HP5 - Contrast Index [CI] curves

[Gabino]

Hi Everybody -

I was wondering if anybody have come across with CI curves for HP5 similar to those available for TriX400 (attached) for several developers ?

thanks for comments,
Regards,
Gabriel

 

[Jim Noel]

THere is a lot of info on the HArmon site about their films. Kodak's charts are unique to them, but you should be able to interpret all the info you need from other presentations.

 

[Gerald C Koch]

The term Contrast Index was devised by Kodak and was never accepted by any other manufacturers. It is calculated in a slightly different manner from the more common Gamma value. So when looking for information on non-Kodak films you will probably be more successful using the term Gamma rather than Contrast Index.

 

[Gabino]

thanks Jim -

Gerald: should I find and then compare Gamma values for combinations of Developers and Developing times ? thank you !

 

[Gerald C Koch]

thanks Jim -

Gerald: should I find and then compare Gamma values for combinations of Developers and Developing times ? thank you !

A brief search of the net failed to find anything similar to Kodak's graph on the Ilford site. You might find something on a developer manufacturer's site.

 

[Bill Burk]

Gabino,

I think those time-contrast curves are the most beautiful thing, maybe I'm starry eyed because I make them up for myself and so I think everyone should maintain their own set of curves.

All you have to do is figure out how to measure a developed film's contrast. The time is obvious (I laugh because on APUG nothing is obvious. The time is how long you developed that film).

You developed some film for X minutes and you got Y contrast. You get a point for every combination you try.

This is where it helps to stick to one developer and film, because it doesn't take long before you have a time-contrast curve of your own.

If you DO locate published curves, you can compare your results to the curves, and draw a conclusion such as... "My times tend to be a little longer than published times"...

Or if you are like me, you find "My times are consistent with the published curves, so I can expect good approximate results if I change developer"

In a recent thread I told how I always worked to time-temperature charts from manufacturer, and this force of habit helped me in the long run, because really my times do agree well with published times... Except in certain cases such as tray processing.

 

[Gabino]

Gerald : Yes, I had searched on Ilford's site but I haven't yet on the developers data sheet or website. Thanks !

Bill Burke : Reading off of 'The Negative' by AA, contrast (gamma) corresponds to the slope of the straight-line portion of the curve. Ok, so, for this I necessarily have to use a densitometer, right?. I am stalled there... I don't have one. It was a nice idea to use these curves if they were available from the manufacturer. But I can move on without them. I am on my second year of my PhD and nights are getting shorter and shorter as it is. thanks anyway !

 

[Bill Burk]

Gabino,

Yes, contrast is the slope of the straight-line...

Of course you can proceed with or without time-contrast curves. Most people do, and do fine.

But if you have anything that can measure or compare a negative's densities, even approximately, I (we at APUG) can help you get film processing under control... To a degree that isn't commonly achieved by amateur photographers.

The thread might get kind of long if we go into details... But the procedures that get worked out will likely be very simple.

It might be as simple as taking two shots - two f/stops apart... and seeing if one shot takes twice as long to print as the other.
-If you can do that, you have 0.50 contrast (gamma), which contributes a point on your development time-contrast curve.

 

[Xmas]

The useful thing is the toe or run out slope at the bottom of exposure. When you make an exposure error...

Im told HP5+ is softer than Trix, ok that HP4 slope was softer so never bothered to try Trix... Although Double-X is not much different from HP5+.

 

[ic-racer]

Be careful interpreting those graphs in the OP. They are intended to show two things.
1) How careful one needs to be with time/temp control for various film/developer combinations
2) Useful range of times at 20c

The actual CI values in the graph are of little value to you without access to the Kodak research darkroom in which the studies were conducted.

 

[Gabino]

Bill -

Besides a densitometer I see that I need a darkroom for printing. I scan my negatives though. Well, I signed up this summer for the use of the darkroom at the University of Waterloo, but I haven't been able to make it there yet. I don't know if they have a densitometer there but I'll ask.

As few as two shots, ah? that's certainly doable. I'll get back to you. Thanks for your comments !

Xmas and IC-Racer: thanks for your comments.