Interesting Observation with Tmax 100

14 July 2007

This afternoon I was doing some film testing using Tmax 100 developed in
HC110 (1:79) when I came upon a very strange effect. A little background is needed here. I exposed two sheet of 4x5 film in such a way as to create a "step wedge" that ranged from fb+f to Zone VIII exposure. My target was a grey card metered to Zone V. I am processing using a Jobo tank on a motor base. I rated the film at EI = 80. I measure gamma between OD for Zone III and Zone VIII exposures.

In searching for the correct development time I processed one sheet for 9:15 min and another at 11:00 min. When I measured the density of each step, and the two sheets had exactly the same OD values (gamma = 0.52). This did not make sense to me at all, especially when Delta 100 (tested at the same time) showed the normal progression of more density with longer development.

A review of the technical bulletin published by Kodak for Tmax 100 states that if this film is exposed at EI = 100 or 200 the development times are the same for all developers listed. However, when the film is exposed at EI = 400 then the development times increase between 40% and 100%. This does not make any sense to me. Does any one have and explanation?

Regards,
Darwin

The EI of a film is not a fixed value. It changes as a film is developed longer or shorter. So if a film is exposed at two stops less, it would require a longer development time to arrive at a useable negative. Of course there are limits on this.

Also Tmax films have a larger exposure latitude than conventional films. This means that "underexposing" by one stop (rating Tmax100 at ASA200, or Tmax400 at 800) shows little difference in neg quality compared to when exposed at the rated ASA when developed at the same time, temp and agitation.

The flip side of this is that Tmax films supposively have a reduced development latitude than conventional films...changes in time, temp or agitiation will have a greater effect in contrast than with conventional films.

Vaughn

One possibility--you're using a fairly dilute solution of HC-110, and in a Jobo you would be using less solution per sheet than with other methods. It may be that the developer is becoming exhausted before 9:15, so additional development time isn't producing any additional development.

Try a more concentrated solution and see if you get the same result.

Vaughn said:

Also Tmax films have a larger exposure latitude than conventional films. This means that "underexposing" by one stop (rating Tmax100 at ASA200, or Tmax400 at 800) shows little difference in neg quality compared to when exposed at the rated ASA when developed at the same time, temp and agitation.
...
Vaughn

Click to expand...

TMax 100 does indeed have a lot of latitude, but most of this is at the high (increased exposure) end rather than the toe. That is simply because of the way the ISO speed is determined. You can not recover the low light values (Zones I and II) by pushing badly underexposed film. There just were not enough photons to make an impression on the film. What pushing does is to expand the midtone cotrasts to give a more presentable picture from the undrexposed negative. The picture looks OK because there usually isn't much important detail in the deep shadows. Yes, the EI goes up a bit with increased development, but not usually more than about half a stop.

It almost sounds like the film isn't very sensitive to development time differences up to a threshold at which the EI suddenly increases. I'm a big fan of Tmax 100, but I don't do much experimentation. On the other hand, I do vary the development time to compensate for temperature differences from session to session, so it's always been my assumption that the film does respond to small changes in time. Since I don't do any density measurement, this could be all in my mind (a very fertile place to grow misconceptions).

David A. Goldfarb said:

One possibility--you're using a fairly dilute solution of HC-110, and in a Jobo you would be using less solution per sheet than with other methods. It may be that the developer is becoming exhausted before 9:15, so additional development time isn't producing any additional development.

Try a more concentrated solution and see if you get the same result.

Click to expand...

Agree, sounds like there is not enough developer. Using dilute solutions with the Jobo rotary sometimes requires some clever processing. When I am using Rodinal at 1:100 I use from 6 to 8 changes of solution, during the developmenmt process. http://www.largeformatphotography.info/forum/showthread.php?t=23322

Also, when I used TMX as my main film (this was the old version of TMX), I did the standard Zone System tests using a densitometer, and found that it was quite responsive to changes in development time.

Not to mention--John Sexton at one time used TMX as his main film (I'm not sure if he might be shooting more Tri-X these days, since he endorsed Tri-X not too long ago in a Kodak ad campaign, but one never knows quite how to read such things)--and was certainly using the Zone System.

nworth said:

TMax 100 does indeed have a lot of latitude, but most of this is at the high (increased exposure) end rather than the toe. That is simply because of the way the ISO speed is determined...

Click to expand...

I have not tested the film, other than make some pretty good negs/prints with it, but I have always made the assumption that the toe end of the curve does indeed have more latitude (if that is the way to state it) than conventional films. This also is reflected in the reduced amount of reciprosity failure in Tmax (and Acros) films. Under the redwoods, my exposure times are normally at least 10 seconds and often much more -- that low light responce of Tmax 100 is nice to work with.

But ASSumtions have made an ass out me more than once!:rolleyes:

Vaughn

Vaughn said:

I have not tested the film, other than make some pretty good negs/prints with it, but I have always made the assumption that the toe end of the curve does indeed have more latitude (if that is the way to state it) than conventional films. This also is reflected in the reduced amount of reciprosity failure in Tmax (and Acros) films. Under the redwoods, my exposure times are normally at least 10 seconds and often much more -- that low light responce of Tmax 100 is nice to work with.

But ASSumtions have made an ass out me more than once!:rolleyes:

Vaughn

Click to expand...

I guess it depends on what one means by latitutde. However, compared to a film like TRI-X Tmax-100 has a lot less latitude because its curve shape is almost completely linear, or straight. If you expose right for the conditions, then you hit it right on, but if you underexpose you lose shadow detail. TRI-X, on the other hand, has a long toe, which gives a lot of what I understand as latitude. You can expose the film with a fairly wide range of EI and get shadow detail, though the separation will not be good until you expose enough to bring the shadow up into the straight line area of the curve.

In terms of low light work there is no queston but that the low reciprocity failure of Tmax-100 and Tmax-400 make these films a pleasure to work with in low light conditions. In these type of conditions one will often find that the correct exposure fore Tmax-100 is a lot less than for TRI-X.

Sandy King

ic-racer said:

Agree, sounds like there is not enough developer.

Click to expand...

A third vote for this. I believe Kodak has published a recommended minimum quantity of stock solution for 80 sq in of film for HC-110, but I can't recall what it is. For XTol, it is 100ml.

Ed