Is the Kodak document which is quoted by bernard_L the December 2017 J78? Certainly his quote about what appears to be minimum stock solutions seems to be from that document:
Most likely yes - all the relatively recent versions use similar language.
To repeat those instructions they say "You can develop one 135-3 roll (80 square inches) in 473 mL (16 ounces) or two rolls together in 946 mL (one quart) of diluted developer. If you process one 135-36 roll in a 237 mL (8-ounce) tank or two 135-36 rolls in a 473 mL (16-ounce) tank, increase the development time by 10 percent (see the following tables). "
I am having difficulty understanding if the last sentence is describing a "like for like" situation
In the first sentence it suggests that you can develop one 135 (80 square inches) in a diluted developer of an unspecified dilution but I presume 1+1 in 473ml or 2 films in twice as much. So far so good but then in the second sentence it speaks of processing a single 135 film in a 237 ml tank or 2 x 135 in 473 increasing the development time by 10% and refers the reader to the following tables.
On the next page there are times for small tanks and large tanks and there is in fact slightly more than a 10% increase. Tri-X for instance goes from 8 to 9 mins but I assume this is simple rounding up of 48 sec to 1 min. Am I right?
So it would seem that if you want to develop 1 x135 film in a diluted developer which I assume to be 1+1 a 10% increase in development time compensates for a reduction in stock volume from 237 to 119. For ease lets call those 240 and 120 ml respectively
You are reading the wrong table. You need to read the 1:1 table. And the tanks we are talking about here are all small tanks. The large tanks refenced on those tables are the ones with gallons of developer and either take racks with multiple reels in them or use dip and dunk technology.
The references to smaller than 16 oz tanks for more than one roll suggest a 10% increase. So you pick the time recommended for your film and temperature combination in the small tank part of the 1:1 table, and add 10%. If the table time recommended is 10 minutes (20C, Tri-X, D76 1:1), then add an extra 10% = 1 minute more.
Just as an aside 80 square inches seems a lot for a 135 or 120. The exposed frame are is about 54 sq inches so is the rest the leader and trailer areas and do these amount to almost half the exposed frame area?
A roll of 135-36 is 64.5 inches long by 1.4 inches wide - including the edges and sprocket holes. That makes for a total area, including the leader, the trailer and the holes, of slightly over 90 square inches.
Someone probably knows what the total area of the sprocket holes is - cue "A Day in the Life" here.
A roll of 120 film is ~ 32.5 inches long by ~2.4 inches wide, including the edges. That makes for a total area, including the leader and the trailer, of approximately over 78 square inches.
So it would seem that if you want to develop 1 x135 film in a diluted developer which I assume to be 1+1 a 10% increase in development time compensates for a reduction in stock volume from 237 to 119. For ease lets call those 240 and 120 ml respectively
So to summarise, the minimum stock of D76 required for a 135 and 120 film is 120ml
As I've posted earlier, D76 is a bit different from other developers, in that some developer exhaustion can be (mostly?) compensated for by increasing development time.
So to summarize, the minimum stock of D76 required for a 135 and 120 film is 120ml,
if one doesn't extend the development time. And Kodak limits its recommendations for less stock to the situation where the amount of stock is reduced by 1/2.
I note that Kodak does not give times for 1+3 dilutions unlike Ilford's equivalent which is ID11.
Correct.
Nor in fact times for 1+1
Incorrect - read from the 1:1 table instead.
Finally if 120ml is the minimum stock for a 135 or 120 film then I presume that at 1+3 this requires 480ml so a 480-500ml tank will be enough a single 135 or 120 at 1+3?
Probably, but not necessarily.
While ID-11 is in most ways extremely similar to D76, there are some differences arising from, among other things, the originally patented Kodak packaging advancements that permitted a single package, instead of two packages. For the same reason, Ilford 1 +3 times may work well for D76, but the differences in the two products are important enough to test for your optimum times.
Here is a screen shot of the applicable 1:1 table from the datasheet
Hope this helps