1. Exposure determines shadow density of the negative (transparent areas).

2. Development time determines highlight density of the negative (dark areas).

2. The difference between the two determines contrast.

4. Since the modern practice is to use minimum shadow density, the only way to
adjust contrast is to change the highlight density.

5. Reducing development time reduces highlight density and will therefore reduce
contrast. Increasing development time will increase contrast.

6. If you chose to ignore item 4 above increasing exposure without changing
developing time will also reduce contrast, but will result in a denser grainier
negative.

BTW, diluting the developer and extending the time results in the same level of
 development, but you do tend to get higher edge definition. You can dilute the
developer, or reduce the time, to reduce the contrast of the negative.

--

Negative contrast is a function of development time. To reduce contrast, cut
your development time. Diluting the developer usually has the same effect of
cutting development time (assuming the development time remains the same).

With the dilution you're using now, try reducing agitation (say, every
three minutes instead of every minute); this may require extending
development somewhat, but should allow you pretty fine control of
contrast by small alterations in time combined with alterations in
agitation.  Generally, less agitation gives lower overall contrast,
without (much, if any) loss of shadow detail.

  Contrast is a function of development time, overall
density a function of exposure. However, lowering
development time may also require an increase in exposure to
keep the minimum density from falling off the toe.

  Diluting developer allows lengthening the development
time so can be useful for reducing contrast where the time
gets too short. For other than machine processing a time of
around 8 or 10 minutes is desirable to insure uniform and
controlable development.
  For most films a change of one paper grade will be gotten
by adjusting the time + or - about 30%, for shaped crystal
films like T-Max the same change in contrst may take only a
20% change in time. The change in effective EI from "normal"
contrast will be about 3/4 stop.

  What sort of subject are you shooting and how do you
print?

  Time and time and time again. What about temperature? Is it a
dirty word?
  I think the reduced agitation suggestion something I
would try.
  You may be expecting too high an ISO from your film. It
may be due to metering inaccuracy. Your film may be returning
an ISO of over 400.
  At the medium format NG a very recent series of posts has covered
that very variable. Search there for, spectral response .        Dan

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Your approach should be contingent upon the film format your using, and the
type of enlarger you plan to use. If your using 35mm I would try a low contrast
developer like D23 and stick with minimum development. If your shooting 645 or
better you may try Rodinal at various dillutions.
In 6x7 TX loves Rodinal.

1+25 for low contrast

1+50 for medium contrast

1+ 100 for high contrast

or you can reduce your film rating (as you have) and also reduce your
development time. Before you may do this you must first establish a personal
iso for your camera, lens, developer, and development of the films you like
most.

If you shoot People, use an electronic flash utilizing syncro-sunlight
techniques, to even out the contrast.

Right now, I have to establish a new personal EI for the new 400TX. I shot a
couple of rolls last week and the neg's are too thin for my taste. Oh well here
I go again, my testing usually takes about 5-8 rolls of film and several hours.

Regards.

Bob McCarthy