Here is a really lousy shot from one of my 9 year old Delta 100 rolls that I found a while back. I have been using it to shoot "stupid stuff". Sort of what I use digital for in a lot of cases. I am a big advocate of shooting stupid stuff. You know - the kind of stuff you know won't work but it's fun anyway.
Anyway I wanted to demonstrate something regarding Pyro developers that you really have to see for yourself but I find fairly cool. Whenever there are storms coming or going the birds around here get nuts. They fly around and land. Then they explode and go somewhere else. When the wind is blowing they go at like 60 MPH. Hence why they are a little blurry. Anyway - I had a bunch of stupid stuff on this roll and was planning on developing the whole thing at N+ because of the subject matter. Then I shot this - I shot it the same way I would have shot anything else that day, same exposure, meaning the sky was off the charts in terms of brightness and exposure. Heck it was the light source - so I shot the light source at the same exposure you would use for stuff lit by the light source. On my contact sheets it showed up as expected, pure white.
Now here is where the cool part comes in. I still developed the roll at N+ (high contrast) which put the sky in this scene even further into the woods but looking at the negative I could see there was some tonal variations. What to do? I just printed it down and look ma, great differentiation in the clouds. I swear without a lot of attention the sky that day seemed just plain grey with not a bunch of cool clouds. As they say the camera does see more than the eye.
Now this part is where you have to trust me when I say this is what "they" are talking about when people rave about highlight differentiation vs other developers. Trust me if you use say… D-76, which is perfectly fine and put big parts of your image in say zone IX they you over develop it and try to print down or burn in that area what you will end up with is blah grey instead of pure white with not a whole lot of tonal separation. This is why I like pyro developers. I can develop the crap out of the negative for good local contrast (similar to Rodinal) and still be able to print down or burn in highlights with lots of separation. Very cool.