film speed and development time.

[mitch brown]

i am just starting to shoot arcos 100 and want to do a film speed test. the formulary states 14m at 70 d for PMK which is the developer i use. ed buffalos site says 11 m at 70 d ei of 50 for pmk. to determine my film speed which should i use? what effect would the 11m @70d have on the film speed vs iso 100 for 14 m@70.
mitch

 

[Steve Sherman]

The speed of the film is determined by exposure not with development almost without exception.

That portion of the film development test is done very early in the development, extended periods of time in chemistry will only add base fog.

Rule of thumb, cut the film manufacturer's rating in half and you'll be close.

Cheers, Steve

 

[Paul Howell]

The old adage is that exposure sets the shadows, development sets the highlights. That being said there are many factors that need to be taken into account such as the accuracy of your meter and shutter. I tend to agree that for me to obtain good shadow details I tend to rate my personal film speed lower than the box speed. I shoot 35mm, medium fortmat and 4X5, each system has a differnt personal film speed for the same film.

 

[mitch brown]

i understand what has been discussed above. i am confused as to which development time to use as they are 30% apart.
mitch

 

[Ray Heath]

The speed of the film is determined by exposure not with development almost without exception.

g'day all
Steve, isn't that a little simplistic and wrong?

Surely exposure and development determine film speed (sensitivity).

To create 'good' negs of the type of subjects I normally photograph, my experience is to use a good quality film exposed at half the stated ISO, developed in a 'normal' (manufacturers recommended) developer for 30% less than the recommended time i.e. over expose and under develop.

 

[Steve Sherman]

g'day all
Steve, isn't that a little simplistic and wrong?

Surely exposure and development determine film speed (sensitivity).

What the statement means is the lower values, Zone 1 for instance is set by the amount of light which strikes the film, no amount or variation of chemistry is going to significantly raised the density of Zone 1. Therefore, film speed is determined by exposure. Highlight density can be altered any number of ways through time, temperature, agitation technique, chemistry and still other variables which would only serve to confuse the issue.

My initial response was aimed at the 30% time difference and the fact that it would have no impact on the speed of the film.

A good friend of mine, Kodak Rep for 25 years, he once told me that ALL film is developed in 2 minutes, the rest of the time is just to build contrast.

He basically meant that the low values on the negative were developed at the very beginning of the development cycle and would not increase in density due to time in chemistry.

We are both talking about the same principles I believe.

Cheers.

 

[srs5694]

Tom Halfhill wrote an article on finding your film speed. (Part 2 is posted separately on the Web.) The process he espouses involves testing film at whatever development time is recommended or that you guess and then possibly running the test again at another development time, depending on the results you get. I'm not enough of a film theoretician to either endorse or debunk his procedure, but I've tried it on a couple of film/developer combinations with results that satisfy me.

 

[jim appleyard]

Thanks, I belive that article appeared in Shutterbug. Very good it was/is.

 

[Roger Hicks]

i am just starting to shoot arcos 100 and want to do a film speed test. the formulary states 14m at 70 d for PMK which is the developer i use. ed buffalos site says 11 m at 70 d ei of 50 for pmk. to determine my film speed which should i use? what effect would the 11m @70d have on the film speed vs iso 100 for 14 m@70.
mitch

Dear Mitch,

Isn't that the point of testing, really, in order to find out?

Manufacturers' ISO speeds are almost invariably correct to better than +/-1/3 stop and are replicable by anyone working to ISO standards and using the same developer.

This is not the same as saying that ISO contrast/speed suits you, or that you will get the same speed in another developer.

As soon as you depart from ISO development condtions a great deal depends on curve shape. Some films will change very little in speed with changes in development. Others will change quite a lot.

It's also easier to wipe off true ISO speed than to gain extra ISO speed by developer choice.

Most people find they like the tonality most -- which is NOT the same as ISO speed -- when they expose generously: 1/3 stop to 1 stop more than the ISO speed. But a lot depends on how you meter, too. Meter the shadows with a spot meter, and don't under-develop, and you'll usually be able to use the full ISO speed. Use a broad-area reflected light meter, or a matrix meter, or worse still incident light metering or a grey card (both of which key exposure to highlights, not shadows) and your EI can go all over the place, almost invariably down, even before you start faffing around with developers and development time.

Cheers,

Roger (www.rogerandfrances.com, where you'll find more about this sort of thing)

 

[Nick Zentena]

One problem with published times is they seldom mention what contrast they are aiming for. Both the times mentioned could be correct for different contrast points. Or maybe they use different types of agitation.

 

[Scott Peters]

Roger brings up a great point. i.e. the film curve and how you meter in the field (some films perform better in different sbr ranges) plus consider what process you are printing (i.e. silver or alt. process) and developer type which may increase speed...

So, I would actually test in field with real metering and sbr ranges, etc. with different exposures and development and actually make prints to see what works best. Shoot six of the same images in the field - three at box, three at half - using your metering technique. develop normal, minus and plus...and then attempt to make your best print. SEE what you like...

 

[gainer]

One thing we tend to forget. When the H&D curves are plotted, the extensions of the straight portions of the curves usually meet at a point, which is often below the horizontal axis. Even if they do not, if you look at those curves and at the curve of contrast index vs development time, you can predict the variation of effective film speed with change in C.I. If you always develop for the same C. I., you always get the same film speed. If you don't care about highlights, you can overdevelop and sometimes get more shadow detail, but you can tell from the curves if that's going to work.