Temperature Compensating timer for the SP-445

[neil poulsen]

I don't see the need for a compensating time so much for printing as for film development.

I have my own dip and dunk method for film development, and using my Zone VI compensating time, my batch to batch consistency is really excellent. During calibrations, I use 12 sheets of film developed in three batches of four each for each zone. Looking at my densitometer based graphs, there's no evidence that the graphs cross three different developments. For me, this consistency is important to get effective results.

If one is printing a negative from notes they've collected previously, and they want to get exactly the same result, then I can see that a temperature compensating time AND a compensating enlarging timer would both be important.

But for me, printing is an iterative process. I will always check the print for the result I want as I print, versus relying on a previous time. If one needs any compensating effect during printing, it's enough for me to occasionally check the developer temperature periodically and then heat or cool the developer appropriately during the printing session.

Another comment, even when using my developing compensating timer, I try to make sure that I'm within about a degree F (or maybe a little more) of my desired temperature of 70 degrees. My Zone VI timer has two settings, one for film and one for paper. Compensation for these is based on two different logarithmic relationships from a family of logarithmic relationships. That doesn't mean that they are necessarily the "perfectly correct" logarithmic relationship for each type of development. Any problem that the original Zone VI choices for these two relationships might cause is minimized by at least staying reasonably close to my desired temperature. My compensating timer can make up the difference within that range.

[Drew Wiley]

I use the Zone VI timer for both film and paper development, and would hate to be without it for either. Yes, I know all about drfit-by temp control and own
several other devices dedicated to maintaining temp, including an expensive thermoregulator that can keep temp consistent within 1/10 degree F for really
fussy applications like matched color separations. But for ordinary work, the Zone VI probe is ideal, and I'm certain that if you gave this or the new equivalent to one of our lurking skeptics as a Christmas present, they'd never return to their old habits again. Of course, you need to be reasonably within
the temp ballpark to begin with. Most developers simply don't perform as planned if the temp is way out of whack.

[peter schrager]

I realise that this is an old thread but I found it when we were working on a new temperature-compensating timer, which is now available. It offers similar functions to the ZoneVI timer.
http://www.dlgelectronics.com/compensatingtimer.html

good job David!!

[Dave Gooding]

Neil, Drew,

Completely agree with your comments on compensation being imperfect and the need to remain reasonably close to the “optimum” temperature.

Although I have only very limited experience of photographic processing we did consult with a former professional large format photographer throughout the development of this timer, and also together with him reviewed his fairly extensive library of suitable books. The conclusion of this effort can be summarised as - any attempt to compensate for temperature during development is a bit of a fudge and will give a first-order approximation only. Second order effects remain. Therefore, keep the temperature as close to the nominal as is reasonably practicable and apply temperature compensation at roughly the right temperature coefficient to address the remaining temperature error.

We have published a document on our website outlining our rationale for the compensation curves implemented in the timer (and which also gives a selection of time-temperature charts) - http://www.dlgelectronics.com/docume...T-004%20V1.pdf. This may be of some interest to those who take an interest in this sort of thing.

[Bill Burk]

For a person who really wants to achieve consistency in their results, a compensating timer is a great thing to have.

Before I got hooked up with one, I would spend the first hour of darkroom time regulating my running water temperature trying valiantly to hit a steady temperature as close to 68-degrees F as possible. If temperature fluctuated more than a couple degrees F I would defer starting a process until I got better control.

Now I focus my attention on getting a steady temperature near 68-degrees F. Then I let the compensating timer take care of the time adjustment.

It's a minor difference in phrasing, but it reflects a big change in attitude. One is a somewhat stressful focus on trying to reach perfection... The other is a more relaxed focus on getting the temperature in range.

Looks like a great device Dave Gooding, best of luck.