Film speed test failure?

Several months ago I had a film speed test done for me, HP5 400 in D76 1:2 at 75 degrees ( I live in Florida, cooler is difficult). The test (exposed negs that I developed only) resulted in a speed of 160. I did my own test yesterday, same film but D76 at 1:1, and the result was that 400 was the speed I should use.
Could the dilution affect the result? The fact that my camera was used? Should I re-do the test coz I probably messed up?

I'd stick to 1:1 for D-76.

Thanks Nicholas, but do you think the difference in dilution would account for the discrepancy in film speed?

coops said:

Several months ago I had a film speed test done for me, HP5 400 in D76 1:2 at 75 degrees ( I live in Florida, cooler is difficult). The test (exposed negs that I developed only) resulted in a speed of 160. I did my own test yesterday, same film but D76 at 1:1, and the result was that 400 was the speed I should use.
Could the dilution affect the result? The fact that my camera was used? Should I re-do the test coz I probably messed up?

Click to expand...

Did you test exactly the same as the person who made the other test several months ago? If not, describe your method of testing.

There are many things that could explain a difference in results, from conceptual errors of methodology to simple errors in execution.

Sandy King

D-76 will work fine at various dilutions, or no dilution at all. The key is being consistent.

This is a good example of why we do film speed tests in the first place. A film speed test done by someone else is no better than using box speed.

The point of the test is to determine what speed you get using your equipment, your water, your development methods, etc. If you aren't doing that, you might as well use box speed. It varies person to person.

It also, of course, matters how you determine film speed. Do you do it off of middle grey? 0.10 above FB+F? Did you both use the same densitometer, and were both properly calibrated?

Usually, the more dilute developer will make for a higher film speed, if using the 0.10 over FB+F method.

However, there are many variables. It could be one of many things that caused the different results, human error and equipment error being high on the list, as always.

(FWIW: Personally, I now usually prefer to rate a film at box speed and just learn its natural dynamic ranges for different amounts of exposure and development, as opposed to finding a film speed for a theoretical zone I density and tweaking things until a highlight lands at a certain density in relation to that. However, the 0.10 method has worked and continues to work fine. The difference is that in doing this, you manipulate the film in testing in order to make it as linear as possible, while with what I do, you simply analyze during testing, and let the film be whatever it is from the factory. Both have their uses, but I generally prefer the latter.)

sanking said:

Did you test exactly the same as the person who made the other test several months ago? If not, describe your method of testing.


Sandy King

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The testing was done by the Viewcamera store: I developed 5 pre-exposed 4x5 negs in D76 at 75 degs using their tubes. They provided me development times and effective film speed. The spped I shoot at based on that is 160.
This time I did my own testing, following the instructions laid out in Bruce Barlows Finely Focused cd.
I developed the film in D76 1:1 this time. Still with the tubes at 75 degs.
Bruce included a nd filter to compare exposures, and the one closest to the neg that receives no exposure should be the effective film speed. My result was somewhere between 320 and 400, but closer to 400.
The viewcamera store test did not require me to shoot the film at all. How do they determine my film speed? Based on their own testing? I am kinda new to this so trying to figure this all out.
Thanks

coops said:

The testing was done by the Viewcamera store: I developed 5 pre-exposed 4x5 negs in D76 at 75 degs using their tubes. They provided me development times and effective film speed. The spped I shoot at based on that is 160.
This time I did my own testing, following the instructions laid out in Bruce Barlows Finely Focused cd.
I developed the film in D76 1:1 this time. Still with the tubes at 75 degs.
Bruce included a nd filter to compare exposures, and the one closest to the neg that receives no exposure should be the effective film speed. My result was somewhere between 320 and 400, but closer to 400.
The viewcamera store test did not require me to shoot the film at all. How do they determine my film speed? Based on their own testing? I am kinda new to this so trying to figure this all out.
Thanks

Click to expand...

In that case, your shutter must be slower than the one they used to expose the sheets they shot, and/or their meter and/or metering method is different, and/or the color temperature of their light source is different, and/or the film batch is markedly different for some reason.

As you can see, it is something that you must do using the same equipment and techniques that you will be using in "the field". Otherwise, the whole point is missed. I can understand the View Camera Store offering a densitometer service, but selling pre-exposed film for testing makes little sense to me.

2F/2F said:

As you can see, it is something that you must do using the same equipment and techniques that you will be using in "the field". Otherwise, the whole point is missed. I can understand the View Camera Store offering a densitometer service, but selling pre-exposed film for testing makes little sense to me.

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The View Camera system is based on BTZS testing, which takes the camera and metering system out of the equation. So it actually makes a lot of sense for the View Camera Store to sell the pre-exposed film since they would be using some kind of very accurate exposing system that is repeatable for all of their testing, and would have by this point calibrated the plotter program to real life experience so the *relative* EFS values that their analysis suggests would be very accurate, assuming that the method of development employed by the user is similar to that upon which their calibrations have been made.

The View Camera store would be using basic BTZS type development, which is remarkable portable in that their results would vary very much from mine or from that of another person doing the same type of testing.

Sandy King

I had Fred Newman do me a HP5 Film Test and surprise surprise it also came out at about 160ASA in ID11 @ 1+1 (Ilford ID11 & Kodak D76 are virtually identical)

However, the results from The View Camera Store are only the start of the journey.

You then need to adjust these Film Speeds & Dev Times to your equipment, your method of metering and your typical subject matter.

I am surprised you found as much as 1 whole stop between the two methods but if all the errors stack up in one direction then it may be perfectly possible.

Not sure why after going to the effort of having Fred run you a film test at D76 @ 1+1 why you would then run a second but different film test at D76 @ 1+2 - it might be better to repeat the your own version of the BTZS test first and then try out some other variables.

Martin

I understand that they have perfectly adjusted their exposure mechanism. However, the key is not absolute technical perfection of exposure, but matching what the shooter will be doing. I don't see how the two tests could perfectly match. The photographer does not take pictures using the shop's perfect equipment. He/she takes them with his/her equipment, which may (in fact, almost certainly does) vary from the stuff that was used to expose the test sheets. The camera and metering system are never out of the equation, because they are what is actually used. How using this system is any better than using the film manufacturer's does not equate with me. They are both tests performed by distant strangers using specialized equipment that the shooter will not be using in "the field".

I would call up the shop, and talk to them. Also, try the test again with D-76 1:2 and see what happens.

2F/2F said:

I understand that they have perfectly adjusted their exposure mechanism. However, the key is not absolute technical perfection of exposure, but matching what the shooter will be doing. I don't see how the two tests could perfectly match. The photographer does not take pictures using the shop's perfect equipment. He/she takes them with his/her equipment, which may (in fact, almost certainly does) vary from the stuff that was used to expose the test sheets. The camera and metering system are never out of the equation, because they are what is actually used. How using this system is any better than using the film manufacturer's does not equate with me. They are both tests performed by distant strangers using specialized equipment that the shooter will not be using in "the field".

I would call up the shop, and talk to them. Also, try the test again with D-76 1:2 and see what happens.

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In BTZS testing the camera and metering system is indeed taken completely out of the equation. That is a simple fact. Get a copy of Beyond the Zone System, study the method, and you will understand what I am talking about.

One then confirms the results with field work, but the basic BTZS testing does not involve the use of a camera system. I can understand that people who have never tested film this way would have some doubts since the prevailing view is that you must test using the actual equipment. That is simply not true.

Sandy King

sanking said:

In BTZS testing the camera and metering system is indeed taken completely out of the equation. That is a simple fact. Get a copy of Beyond the Zone System, study the method, and you will understand what I am talking about.

One then confirms the results with field work, but the basic BTZS testing does not involve the use of a camera system. I can understand that people who have never tested film this way would have some doubts since the prevailing view is that you must test using the actual equipment. That is simply not true.

Sandy King

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Testing must be done, but it is testing of the personal equipment using the BTZS findings as criteria. Camera lens and shutter settings are not always telling you the "Gospel Truth."

gainer said:

Testing must be done, but it is testing of the personal equipment using the BTZS findings as criteria. Camera lens and shutter settings are not always telling you the "Gospel Truth."

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For those who are not familiar with BTZS testing the ininitial work is applied sensitometry, and the results are fairly portable from one person to another assuming one uses the same film, developer and type of agitation. The traditional method of testing is with the film in tubes and agitation is constant by rolling the tubes in a water bath. The only wild card in the mix is how fast you roll the tubes as slow rolling will give less contrast within a given period of time than fast rolling. My own method of testing must be very similar to the method used by Phil Davis because when I have compared my results with the sample film/developer combinations that come with the Winplotter program they are remarkably similar.

So in essence BTZS testing gives you a base line for exposure and development, and then you adjust the equipment to the base line. This system is much more efficient, and accurate, than traditional zone type testing where your results are really only accurate for one set of conditions.

Sandy King