(Apologies for not filling the graduates with water for the photograph.)
Manufacturers’ developing times for b&w films seem to be universally specified for nominal developer temperatures of 20ºC or 68ºF. Many believe that only this temperature will produce good results and go to elaborate lengths using things like water baths, immersion heaters, refrigerators, ice cubes, etc. in an attempt to keep all of their chemicals and wash water at exactly that temperature for the entire process.
I was fortunate in my very early days of photography to have a more experienced friend whose darkroom was a tiny closet in a badly heated and not air conditioned apartment in New York City. All of his processing, including developing film, was done with developer temperature at room ambient. And his work, usually in 35mm, regularly won awards.
And film manufacturers, recognizing that some customers will want to develop their film at temperatures other than 20ºC/68ºF, provide recommended developing times for other temperatures. For example, in their spec sheet Ilford says “HP5 Plus film can be processed over a range of temperatures” and specifies developing times for temperatures from 14ºC to 24ºC or from 56ºF to 76ºF.
I do not particularly enjoy developing film. I would rather spend my photography time taking pictures and making prints. So I am always interested in ways to streamline my processing, including not having to regulate film development temperatures, and this is what I do:
I store a one gallon jug of distilled water, a one liter bottle of fixer working solution, and a small bottle of stock developer if I am not using Rodinal* in a pantry next to our guest bathroom where I develop my film.
When I am ready to develop a roll of film I start by mixing the stock developer with distilled water in a plastic graduate and inserting a dial thermometer.
After everything is measured out in the graduates (developer, water stop bath, fixer, first water wash) and I am ready to start I note the temperature of the working developer solution, look up the appropriate developing time for that temperature and proceed with the processing.
Note that because the only water I use for the whole developing process, including washing the negatives, is about one and a half liters from the jug of distilled water all of the liquids are at exactly the same temperature, and because they are at room ambient they do not change over time.
*With just 5ml of Rodinal (1+50) in a 250ml developing tank the temperature of the stock Rodinal is irrelevant.
Mere Film Photography 
The bathroom where I develop my film runs warm 9 months of the year. I’ve learned to just adjust for the temp I get and move on. And I don’t love developing film either. It’s a means to an end.
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Our AC thermostat is set to 75ºF but there is only one zone so the temperatures in the different rooms aren’t uniform as the direction and intensity of the sun changes. More often than not the bathroom is down around 72ºF. In the winter the dedicated baseboard heater in the little room holds the temperature at a rock steady 66ºF. During the two brief seasons when we turn off both the AC and the heat and open the windows the temperature varies a lot and the time/temperature table gets a proper workout.
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The Rodinal note at the end is interesting; I’ve found another developer that seems to very much not care about temperature (within a reasonable +/- 5-6 degrees) but it’s a homebrew 2-part concoction (3 ingredients) that Jay DeFehr told me about, he calls it Master’s Metol:
Stock part A:
-50g metol
-50g potassium metabisulfite
-distilled water to 1l
Part A is acidic enough to keep for a long time in a dark, bellows bottle.
Stock part B is a simple alkali to activate part A. In my case, he suggested 50% potassium carbonate solution; others can be used depending on aggresivity desired. I needed something that would develop microfilms to pictorial contrast.
Used 1:50 and 1:100 in 1l of water, development can take place between 7-9 minutes, between 18-25C, and the only agitation is the initial 15s. The rest is stand development.
It’s a pretty neat solution to a problem we all have in summer, of getting solutions down to 20C.
Peace out 🙂
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Two part developers and highly diluted developers used for stand development are both tolerant of temperature variation because they depend on exhaustion of one or more of the developing agents. That was not the situation I was addressing concerning Rodinal. Rather, with a 1:50 dilution the temperature of the working solution will be very close to that of the water regardless of the temperature of the undiluted Rodinal.
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Ah, gotcha.
Yes the problem at the moment is not being able to make the water to dilute the stock solution to working solution cold enough, it’s flowing at 22C currently and will only get warmer.
Maybe it’s time to shoot colour for a while 🤣
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