developers and time question

More as a curiosity than anything else... I have 2 rolls of 35mm to do right now - one is HP5 and the other is Tri-X. I have a tank that can hold both. I looked up times for Sprint developer and both films work with 10 minutes at 68 F/ 20C. Yet with Ilfosol S, HP5 is recommended at 7 and Tri-X at 10. Why the difference? I've gotten the times from more than just the Massive chart, but they could be from the same original sources, not sure.
Is this a real chemistry difference (I know the 2 formulations aren't the same, but that doesn't quite explain it) or is it just that someone used X time and it worked, so it's out there as a starting point?
I'm not asking which I should use 'cause I have a roll of HP5 in the camera, so it'll get done with the other HP5 and I'll do the Tri-X on its own. I'm just curious about the differences in times now.

I wouldn't trust all the times on the Massive chart. They come from too many different sources.

Ilford publish identical times for HP5+ and Tri-X in ID-11, both @ 400 EI, but different times for Ilfosol 3. But raelly you need to find the time that suits you best.

Ian

I don't claim to understand the cause, but I've seen differences such as you note in my own development -- Film A in Developer X takes more time than in Developer Y, but for Film B, Developer Y requires more than than Developer X. I expect it has to do with the way the emulsions interact with the specific developers, but I don't understand the chemistry well enough to provide any scientific explanation.

All of the above! Your reasons are valid, Ian's are valid and so are SRS's. The MDC should be considered a starting point only and you can find some crazy times. These are submitted by people and who knows their reasons for that dev/time combo. The chart should used with test rolls in mind. If they work, great, make a note of it and you can use that time again.

Over the years I've only ever found one company who's development times for their films (and other brands too) with their own developers and suggested EI's that was accurate. That's Agfa, and all because they use the far more accurate DIN method for testing. It's still there in the ISO speed 100/21°.

Ian

I do only use MDC for starting times, but the difference on this one made me ask why (more as a philosophical question as I've been reviewing chemistry again). The times for Ilfosol S match up with Ilford's info and the times for Sprint match up with their info. I haven't had bad results with Sprint, but I haven't used Ilfosol S much. I'm sure someday I'll get converted to rodinol or some such....