testing film without a densitometer?

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djkloss

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Is it possible to use a different method? My father used to use an Ohm meter and a photo cell? Any thoughts on using something like this to test film?

Thanks,

Dorothy
 

Donald Miller

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There was an article published on Apug sometime ago about using a spot meter. If you have just some film that has been exposed to a step wedge and want readings, you can contact me and I will read them for you...
 

gainer

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You may learn a lot from film exposed through a step wedge simply by printing both the step wedge and the image of it on various grades of printing paper. The print of the wedge can show you the exposure range of the paper. The print of the negative of the wedge can show you the printable subject brightness range of the film-developer combination. The ratio of the paper range to the negative range can tell you the useful contrast index of the film-developer combination if the film and step wedge are printed side by side. You will be able to see the effect of time, temperature and type of developer on usable SBR, etc. Your eyes are pretty useful after all. You may also learn quite a bit about the shape of the characteristic curve by changing the printing exposure of the image of the step wedge.

Remember, you still must correlate densitometer measurements with what you see, even if you have a very expensive densitometer.
 

RalphLambrecht

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djkloss said:
Is it possible to use a different method? My father used to use an Ohm meter and a photo cell? Any thoughts on using something like this to test film?

Thanks,

Dorothy


Dorothy

One useful method is to calibrate a darkroom lightmeter and then measure the densities under the enlarger. An Ilford EM-10 works great for that. Don't be fooled by how cheap they are.
 

df cardwell

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Using your imagination and judgement is always more effective than using a densitometer.
 

Will S

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df cardwell said:
Using your imagination and judgement is always more effective than using a densitometer.

Amen to that.

David Vestal has a great system for printing, I think somewhere around 25 prints at N, N+1, N-1, N+2, N-2 etc. all bracketed in his b&w darkroom book. I wonder if anyone has actually ever done it? I would definitely show you not only your film, but how it looks on your favorite paper with your developer.

And there is the no-zone stuff from Barry Thornton too.

Best,

Will
 

Earl Dunbar

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Nearly all of my calibration has been done without a densitometer. Pick up a (old) copy of Picker's Zone VI Workshop. And before anyone jumps on me, forget the word "zone" in the title. The section dealing with dialing in film speed CAN be done without a denistometer. I know. I did it. And my exposures improved immensely. Other guides my work as well, YMMV, etc.
 

kunihiko

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I like and have been doing the "minimum time - maximum black" method.
Bracket a plain subject and keep an unexposed frame. Print the unexposed frame(fb+f) onto your papers and find the shortest exposure time which gives maximum black.
Then, print other bracketed frames with the same exposure time. You'll have a set of graded tones. A frame slightly lighter than max-black which you think Zone I is your Zone I.
 

Jim Jones

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I wonder if negatives can't be scanned and a reading made on an image editor? You wouldn't have an absolute reading, but even a comparative reading might be useful.
 

George Collier

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I scan a bit of my stuff for evaluation (exploring the image) and marketing. The settings can be open to discussion and a standard may be elusive. I vote with Don Cardwell - pick the film / developer and paper you want to use. As Fred Picker used to say "Try it, try it, try it". Find the contrast level of the paper that separates the values to your taste (or just pick grade 2 to start), find the exposure that gives you detail in the shadows you want to have detail, and find the development time that works with the paper contrast. Then take pictures, make art, and watch how it works. Your sensitivity will increase, and you'll know when it's time to change something.
Next year, when you try a new, film, it'll all fall into place quicker.
Someone else, however, might tell you something completely different. Cool.
 

Dan Henderson

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Jim Jones said:
I wonder if negatives can't be scanned and a reading made on an image editor? You wouldn't have an absolute reading, but even a comparative reading might be useful.

Yes, you can scan negatives in along with a Stouffer step wedge, and then use a program available free on the internet to match values from the step wedge to values in the negative.
 

aoresteen

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Ditto on the Zone VI Workshop. A proper proof will tell you right off what the correct EI is for your film.
 

Chan Tran

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1. A spotmeter would work out quite well.
2. Using a scanner and compared the reading with a known density step wedge could work, although I have not done it. I did use a scanner, the Minolta dimage dual scan IV, in manual mode and scan a known step wedge and was able to calibrate the scanner to give pretty close reading.
3. It's possible to use a photocell and an ohm meter. This method is fairly accurate once you calibrate the photocell using again a known step wedge. The problem is unless you already have a good ohm meter it could cost more than a good used densitometer on ebay.
 

Tach

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Chan Tran said:
3. It's possible to use a photocell and an ohm meter. This method is fairly accurate once you calibrate the photocell using again a known step wedge. The problem is unless you already have a good ohm meter it could cost more than a good used densitometer on ebay.

You don't need to calibrate the photocell. Just take a reading of negativeless carrier, and that's your 100% transmission. A multimeter is inexpensive; about 10-20 US$ and quite useful around the house.

The biggest advantage of the photocell + enlarger + multimeter method is that the density you read is automatically calibrated to your enlarger light source . In other words, your cell sees what your paper will see. If you use a normal ensitometer, the density reading may or may not correlate to the real density your enlarger will produce.

Using the same negative, my condenser (Valoy II with small bulb and masked lamphouse reflector) sees a z8 density of 1.3, while my diffuser enlarger sees a z8 of 0.95. Based on this, I can exactly match contrast between my two enlargers with the same negative.

A commercial densitometer does not take in account your enlarger characteristics, and you have to mentally convert using rules of thumb, which may or may not be accurate.

See this thread
 

Chan Tran

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If you put the photocell under a negativeless carrier and it read 500 ohms. When you put in your negative it reads 2500 ohms then what is the density of your negative?
 

Tach

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Chan Tran said:
If you put the photocell under a negativeless carrier and it read 500 ohms. When you put in your negative it reads 2500 ohms then what is the density of your negative?

ln(2500) - ln(500) = ln(2500/500) = ln(5) = 0.70

I do generally take a b+f reading using a clear negative, and deduct this from subsequent readings.
 
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Chan Tran

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If the light level without the negative is 5x the light level with the negative then you're correct. However, photocells do not respond in such a manner.
 

Tach

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Chan Tran said:
If the light level without the negative is 5x the light level with the negative then you're correct. However, photocells do not respond in such a manner.

I'd strongly suggest taking a look at a typical photocell datasheet, before pursuing this line of arguing.

A CdS photocell does have an exponential response to light level, between some lighting thresholds. An lot of lightmeters would be b0rken if that were not the case :smile:

The general formula for negative density is ln(resistance of cell with negative) - ln(resistance of cell with clear carrier).
 

vanannan

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Hi Dorothy
All I can say is that I have been using a densitometer for years both for reflection readings which helps to determine maximum print density etc. and transmission readings to help determine film speed and correct and consistant development times, I bought a second spare reflection/transmission unit on Ebay recently for just £20 and it works perfectly.
Good luck
Regards
Tony
 

gainer

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Silicon phototransistors are quite linear in the current mode. Connect one between the positive supply and the inverting input of an IC operational amplifier with a resistive feedback to get a linear output. Use a silicon diode as feedback to get a logarithmic output over a very wide range of input. The negative input of an op amp with feedback is a virtual ground for the phototransistor.
 

MattKing

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RalphLambrecht said:
I wonder what you can do with imagination and a densitometer then.

I agree, but I think it varies from photographer to photographer.

IMHO the trick is to use the objective but unimaginative equipment (such as a densitometer) to support and enhance the imagination and judgement. For some people, use of equipment like a densitometer comes naturally, and aids them in their task. For others, use of such equipment is awkward and counter-intuitive.

Say you come across a scene that your imagination indicates will photograph well. In order to accomplish that, it may be necessary to make full use of the technical and interpretive abilities of your eye, light meter, camera, film, chemistry, paper and process.

If you have strong intuitive abilities, and are uncomfortable with numbers and non-intuitive readings (like log values), then you are more likely to put less weight on the readings of a densitometer, and more weight on your experience and perceptions, and you would be wise to do so.

However, if you are comfortable with numbers and such, you may be able to correlate both your intuitive observations and the results of densitometer tests.

In either case, you will only be consistently successful, if you have done the work in preparation (with a densitometer, or calibrating your development conditions, or adjusting your enlarger, or familiarizing yourself with the paper, etc.) that make the results both good and dependable.

For people who are comfortable with them, a densitometer makes it easier to get dependable results. That can free you from technical uncertainty, and allow you to focus more on the imagination and judgement.

For people who think they would be uncomfortable using and relying on densitometric tests, but have never tried, they should probably experiment, if they can, because they might be surprised.

By the way, thank you very much for your website (particulary the fine photography, and the great tools in the library!).

Matt
 

df cardwell

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RalphLambrecht said:
I wonder what you can do with imagination and a densitometer then.

That's an easy one isn't it ?

Once you have a negative that makes the prints you like, then you can play with a step wedge... or a densitometer. THAT will take away the superstition from getting other films ( faster, slower, whatever ) to give you similar results to the film you like.

But until the PRINT tones have meaning to you, the density numbers have no meaning, and therefore, no value. And no need for a machine to read valueless numbers.

If you have animagination, and only want to work with ONE film ( and what is wrong with that ? ) you can get some little antlers and dress up your densitometer like one of Wegman's dogs. OR, if you have an older Macbeth, you can pretend you're Buck Rogers and make squeeky noises while you're spinning the colored dials trying to escape from Ming's storm troopers.

But I don't have THAT much imagination, so my densitometer sits in the dark until I need it.

And I second Matt's comments about your site :cool:

don
 
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djkloss

djkloss

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Chan Tran said:
3. It's possible to use a photocell and an ohm meter. This method is fairly accurate once you calibrate the photocell using again a known step wedge. The problem is unless you already have a good ohm meter it could cost more than a good used densitometer on ebay.

My dad gave me his ohm meter and photocell that he made from a Heath Kit. He's an engineer... and the price was right. Tieing him down to fix it is another story. I managed to pick up a Kodak 'manual' densitometer...very basic...but the price was again...just right. (free!) I guess I have a bit of techno-envy for all the brains on this site and want to be more educated. And at the same time not waste so much time and materials on test strips. I want to learn how to plot curves and test film for personal EI.

Thank you all for the wealth of information. I'm excited about trying all the methods presented here...and forcing my brain to stay awake. I think knowledge is a good thing...it provides options.

---Here's what I've done so far...
I shot a roll of 35mm PlusX - mfg suggested ISO -
Using a gray card taped to a wall I started with a blank frame (lens cap on) (in the shade) then the meter reading of Zone V, then IV, III, II, I, V, VI, VII, VIII, IX, X. I was planning on experimenting with this and then once I learn how to plot, I can do some more in-depth testing.

Thanks again!
-Dorothy
 

RalphLambrecht

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Thanks Don and Matt for the comments to my site. I have uploaded some dual-filtration and exposure tables for some papers (more to follow). Let me know if you find them useful.

Back to the subject of densitometers:

Mr. Drieffield (co-inventor of the H-D curves) said a 100 years ago:
The artist will make the better picture, but the scientist will make the better negative.

I can't resist to have both.
 
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