Newbie: Use of Contrast Filters and Exposure Time

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KS - 20 Aug 2004 17:33 GMT

I'm printing on Kodak RC VC paper. When I use say a +3 contrast filter
should I be adding time to my exposure? Thx.

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Francis A. Miniter - 20 Aug 2004 19:10 GMT

Very definitely. Kodak has a darkroom handbook with a wheel for
calculating how much more time.

Francis A. Miniter

>I'm printing on Kodak RC VC paper. When I use say a +3 contrast filter
>should I be adding time to my exposure? Thx.

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dr bob - 21 Aug 2004 14:27 GMT

> I'm printing on Kodak RC VC paper. When I use say a +3 contrast filter
> should I be adding time to my exposure? Thx.

There are variations in the way VC paper reacts to contrast filters.
Usually as the filter No. increases (from yellow towards blue) additional
exposure is required. The exact amount in stops or time can be calculated
by various methods, but I find a trial and error approach using small paper
pieces a much quicker path to the desired result. E.g., cut (or tear) an
8x10 sheet of the target paper into rough quarters. Place one in a
conspicuous area of the image and expose. It usually requires no more than
two trials to acquire sufficient data for a full size print. Remember: the
first full size print is still just a "working" print. You will usually
want (need) to tweak the print in many ways before satisfaction is achieved.

Truly, dr bob.

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KS - 22 Aug 2004 21:41 GMT

> > I'm printing on Kodak RC VC paper. When I use say a +3 contrast filter
> > should I be adding time to my exposure? Thx.
[quoted text clipped - 11 lines]
>
> Truly, dr bob.

I actually found the instructions for my Kodak Polycontrast II Filter Kit.
It says no exposure adjustments from 0-3.5 and then double the exposure when
using 4-5.5. Go figure. To quote: " Each half grade step changes the
log-exposure range of Kodak papers approximately 0.1 units. Filter 2 is
intended to accommodate a negative density range of 1.2 in a typical
semi-specular enlarger with tungsten lamp..."

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dr bob - 23 Aug 2004 14:04 GMT

> > > I'm printing on Kodak RC VC paper. When I use say a +3 contrast filter
> > > should I be adding time to my exposure? Thx.
[quoted text clipped - 22 lines]
> intended to accommodate a negative density range of 1.2 in a typical
> semi-specular enlarger with tungsten lamp..."

True. And Ilford instructions are similar. However, I have experienced
slight and somewhat more than slight differences in exposure when moving
from one filter situation to another. IOW, "correction" of the contrast for
one gray level _may_ create the need to modify the overall exposure in order
to maintain a desired level in another. So far my approach is to be more
empirical than less. Tests work well.

Truly, dr bob.

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Pieter Litchfield - 23 Aug 2004 18:29 GMT

I was stunned when I went to photo school and experienced changing contrast
settings (via dial) on an enlarger made for the purpose - no time changes
after a desired exposure was made at any contrast!

At home, on the other hand, I use a contrast filter under the enlarger lens.
I think any change in contrast is worth running a new test strip. By the
way, I am printing on Ilford multigrade IV using Kodak filters. I have been
assured that the Ilford and Kodak filters are completely interchangable.

> > > > I'm printing on Kodak RC VC paper. When I use say a +3 contrast filter
> > > > should I be adding time to my exposure? Thx.
[quoted text clipped - 35 lines]
>
> Truly, dr bob.

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Mike King - 25 Aug 2004 14:29 GMT

First of all, both Kodak and Ilford claim that the lower grade filters are
"speed matched" in other words no time compensation is required when
changing filter grades, and I suppose that's true for one particular point
on the gray scale but in the real world we change filters to change the gray
scale so a retest of exposure is often necessary.

Second, the claim that Ilford and Kodak filters are completely
interchangable is also not quite true, you will often get different results
when switching from one brand of filters to the other and may not be able to
obtain the complete contrast grade range of a variable contrast paper unless
using filters from the same maker. That being said, most of the time most
of your work will not be made with either the highest or lowest contrast
available and will be perfectly satisfactory using brand X paper with brand
Y filters.

Signature

darkroommike

----------

> I was stunned when I went to photo school and experienced changing contrast
> settings (via dial) on an enlarger made for the purpose - no time changes
[quoted text clipped - 50 lines]
> >
> > Truly, dr bob.

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Bob Salomon - 25 Aug 2004 14:44 GMT

> > I was stunned when I went to photo school and experienced changing
> contrast
> > settings (via dial) on an enlarger made for the purpose - no time changes
> > after a desired exposure was made at any contrast!

This is a function of some MG heads. Others may require different times
at different settings. The Kaiser MG head is one example of one that has
constant time at any grade (unless you dial in the ND filter control on
the head).

However it is always best to run a test before printing to make sure you
are happy with the changed contrast, as well as to see if the time
should be increased or decreased for the effect you want.

Signature

To reply no_ HPMarketing Corp.

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Phil Glaser - 22 Aug 2004 23:33 GMT

> I'm printing on Kodak RC VC paper. When I use say a +3 contrast filter
> should I be adding time to my exposure? Thx.

The Variable Contrast Printing Manual by Steve Anchell outlines an
entire procedure for materrials testing to determine the degree of
exposure change when going from one contrast filter to another.

Although I know about these methods for testing, so far I've been
getting along using Ilford's (Multigrade IV) chart, according to which
the paper speed is constant up to filter 4, at which point it drops by
one stop (requiring a doubling of exposure). My sense is that this
approach is ok for me, for now, because Ilford's test were with a
tungsten light source (as mine is) and because I'm using Ilford's
standard Multigrade developer. I'm still seeing how consistently the
paper speed remains constant between filters, but so far it seems ok.
Ultimately I will do these tests, especially as I get into different
developers and papers. (As it is, I'm trying to balance my obsession
for technical precision with my aspiration to understand form and
compisition, and so I'm skimping on the paper testing for now.)

Also, one thing I do is to _always_ start with _a_ filter. For me # 2
seems to be the right one (bearing in mind that # 2 is not necessarily
the equivalent of grade 2; again, see Anchell for details). My
experience is that the absence of any filter with VC paper gives a
result that is, well, undefined: I'm just not sure what's going on.

Bear in mind that there are lots of variations that can affect the
tests and your outcomes in general. Public enemy number 1 in this
department is voltage fluctuations. See this discussion thread for
further details: http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&threadm=a3f95acc.0406180351.3
8b630eb%40posting.google.com&rnum=1&prev=/groups%3Fq%3Dglaserp%2540sustainsoft.c
om%2Bgroup:rec.photo.darkroom%26hl%3Den%26lr%3D%26ie%3DUTF-8%26group%3Drec.photo
.darkroom%26selm%3Da3f95acc.0406180351.38b630eb%2540posting.google.com%26rnum%3D
1

HTH.

--Phil

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