P.S. If you just don't want to or can't afford the chart, you can use a grey card. To do this, the shooting procedure is a bit different. You must actually tonally "place" the card at various spots on the grey scale via exposure. IMO, the chart is much easier, as you get the whole grey scale in one shot.
"Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."
- Rob Tyner (1944 - 1991)
I'm more obsessed with highlight detail..Evan Clarke
Originally Posted by clayne
Originally Posted by aleckurgan
Actually you missed something Ron
Originally Posted by Photo Engineer
This is a very old and extremely well known test which has largely gone out of use since WWII.
The Watkins test dates back to 1893, and essentially every developing agent has a factor in the case of D31 & Metol it's 17.
It's probably no worse than developing almost to completion to find the minimum time to give a full D-max, as that will almost certainly give over developed contrasty negatives.
When you start with the strip, it is entirely the same density. Dip one end in developer, and it begins to darken (and lighten) at the same time. It darkens due to development and lightens in some cases due to loss of acutance and trimmer dyes which differ from film to film.
You end up with a light end and a dark end. The only time that they can match is at the very instant the test starts. And, the rate of change will vary from film to film more due to the dyes which were not present to any extent before WWII.
Therefore, there are a number of problems with this test, as written above.
Perhaps Ian can rewrite the procedure so that it can be clearly understood. I have read and studied it a number of times and it is as clear as well used Pyro stain.
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As the Watkins test is to measure the time for the first visible signs of development starting Alec's method is quite an elegant method although perhaps a control with a piece of in water as well would be useful.
It's a bit academic as it's better to do some quick and simple development test. But the Watkins test was once relied upon by some photographers and experience would improve a users accuracy of interpretation.
In modern films, as I point out, the color of the film is often dependant on dyes in the film, whereas in old films this was not the case. Since dye removal is diffusion dependant, and this is also dependant on thickness this introduces a fault into the method.
Modern films use t-grains and also development rate modifiers. This affects rate.
I see this and observation errors interfering with the test. Also, do you look at the emulsion or the base side? That would be an important factor to include.
I think this test is not well described above and even so, would appear to be outmoded by modern films. Have you tried it since 1944 Ian?
I'm not as old as you Ron so I'd no chance to try the test in 1944
Originally Posted by Ian Grant
I can see the test working as described, but how well neither you or I can possible know or guess as we haven't tried it. I can also see all the potential problems but then the dyes used for early sensitization would have also cloudied the results 80-90 years ago.
That's why I think it's academic, but may work as described with certain films & developers.
actaully, on a related note.
i have been taking published times from manufactures, sites and people on here and trying to generate the mathmatical functions around each of the developer, film and so forth. The easiest has been with xtol replenished, which has a great polynomial function and a nice high r^2 in the warmer temperatures (with neopan 400), though it does seem to have a bit lower fit quality at colder temperatures.
the forumula so far with the data ive coolected neopan400 in replenished (large tank) xtol
y = 2.4737x^2 - 148.41x + 2472
My reason for mentioning this is that there, as im sure everyone reading this knows, there is not a linear relationship back and forth between different soups and films, and not even within the same developer and film combination, neo400 in stock (fresh) vs stock(replenished) the same function does not apply, nor is the responce looking to be polynomial for the stock(fresh).
This is all just me being a every curious scientist.
Originally Posted by BetterSense
I've always taken the film Mfgr's suggestion for D-76 (straight) as a starting point for D-23. It is close enough. So, for example, whatever Fuji recommend for Acros in D-76, that is what I would start with for D-23. Your method sounds pretty good too. No matter what you do, even if the mfgr provided an number or there were a number on the MDC, you would still have to do your own testing and, very likely, you would come up with your own number. There is just simply no hard and fast absolute when it comes to development time or exposure index.