Different times for Delta400 @1600 in Xtol 1+1 by Ilford and Kodak

I really love Delta400 and I really love Xtol. I like to push my film to 1600 to shoot indoors. Usually I develop my Delta using the recommended 14:30mins at 20C published by Kodak. Only recently I discovered that Ilford recommends 20mins. Why is there such a large difference in recommended development time. I know that these are just starting points and you should test your film and find your own sweet spot. I am just curious why.

Thank you and all the best, Christian

Welcome to Photrio.
Most likely because Kodak's recommendation for two stop under-exposed film is weighted toward maintaining highlight rendition, at the expense of not maximizing near-shadow and mid-tone contrast, while Ilford's recommendation is weighted toward enhancing near-shadow and mid-tone contrast, at the expense of highlight rendition.
Kodak uses similar rationale when they recommend that you not increase developing time when you under-expose the T-Max films by one stop.

It may also be that Kodak is using a Contrast Index for developing time and Ilford is using a Gamma. The two methods are similar but not the same. The math is entirely different, but we are photographers not mathematicians.

darkroommike said:

It may also be that Kodak is using a Contrast Index for developing time and Ilford is using a Gamma. The two methods are similar but not the same. The math is entirely different, but we are photographers not mathematicians.

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I hadn't realised there was such a big difference( 38%) until I saw this thread. I was shocked like the OP. The same large percentage difference in Kodak and Ilford times apply to HP5+ when exposed at EI1600 so the above looks as if it might fully explain the differences. However I then had a look at times for both films at box speed in Xtol and now the difference in Kodak and Ilford times for HP5+ is zero. For D400 at box speed Ilford time is longer but only by one minute - 11.5 mins Ilford and 10.5 mins Kodak - which makes the difference only about 9%

So is there something else at play here other than different measures such as C.I. and Gamma?

Thanks

pentaxuser

pentaxuser said:

So is there something else at play here other than different measures such as C.I. and Gamma?

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Yes - see my post earlier in the thread.

Thanks Matt. I had looked at your explanation but it seemed to be aimed at explaining the Kodak/Ilford differences for underexposure in terms of different emphasis by the 2 companies on hightlights v shadow and mid-tones and it certainly seems to fit with the OP's questioning the time differences. In other words at 2 stops underexposed there is no such thing as a "free lunch" and a choice between mid-tones or highlight has to be made. Each company has made a different choice and the person who underexposed the film by 2 stops can decide which is the right emphasis for him - of he uses Xtol(see below) .

However when we move to box speed there is no difference in one film (HP5+ ) and almost no difference in the other D400.

Is it the case that at box speed such choices of emphasis between near shadow and mid-tones v highlights are no longer required so the developer(Xtol in this case) adequately covers all tones equally in D400 at a common development time?

I had a quick look at only 2 identical developers used by Kodak and Ilford (D-76 &ID11) and for D400 @1600. Here the times are identical which is intuitively what you would expect. Does this indicate that with 2 stop of underexposure, some developers do not require an either/or choice as you refer to in your post but others such as Xtol act differently on the tones when dealing with a 2 stop underdeveloped film and a choice is required by the user as to whether he wants to emphasise near shadows and mid-tones or highlights? It would look as if on that basis he can avoid an either/or choice by using either ID11 or D76 but with Xtol he must choose

Is that a reasonable conclusion I have drawn or are there flaws in it?


pentaxuser

pentaxuser:
I think my head hurts .
Different films react differently with different developers.
Clearly, both Kodak and Ilford agree about the best development time to use when the films are exposed at their optimum setting (the box speed).
But once you stray into the area of meaningful under-exposure, accompanied by a potential change in development, the opinions diverge.
It isn't so much the effect of under-exposure we are talking about here, it is the effect of the increased development. The under-exposure affects the shadows in basically the same way, whether you develop normally or increase the development. The highlight (and to a lesser extent the near shadows and mid-tones) are more likely to be affected.
If the highlight areas in the films respond more to increased development in X-Tol then they do in D-76/ID-11 (or vice-versa), than that leads to a different judgment about the compromise one chooses to make.
It may be that D76/ID-11 causes Delta 400 to block up quicker, so there is no benefit to going as far as you are able to go with X-Tol.

Thanks Matt. For sure it is a complicated business

pentaxuser

pentaxuser said:

Thanks Matt. For sure it is a complicated business

pentaxuser

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It is but it doesn't have to be. Pick one film and one developer and find results that you like. And then, when ready to move on, change one thing at a time.

Thanks darkroommike. My reference to "complicated" was aimed at working out why times between Kodak and Ilford vary by a lot in some developers(Xtol and D400 @1600 being a good example) and almost nothing in others(HP5+ @1600 in Xtol being another good example) when you compare Kodak and Ilford times. Actually it was you who make what may be a pertinent point in an earlier post. It may be, probably is, that the problem lies in Kodak and Ilford working to different levels of contrast Kodak actually states C.I.(contrast index) in its tables but what does Ilford use? Whatever it is, is there a "conversion" available that puts the Ilford contrast on the same level as Kodak and from can the time differences be reconciled?

So if the Kodak CI of say 0.65 for D400 @ 1600 in Xtol for 10 mins is converted for the Ilford chosen contrast then would this result in the Kodak time being close to the Ilford time?

I hope I have managed to explain my point properly.

pentaxuser

I'm wondering whether the sensitometry experts here could chime in on this.
Contrast, Contrast Index and Gamma are measured in different ways. I expect that a choice made to emphasize different factors (e.g. mid-tone separation vs. highlight separation) leads to different measurements, whatever measurement standard is used.