Re: Step wedges

Peter Marshall (petermarshall@cix.compulink.co.uk)
Sun, 24 May 1998 09:33 +0000

In-Reply-To: <Pine.SUN.3.94.980523142226.21037B-100000@panix2.panix.com>
>
>
> On Sat, 23 May 1998, Peter Marshall wrote:
>
> > Layering up the film will work by the way - film base and fog just
> > contribute to the overall density and so become irrelevant here - if
> > the total density of one layer is 0.15 then the total density of 2
> > would be twice this. As I posted earlier this is really too small a
> > step to work with by this method.
>
> But if you're going to have 20 or 21 layers of film, surely it would
> interfere with contact. It's very handy to put one of these little
> 21-steps next to the negative when making a print. In my experience,
> even one piece of masking tape on the negative can spoil contact.

You are confusing two things here. First the reason I said the step was
too small is that is obviously wont work for 21 layers - but it will for
say 5. This is why the 0.15 step is too small. Although simple it is crude
- which is why I advised not doing it! Either buy one or make your own by
the method I described.

Anyone who hasn't got a densitometer you can actually make them accurately
enough by visual comparison with an existing step wedge if you can borrow
one of these. It's not a bad idea to buy one and keep that in a safe place
and make your own to actually use that match it. If you are going to do
any volume of work its handy to have quite a few isn't it.

Second the writing on of the numbers is what you do on any step wedge that
comes without them - either from Kodak or Agfa or one homemade by the
simple method I described. Of course for the homemade one you do really
need a few minutes with a densitometer to find the numbers, although it
doesn't usually matter if they are accurate.

>
> I would assume also (judging by my experience with the 19th-century
> method
> of adding up pieces of translucent paper) that numbers written on by
> hand
> would get so strongly diffused through all those layers that the basic
> information of contact, sharpness and emulsion behavior conveyed by how
> those numbers *print* would be lost.
>
> Judy
>
>

Peter Marshall

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