Film testing

[JRoosa]

So, after twenty years of photography, I dug out my copy of The Negative and read the appendix on film testing.

It is a lot less complicated than I remember from years ago when I thought, "yeah, right."

I can can see with my highly calibrated eyeball that my film doesn't record zone I. It starts to be about right around 2/3 stops more exposure.

I'm headed to radio shack to get some photoresistors for a home brew densitometer to do a little measuring.

My motivation was that I was losing shadows on my prints, and that maybe with some rough calibration I can salvage some old film for at least snapshots and for the kids to play with. Also my new (to me) film cameras with good matrix metering were giving me very consistent negatives shot-to-shot that made printing much faster and easier. I think with a little more tweaking, I can get my negatives to behave even better. Plus my F100 has a good spot meter function, adding a little more science to the system.

Wish me luck.

J.

 

[Mainecoonmaniac]

Good luck! Have you ever tried to use your spot meter as a densitometer?

 

[Old-N-Feeble]

Good luck! Have you ever tried to use your spot meter as a densitometer?

How does one do that?

EDIT: Apparently it's very easy. Read through the meter with a piece of unexposed processed film then find the right exposure to find .1 EV increased density. That becomes the EI of your film... assuming .1 over film base plus fog is appropriate for your film of choice.

 

[Rudeofus]

If shadows are important to your images, you can always overexpose by a few stops. Modern negative film is very insensitive to overexposure, which means we can get away with a lot less testing than Ansel Adams did.

 

[Mainecoonmaniac]

For a density reference, use one of these.

http://www.stouffer.net/TransPage.htm

 

[horacekenneth]

How does one do that?

EDIT: Apparently it's very easy. Read through the meter with a piece of unexposed processed film then find the right exposure to find .1 EV increased density. That becomes the EI of your film... assuming .1 over film base plus fog is appropriate for your film of choice.

Could you explain this again?

 

[Gerald C Koch]

Rudeofus is right, if you are interested in shadow detail you typically over expose the film by a stop or more. You must remember that books like the AA series were written decades ago. Some of the information in them is quite outdated. Modern QA by film manufacturers and the wide availability of VC papers have made some things unnecessary.

 

[Old-N-Feeble]

Could you explain this again?

HERE

 

[snapguy]

Olde school

I guess I am a member of the Olde School. I look at the scene to be photographed and I wet a finger and hold it up to "test" everything. Not very scientific, I am afraid. But I figure if I don't know it by now, I never will.

 

[Ken Nadvornick]

I'm headed to radio shack to get some photoresistors for a home brew densitometer to do a little measuring.

If you might find it a bit quicker to reach your goal, I'd be willing to read your exposure tests on a densitometer to help out. You would mail them to me (near Seattle, WA), I would PM the results immediately back to you, then return the test materials by mail.

I've offered this free service before to other APUG members and had them take the offer. The instrument is a modern Heiland. The procedure takes only a few minutes. And besides, we're supposed to be a community...



PM me if you are interested.

Ken

 

[JRoosa]

If you might find it a bit quicker to reach your goal,

Thanks! I might take you up on it to verify my data.

I already have the setup together though.

$0.70 photoresistor
$4.00 Banana plugs (gotta make it look professional)
Wire, tape, solder, film can, multimeter, enlarger already in hand.

Basically I set up the resistor in the bottom of a 35mm film can, drilled a hole in the top to keep stray light out, and I set it on my enlarger base looking up at the lens.

I have a linear function when I go down through the F stops. Basically I take the log of the resistance off the meter and graph it against the density. Density is the log of the opacity, and opacity is (f/2.8=1, f/4=2, F/5.6=4 etc.). I zero the log of the resistance to what I get with f/2.8.

Here's the graph thanks to Xcell. I need to figure out how it calculates the trend line and then I can convert Log(resistance) to density when I put in my negative. I can't believe it's working.

The main source of error would be if my enlarger lens isn't truly dropping the light by 1/2 for each stop, but this might be more than close enough for what I need. I would buy a calibrated step wedge, but since I'm $4.70 in and it's up and running, I might just send you some negatives at some point to verify my numbers.

-J.

 

[JRoosa]

Found it, you just click "display equation on chart." Dang, I love computers sometimes.

y = 0.6997x - 0.0158

-J.

 

[Ken Nadvornick]

Well now that's cool. Nice job!



Sure, just let me know if/when you might like to verify. I'm the original owner, and the instrument is well-kept and still matches its original factory calibration strips exactly.

Ken

 

[LJH]

Once you've done this testing, how do you intend to use the results (assuming you're shooting roll film)? I ask this based on the premise that testing allows you to then control development times to expand/contract highlights. This is fine for individual images (i.e. sheet film), but becomes less applicable/non-applicable when dealing with multiple images being developed at the same time/on the same roll if there is a variety of exposure ranges...

Are you considering divided dev?

 

[JRoosa]

Are you considering divided dev?

No. I just want to get my roll film performing well with normal development, and I want to have a good idea of what that is. Also there is a certain "because I can" element to it. The reason I never bothered before is that a densitometer costs about as much as a new camera or lens, and I'd get much more enjoyment out of one of those. Once I stumbled on the plan for a homebrew densitometer, it made the project more or less free.

It's already been helpful to show me that zone I placement is actually zone 0 with my current setup. It may only be academic, though.

I am considering figuring out N+1 and N-1 for special situations where I would develop the whole roll as such. I bet N-1 would be useful for winter around here with bright sun and snow. I've been thinking about making N-1 the default to save any contrasty shots, but we'll see.

Some day soon I'll get a MF (with swappable backs) or LF camera, and it will be nice to have the system in place for then.

Oh, BTW, the axes above are backwards...not that it matters to anybody but me.

-J.

 

[RalphLambrecht]

So, after twenty years of photography, I dug out my copy of The Negative and read the appendix on film testing.

It is a lot less complicated than I remember from years ago when I thought, "yeah, right."

I can can see with my highly calibrated eyeball that my film doesn't record zone I. It starts to be about right around 2/3 stops more exposure.

I'm headed to radio shack to get some photoresistors for a home brew densitometer to do a little measuring.

My motivation was that I was losing shadows on my prints, and that maybe with some rough calibration I can salvage some old film for at least snapshots and for the kids to play with. Also my new (to me) film cameras with good matrix metering were giving me very consistent negatives shot-to-shot that made printing much faster and easier. I think with a little more tweaking, I can get my negatives to behave even better. Plus my F100 has a good spot meter function, adding a little more science to the system.

Wish me luck.

J.

for a superfast,no-testing calibrationsubtract 2/3 stop from your box speedand stick to the film manufacturer's development.that will give you sufficient sfadoe dtail and full Zone I.

 

[RalphLambrecht]

Rudeofus is right, if you are interested in shadow detail you typically over expose the film by a stop or more. You must remember that books like the AA series were written decades ago. Some of the information in them is quite outdated. Modern QA by film manufacturers and the wide availability of VC papers have made some things unnecessary.

Even with VCpapers;it's bst to startwitha properly exposed and processed negative.The Zone System and film testing are as valid as thry ere in AA's times,the Zone System even works with digital,without the film testing of ourse.

 

[JRoosa]

So, here are my initial data:

[TABLE="width: 130"]

[TD="class: xl63, width: 65, align: right"]0.000 [/TD]
[TD="width: 65"]FB+Fog[/TD]


[TD="class: xl63, align: right"]0.003 [/TD]
I


[TD="class: xl63, align: right"]0.001 [/TD]
I-1/3



[TD="class: xl63, align: right"]0.008 [/TD]
I-2/3



[TD="class: xl63, align: right"]0.032 [/TD]
I+1/3



[TD="class: xl63, align: right"]0.052 [/TD]
I+2/3



[TD="class: xl63, align: right"]0.066 [/TD]
I+1



[TD="class: xl63, align: right"]0.485 [/TD]
V



[TD="class: xl63, align: right"]1.227 [/TD]
VIII


[/TABLE]

This is with new Tri-X, D76 1:1 at 68deg for 9:45

It looks like I need to be shooting it at about 160 instead of 400.

Now I have to think about my zone V and VIII numbers for a little while.

Time to shoot another roll and play with development time. This is fun! It's really going to change my printing parameters.

-J.

 

[JRoosa]

OK, am I thinking about this right? I don't want to blow a roll on this...

I need to add 1.3 stops to everything in order to keep the 0.10 above FB+Fog with this film. Lets call FB+Fog zero for this discussion.

That means that my zone V exposure in this test is equivalent to about zone IV at EI160, and the zone VIII is zone VII at EI160.

If things are linear up to around zone V, then I'm getting about 0.13 increase in density per stop. Between IV and VII I get about 0.24 increase per stop.

So that would predict that if I repeat the test at EI 160, I would get a density of about 0.63 when I shoot zone V, and about 1.47 for zone VIII.

It sounds like I'm going to want to end up with shooting at 160 and then pulling it back about a stop's worth of development to hit "normal."

I think that I'm going to repeat the test at EI160, and develop as before to check my measurements. I'm tempted to split the roll and then pull out one half at about 30% shorter development to see what that does.

Very interesting.

-J.

 

[Bill Burk]

JRoosa,

Zone V to VIII difference in density is the "rise" (0.74) divided by the "run" (3 stops x 0.3 density units in terms of stop = 0.9)

0.82 gradient... This is slight overdevelopment - but take into consideration your "densitometer" may not be calibrated yet...

 

[JRoosa]

It's still linear up above V. I have another roll drying, half with less development.

Who knows if it's calibrated. I'm going to shoot some actual pictures and see what I get. If it's better, great. Fun project.

J.

 

[ic-racer]

Nice project, thanks for sharing. The multimeter is a great idea. The logic all looks good and I'll bet your error on the low end is very small and the error on the high end is less than 1/3 stop. If you zero your film base to the same ohm reading you have a repeatable system. This thread should probably be a 'sticky'

Reminds me of a darkroom exposure meter I made from RadioShack parts back in 1974 using a CDS cell and 9v battery. I calibrated the meter needle scale the same, way you did; using f-stops on the enlarger lens. However, without the digital multimeter it was a much cruder device than what you have described.

The box below the meter is a 555-based timer from a Popular Electronics article.

I agree, don't dwell too much on the numbers at this time. Go shoot some film at your new exposure index and see how it prints and go from there. You need to figure out for yourself how much density you need in the upper values to print with your paper and enlarger. Probably does not matter if your gamma is the same any of us would get, it is just a number. As long as you keep using the same photoresistor.

 

[JRoosa]

If one of the mods wants to make it a sticky, I can write a how-to that might be easier to follow. Maybe I'll send a strip to Ken to check my results.

Here are the results for EI160:

D76 1:1 68deg 9:45 (recommended development)

[TABLE="width: 130"]

[TD="class: xl63, width: 65, align: right"]0.000[/TD]
[TD="width: 65"]FB+Fog[/TD]


[TD="class: xl63, align: right"]0.131[/TD]
I


[TD="class: xl63, align: right"]0.098[/TD]
I-1/3


[TD="class: xl63, align: right"]0.064[/TD]
I-2/3


[TD="class: xl63, align: right"]0.039[/TD]
I-1


[TD="class: xl63, align: right"]0.164[/TD]
I+1/3


[TD="class: xl63, align: right"]0.211[/TD]
I+2/3


[TD="class: xl63, align: right"]0.255[/TD]
I+1


[TD="class: xl63, align: right"]0.836[/TD]
V



[TD="class: xl63"]Cut negative wrong!
[/TD]
VIII


[/TABLE]

Here's with reduced development by 30% (7:00) per the book by the esteemed Mr Adams.

[TABLE="width: 130"]

[TD="class: xl63, width: 65, align: right"]0.000[/TD]
[TD="width: 65"]FB+Fog[/TD]


[TD="class: xl63, align: right"]0.061[/TD]
I


[TD="class: xl63, align: right"]0.051[/TD]
I-1/3


[TD="class: xl63, align: right"]0.045[/TD]
I-2/3


[TD="class: xl63, align: right"]0.017[/TD]
I-1


[TD="class: xl63, align: right"]0.093[/TD]
I+1/3


[TD="class: xl63, align: right"]0.122[/TD]
I+2/3


[TD="class: xl63, align: right"]0.164[/TD]
I+1


[TD="class: xl63, align: right"]0.558[/TD]
V


[TD="class: xl63, align: right"]1.042[/TD]
VIII

[/TABLE]

-J.

Postscript:

Looking at the book, I think I found N+1 and N-1, respectively. I'll have to play around a bit, but I think I'll split the difference in developing time and call that Normal.

Now on to FP4+!

 

[Bill Burk]

Hi Jroosa,

Here's how your numbers so far look on graph... The x-axis is arbitrary, I just put zero from your first run at 3.00.

Then where your curve crossed 0.10 above B+F I deduced as "400" speed point. When you changed your speed to "160" I shifted the starting zero 0.40 to the right. Notice how your first and second curves practically coincide.

Now the calibration issue... I am only concerned about the high density readings. Below 0.90 density it looks like you have a good curve family started. But the high density just looks "wrong" - I'd throw the high numbers out for the time being, everything else looks great.

Now if you can't really get trustworthy readings above 0.90, you might expose your "straight line portion" at lower Zones, for example Zone III and Zone VI instead of Zone V and VIII.

 

[Bill Burk]

p.s. What great results from your simple densitometer. Kudos.

p.p.s. I really think your film speed would come in between 200 and 250, and you should try to keep the development "for normal" in control with this system you established. (You can define what is "in control" but I think you will find your negatives are good anywhere between these two curves at 7:00 and 9:45)