Finding starting point developing time without data

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.

Ian

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?

PE

Ian Grant said:

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.
Ian

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I'm not as old as you Ron so I'd no chance to try the test in 1944

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.

Ian

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.

BetterSense said:

I recently switched to d23 and found it hard to find development data compared to d76. I actually went to the MDC and made a spreadsheet comparing average ratio of d23 times to d76 times so I would have some idea where to start on films like Acros that have no data available (I found that about 75% of the d76 1+1 time was average for a d23 time). Even Kodak datasheets don't give d23 times.

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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.

As Kodak used to suggest the D76 times for D23, then what your saying Brad is 100% applicable

Ian

I can see a problem with well aged Rodinal. You can't see the part that is submerged. I guess the agitation wold have to consist of dipping and removing.

hallo
my newest d-23 experiences:
no theoretical formulas etc. test in the field with tri-x 400 pushed at 1600 in d23 1+3 for 45 minutes (d76 20 min multiplicated with 2.25 for puh 2) continous agiating for the first minute then 3 times all one minute.
works well->printable negatives (so far i can see, because no darkroom at this time (scans are ok)

little troubles in the shadows (not all pics)

and there i think is the problem that there are different lightning situations and so on.
the combination works well for the one but not for the next.

I did try the method with FP4+ and EDU 400 Ultra. I found that the part under the surface IS initially lighter than the part above. It does darken, of course. The time at which the match occurs required a little anticipation as the change was accelerating. I found a factor of 17 to work pretty well with both accurately measured D-76 and a personal PQ formula that I used years ago and measured by the spoons. I had forgotten my developing times, so needed a starting point. I hit both of them dead on for a straight print at normal paper grade. I jumped the gun in this post, as I meant to see if the film was lighter in plain water than dry. I'll go back into the dungeon and let you know, or you can test it for yourself.

It appears to be something in the developer that causes the initial lighter cast of the submerged part. Both contained sulfite and hydroquinone. Anyway, I'll keep using the method until it fails. I have a bountiful sufficiency of sulfite-free developers.