Tray development vs rotary development of black and white film

**Marco Annaratone** · 3-May-2022, 10:37

During the characterization of some 4x5 film as per the BTSZ approach I realized it could have been useful to measure the difference in densities between a conventional tray-based development and a rotary one (Jobo CPP-2 with 2520 tank, in my case).

=== The experiment ===

Ilford Delta 4x5 100 Pro developed in XTOL 1+1 @ 70F.

Five times: 4:00, 5:45, 8:00, 11:15, and 16:00 (minutes).

The 5+5=10 plan films were exposed sandwiched with a Stouffer TP4x5-21 step-wedge under identical light conditions. Exposure time: 0.5s.

Five films - one at a time - were tray-developed, 350ml developer, constant agitation.

Five films - one at a time - were developed in a Jobo 2520 tank with rotation speed "F".

All films densities were measured with a two-year old Heiland TP2 densitometer that I purchased new. I turned on the densitometer and waited a couple of minutes so that it reached thermal equilibrium. All films were allowed to dry for 24 hours before measurements took place.

The first graph shows the densitometric curves of all 5+5 films.

https://tinyurl.com/s86vv9xv

The rotary development produces negatives that are always (slightly) darker than those obtained through tray development.

The second graph - more interesting from a quantitative point of view - shows the difference in density - wedge-by-wedge - between each tray-developed and rotary-developed film, same development time.

https://tinyurl.com/vkzee6p3

=== Results and comments ===

Each curve pair (tray/rotary) - irrespective of development time - shows a difference in density within one third of a stop. The entire tray-developed family - when compared to the whole rotary developed family - shows a difference in densities between +1/3 stop and -1/6 stop.

The development temperature was controlled by the Jobo system. In the case of trays I prewarmed the development tray. Room temperature during tray development was 68F, i.e., slightly cooler than the developer.

This is only a single <film/developer> data point, I realize that, but these results are somewhat encouraging when one wants to use BTZS curves obtained by tray developing in a rotary setting and viceversa.

As far as vertical tank development is concerned, I'd rather see someone's experiment before assuming that film characterizations obtained in a vertical tank can be used in tray or rotary development. For one thing, vertical tanks do not typically assume continuous agitation.

More such experiments would certainly help. I am sure others have done similar tests, it would be great if someone posted some links.

Cheers

**Michael R** · 3-May-2022, 10:57

Looks pretty good.

Keep in mind development non-uniformity can easily contribute to differences of a few density points from sheet to sheet (even if they are exposed/processed identically), so there will always be variation from that, in addition to normal error/noise. One way to improve the data (albeit only slightly) is to average several densitometer measurements for each wedge step, but this obvious becomes time consuming and in the end adds little value.

**xkaes** · 3-May-2022, 11:37

This is a great report, and a lot of work. I've done similar tests but only to determine film density with my rotary tubes -- to determine effective ISO for my films -- not to compare processing methods.

I think if you expand the Y-axis on the second graph to +/- 1 f-stop, the differences would appear more realistically -- very minimal.

Well done!