kaiyen said:
Jobo's might be continuous, but they are not violent. And there is a perhaps subtle but definitely important difference between strong and violent agitation. It is possible to agitate too little (unevent development, insufficient breakup of flow from being too regular), but it isn't really possible to agitate too much. But it is possible to agitate too violently (surge marks).
As others have said, DON'T change your agitation method UNTIL you have changed your dev time and proven that inadequate. If you can stick to your agitation scheme and find that changing the dev time is sufficient, then there you go. But perhaps you come down to 3.5 minutes, which is too short. Well, then maybe you can decrease your agitation. BUT - even then it's more advisable to dilute more rather than agitate less.
For reference only, I do 5 inversions in 10s. 10s of agitation per minute.
allan
By the way - you raise a good point, and it might be good to explain it further for those who are new to B&W developing - the issue of the developing time being 'too short'.
As most of us know, for most developers, you can adjust several factors to affect the level of development of your film:
1) Temperature
2) Developer strength
3) Agitation method and duration
4) Time in developer
Within a given range, temperatures that are warmer will cause faster development than temperatures that are cooler. Not true of all developers - some are 'panthermic' or 'all temperature'. But not many are, and they are usually labeled as 'panthermic' if they are.
Developer strength can generally be adjusted by the dilution with water one gives the developer working solution by mixing. Common dilutions are 1+1, 1+19, 1+50, but there are others. One thing to consider is that different developers take on different properties when dilution is increased - more grain and more accutance, for example. One must read the directions for that particular developer.
Agitation is usually a personal decision. Some is usually needed, but many differ on how much is enough and how much is too much. Suffice to say that more agitation will tend to increase development and too little will cause uneven development as developer is exhausted and stops working in one area, while micro-currents bring fresh developer to another, etc. Usually best to find some method that works for you and ALWAYS DO THAT, whatever THAT is.
Time in developer is the really interesting part. You see, it is best to avoid soaking your negs for a really long time. Although many have reported soaking negs overnight (yikes!) with no ill effects, the emulsion is made of gelatin (jello, essentially, ground up boiled horses hooves and etc) and it is instantly soluble in water. The longer in the developer, the more chance of physical damage.
However, one must also avoid developer time that is 'too short' as Kaiyen mentioned. What is 'too short' and why?
This is due to the mystery of proportions.
Imagine a rectangle with a diagonal line going from the lower left corner to the upper right corner. This line represents percentage of development - from 0% at lower left to 100% at upper right. The X axis (along the base of rectangle) represents time. The Y axis (up and down along the sides) represents percentage of development. As you can imagine (I hope), the less time you have, the steeper the line, so more actual development happens 'per minute' of time passed.
And film doesn't actually develop in a straight line - it offers more 'food' for the developer to much on at first, and later the developer has to hunt for crumbs. So the line is more of a upsweeping curve than a straight line. The last minute is less important that the first minute - but if there are fewer minutes, you interrupt more development by stopping development early or going too long.
Since, most of the film developing happens first, with less and less happening as each minute passes. Eventually, it would reach a point where there was no more silver halide to be converted and development would cease, but for most developers, this is to be avoided - your negs would be seriously overdeveloped, giving 'lith' effects or even totally black!
So if you make a small timing error in a ten minute development time, it means a tiny bit of remaining development gets interrupted. If you make a small timing error in a five minute developing time, a much larger percentage of the development has been stopped before it can happen.
It is therefore much harder to control precise development of B&W film with times that are less than five minutes - this is usually considered the absolute minimum. Ten minutes is much easier to work with, and longer times even less likely to mess up due to miscalculation of developing time.
However, you can't just 'decide' to increase your dev times. You must compensate with something else or you will over develop your negs. Lower film temperature, lower concentration of developer to water, something like that.
There are compensation charts that will get you in the general area, or you can use resources like the Massive dev chart to find out what has worked for others before with your film/developer combo. You may notice that most dev times listed are more than 5 minutes. Some few venture into 3 minute territory, but frankly, I find that impossible for me to control properly.
So that's what it means when people say to avoid dev times that are too short.
Best Regards,
Bill Mattocks
