Development time versus negative denstiy

So I just finished developing two rolls of Delta 100.

I just realized that I had been developing for too short a time.
The package says 20c for 10 minutes, but I had been developing
at the ISO50 mark of 6'30...

So my problem is that I now have really thin negatives. Is this correct?
Why, if I were actually shooting at the correct F-stop/shutter speed,
would more development time create thin negatives across the board?

Perhaps I need to rethink something... any thoughts?
All the rolls that I have shot previous were not thin, in fact, they
produced some really great negatives. All these were developed at
the wrong time of 6'30.

Dear JohnRichard,

Believe it or not, one stop is not the killer than many imagine. You don't say how you determine your exposure so it is difficult to determine just what your situation is. It is much more probable that there is a variation in your process (exposure through development) that you are unaware of than a problem with your camera or film. While there are many possibilities, without more information on how you work the guessing could go on forever. Do you use fresh developer when processing film?

"Why, if I were actually shooting at the correct F-stop/shutter speed, would more development time create thin negatives across the board?" More development time would not create thin negatives.

Neal Wydra

Well, thanks for the responce Neal. I ran another 2 rolls through the soup at my regular 6'30 (wrong time per instructions mind you) and the negatives came out "regular" for me...
So I don't know. I guess I'll just stick with my time tested method. Who knows...


JRY

Sounds to me as if you had in fact made an error in exposing the two bad rolls. Generally speaking, increasing development increases contrast. The shape of the curve of contrast vs time of development is similar to the time history of the EMF on a capacitor being charged through a resistor to a fixed voltage, if that means anything to you. The contrast rises at a rapid rate initially, and the rate reduces as the contrast approaches the maximum attainable.

If you do a test roll and develop half of it for 6.5 minutes and the other half for 10 minutes, you should not see a great difference between them.