OK..OK..OK..So I can't spell ;-( Both of my parents were public school
teachers before they retired. I'm afraid I'm the "black sheep" of the
family. Yes I did mean "diopter" filters, commonly known as "close-up"
filters (although they may technically be lenses, rather than filters).
My second GREAT disappointment this morning came when I checked the
archives. I was certain I was going to get to post a message to Judy
saying "It is in the archives!" That would have been fun!!!!! I remember
writing such a post, but it is either under an illogical heading or on a
different group...too bad ;-(
Don wrote a very good post on how this is done "completely and
correctly". Much like owning a calibrated step wedge, I find the complete
Davis method overkill for what "I" need.
The three limitations of this system are flare in the metering, light
source evenness, and the size of the negative area measured. Before I
begin the "how to" section of this post ........ Let me say again .......
many people are very good at visually matching negative densities and step
numbers using the "small hole in a card" trick (see PF). The method below
is ONLY needed for those of us (me) that don't seem to be good at that :-(
I own a Pentax 1 degree spot meter, but any similar meter will do. Buy a
"set" of close-up filters for the meter. Mine takes 40.5mm filters, which
are available from Tiffen. The set will include a +1, +2, and +4 diopter.
An option I didn't think of when I made mine was to use a filter size that
would fit my 35mm gear, and a step up ring on the meter.
Screw the +4 filter onto your meter, place a round piece of flat black
paper over the front of the filter with a 3/8 inch (10mm) hole in the
center. This paper "baffle" is cut so it just fits inside the filter,
without interfering with it's threads. Next: screw the +2 filter onto the
+4 filter. Place a similar piece of black paper over the front of the +2
filter, but with a 3/4 inch (19mm) hole. Finally screw the +1 filter onto
the +2 filter. You now have (in this order) the meter, +4, paper, +2,
paper, +1. The order is said to be important (strongest filter nearest the
meter, I didn't test), the black papers are for flare control (in my tests
they helped slightly).
Next you need a light source. I found that the light tables I owned were
not as even as I thought. I found my friends were not only uneven, but
"flickered" enough to confuse my meter. I decided to build a simple box
with a light bulb inside, and the top made of white plex. Then I realized
that I still had the head from my first 35mm enlarger in the garage.
Turned it upside down, and I had a light source. I found it best (to
control flare) to cover all the light source but a 3/8 inch (10mm) hole. A
nice refinement I added later was a dimmer switch. This allows me to
"calibrate" the system.
In a dimly lit room, place the negative on the light source, with the area
you want to measure over the opening. Hand holding the meter/filters aim
directly at the light source (stay roughly parallel to the source) and move
the meter toward the negative until you are reasonably focused. Note the
reading on your meter. Continue with other areas of the negative you are
interested in.
Finally
Without a dimmer: meter the wedge on the light source and find the steps
that match your negative.
With a dimmer, I simply adjust it before use. Step 8 should meter at
9-2/3. I have no idea how I settled on that standard! I have a chart on
the wall that translates meter readings directly into step (density) values.
When I'm done, I simply unscrew the +4 filter from the meter. This leaves
me with a completely normal 1 degree spot meter and a stacked set of
close-up filters.
Perhaps the biggest limitation of this system is the size of the area
measured. It is about 1/8 inch (3mm). Seeing as I generally use 8x10 or
11x14 negs, I'm happy. If I was trying to measure 4x5 or smaller negs, I
would try using all +4 diopters, or perhaps some of the stronger diopters
are available from ??????
Unlike Davis's method: mine can not be focused. I do that by moving the
meter physically closer or farther from the negative. I also don't have
mine mounted to a stand. It is necessary to aim the meter nearly parallel
to the negative, or I'll get incorrect readings. I suspect this would be a
larger problem if I was trying to use it as a refective meter.
Hope this helps.
tomf2468@pipeline.com (Tom Ferguson)