Contrast Index Quick Check

[ic-racer]

Using a camera, expose a frame of a uniform target three stops over-exposed from the EI established previously.
Print the image on Grade 2 so film base is 'just black' (don't go for super-black); development is correct if you can just see the outline of a coin on the paper.

 

[gzinsel]

o,k. I get it . . . . But "on the flip side" pun intended. how much is your time worth? ( rhetorical) I bought a used densimeter for under a 200 USD, and i have seen some less than a 100 USD. I know for some that is a lot of money, but if you are trying to accurately and quickly determine a C.I. for your film. I suggest you save your money and buy one. the amount of time, materials ( chemicals, paper. film) seem to be excessive, for what could be done quickly with the right tools. you might want to try if someone in your area has one you can use or borrow? if you live in Milwaukee, WI- USA you can use mine any time at my shop!

 

[PeterB]

Using a camera, expose a frame of a uniform target three stops over-exposed from the EI established previously.
Print the image on Grade 2 so film base is 'just black' (don't go for super-black); development is correct if you can just see the outline of a coin on the paper.

I'm missing something. Was I supposed to put a coin on the uniform target?

".....so the film base is just black" do you mean keep adjusting the development until the "just black film base" gives a print where you can just see the coin outline?

 

[whojammyflip]

I think the idea is when making the 3 stops over exposed image, there should be a coin in the image...if it just appears in the contact print, then you have got detail in zone 8, which is by definition what should be seen in zone 8, hints of highlight detail.

Cheaper than a densitometer, although requiring more frames of film, shoot zones Z1 through to Z8 and then get a Darkroom Automation meter to measure the light intensity under the enlarger of each frame. Also shoot a reference blank frame for measuring Base+Fog. You dont need to even put the negative in the enlarger, just lay it over the top of the meter. Calculate contrast index by subtracting Z8 from Z2 reading, and then dividing by 6.

I've just done this for some TMAX 400: I got light readings of 8.91, 8.22 (base + fog), 8.04, 7.75, 7.53, 7.10, 6.63, 6.13, 5.63, 5.17, 4.42, 4.04. To interpret this for CI, I've got a change of 7.75-5.17 for Z2 vs Z8, so a 2.58 stop change in light intensity for a 6 stop change in exposure. This means a CI of 0.43. This means I am underdeveloping my film. Interestingly, and tallying with the theory, my Z1 is nearly still ok, at 0.16 stops over B+F.

Depending on the aperture range of the lens, you can be lucky and get the light adjustment by altering aperture and leaving shutter on one setting, to avoid discrepencies brought about by changing shutter speeds (this works on my Pentax M 50/1.4, which runs from f22 to f1.4, just meter at f5.6 for Z5. You could just shoot a blank frame and then a few zones, but by shooting the whole lot of zones, you can ascertain whether your EI is wrong, all at the same time.

 

[PeterB]

Using a darkroom automation meter is a great idea however that requires the user to purchase one ! If the requirement is for the user to determine an acceptable CI using nothing other than their camera, exposure meter (most likely built in to the camera) and enlarger then ic-racer's suggestion fits those requirements. This procedure will cover >99% of the photographic community especially amateurs who we don't want to put off by requiring they purchase a D.A.M.

 

[ic-racer]

o,k. I get it . . . . But "on the flip side" pun intended. how much is your time worth? ( rhetorical) I bought a used densimeter for under a 200 USD, and i have seen some less than a 100 USD. I know for some that is a lot of money, but if you are trying to accurately and quickly determine a C.I. for your film. I suggest you save your money and buy one. the amount of time, materials ( chemicals, paper. film) seem to be excessive, for what could be done quickly with the right tools. you might want to try if someone in your area has one you can use or borrow? if you live in Milwaukee, WI- USA you can use mine any time at my shop!

I have three different densitometers and three different sensitometers with incandescent, Xenon and LED light.

Reflection sensitometers can be notoriously inaccurate with the interrogation of photographic papers. Observation of a faint outline of a coin placed on the printing paper could be argued to be superior.

 

[ic-racer]

I'm missing something. Was I supposed to put a coin on the uniform target?

".....so the film base is just black" do you mean keep adjusting the development until the "just black film base" gives a print where you can just see the coin outline?

Adjust printing time for the coin exposure so the film base prints 'just black.'

The coin is placed on the printing paper during the exposure of the dense negative under the enlarger. The goal is to see a faint outline of the coin against a near-white background.

 

[PeterB]

Adjust printing time for the coin exposure so the film base prints 'just black.'

The coin is placed on the printing paper during the exposure of the dense negative under the enlarger. The goal is to see a faint outline of the coin against a near-white background.

That makes sense, thanks. So simple.