result of this is that the 
> print will loose overall contrast but the shadows will never go 
> completely dark.
> 
> 
> 
> Sandy King
> 
> 
> 
> 
>-- 

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