<p>At what speed are you rating your film...what developer are you using...<br>
12:30 sounds like a slight "pull" of the HP5, if you're using ID11 as your developer, (don't know which Delta you're referring to), and as Mr. Monday states, highlights will be affected most. If your exposure is a little under, say 1 or 2 thirds of a stop, you should still get very reasonable results, your contrast will increase a little, nothing wrong with that if that's what you're after. Most B/W films are very forgiving, and can tolerate a little in either direction whether it be exposure or development.</p>
<p>I think that small percentages in development times aren't too problematic, but when you start getting into the 10% range and above, that's where things start to show noticable differences.<br>
Key is, be consistent in your methods so that results are repeatable. Don't be afraid to experiment with exposures and development, that's how we've all learned. <br>
One other thing to consider...are you printing in a darkroom, or...do you intend to scan the negatives and then have them printed?<br>
Most of all...have fun with it!</p>
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